interesting article

[Chris_T]

It takes quite a bit of overexposure to blow out blue sky, since neither the luminance nor saturation of clear blue sky is that high. Much more likely, is blowing out of the clouds in a blue sky as shown in the shot of the Golden Gate Bridge in Bruce Fraser's article. With the histogram in ACR it is easy to see which channels are blown. In my experience with ACR and my shooting, the blown channels most often show as white in the histogram, as in Bruce's example, indicating all three channels are blown in the white balanced image. Your mileage may vary, but the essential point is that highlight recovery requires data in at least one channel.

http://www.macworld.com/2005/03/secrets/marcreate/index.php
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Recovering highlights wih only one or two unclipped channels is not that easy. Often, such highlights are very saturated and out of (printer profile) gamut. At least that's my experience with film scans.

While PS RAW histograms display separate channels, do in-camera histograms do so also? If not, won't ETTR relying on histograms result in potential clipped channels?

[bjanes]

Recovering highlights wih only one or two unclipped channels is not that easy. Often, such highlights are very saturated and out of (printer profile) gamut. At least that's my experience with film scans.

While PS RAW histograms display separate channels, do in-camera histograms do so also? If not, won't ETTR relying on histograms result in potential clipped channels?
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I haven't scanned any film since I went digital, so I have no experience recovering highlights in that situation and did not even know it was possible. Fortunately, you still have your original and can re do it.

The single histogram on most cameras is unfortunately a luminance histogram, not what Adobe calls an RGB histogram. In the luminance histogram, the RGB colors are weighted according to the sensitivity of the eye, and the red and blue channels do not get much weighting.

[a href=\"http://www.cambridgeincolour.com/tutorials/histograms2.htm]http://www.cambridgeincolour.com/tutorials/histograms2.htm[/url]

With a lumonsity histogram it is very easy to blow a blue or red channel. Here is an example from my own experience. I exposed this red flower to the right according to the lumonsity histogram on my D70. In Photoshop, the lumonsity histogram looks fine (look at the black and white histogram) and resembles what I saw on the camera. However, the RGB histogram shows clipping of the red channel. My new D200 has separate RGB histograms which would avoid this problem, as do the professional Nikons and Canons. If a camera had only one histogram, one would think that it should be what Adobe calls the RGB histogram so as to avoid this problem.

[attachment=522:attachment]
[attachment=523:attachment]

BTW, the camera histogram does not show the RAW channels, but those of the JPEG preview, which has been converted to the assigned color space with the current camera settings. If you use ProPhotoRGB in ACR, the red clipping does not occur in the wider color space. Unfortunately, this space is not available on most cameras. (These screnshots are posted as GIF to better show text, hence the posterization in the colors)

[attachment=524:attachment]
[attachment=525:attachment]

[Ray]

It takes quite a bit of overexposure to blow out blue sky, since neither the luminance nor saturation of clear blue sky is that high. Much more likely, is blowing out of the clouds in a blue sky as shown in the shot of the Golden Gate Bridge in Bruce Fraser's article. With the histogram in ACR it is easy to see which channels are blown. In my experience with ACR and my shooting, the blown channels most often show as white in the histogram, as in Bruce's example, indicating all three channels are blown in the white balanced image. Your mileage may vary, but the essential point is that highlight recovery requires data in at least one channel.

[a href=\"index.php?act=findpost&pid=63970\"][{POST_SNAPBACK}][/a]

Golden Gate Bridge? I'm talking about clear, unpolluted deep blue sky with the odd cloud that varies from dark grey to brilliant white.

A Chinese gentleman who lived about 2500 years ago is reputed to have said, but probably never did say, that a picture is worth a thousand words. There's no blue sky in S.E Queensland at the moment of writing this, so I can't demonstrate my point with a picture, and since I'm so careful about this issue of overexposure of sky, I can't off-hand find a good example in the limited archives at my disposal at this location.

If one is doing a cloud study and exposing for the cloud highlights, then that's fine. You'd possibly get some interesting, dramatic shots showing every nuance of cloud detail, and a very dark blue sky. However, if  a bit of the scene was terra earth in the foreground, you'd be stuffed as regards extracting noise-free detail.

We generally expect white clouds to be clipped to some extent, and the clipping seems (in my experience) to simply produce greater areas of pure white without any obnoxious color shift, and is quite acceptable.

