Luminous Landscape Forum

Equipment & Techniques => Beginner's Questions => Topic started by: BillMc on July 18, 2012, 02:12:01 pm

Title: lower EC or ETTR?
Post by: BillMc on July 18, 2012, 02:12:01 pm
I am confused about two pieces of advice one often sees, that seem to me to be contradictory.  On the one hand, one sees advice to leave exposure compensation set on -1/3, in order to get better color.  This is especially urged on small sensor cameras, which have a tendency to blow out highlights.

On the other hand, one reads articles urging photographers to expose to the right, which I gather means that in taking a photograph, one should examine the histogram and if necessary boost exposure compensation so that the curve shifts over toward (but does not touch) the right side of the histogram.

These pieces of advice seem to be at cross purposes. Can someone enlighten my understanding?
 
Title: Re: lower EC or ETTR?
Post by: Schewe on July 18, 2012, 03:04:39 pm
On the one hand, one sees advice to leave exposure compensation set on -1/3, in order to get better color.  This is especially urged on small sensor cameras, which have a tendency to blow out highlights.

You can forget about this one...it's wrong. Assuming you are shooting raw the "color" you get is directly related to the raw processing you do. As long as you don't clip any textural highlight information, a normal or ETTR exposure is equally capable of having the color adjusted, so under exposing to get "better color" is a load of crap...
Title: Re: lower EC or ETTR?
Post by: Tony Jay on July 18, 2012, 04:09:09 pm
Bill, the advice you are getting is not contradictory because it likely relates to shooting with different purposes in mind since reducing the EC in the way that you describe relates to shooting JPEG's while ETTR techniques relates to shooting RAW files.
The key point is that, even in Lr with non-destructive parametric editing, JPEG files respond poorly to tonal editing so what you get out of the camera is the probable endpoint.
Obviously RAW files lend themselves very well to tonal manipulation so in this case ETTR just optimizes the file information for the process of tonal manipulation.

Broadly, shooting JPEGS the approach to shooting is similar to shooting colour film while shooting RAW demands a completely different approach summed up as ETTR.

Regards

Tony Jay
Title: Re: lower EC or ETTR?
Post by: BillMc on July 18, 2012, 05:31:58 pm
Thanks very much.  This helps a lot. I do shoot RAW, and so I'll use my histogram to expose to the right and adjust the color later in processing.
Title: Re: lower EC or ETTR?
Post by: luxborealis on August 04, 2012, 09:18:23 am
Furthermore, depending on the sensor you have, you don't always need to limit yourself to the right side of the histogram. Some sensors allow you to clip by upwards of 1 stop and still recover detail in the highlights.

Check your system carefully by shooting a scene with bright highlights (e.g. brightly lit clouds) using what I call "highlight bracketing": Shot 1-not clipped; Shot 2-clipped by 1/3 stop; Shot 3-clipped by 2/3s stop; Shot 4-clipped by 1 stop; etc. Then bring them into your editing app (LR, Aperture, CaptureOne) and process them to see what detail you can recover. That way, you can learn about the boundaries of your equipment, your visualization and shooting techniques. I have been amazed at how much can be recovered in my D800e files using LR 4.1 from areas that show as "clipped" on the histogram and with the highlight clipping indicators.
Title: Re: lower EC or ETTR?
Post by: hjulenissen on August 04, 2012, 10:56:35 am
On the one hand, one sees advice to leave exposure compensation set on -1/3, in order to get better color.  This is especially urged on small sensor cameras, which have a tendency to blow out highlights.
If your sensor clips, you will have erroneous data in the affected pixels. Clever raw developers may do a good job of concealing that error if the clipping is not too severe, but it will still be a "guess".

If your cameras auto exposure is too "hot" for your taste and processing, it might be a good advice to do some negative exposure compensation. Current cameras are not doing a good job of telling you how close to clipping any given image was.

-h
Title: Re: lower EC or ETTR?
Post by: Graystar on August 09, 2012, 09:27:31 pm
I am confused about two pieces of advice one often sees, that seem to me to be contradictory.  On the one hand, one sees advice to leave exposure compensation set on -1/3, in order to get better color.
As already said, reducing EC to get better color is wrong. 

Quote
This is especially urged on small sensor cameras, which have a tendency to blow out highlights.
It's wrong here as well.  Highlights are usually blown by the one-size-fits-all image processing of the camera.  Also, so-called "intelligent" metering modes may increase exposure to avoid underexposure.  These modes attempt to apply their own exposure compensation to the shot.  They may over or underexpose the image if they guess wrong.

Quote
On the other hand, one reads articles urging photographers to expose to the right, which I gather means that in taking a photograph, one should examine the histogram and if necessary boost exposure compensation so that the curve shifts over toward (but does not touch) the right side of the histogram.

These pieces of advice seem to be at cross purposes. Can someone enlighten my understanding?

ETTR is an interesting concept, but it's very tricky.  It's only valid at your base ISO (which may not be your lowest.)  If there's any white in the scene, then you can't ETTR.  If there's any bright red in the scene, then you can only ETTR by 1/3 stop or so before getting into trouble.  I guess if you're taking shots of black cats lying on coal piles all day long, then ETTR will have value.  Otherwise, you may find it more trouble than it's worth.

ETTR works well in the studio environment, where you have control over lighting.  Then it's easy to create situations that have one stop's worth of highlight leeway.  You can overexpose by one stop and then pull exposure down in post to get less noise.

If you have a camera with an expanded ISO range, then you have ETTR built in.  All you need to do is to utilize your expanded ISO.  For example, my Nikon D90 has a base ISO of 200, and an expanded ISO of "L 1.0" (much like ISO 100, but I lose one stop of highlight space.)  I just use L 1.0 when I want to ETTR (under the right conditions, of course,)

I find that I get the best exposure by using a gray card.  Well, I don't actually use a proper gray card...I just use my white-balance reference card that I carry in my back pocket.  Through a simple "calibration" process I determined that I can meter the WB reference and set EC to +1.3 for standard exposure.  That gets the whites as bright as possible without clipping (regardless of what the camera's histogram says.)

Title: Re: lower EC or ETTR?
Post by: jeremypayne on August 09, 2012, 10:16:41 pm
If there's any white in the scene, then you can't ETTR.  If there's any bright red in the scene, then you can only ETTR by 1/3 stop or so before getting into trouble. 

Care to explain these statements?  They don't really jive with theory or my experience ...
Title: Re: lower EC or ETTR?
Post by: Graystar on August 09, 2012, 11:44:21 pm
Care to explain these statements?  They don't really jive with theory or my experience ...
Sure.

First, let's make sure we're on the same page (so to speak.)  Spot/CW metering on all cameras is calibrated to 12.7% reflectance.  That's easy to verify...just spot meter an evenly lit white wall and take a picture.  You should get a gray image with the metered area around sRGB 100, 100, 100, which is about 12.7% gray (you need a RAW converter and a "neutral" profile that doesn't apply any processing to the image.)  That gives you nearly 3 stops of highlight space above 12.7% gray (12.7%x2=25.4%x2=50.8%x2=101.6%...you can't have a signal greater than 100%, so it's just a smidge under three stops.)

So let's say you have a 12.7% gray card (Lastolite makes one) or an 18% gray card + 0.5 EC (Kodak and others) or as I have, an RM Imaging Digital Gray Card (designed and marketed as a white-balance tool) + 1.3 EC (an EC amount I determined through a "calibration" process.)  Any of these metering references will get you the same exact exposure.

So you spot meter your chosen reference, apply EC if called for, and take a picture.  This exposure level would constitute standard exposure.  Any white objects that are reflecting 90%+ of the light falling on them will be giving you a signal near saturation on the green channels.  You can use something like RawDigger to see the RAW histogram.  If you try to push the exposure by even 1/3 stop, you'll likely clip the green channels.  This is why I say that you can't really ETTR if you have anything white in your image...because standard exposure already gets your white objects near saturation.

As for red...what I've found is that when you push red a little, even though you don't clip the channel, the scaling factors will cause the red channels to clip in the RGB conversion.  So technically, the RAW channels aren't clipped, but you have to deal with the red clipping after the RGB conversion.  That can be done by messing with the scaling factors and with functions such as highlight protection.  I find that it takes a bit of work to get things to look right.

So my bottom line is that for most scenes, standard exposure gives the best exposure level.  As I said previously...if you've got the lighting under your control then you can certain create a situation where you can overexpose by a stop or so, and then ETTR.

I think the problem that faces most people is that of being able to set standard exposure reliably.  In just about any scene that's static enough to implement ETTR, you should be able to use a gray card to set standard exposure.  But you do need to have a card with a good quality matte surface...otherwise the reading will be all over the place.
Title: Re: lower EC or ETTR?
Post by: ckimmerle on August 11, 2012, 08:25:10 pm
I think the problem that faces most people is that of being able to set standard exposure reliably.  In just about any scene that's static enough to implement ETTR, you should be able to use a gray card to set standard exposure.  But you do need to have a card with a good quality matte surface...otherwise the reading will be all over the place.


There is no such thing as "standard exposure". Not only will each scene have its special exposure considerations, but different photographers will meter each scene slightly differently, depending on how they visualize the resulting print. As for an 18% gray card, they pretty much became useless with the advent of the histogram which, unlike an 18% gray card, actually provides you with useful/vital exposure data.

I'm not sure where you are getting your information, but much of it is simply not correct.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 11, 2012, 09:22:49 pm
There is no such thing as "standard exposure". Not only will each scene have its special exposure considerations, but different photographers will meter each scene slightly differently, depending on how they visualize the resulting print. As for an 18% gray card, they pretty much became useless with the advent of the histogram which, unlike an 18% gray card, actually provides you with useful/vital exposure data.

I'm not sure where you are getting your information, but much of it is simply not correct.

Actually, all my information is correct.  Standard exposure is what you get from ISO metering standards.  If there were no standards, you couldn't use a handheld meter to set your camera.  Standard does not mean "correct".  It simply means "based on a standard."

You're talking about the preferred exposure for the scene, which is completely subjective.  However, your notion of exposure is out of place in this thread because we're discussing ETTR.  And the rules for setting exposure via ETTR are short and sweet...maximize your exposure so that the brightest highlights you care about are near saturation.  So someone taking a picture of a black cat sleeping on a pile of coal is going to overexpose his image by 5 stops.  In post, the photographer will apply -5 EC (or as much as he likes) to restore the look of the scene. That's ETTR.

I personally find the histogram to be useless.  It's too small to indicate certain important clipped highlights, such as the whites of the eyes, and it doesn't tell you if those overexposed areas are specular in nature (in which case you should probably leave them be.)  I find the "blinking" function to be far more useful.  For scene with a wide contrast range, the gray card tends to give me the maximum exposure possible.
Title: Re: lower EC or ETTR?
Post by: jeremypayne on August 11, 2012, 11:28:56 pm
Actually, all my information is correct.

So for every possible image there is only one exact place to put "the grey card" and one and only one exposure that meets "ISO standards"?
Title: Re: lower EC or ETTR?
Post by: ckimmerle on August 11, 2012, 11:31:23 pm
However, your notion of exposure is out of place in this thread because we're discussing ETTR.

Umm....you were the one who started talking about gray cards and standard exposure (neither of which was relevant to the OP). I was only responding.

And the rules for setting exposure via ETTR are short and sweet...maximize your exposure so that the brightest highlights you care about are near saturation.

Actually, that is incorrect. When using ETTR, you should only increase exposure enough to ensure that there is relevant detail in the important shadow areas (minimize noise). That might mean increasing exposure only one stop. Pushing the histogram so far than you're near clipping is simply bad practice as you're possibly sacrificing tonal range in the highlights. ETTR is all about increasing the SNR in the shadows. That's all does.

I personally find the histogram to be useless.  It's too small to indicate certain important clipped highlights, such as the whites of the eyes, and it doesn't tell you if those overexposed areas are specular in nature....I find the "blinking" function to be far more useful

Sure, the histogram doesn't plot every exposure level on the image, but it offers a helluva lot of information for the photographer. Most importantly, it displays placement and amount of the brightest and darkest areas of the image. Also, the slope of the end points, for instance, tells a lot about the tonal ranges of shadow and highlight regions. As the camera uses the jpeg preview to calculate the histogram, worrying about specular highlights is a waste of time as the resulting image, especially if RAW, will have a much greater overall tonal range than the camera histogram indicates. As for the blinking function, it uses the same data set as the histogram, so offers nothing new.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 12, 2012, 12:16:48 am
So for every possible image there is only one exact place to put "the grey card" and one and only one exposure that meets "ISO standards"?
No.  For whatever you meter, you get standard exposure.  If you meter a white wall, you'll get standard exposure and the wall will come out gray.  If you meter a black wall, you'll get standard exposure and the wall will come out gray.  That's how reflective metering works.  The meter starts with a presumption that the world is gray...12.7% gray, to be exact.  It then computes exposure so that the metered area comes out a gray of 12.7%.

Obviously, the meter is wrong on the white and black walls.  That's why it's "standard" exposure, and not "correct" exposure.

If you meter a 12.7% gray reference, then your exposure of white objects will be near saturation and anything illuminated by that same light source will appear in the photograph as it did in the live view.  If your scene has two light sources, like many outdoor scenes with part of the scene lit by the sun and part in open shade, then each area of illumination would require its own "standard" exposure.  There's no correct exposure for such scenes...you simply have to decide what's important and make a decision, and adjust exposure as you see fit.

Standard exposure is a tool...not a destination.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 12, 2012, 12:29:19 am
Umm....you were the one who started talking about gray cards and standard exposure (neither of which was relevant to the OP)

That's because I was responding to a specific question posed by a poster other than the OP.

Quote
I was only responding.

And so was I.  And my response was in context to a question relating to ETTR.

Quote
Actually, that is incorrect. When using ETTR, you should only increase exposure enough to ensure that there is relevant detail in the important shadow areas (minimize noise). That might mean increasing exposure only one stop. Pushing the histogram so far than you're near clipping is simply bad practice as you're possibly sacrificing tonal range in the highlights. ETTR is all about increasing the SNR in the shadows. That's all does.

That's not right.  You don't sacrifice tonal range in the highlights by pushing exposure to near saturation.  Exposure on digital sensors is linear.  As long as you don't clip the highlights you'll capture the full tonal range.

Quote
Sure, the histogram doesn't plot every exposure level on the image, but it offers a helluva lot of information for the photographer. Most importantly, it displays placement and amount of the brightest and darkest areas of the image. Also, the slope of the end points, for instance, tells a lot about the tonal ranges of shadow and highlight regions. As the camera uses the jpeg preview to calculate the histogram, worrying about specular highlights is a waste of time as the resulting image, especially if RAW, will have a much greater overall tonal range than the camera histogram indicates. As for the blinking function, it uses the same data set as the histogram, so offers nothing new.

The blinkies tell you where the clipping is.  You'll see the whites of a person's eyes blinking...but you won't see the clipping of such a small area in the histogram.  And I can see the tonal ranges with my eyes...I don't need a histogram to show them to me.
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 12, 2012, 09:40:35 am
Exposure on digital sensors is linear. 

http://forums.dpreview.com/forums/readflat.asp?forum=1041&message=42236844

"...However the question is of colour linearity, that is - if we apply a matrix transform to two shots of the same scene with exposure difference, we will have different L* obviously; but do we have same a/b? In other words, what is the deltaE2000 between those two shots after the linear exposure compensation in the raw converter? One even does not need to have an accurate colour profile to check it - just any matrix will give an idea being assigned to a binned raw data..."

so did you test yours ? provided that your raw converter indeed does linear EC
Title: Re: lower EC or ETTR?
Post by: Graystar on August 12, 2012, 09:26:55 pm
http://forums.dpreview.com/forums/readflat.asp?forum=1041&message=42236844

"...However the question is of colour linearity, that is - if we apply a matrix transform to two shots of the same scene with exposure difference, we will have different L* obviously; but do we have same a/b? In other words, what is the deltaE2000 between those two shots after the linear exposure compensation in the raw converter? One even does not need to have an accurate colour profile to check it - just any matrix will give an idea being assigned to a binned raw data..."

so did you test yours ? provided that your raw converter indeed does linear EC

An ETTR discussion on an m4/3 forum??  Tell them to just buy bigger sensors!  :P

Yes, I've tested it many times.  I've attached an example I just created...

They're obviously different...they must be, as one was created with only 1/4th the light of the other.  There's more noise, and it's most noticeable in the black patch.  Still, the colors look fairly similar.
Title: Re: lower EC or ETTR?
Post by: stamper on August 13, 2012, 04:58:13 am


The blinkies tell you where the clipping is.  You'll see the whites of a person's eyes blinking...but you won't see the clipping of such a small area in the histogram.  And I can see the tonal ranges with my eyes...I don't need a histogram to show them to me.
[/quote]

The problem with the blinkies is that you don't know where the camera manufacturers have set the limit? I think it is wrong to assume it is 255 255 255 or 100%. I believe it is a lower value but they won't tell. Are you serious when you say that you are concerned about the lightness values in a small area such as a person's eyes?
Title: Re: lower EC or ETTR?
Post by: hjulenissen on August 13, 2012, 05:17:10 am
I must confess that I fail to see why "18%" or "12.7%" would ever have to be mentioned in a discussion about digital cameras. Film cameras might be another story, but I don't know much about those.

A digital camera sensor seems to be fairly well modelled (in this context) as a linear ADC with some additive noise-floor. Sure there is more to it, but when it comes to selecting exposure, you will capture the most information about the scene (provided that exposure time and aperture allows) if the brightest pixels of interest are exposed close to the saturation limit, thus maximizing SNR for every sensel without clipping. If the scene has a wider dynamic range than the sensor can reliably capture, one might want to clip e.g. highlights. In that case, it becomes a trade-off between "bright pixel error" (clipping) and "dark pixel error" (noise). The same methology can be used for this case if you are able to define the brightest pixel of interest.

This leads to the conclusion that ETTR (or as digital audio engineers have known for some time: record using hot levels, but not too hot - HLNTH) is a sound principle for digital camera capture if you want to maximize information captured. A relevant question then might be: are you (as a photographer) primarily interested in capturing the largest possible amount of information, or in "making the best images"? I have little doubt that "ETTR" will maximize the information about the scene, but that may do you little good if fiddling with the histogram means that the bird has left the scene, or if your raw editor makes it cumbersome to compensate exposure predictably (for a pleasing rendering exposure). Purchasing a new Sony-sensor-based camera might provide a similar "DR headroom" as fiddling with ETTR on an older camera.

-h
Title: Re: lower EC or ETTR?
Post by: bjanes on August 13, 2012, 10:38:36 am
Furthermore, depending on the sensor you have, you don't always need to limit yourself to the right side of the histogram. Some sensors allow you to clip by upwards of 1 stop and still recover detail in the highlights.

Check your system carefully by shooting a scene with bright highlights (e.g. brightly lit clouds) using what I call "highlight bracketing": Shot 1-not clipped; Shot 2-clipped by 1/3 stop; Shot 3-clipped by 2/3s stop; Shot 4-clipped by 1 stop; etc. Then bring them into your editing app (LR, Aperture, CaptureOne) and process them to see what detail you can recover. That way, you can learn about the boundaries of your equipment, your visualization and shooting techniques. I have been amazed at how much can be recovered in my D800e files using LR 4.1 from areas that show as "clipped" on the histogram and with the highlight clipping indicators.

Good suggestions, but I would not rely on lightroom 4.1 or ACR 7.1 with PV2012 to judge highlight clipping, since they incorporate automatic highlight recovery and also have a baseline offset exposure of +1/3 EV. The former mitigates highlight clipping, while the latter aggravates it. It is advisable to look directly at the raw files with a program such as Rawdigger.

I performed such a test on my 800e using  Stouffer step wedge. The steps are in 0.3 EV increments.

Image 1 at 1/13 sec is the optimal ETTR exposure. The highlights are nearly 0.3 EV from clipping, but the exposure at 1/10 second shows clipping. Looking at the camera histogram shows for the 1/13 s exposure shows clipping and the blinking highlights indicates clipping of the brightest two steps. The histogram is conservative and the blinking highlights are even more conservative. These indicators are useful, but one can allow exposures that appear slightly blown and rely on highlight recovery to correct the situation. The camera has excellent noise characteristics and ETTR is less important than with some cameras, and one can not go far wrong just relying on the camera histogram and blinking highlights.

Rsw histogram for 1/13 s exposure:
(http://bjanes.smugmug.com/Photography/D800-Stouffer/i-HRmbjv9/0/O/img1.png)

Raw histogram for the 1/15 s exposure:
(http://bjanes.smugmug.com/Photography/D800-Stouffer/i-S5CMWnV/0/O/Img7.png)

Camera histogram for the 1/13 s exposure:
(http://bjanes.smugmug.com/Photography/D800-Stouffer/i-NCq7XxX/0/O/LCD0001800.png)

Blinking highlights for the 1/13 s exposure:
(http://bjanes.smugmug.com/Photography/D800-Stouffer/i-GdLjsxV/0/O/LCD0001h.png)

Regards,

Bill
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 13, 2012, 11:13:36 am
An ETTR discussion on an m4/3 forum??  Tell them to just buy bigger sensors!  :P

the posting was from I. Borg (of Rawdigger/Libraw and RPP)...
Title: Re: lower EC or ETTR?
Post by: Graystar on August 13, 2012, 01:52:02 pm
The problem with the blinkies is that you don't know where the camera manufacturers have set the limit? I think it is wrong to assume it is 255 255 255 or 100%. I believe it is a lower value but they won't tell.

Whether it's 245 or 255 is of no concern because such a difference would represent about 1/6th of a stop in exposure...you're still going to drop exposure by 1/3 stop either way.  Besides...it's the RAW data that we're concerned about most...what's most important is that you understand the relationship between the RAW data and the RGB image that is the basis for the histogram (which is what UniWB is all about.)


Quote
Are you serious when you say that you are concerned about the lightness values in a small area such as a person's eyes?

Have you ever taking portrait shots?  Clip the eyes or the teeth and it's noticeable...it looks like there's something wrong with the image (and there is.)
Title: Re: lower EC or ETTR?
Post by: Keith Reeder on August 13, 2012, 01:57:21 pm
Much as I'm enjoying this discussion, can I just remind you all that this is the Beginners forum - I imagine that the OP will be sitting under a table, clutching his knees to his chest and rocking gently back and forth by now..!

;)
Title: Re: lower EC or ETTR?
Post by: Graystar on August 13, 2012, 02:10:27 pm
I must confess that I fail to see why "18%" or "12.7%" would ever have to be mentioned in a discussion about digital cameras. Film cameras might be another story, but I don't know much about those.

The gray reference is still important to digital cameras because that's how the camera meter works.

Lets look back several posts.  I made the statement that if there's any white in the scene, then you can't ETTR.  I was asked to explain that statement.  The explanation is that if you set standard exposure...that is, set your exposure by spot metering a 12.7% gray reference, then any objects that are white will be near saturation.  Therefore, you can't ETTR ("ETTR" taken to mean pushing exposure beyond standard exposure for the purpose of increasing signal.)

If your scene consist entirely of mid-tones, then you can ETTR, increase signal, and reduce noise.  But the brighter the highlights in the scene, the closer you'll get to standard exposure because your overexposure latitude keeps shrinking as the highlights get brighter.

Yes, ETTR is a sound concept.  Just have to realize that on scenes with white objects and bright highlights, standard exposure is pretty much the same as an exposure arrived at through ETTR.
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 13, 2012, 05:02:39 pm
.that is, set your exposure by spot metering a 12.7% gray reference, then any objects that are white will be near saturation.  
you are assuming that amount of light falling on two does not influence the outcome... you might gave a grey object illuminated so that it will reflect more light in the end than white object... plus 12.7% is how spot meter assumes the reflectance of the target (and it varies - you need to check how your camera model meters, even around 12.7% is how most of them do), not actual reflectance of the gray reference.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 13, 2012, 05:52:47 pm
you are assuming that amount of light falling on two does not influence the outcome... you might gave a grey object illuminated so that it will reflect more light in the end than white object... plus 12.7% is how spot meter assumes the reflectance of the target (and it varies - you need to check how your camera model meters, even around 12.7% is how most of them do), not actual reflectance of the gray reference.

You're creating random situations, and that's of no help.  Exposure is based on the light source.  When you have a single light source, setting exposure by spot metering a 12.7% card (or equivalent, compensated reference such as an 18% card with +0.5 EC applied) will give you an exposure where white (90%+ reflectance) will be near saturation...always.

When a scene has two light sources then you have to start making compromises.  That's what you have in outdoor scenes where part of the frame is lit by direct sunlight and the other part is in open shadow (the sky glow is the light source, which is why light in open shade is so blue.)  In such a case, you have to decide what's important and adjust exposure accordingly.  But just because such situations exist doesn't mean we toss the basic knowledge.  A gray card is just a tool...but a valuable one if you understand how to use it.


And the 12.7% doesn't vary.  Otherwise, you couldn't use a handheld meter to set exposure.

There's a youtube video of some guy attempting to demonstrate how to calibrate a Canon 7D to a Sekonic meter.  It's terrible.  But although everything he did was wrong, the video indirectly demonstates that the 7D, Sekonic, and another Minolta meter that he used were all calibrated exactly the same way (before he ruined the Sekonic with his "calibration".)  Nikon is also 12.7% gray.

I keep hearing that exposure varies but I never see it demonstrated.  On the other hand, I know that if you spot meter a white or gray wall, the metered area will be rendered as sRGB 100 (before any processing) on Canon, Nikon, and Pentax at least (and Sekonic meters will give the same exposure values.)

Title: Re: lower EC or ETTR?
Post by: Tony Jay on August 14, 2012, 01:46:07 am
...Yes, ETTR is a sound concept.  Just have to realize that on scenes with white objects and bright highlights, standard exposure is pretty much the same as an exposure arrived at through ETTR...

Read all the entries but this summary statement is pretty much spot on.

Regards

Tony Jay
Title: Re: lower EC or ETTR?
Post by: stamper on August 14, 2012, 05:52:07 am
The gray reference is still important to digital cameras because that's how the camera meter works.

I take it then you aren't a fan of the zone system of metering?
Title: Re: lower EC or ETTR?
Post by: Tony Jay on August 14, 2012, 07:10:48 am
The OP is certainly getting his money's worth from his question.

Zone system metering was not part of the original brief but is a valid approach to metering.
In a lot of outdoor situations a similar exposure to ETTR will result because of the high dynamic range of the scene.

Regards

Tony Jay
Title: Re: lower EC or ETTR?
Post by: hjulenissen on August 14, 2012, 07:35:11 am
If you adjust exposure so as to minimize the headroom above the brightest parts of the scene, you are moving the histogram such that it almost touches the clipping point. Some call this ETTR, but I think that it is counter-productive. The procedure should be to move those parts of the scene that you _care_ about as far as possible to the right. This could mean clipping highlights if you only want them approximately recorded (or plan to crop them later on). The point is to maximize the recorded signal level without clipping, assuming that higher recording levels means higher SNR. We might call this ETTR or whatever, I might call it "sensible digital recording levels", or SDRL :-)

An exposure strategy based on placing the middle part of the histogram (or some other particular quantile) at any particular place along the camera DR is fundamentally different. It seems suited for a camera technology that have symmetric error mechanisms in highlights and shadows. It _might_ happen to give similar exposure values as ETTR for some scene/camera combinations, but that is more of a coincidence.

http://www.cambridgeincolour.com/tutorials/camera-metering.htm
"What constitutes middle gray? In the printing industry it is standardized as the ink density which reflects 18% of incident light, however cameras seldom adhere to this. This topic deserves a discussion of its own, but for the purposes of this tutorial simply know that each camera has a default somewhere in the middle gray tones (~10-18% reflectance). Metering off of a subject which reflects more or less light than this may cause your camera's metering algorithm to go awry — either through under or over-exposure, respectively.
...
many cameras contain sophisticated algorithms which try to circumvent this limitation, and estimate how bright an image should be. These estimates frequently result in an image whose average brightness is placed in the midtones. "

-h
Title: Re: lower EC or ETTR?
Post by: Graystar on August 14, 2012, 07:53:47 am
I take it then you aren't a fan of the zone system of metering?

I don't understand what zone metering has to do with this.

First, most people don't realize that Adams' Zone System included film development and print processing in order to produce an image of Adams' vision of the scene...which may or may not (more often not) match human vision of the scene.  First you meter the different areas of the scene to get the luminance differences, then you decide what you want those differences to actually be, and where you want them on the EV scale.  Finally you expose and develop and print to realize your vision.  The Zone systems is more about producing and image than capturing an image.

Regardless...you still need to understand how the meter works, and that's all that I explained.  Spot meter a 12.7% gray surface, and white objects are near saturation.  That's how it works.
Title: Re: lower EC or ETTR?
Post by: stamper on August 14, 2012, 08:35:14 am
You answered the question I posed. The reason I posed it was that it is indeed a different method.

<The Zone systems is more about producing and image than capturing an image.>

I don't see why you differentiate between producing and capturing? It is surely the end product that counts? Assuming that there isn't a "correct" way of getting an exposure and only a subjective way then what ever it takes is surely valid? The zone system uses lower EC as well as higher EC which means that it is pertinent to the OP,s question.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 14, 2012, 08:52:03 am
"This topic deserves a discussion of its own, but for the purposes of this tutorial simply know that each camera has a default somewhere in the middle gray tones (~10-18% reflectance)."

No source for this information is listed.  As I said, Canon, Nikon, Pentax cameras are calibrated to 12.7% (sRGB 100, 100, 100), and Sekonic meters are supposedly 12.5% (sRGB 99, 99, 99) according to their website.  I can't speak for all cameras, but if a camera meter is calibrated to ISO standards then it should turn out to be 12.7%.

Title: Re: lower EC or ETTR?
Post by: Graystar on August 14, 2012, 08:58:36 am
I don't see why you differentiate between producing and capturing?

I'm not differentiating production and capture generally...only as related to the application of the Zone System in its classic form.  The Zone system was applied through the entire process, whereas ETTR is applied at capture time.  The resulting capture should allow you to accomplish your pictorial goals, but the goal of the process called ETTR is achieved entirely at capture time. I was simply drawing a distinction.

Title: Re: lower EC or ETTR?
Post by: stamper on August 14, 2012, 09:14:57 am
I think you are confusing film thinking with digital thinking. The original zone system was perfected for film and later adapted for digital. The digital way of doing things is implemented at capture. A previous poster also pointed out that the mid tone way of doing exposure is more suited to film than digital. A lot of photographers who make the leap from film to digital still try to use a mid tone and some a light meter. They then struggle to implement the thinking to adapt to digital and struggle.  :)
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 14, 2012, 10:10:36 am
And the 12.7% doesn't vary.  Otherwise, you couldn't use a handheld meter to set exposure.

actually it does - http://www.libraw.org/articles/Canon-5Dmk2-headroom.html


Title: Re: lower EC or ETTR?
Post by: jeremypayne on August 14, 2012, 10:46:04 am
Spot meter a 12.7% gray surface, and white objects are near saturation.  That's how it works.

Really?  It doesn't depend at all on the lighting of the scene, where in that scene the grey surface is or what the dynamic range is of the capture device?

This works the same for my RX100, my iPhone and my D700?  Really?
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 14, 2012, 10:51:14 am
Really?  It doesn't depend at all on the lighting of the scene, where in that scene the grey surface is or what the dynamic range is of the capture device?

This works the same for my RX100, my iPhone and my D700?  Really?

calibrate your camera spot meter for various illumination = http://www.rawdigger.com/houtouse/lightmeter-calibration
Title: Re: lower EC or ETTR?
Post by: Graystar on August 14, 2012, 12:38:47 pm
actually it does - http://www.libraw.org/articles/Canon-5Dmk2-headroom.html

I'm not sure what I'm supposed to get from that.  After presenting the same unsubstantiated information that everyone else does and making some quesitonable presumptions, it seems like he took a few pictures and then proceeded to draw conclusions that probably should have been experimentally verified with an additional set of captures demonstrating saturation at the predicted overexposure levels.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 14, 2012, 12:50:45 pm
Really?  It doesn't depend at all on the lighting of the scene, where in that scene the grey surface is

If you had read the thread you would have found this...
http://www.luminous-landscape.com/forum/index.php?topic=68930.msg551425#msg551425


Quote
or what the dynamic range is of the capture device?

DR of the device doesn't matter.


Quote
This works the same for my RX100, my iPhone and my D700?  Really?

Yes, really.
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 14, 2012, 01:02:12 pm
I'm not sure what I'm supposed to get from that.  After presenting the same unsubstantiated information that everyone else does and making some quesitonable presumptions, it seems like he took a few pictures and then proceeded to draw conclusions that probably should have been experimentally verified with an additional set of captures demonstrating saturation at the predicted overexposure levels.


well to his credentials he is one of two people behind rawdigger and libraw (along w/ Iliah Borg)... and yours ?
Title: Re: lower EC or ETTR?
Post by: Guillermo Luijk on August 14, 2012, 01:58:48 pm
Quote from: hjulenissen
I must confess that I fail to see why "18%" or "12.7%" would ever have to be mentioned in a discussion about digital cameras. Film cameras might be another story, but I don't know much about those.

I agree.

The gray reference is still important to digital cameras because that's how the camera meter works.

In a modern digital camera (unfortunately this still excludes most DSLR cameras), the camera meter is completely unnecesary and obsolete. In my M4/3 camera (those ones you ridiculize because of their optimized sensor size), I don't need to meter anything to quickly obtain accurate exposure (which can be either ETTR or a perfect JPEG), basically because its electronic viewfinder allows me to use a real time pre-visualization method (you can see how the final image will result before clicking the shutter), versus the old fashioned metering + post-visualization scheme most DLSR's use (that often requires iteration to obtain accurate exposure).

Most camera users don't shoot in a studio with several flash lights, and don't want heavy and bulky gear hanging in our necks. We just take pictures in our trips, countryside and city walks, or friends and family meetings. For us digital capture using the camera meter is a completely obsolete technique. It's just the big camera manufacturers haven't realised yet and even in their entry level cameras still prefer to implement this obscure and rudimentary tool:

(http://www.melissamccrottyblog.com/wp-content/uploads/2011/02/camera-light-meter.jpg)

rather than providing the user a real time scene's preview where underexposed and clipped areas are displayed in an intuitive way.

Regards
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 14, 2012, 03:03:14 pm
I don't need to meter anything to quickly obtain accurate exposure (which can either be ETTR or a perfect JPEG), basically because its electronic viewfinder allows me to use a real time pre-visualization method (you can see how the final image will result before clicking the shutter), versus the old fashioned metering + post-visualization scheme most DLSR's use (that often requires iteration to obtain accurate exposure).

ever tried tungsten light - how accurate is your meter (w/o you adjusting what camera meters)
Title: Re: lower EC or ETTR?
Post by: Graystar on August 14, 2012, 03:43:36 pm
well to his credentials he is one of two people behind rawdigger and libraw (along w/ Iliah Borg)... and yours ?

I don't have any.  That's why any information I give can be easily verified by anyone reading.
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 14, 2012, 04:06:27 pm
I don't have any.  That's why any information I give can be easily verified by anyone reading.

 ;) ... an everybody w/ Canon 5D mkII can verify spot metering himself/herself based on the technique described
Title: Re: lower EC or ETTR?
Post by: hjulenissen on August 14, 2012, 04:41:04 pm
You seem to be very much concentrated on describing how Auto-Exposure in most current cameras work. That is important knowledge for most of us.

Knowing that no man-made Auto-anything is perfect, I am more interested in how exposure ideally should be set (either using manual labour, or some improved algorithm).

From my point of view, positioning the middle tones at some pre-defined point along the sensor DR without regard for saturation is just backwards for digital sensors. The fact that it has worked for many years for film, and that many digital manufacturers/users are able to make good images using rules of thumb does in no way prove that it is the best way to do things.

An example (mentioned by Graystar?) is a landscape where 1/2 is directly lit, while 1/2 is in the shade, or 1/2 is the evening sky, while 1/2 is landscape below. The photographer might want to capture as much information as possible about the entire scene (perhaps expecting to use a simulated graduated ND filter in Lightroom afterwards). The best way to utilize a limited DR digital sensor would probably be to bring the bright parts as close to the clipping/significantly non-linear part of the sensor as possible. Then the dark parts would be raised as high as possible above the noise-floor, and hopefully acceptable. If the scene DR is too high compared to the sensor DR, no single-image non-ND-filtered shot is going to capture it satisfactory, no matter what exposure technique.

-h
Title: Re: lower EC or ETTR?
Post by: digitaldog on August 14, 2012, 04:46:20 pm
Before we talk about exposure, exposure meters, what percentage they ‘see’ (which shouldn’t be important), don’t we have to properly define the processing too? We’d never take color neg film, pop the ISO suggested into the meter and then blindly accept that without bracketing quite a bit, then including the processing of the film into the proper exposure system would we?

The meter may tell us one thing. Is it really automatically dialed into the raw processing? Nope. Do we know the limit the sensor can record the highlight data we want to capture (not blown out), without bracketing and testing the raw processor to see at what point we really do clip data versus seeing what appears to be clipped that isn’t until we normalize the rendering using the various sliders? What appears totally blown out using the meter recommendation on the LCD is absolutely no indication the data (raw) really is blown out. I don’t see how we can discuss exposure without introducing development into the process. At least for raw.
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 14, 2012, 06:05:17 pm
to bring the bright parts as close to the clipping/significantly non-linear part of the sensor as possible.

but then you need to decide if those bright parts are more important colorwise than noise in shadows - may be you can allow yourself to place bright parts into non linear area and sacrifice there to gain better SNR for shadows (that is when bracketing, graduated filters, etc can't be used)... so it is case by case decision.
Title: Re: lower EC or ETTR?
Post by: Guillermo Luijk on August 14, 2012, 06:33:52 pm
From my point of view, positioning the middle tones at some pre-defined point along the sensor DR without regard for saturation is just backwards for digital sensors. The fact that it has worked for many years for film, and that many digital manufacturers/users are able to make good images using rules of thumb does in no way prove that it is the best way to do things.

I agree again with you guy ;D
Let's consider the 3 stages in a digital workflow: scene -> capture (RAW file) -> output image (print, digital image,...):


Regards
Title: Re: lower EC or ETTR?
Post by: hjulenissen on August 15, 2012, 01:43:25 am
but then you need to decide if those bright parts are more important colorwise than noise in shadows - may be you can allow yourself to place bright parts into non linear area and sacrifice there to gain better SNR for shadows (that is when bracketing, graduated filters, etc can't be used)... so it is case by case decision.
Yes, if the scene DR is larger than the sensor effective DR, you might have to compromise both the top end and the bottom end (if you want to do it in one shot, no graduated ND etc). There are two ways of seeing this:
1. You are off into subjective land, and only trial & error, experience and good old luck will guide you
2. You may be able to sacrifice highlights, either because you don't care about them, or because you believe that they can be salavaged. This sacrifice may or may not be sufficient that you can "ETTR" the next-brightest parts.

-h
Title: Re: lower EC or ETTR?
Post by: hjulenissen on August 15, 2012, 01:49:40 am
What appears totally blown out using the meter recommendation on the LCD is absolutely no indication the data (raw) really is blown out.
I don't think that there is _no_ correlation between those two. The problem is that the correlation is far from perfect?

Yes, camera manufacturers do their best to make this hard. Amazing, really. Up until they get their act together, I think that a lot of confusion can be avoided by trying to figure out how exposure ideally should be (on digital cameras). Many people seem to have wildly different ideas of how exposure should be, perhaps based on experiences with film, with complex raw developers, or with misleading intuition. We all have to accept compromises, and 1 or 2 stops of metering uncertainty headroom may be one of those - for now.

-h
Title: Re: lower EC or ETTR?
Post by: hjulenissen on August 15, 2012, 02:05:25 am
  • What it's new and interesting IMO is the correspondence between scene and output image. Camera metering/Zone System exposure based criteria said a 18% gray card should end in the middle point of the perceptual luminance scale. Does it make sense? or this was just an arbitrary rule that worked in the past but can be ignored? should every particular reflectivity in real life end at the same luminance point in the output? should a picture of a Kodak graycard be L*=50% in the output no matter if the picture was taken at 12h00 in a sunny day or at 21h00 with the sun set and the sky darkening?
Pure guesswork:
Film had a more _symmetric_ error behaviour than digital. The brightest parts and the darkest parts of the scene were somewhat gradually distorted. Due to this, it made sense to center the histogram close to the mid-point (assumed most linear). For high DR scenes, you either used wide DR film, or the highlights would be compressed and the shadows would be noisy, and that was ok.

If I am right, the "18% gray" rule really is more about capture exposure than end-to-end exposure. Only because the two were practically interlocked did they not separate.

It would be interesting to know what those who shoot film today (with its response curves), but using a digital postprocessing approach (with the freedom to manipulate exposure and tonality afterwards) do with their field exposure?

Capture exposure and rendering exposure can never be perfectly separated (even though we would like it):
If you know that you want to do a (extreme) high-key or low-key image, you might only be interested in a small portion of the histogram. Then ETTR digital or 18% film may not be the best option simply because most of the captured information is going to be clipped in print anyways, and the (histogram tail) information that you do care about might not be captured optimally. So ETTR and similar should not be stated "push the brightest parts of the scene as far to the right as possible without entering sensor nonlinearity". It should be stated "push the brightest parts of the scene that you care about as far to the right as possible without entering sensor nonlinearity"

-h
Title: Re: lower EC or ETTR?
Post by: Graystar on August 15, 2012, 07:38:55 am
;) ... an everybody w/ Canon 5D mkII can verify spot metering himself/herself based on the technique described

That's right.  But even if verified as correct (because at this point they haven't been, as far as I know,) the results only matter to ETTR practitioners.  And even then, no metering methodology was described.

I don't have a 5DMII, but unless its meter calibration is vastly different than other Canons like the 7D, I can tell you that if you spot meter a neutral, evenly lit surface, then a white-balanced RAW conversion of the resulting capture, with no additional processing, will have sRGB values of 100, 100, 100 at the metered area.  That's 12.7% gray.  The reason that's important is because it tells you exactly how much headroom you have above the metering point...which is just under 3 stops.

The article stated that the metering point gave 3.6-3.8 stops (or thereabouts) of headroom.  But what about tungsten light (as you've mentioned) or worse, sodium lights?  That headroom is gone in those instances.  I don't practice ETTR and even I have to cut back my exposure by 1/3rd stop in those conditions.

The camera makers cannot base their metering systems on ETTR practitioners.  The metering is (currently) designed to match film-based metering.  And when metering as such, the processing has to allow for no clipping of reflected white under a very large range of lighting conditions.  And if that requirement resulted in some unused headroom in daylight conditions, then so be it.  ETTR practitioners can make use of the headroom when it's available, or just overexpose to their liking...whatever.  But don't invalidate other's metering methods just because they don't fit with YOUR view of how digital should be metered.

I have an RMI Digital Gray Card that I use for both white balance and for setting exposure when in constant-light conditions.  The reference itself is marketed as a WB tool only, as it's about 30% gray.  But I determined an appropriate EC value by shooting some 92% bright copy paper under a 5000K light until RawDigger indicated saturation, then just placing the reference in the spot-meter area to see the difference in metering.  That's my EC, which turned out to be about 1.3 EV (1.0 EV when the light gets red.)

Anytime I step into new light I will pull the gray card from my back pocket, perform a custom white balance, and if the light is constant, I'll just press my AE-L button to lock exposure.  That's it...I'm done with exposure.  I can photograph anything illuminated by the same light and know that I won't clip any reflected highlights.  Could I have pushed exposure by 1/3 or 2/3 stops in some cases?  Sure...but I rarely shoot scenes that are so static that I have time to figure that out, and I usually don't care about having 2/3 stop more noise.  The only time it matter to me is when photographing my black dog.  In that case I'll just use the ETTR that's built-into my camera...the expanded ISO range.  I'll just set my Nikon to L1.0...instant ETTR.
Title: Re: lower EC or ETTR?
Post by: digitaldog on August 15, 2012, 10:17:09 am
I can tell you that if you spot meter a neutral, evenly lit surface, then a white-balanced RAW conversion of the resulting capture, with no additional processing, will have sRGB values of 100, 100, 100 at the metered area. 

What raw converter with what (default) settings?
Title: Re: lower EC or ETTR?
Post by: Graystar on August 15, 2012, 11:07:42 am
What raw converter with what (default) settings?
LightRoom with its neutral profile...I forget the name of it, but it doesn't apply any processing.

Raw Therapee with the "Neutral" profile.

Rawnalyze with sRGB.
Title: Re: lower EC or ETTR?
Post by: digitaldog on August 15, 2012, 12:01:36 pm
LightRoom with its neutral profile...I forget the name of it, but it doesn't apply any processing.

Neutral Camera profile? Neutral (default) rendering settings? Who says either are ideal? They are just a starting point. I can set the camera to ‘over expose’ 1.5 stops past what the meter recommends, normalize the image in LR using Exposure. So what makes my capture and your capture different, which is ideal?

Again, I don’t see how we can separate the exposure from the processing. Setting a 1.5 stop increase will blow out the JPEG but the raw is just fine after normalizing in my raw converter.
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 15, 2012, 12:22:26 pm
But what about tungsten light (as you've mentioned)
metering will underexpose...
Title: Re: lower EC or ETTR?
Post by: Graystar on August 15, 2012, 12:38:37 pm
Neutral Camera profile? Neutral (default) rendering settings? Who says either are ideal?
Not me.  My words on the subject, located elsewhere in the thread, is that standard exposure is a tool, not a destination.

Quote
They are just a starting point.
Exactly.  Darn good starting point.

Quote
I can set the camera to ‘over expose’ 1.5 stops past what the meter recommends, normalize the image in LR using Exposure. So what makes my capture and your capture different, which is ideal?
As I said, standard exposure is just a tool.  It allows me to know what I'm getting.  What I get may be just right, or may require an hour or more of processing.  What's important is that I know I've captured a good starting point.

Quote
Again, I don’t see how we can separate the exposure from the processing. Setting a 1.5 stop increase will blow out the JPEG but the raw is just fine after normalizing in my raw converter.
1.5 stop increase over what metering point?  And to what JPEG are you referring to...an OOC or one with no processing?  I'm trying to ascertain whether the blown highlights are from the initial RAW conversion, or from one-size-fits-all default processing.  I'm no fan of OOC JPEGs, but I find that when using the Neutral picture control of my Nikon, that OOC JPEGs won't clip white unless RAW does (red is always another story.)
 
Title: Re: lower EC or ETTR?
Post by: digitaldog on August 15, 2012, 12:43:02 pm
1.5 stop increase over what metering point?  And to what JPEG are you referring to...an OOC or one with no processing?

Yes, 1.5 stops OVER what the incident meter suggested (ETTR) with raw normalization that shows zero blown highlights.

The JPEG I’m referring to is the camera generated JPEG that would be totally blown out using that meter suggestion. You can’t expose for raw and JPEG the same way. One major reason is the processing which I continue to ask: how can we separate that from the discussion and process. The JPEG processing is in-camera, the raw under my control. One is a useless exposure, the other is pristine with far less noise due to ETTR.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 15, 2012, 01:19:50 pm
metering will underexpose...
When metering under tungsten light, if I increase exposure by 1/3rd stop over standard exposure, I will clip the green in bright white objects.  So my Nikon, at least, doesn't underexpose in tungsten light.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 15, 2012, 02:22:58 pm
Yes, 1.5 stops OVER what the incident meter suggested (ETTR) with raw normalization that shows zero blown highlights.
And what did the camera meter suggested?

Quote
The JPEG I’m referring to is the camera generated JPEG that would be totally blown out using that meter suggestion. You can’t expose for raw and JPEG the same way. One major reason is the processing which I continue to ask: how can we separate that from the discussion and process. The JPEG processing is in-camera, the raw under my control. One is a useless exposure, the other is pristine with far less noise due to ETTR.
Well..."far less" might be a stretch...but anyways, I'm not sure why we're concerned about the in-camera JPEG to begin with.
Title: Re: lower EC or ETTR?
Post by: digitaldog on August 15, 2012, 02:26:59 pm
And what did the camera meter suggested?

Probably something equally wrong (considering I was metering with an Incident meter) <g>. Plus I was shooting flash. The images can be seen here (page 4):
http://www.digitalphotopro.com/technique/camera-technique/exposing-for-raw.html

Quote
Well..."far less" might be a stretch...but anyways, I'm not sure why we're concerned about the in-camera JPEG to begin with.

And yet, that is exactly what the meter is aiming for along with a defined and understood processing.
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 15, 2012, 03:10:16 pm
When metering under tungsten light, if I increase exposure by 1/3rd stop over standard exposure, I will clip the green in bright white objects.  So my Nikon, at least, doesn't underexpose in tungsten light.
no Graystar - I was referring to my question/note to Guillermo (see what I was answering above), who was essentially saying that spot metering is not necessary... he saying basically that matrix metering or centerweight metering will be good and I was saying that such metering will underexpose under the tungsten light... he knows that for sure, but his position is (I guess) that w/ modern sensors and raw converters that is OK and we do not need to put any expo correction for such metering in camera under such light...
Title: Re: lower EC or ETTR?
Post by: bjanes on August 15, 2012, 03:38:06 pm
Yes, 1.5 stops OVER what the incident meter suggested (ETTR) with raw normalization that shows zero blown highlights.

The JPEG I’m referring to is the camera generated JPEG that would be totally blown out using that meter suggestion. You can’t expose for raw and JPEG the same way. One major reason is the processing which I continue to ask: how can we separate that from the discussion and process. The JPEG processing is in-camera, the raw under my control. One is a useless exposure, the other is pristine with far less noise due to ETTR.

The DigitalDog is correct: calibration of the meter and calibration of the sensor are two separate and essential components that govern sensor saturation for a given light meter reading determined exposure. Reflected light meters are governed by ISO 2720:1974 (see Wikipedia (http://en.wikipedia.org/wiki/Light_meter)). The sensor calibration is governed by ISO 12232:2006 (again see Wikipedia (http://en.wikipedia.org/wiki/Film_speed#The_ISO_12232:2006_standard)). If the saturation standard is used (as with DXO measurements), exposure of an 18% reflectance card will give 12.7% sensor saturation. This allows 0.5 EV highlight headroom. However, some manufacturers wish to provide more headroom. This could be accomplished by changing the calibration of the meter or the sensor. Changing the calirbration of the meter would cause conflicts with external meters, so the sensor calibration is usually changed.

Phase One backs allow a great deal of headroom as shown by the sensor DXO ISO measurements for Phase One sensors. A light metered exposure of a gray card would give much less than 12.7% saturation. If the raw file is rendered, the tone curve used by the raw developer or in camera JPEG engine also comes into play.

With my Nikon D3 a metered exposure of a gray card gives close to 12.7% saturation, but my D800 gives closer to 15% saturation. ACR 7.1 and LR 4.1 with PV2012 use hot tone curves, and the rendered sRGB values are considerably greater than the expected value of 118.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 15, 2012, 05:21:40 pm
If the saturation standard is used (as with DXO measurements), exposure of an 18% reflectance card will give 12.7% sensor saturation. This allows 0.5 EV highlight headroom.

Actually, exposure of any value of reflectance will give 12.7% saturation.  It's the fact that you used an 18% card that will give you 0.5 EV "headroom", which is the same as being 0.5 EV underexposed.  If you used a 25% card you'd have 1.0 EV of headroom.  But this idea of headroom is questionable, as the most common 18% card, the Kodak, comes with instructions to increase exposure by 0.5 EV.  So anyone using an 18% card as instructed has no headroom.

If the D800's metering point provides 15% saturation then I hope there's an instruction somewhere to disregard Kodak's instructions...otherwise anyone who doesn't will be clipping his whites and not understanding why (other than the obvious "this is not a film camera.")
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 15, 2012, 05:28:07 pm
Actually, exposure of any value of reflectance will give 12.7% saturation.  It's the fact that you used an 18% card that will give you 0.5 EV "headroom", which is the same as being 0.5 EV underexposed.  If you used a 25% card you'd have 1.0 EV of headroom.  But this idea of headroom is questionable, as the most common 18% card, the Kodak, comes with instructions to increase exposure by 0.5 EV.  So anyone using an 18% card as instructed has no headroom.

If the D800's metering point provides 15% saturation then I hope there's an instruction somewhere to disregard Kodak's instructions...otherwise anyone who doesn't will be clipping his whites and not understanding why (other than the obvious "this is not a film camera.")

that is why particular camera model has to be tested and not assumed that its spot meter will be giving 12.x%
Title: Re: lower EC or ETTR?
Post by: Graystar on August 15, 2012, 07:27:53 pm
that is why particular camera model has to be tested and not assumed that its spot meter will be giving 12.x%
That would only be for ETTR practitioners.  For everyone else, all that matters is the unprocessed sRGB values.

When a D800 spot meters and photographs an evenly lit neutral surface...if the resulting image, demosaiced and white balanced only, reads 100, 100, 100 in the metered area, then it meters just like every other Nikon.  I would be surprised if it didn't.  If it does, then the Kodak gray card and instructions will work just fine.
Title: Re: lower EC or ETTR?
Post by: bjanes on August 15, 2012, 11:23:38 pm
That would only be for ETTR practitioners.  For everyone else, all that matters is the unprocessed sRGB values.

When a D800 spot meters and photographs an evenly lit neutral surface...if the resulting image, demosaiced and white balanced only, reads 100, 100, 100 in the metered area, then it meters just like every other Nikon.  I would be surprised if it didn't.  If it does, then the Kodak gray card and instructions will work just fine.


Again, you are confusing the meter reading, which would give an f/stop and shutter speed for a given ISO. How the sensor would respond to this exposure is a different matter. According to the REI (recommended exposure index) that Japanese manufactures use, they may assign whatever sensor ISO they want, and the resulting sensor saturation may or may not be 12.7%. In your earlier posts you made some good points, but more recently you have gotten off track. Please read up on these topics before posting again. Doug Kerr has a good paper (http://dougkerr.net/pumpkin/articles/Exposure_Calibration.pdf) on the subject.

To determine the sensor saturation, one has to look directly at the raw file with a program such as Rawdigger. The first step is to determine the saturation value, which may not be 2^14 -1 (16383) for a 14 bit ADC. One then determines the raw value for the exposure (the ISO mentions an 18% card, but any uniform target (gray or white) will do as you mentioned. One may have to subtract an offset (Canon cameras). The quotient of these values is the percent saturation. The rendered sRGB value can not be used since a tone curve may have been applied.


DXO (http://www.dxomark.com/index.php/About/In-depth-measurements/Measurements/ISO-sensitivity) describes how they determine sensor sensitivity and how the manufacturer may deviate from the saturation standard. Look at the ISO measurement for the Phase One IQ180.

Regards,
Bill
Title: Re: lower EC or ETTR?
Post by: Graystar on August 16, 2012, 03:14:02 pm
Again, you are confusing the meter reading, which would give an f/stop and shutter speed for a given ISO. How the sensor would respond to this exposure is a different matter. According to the REI (recommended exposure index) that Japanese manufactures use, they may assign whatever sensor ISO they want, and the resulting sensor saturation may or may not be 12.7%. In your earlier posts you made some good points, but more recently you have gotten off track. Please read up on these topics before posting again. Doug Kerr has a good paper (http://dougkerr.net/pumpkin/articles/Exposure_Calibration.pdf) on the subject.

To determine the sensor saturation, one has to look directly at the raw file with a program such as Rawdigger. The first step is to determine the saturation value, which may not be 2^14 -1 (16383) for a 14 bit ADC. One then determines the raw value for the exposure (the ISO mentions an 18% card, but any uniform target (gray or white) will do as you mentioned. One may have to subtract an offset (Canon cameras). The quotient of these values is the percent saturation. The rendered sRGB value can not be used since a tone curve may have been applied.


DXO (http://www.dxomark.com/index.php/About/In-depth-measurements/Measurements/ISO-sensitivity) describes how they determine sensor sensitivity and how the manufacturer may deviate from the saturation standard. Look at the ISO measurement for the Phase One IQ180.

I'm not confusing anything.  You're the one who's confusing metering with response and processing.  You're doing this because you can only think it terms of ETTR.  But that's not how cameras are designed to be used.  Camera makers never intended photographers to base exposure from the un-demosaic values, as they provide no tools to access those values.

The meter doesn't produce an f/stop and shutter speed.  The meter combines a luminance reading with the ISO speed (the speed you select, not the REI) to produce an EV.  That EV is then biased by any EC that the photographer has applied.  Then the biased EV is passed to the camera's exposure program.   For example, if you're in Program mode then the EV is looked up on a chart (also considering focal length on some cameras) and then the camera sets the aperture and shutter listed for that EV.  That program-mode chart should be in the back of your camera manual.

Metering works exactly the same way in a digital camera as it does in a film camera, as it does across digital cameras.  My Canon compact, spot-metering my gray card, gives me the same exact exposure settings as my Nikon D90.  This is all defined by ISO 2721.  Metering has nothing to do with REI.

Once the image is captured, however, the camera maker has complete control over how the signals get processed.  This is where REI comes in.  REI is the equivalent of pushing/pulling film...the film has a rated speed (the ISO speed) but you can process it as if it were any other speed, depending on how you decided to expose the film.  REI is the same thing.  The manufacturers process the signals to produce, supposedly, a particular result...that result being an RGB image in the sRGB colorspace.  Although not explicitely defined for REI (it is for SOS,) the sRGB image should have 18% gray right at RGB 118 (referred to as the "standard level".)

By extension, that puts 12.7% gray at RGB 100.  As it is the expressed purpose of REI to match meters (see CPIA DC-004 Explanation) it is reasonable to expect that a meter with a K of 12.7 metering a 12.7% gray reference will produce an RGB image with values of 100.  The problem is accessing that image, as all cameras apply additional processing based on defaults, picture controls, HDR settings, etc.  So how to we see the base RGB image?  We use a RAW converter that allows us to demosaic the RAW and apply white balance and nothing else.

http://www.cipa.jp/english/hyoujunka/kikaku/pdf/DC-004_EN.pdf

Now...as to whether sRGB 100 actually represents 12.7% saturation of the sensor...that's a different topic.  sRGB 255 may not represent full saturation of the sensor, but it's close.  And again, actual full saturation is a concern of ETTR practitioners only. 

And yes, I've read DxO and many of Doug Kerr's papers...including the one you reference, as well as the one where his exposure test produced RGB 100, 100, 100.
http://dougkerr.net/pumpkin/articles/Scene_Reflectance.pdf

I see you edited your post and removed your erroneous comment about 18%.  I'm glad you corrected your error, but I suggest that next time you read up on these topics before posting.
Title: Re: lower EC or ETTR?
Post by: bjanes on August 17, 2012, 08:48:12 am

Metering works exactly the same way in a digital camera as it does in a film camera, as it does across digital cameras.  My Canon compact, spot-metering my gray card, gives me the same exact exposure settings as my Nikon D90.  This is all defined by ISO 2721.  Metering has nothing to do with REI.

Again, you don't seem to understand that REI or any other ISO value for the sensor is needed to determine the EV of the exposure as determined by the light meter. This is why the Canon 5D Mark II yields only 7.5% sensor saturation as shown in the Libraw post (http://www.libraw.org/articles/Canon-5Dmk2-headroom.html) which you have disregarded. Have you looked at your raw files, or are you just spouting theory that you do not understand?

And yes, I've read DxO and many of Doug Kerr's papers...including the one you reference, as well as the one where his exposure test produced RGB 100, 100, 100.
http://dougkerr.net/pumpkin/articles/Scene_Reflectance.pdf

You have read these articles, but your comprehension appears to be deficient. Further discussion with you is pointless, and I am out of here. Where is the kill button?

Bill
Title: Re: lower EC or ETTR?
Post by: Graystar on August 17, 2012, 11:23:09 am
Again, you don't seem to understand that REI or any other ISO value for the sensor is needed to determine the EV of the exposure as determined by the light meter. This is why the Canon 5D Mark II yields only 7.5% sensor saturation as shown in the Libraw post (http://www.libraw.org/articles/Canon-5Dmk2-headroom.html) which you have disregarded. Have you looked at your raw files, or are you just spouting theory that you do not understand?

Once again it is you who doesn't seem to understand what REI means.  The expressed purpose of REI is to produce exposures that match handheld meters.  From DCX400...

"Recommend Exposure Index is an exposure index corresponding to the average exposure in a focal plane recommended by camera (imaging system) vendors (manufacturers etc.) for the purpose of reference to the setting [of] an exposure index (film ISO speed value) when using a separate exposure meter or accessory strobe etc.."

"...when the aperture or shutter speed is to be obtained by using a reflective stand-alone exposure meter or accessory strobe, the average photometry values are used.  Adequate preset value of film sensitivity (exposure index) must be adapted to such equipment during photography, in which case the recommend value preset by the maker (in other words, the value to obtain the 'standard exposure' mentioned above) is the 'Recommend Exposure Index."

So the purpose of REI is to get digital cameras to produce the same results as film cameras when it comes to setting exposure via handheld meters (and also camera meters, I just didn't quote that part.) There is NOTHING in the REI definition relating to sensor saturation.

Still, it would be quite foolish of a manufacturer to design a camera such that 1 1/2 stops of DR are wasted, but yet produce JPEGs that have blown highlights.  Certainly my Nikon D90 does not work this way.  Sure, OOC JPEGs will clip before RAW does, but only by 1/5 stop or so.  And of course, that's only because they're in sRGB.  Set them to AdobeRGB and they clip less.  If we could set them to ProPhoto, they wouldn't clip at all.

And I didn't disregard the 5D test.  I noted that the conclusions drawn were unverified.


Quote
You have read these articles, but your comprehension appears to be deficient. Further discussion with you is pointless, and I am out of here. Where is the kill button?

I'll take that to mean that you photographed a gray card (or white wall) with your D800, saw that the metered areas of the images turned out to be 100, 100, 100 when using a neutral profile, and have no way to reconcile that result with your supposed 15% saturation...and are now looking for a way out.
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 17, 2012, 11:56:18 am
I'll take that to mean that you photographed a gray card (or white wall) with your D800, saw that the metered areas of the images turned out to be 100, 100, 100 when using a neutral profile, and have no way to reconcile that result with your supposed 15% saturation...and are now looking for a way out.

BJanes - may be you can do a favor and post a raw file from D800 please...
Title: Re: lower EC or ETTR?
Post by: Graystar on August 21, 2012, 01:15:05 pm
BJanes - may be you can do a favor and post a raw file from D800 please...

Doesn't look like you're going to get one.  Might I interest you in some Nikon D90 RAW files?

Here are three RAW files from my Nikon D90.  These shots are of my gray card in the sun, blurred.  The filenames start with an underscore because the color space was set to Adobe RGB.

_DSC9254.NEF is straight spot metering.
_DSC9255.NEF is at +2.7 EC.  The green channel isn't clipped.
_DSC9256.NEF is at +3.0 EC.  Here, the green channel is clipped.

ftp://graystar.tftpd.net/ (http://ftp://graystar.tftpd.net/)

12.7% gray, increased by +3, is 101.6%...so it makes sense that clipping is occurring at +3.0 EC.

Knowing this allows me to easily ETTR by simply setting EC to +2.7 and spot-metering the brightest highlight of a scene that I want to retain detail.  I just spot check a few areas to see which is the brightest.  No histogram needed.  That said, I find it simply isn't worth the effort because most of the scenes I shoot have a bright highlight somewhere with detail I want to keep.
Title: Re: lower EC or ETTR?
Post by: bjanes on August 21, 2012, 06:47:43 pm
BJanes - may be you can do a favor and post a raw file from D800 please...

Certainly. I have been out of town, so hence the delay. If you have interesting observations, please post them on the forum.


Stouffer wedge with step 1 just short of clipping in green channels (5000K), :

https://www.yousendit.com/download/TEhXb3BBMm11Yk5jR01UQw

Garden shot with Zeiss 21 Distagon at f/8, ISO 100. Green channels 1 EV short of clipping:

https://www.yousendit.com/download/TEhXb3BPd0E4NVd4djhUQw

Regards,

Bill
Title: Re: lower EC or ETTR?
Post by: Graystar on August 22, 2012, 10:12:27 am
BJanes - may be you can do a favor and post a raw file from D800 please...
If it's just any ol' RAW file from a D800 that you want, Imaging Resource has lots of them...

http://www.imaging-resource.com/PRODS/nikon-d800/nikon-d800THMB.HTM (http://www.imaging-resource.com/PRODS/nikon-d800/nikon-d800THMB.HTM)
Title: Re: lower EC or ETTR?
Post by: deejjjaaaa on August 22, 2012, 06:04:07 pm
If it's just any ol' RAW file from a D800 that you want, Imaging Resource has lots of them...

http://www.imaging-resource.com/PRODS/nikon-d800/nikon-d800THMB.HTM (http://www.imaging-resource.com/PRODS/nikon-d800/nikon-d800THMB.HTM)

I was talking about raw files to use for meter measurement as described in http://www.rawdigger.com/houtouse/lightmeter-calibration , so that you can see if D800 really meters like bjanes says or not...

Title: Re: lower EC or ETTR?
Post by: bjanes on August 22, 2012, 07:40:56 pm
I was talking about raw files to use for meter measurement as described in http://www.rawdigger.com/houtouse/lightmeter-calibration , so that you can see if D800 really meters like bjanes says or not...

Sorry, but I did not know what type of raw files you were seeking. I have uploaded files for calibration procedure to Usendit.

Img 1 is a white target exposed according to the meter. Illumination was Solux lamps.
http://www.yousendit.com/download/TEhXaklqaysxUUJjR01UQw?cid=tx-02002207340200000000&s=19102

Img 5 is a gross overexposure. Interestingly, ACR 7.1 renders the image as bright red on the screen. It looks white with Rawdigger.

http://www.yousendit.com/download/TEhXakl0NEhkMnMwTWRVag?cid=tx-02002207340200000000&s=19102

Readers can perform their own analysis, but here is my evaluation. I took two exposures with the metered reading, and the uploaded shot is exposure 1.

Title: Re: lower EC or ETTR?
Post by: Graystar on August 22, 2012, 08:43:38 pm
Sorry, but I did not know what type of raw files you were seeking. I have uploaded files for calibration procedure to Usendit.

Thank you for those images.  They confirm what I've been saying.

Matrix metering tends to set exposure around 1/3 stop higher than Spot/CW metering (as an aside...I think the actual value is smaller, and depending on the camera settings Matrix is usually 1/3rd stop more exposure and occasionally it's the same as Spot/CW.  At least that's what I've found on my D90, and it would appear that the D800 is the same.)

As stated, the metered value is 15% of the max value.  But that's with Matrix metering.  If Spot metering had been used then the metered area would likely end up around 12%.  It's pretty obviously to me that the D800's metering and RAW levels are much like my D90 (don't see why it wouldn't be) and spot metering a 12.7% gray card will likely get any bright whites under the same lighting near saturation without clipping.
Title: Re: lower EC or ETTR?
Post by: bjanes on August 22, 2012, 09:09:39 pm
Thank you for those images.  They confirm what I've been saying.

Matrix metering tends to set exposure around 1/3 stop higher than Spot/CW metering (as an aside...I think the actual value is smaller, and depending on the camera settings Matrix is usually 1/3rd stop more exposure and occasionally it's the same as Spot/CW.  At least that's what I've found on my D90, and it would appear that the D800 is the same.)

As stated, the metered value is 15% of the max value.  But that's with Matrix metering.  If Spot metering had been used then the metered area would likely end up around 12%.  It's pretty obviously to me that the D800's metering and RAW levels are much like my D90 (don't see why it wouldn't be) and spot metering a 12.7% gray card will likely get any bright whites under the same lighting near saturation without clipping.

According to my own tests with the 800e, if one is using a uniform target which occupies the whole field of view, the reading are the same regardless of the metering mode. This is also what is stated on the Rawdigger site:

"the grey target (a grey patch can also be used, as well as plain white paper, without optical whiteners). Turn off all exposure adjustments and shoot. If the target takes up the entire field of view of the shot, then the setting of the exposure meter does not matter; all settings (spot, matrix, center-weighted) will result in the same exposure. "

According to that article, the exposure results can also vary with the ISO and also the illumination. The spectral sensitivity of the meter may differ from that of the sensor.

Regards,

Bill
Title: Re: lower EC or ETTR?
Post by: Schewe on August 22, 2012, 10:01:27 pm
Not for nothing but you all realize this thread is in the Beginners' Questions forum? Ya all might want to keep that in mind...perhaps a new thread not here would be in order. Pretty sure many/most readers of the thread have run away and hidden already.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 22, 2012, 11:03:20 pm
According to my own tests with the 800e, if one is using a uniform target which occupies the whole field of view, the reading are the same regardless of the metering mode. This is also what is stated on the Rawdigger site:

"the grey target (a grey patch can also be used, as well as plain white paper, without optical whiteners). Turn off all exposure adjustments and shoot. If the target takes up the entire field of view of the shot, then the setting of the exposure meter does not matter; all settings (spot, matrix, center-weighted) will result in the same exposure. "

Technically, that's correct.  However, Matrix meters the entire frame, which includes falloff, and that can cause it to increase exposure over a spot meter reading.  And while the final image may not have much falloff due to the aperture use, metering always occurs wide open...so falloff is always an influence.  Obviously, the lens used is also a factor.  In any case, I've seen spot metering variations on my gray card from RGB 90 to RGB 110 in my D90, depending on the lens and conditions.  So the RGB 108 of your Exp1.NEF file is within the ball park.

My statement that started all this was, "If there's any white in the scene, then you can't ETTR."

Which I further clarified with, "Yes, ETTR is a sound concept.  Just have to realize that on scenes with white objects and bright highlights, standard exposure is pretty much the same as an exposure arrived at through ETTR."

Clearly, this applied to the D800.
Title: Re: lower EC or ETTR?
Post by: Graystar on August 22, 2012, 11:04:56 pm
Not for nothing but you all realize this thread is in the Beginners' Questions forum? Ya all might want to keep that in mind...perhaps a new thread not here would be in order. Pretty sure many/most readers of the thread have run away and hidden already.
You're right, but I think it's practically over now.
Title: Re: lower EC or ETTR?
Post by: bjanes on August 23, 2012, 10:38:02 am
Technically, that's correct.  However, Matrix meters the entire frame, which includes falloff, and that can cause it to increase exposure over a spot meter reading.  And while the final image may not have much falloff due to the aperture use, metering always occurs wide open...so falloff is always an influence.  Obviously, the lens used is also a factor.  In any case, I've seen spot metering variations on my gray card from RGB 90 to RGB 110 in my D90, depending on the lens and conditions.  So the RGB 108 of your Exp1.NEF file is within the ball park.

You raise a good point that I had not considered. In my previous test, I minimized falloff by using f/8 with a 105 mm lens. I repeated the tests with the Zeiss Distagon 21 mm f/2.8, which is an excellent lens but is known to have considerable falloff. Rather than upload the large raw files, I chose to merely show the results. However, the matrix metering results in lower saturation in my tests.

(http://bjanes.smugmug.com/Photography/Exposure/D800e-21-Distagon/i-g5g8jxB/0/O/Zeiss0001-20120823-090541.png)

(http://bjanes.smugmug.com/Photography/Exposure/D800e-21-Distagon/i-2BRNppP/0/O/Zeiss0003-20120823-090653.png)

(http://bjanes.smugmug.com/Photography/Exposure/D800e-21-Distagon/i-GtL5TBV/0/O/ExcelTable.gif)

These differences are not large, but could affect critical ETTR and should be accounted for in critical work. Jeff Schewe may object to these arcane matters in a thread for beginners, but good discussions often veer off in an interesting fashion, and help beginners progress to a more advanced stage.

Regards,

Bill
Title: Re: lower EC or ETTR?
Post by: Graystar on August 23, 2012, 02:17:49 pm
You raise a good point that I had not considered. In my previous test, I minimized falloff by using f/8 with a 105 mm lens. I repeated the tests with the Zeiss Distagon 21 mm f/2.8, which is an excellent lens but is known to have considerable falloff. Rather than upload the large raw files, I chose to merely show the results. However, the matrix metering results in lower saturation in my tests.

That's odd.

I have a different method of demonstrating the falloff effect.  I set the camera on a tripod to photograph a gray card, and then I take 4 images.  The first two, Spot and Matrix, are with a light source very close to the card so that the card exhibits falloff.  The second two, also Spot then Matrix, are with the light source moved further away to minimize falloff.  The result is that my first two images have different exposures, but the next two images don't...even though the only change to the camera, between the images of each pair, was the metering mode.  So that demonstrates that the falloff is affecting Matrix metering.

However, in my shots with the light source close to the gray card, the Matrix image is clearly brighter...which, to me, would be the expected result of a metering mode that is averaging dark areas with bright areas.  So I don't know why you got the opposite result.  I've put the NEF files on my FTP...

ftp://graystar.tftpd.net (http://ftp://graystar.tftpd.net) (this address has to be copied and pasted into the address bar, as the forum software is adding an "http://" in front of it.)

DSC_9310 - light source close, Spot (f/8, 1/640s)
DSC_9311 - light source close, Matrix (f/8, 1/400s)
DSC_9312 - light source far, Spot (f/8, 1/20s)
DSC_9313 - light source far, matrix (f/8, 1/20s)

EDIT: The only time you get standard exposure from Matrix is when Matrix fails to match a scene in its database.  Just wanted to note that with the D800's expanded scene database, it's possible that Matrix found a match between your image and one of its scenes, and applied the exposure compensation related to that scene (this is what makes Matrix so unpredictable.)
Title: Re: lower EC or ETTR?
Post by: bjanes on August 23, 2012, 04:00:14 pm
That's odd.

I have a different method of demonstrating the falloff effect.  I set the camera on a tripod to photograph a gray card, and then I take 4 images.  The first two, Spot and Matrix, are with a light source very close to the card so that the card exhibits falloff.  The second two, also Spot then Matrix, are with the light source moved further away to minimize falloff.  The result is that my first two images have different exposures, but the next two images don't...even though the only change to the camera, between the images of each pair, was the metering mode.  So that demonstrates that the falloff is affecting Matrix metering.

However, in my shots with the light source close to the gray card, the Matrix image is clearly brighter...which, to me, would be the expected result of a metering mode that is averaging dark areas with bright areas.  So I don't know why you got the opposite result.  I've put the NEF files on my FTP...

ftp://graystar.tftpd.net (http://ftp://graystar.tftpd.net) (this address has to be copied and pasted into the address bar, as the forum software is adding an "http://" in front of it.)

DSC_9310 - light source close, Spot (f/8, 1/640s)
DSC_9311 - light source close, Matrix (f/8, 1/400s)
DSC_9312 - light source far, Spot (f/8, 1/20s)
DSC_9313 - light source far, matrix (f/8, 1/20s)

EDIT: The only time you get standard exposure from Matrix is when Matrix fails to match a scene in its database.  Just wanted to note that with the D800's expanded scene database, it's possible that Matrix found a match between your image and one of its scenes, and applied the exposure compensation related to that scene (this is what makes Matrix so unpredictable.)

My method was to illuminate a white screen with 6 Solux lamps equipped with diffusers so that the illumination was uniform. The falloff is entirely due to the lens. With your setup, falloff can be related to both scene illumination as well as lens vignetting. However, the effect on the metering system and the sensor should be the same. Your explanation is reasonable. The take home point is that if one wishes to apply compensation to the metered value (ETTR for example) one should not use matrix, since a compensation has already been applied and the manual compensation may be in the same or opposite direction.

Regards,

Bill