A clipped blue sky seems to behave differently when trying to recover the highlights in ACR with a minus EC setting. Beyond about -1 EC, the blues in the brighter parts of the sky gradually turn cyan and in extreme cases a muddy grey. Basically, a total mess which requires a lot of work in Photoshop to correct.

Okay?  

[bjanes]

Golden Gate Bridge? I'm talking about clear, unpolluted deep blue sky with the odd cloud that varies from dark grey to brilliant white.

We generally expect white clouds to be clipped to some extent, and the clipping seems (in my experience) to simply produce greater areas of pure white without any obnoxious color shift, and is quite acceptable.

A clipped blue sky seems to behave differently when trying to recover the highlights in ACR with a minus EC setting. Beyond about -1 EC, the blues in the brighter parts of the sky gradually turn cyan and in extreme cases a muddy grey. Basically, a total mess which requires a lot of work in Photoshop to correct.

Okay? 
[a href=\"index.php?act=findpost&pid=64092\"][{POST_SNAPBACK}][/a]

Sorry, Ray, but I don't get your point. In the example, Bruce wanted to bring out some texture in the clouds, not merely represent them as white blobs. Sounds reasonable to me.

In my experience a clear blue northern sky generally has a luminance reading on the light meter very similar to that of the overall scene, which is assumed to have a reflectance of 12-18% in most metering schemes. Ansel Adams describes a clear north sky as rendered by panchromatic film as Zone V and I don't think it is much different with digital.

Some digital cameras run the sensor slightly above its linear range, so channel clipping will not be uniform across all channels, and a linear control such as the exposure control in ACR may not correct for this and there will be a color shift. Furthermore the white balance is a factor. These considerations are explained by Bruce Fraser in his ACR book.

If it is your misfortune to have drab overcast skys in your location, overexposure can be a problem. If you expect more than -1EV of highlight recovery in your situation, I don't think you are  being realistic. You could watch your camera histograms and avoid blowing channels or else use a graduated neutral density filter, HDR exposures, etc.

[Ray]

Of course we all bracket our exposures, it would be infantile not to.  Which brackets do I end up using most of the time?-- the one that has caused me to express my opinion to this thread.
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Richard,
Would any of these bracketed shots be an ETTR exposure, by any chance?  

Your method of shooting seems very elaborate and time consuming. 3 bracketed shots around the centre of your very precise measurements seems a good insurance measure and it would hardly add to the over all time of preparing the shot.

I agree in principle, if you are so absolutely sure of your methods and your vision, and you are not interested in changing those at a later stage, then following the tradition of Ansel Adams might serve you well.

Your method seem to me to be the equivalent of shooting transparencies, but in digital mode. You've got a final result which inspires cofidence that that was what you envisioned. The hues and tones are right without relying upon memory.

I understand that approach. But it wouldn't suit me because I rely just upon the camera (a 5D) with its in-built processes, and most of the time I don't have the luxury of hanging around to take precise measurements, even if I had the ancilliary equipment.

Cheers!

[RichardChang]

Richard,
Would any of these bracketed shots be an ETTR exposure, by any chance?  

No way!; I have Color Coded Light Metering in my Photoshoot capture app.  I've got a light meter of each and every pixel, all 22 million of them. I can sample (from point sample up to 21x21) and I can see each pixel's zonal value in the densitometer, and I can see important endpoints as colors.  If I change the developing intention's luminance remap, I see the colors change.  Whether I choose to develop in ACR or Photoshoot, I can optimize the exposure for the developing I'll want to use.  Why not be able to change the exposure of the scene, prior to the developing you want?  Sure you can change the deveoper in ACR, but why limit yourself?  You can have both exposure and developing adjustments on your tripod if you have the capability.

The developing I want has it's roots in film.  I know what a normal development does to lows, mids, and highs.  I know what a normal-minus and a normal plus development looks like too.  When I see a scene that needs a plus in the highs, I'll try to give an exposure that allows me the most flexibilty in getting the rendering I want.  I've tried giving lots of exposure and using Photoshop's H&S, layer masks, etc.  For me, giving less exposure and curve mapping up with more contrast, is the way I want to work.  There's a big advantage for me, if the scene still fits noiselessly in my camera's recording-- when I map up, all the tones below the mapped point will move in context.  Give max exposure and for some scenes, you'll be heading for selections and Photoshop gymnastics to save your shot.  Bear in mind that Photoshop has some highly developed gymnastic routines which have been marketed with enthusiasm and great fervor.  Always great for Adobe but but not maybe so great for you.

>Your method of shooting seems very elaborate and time consuming. 3 bracketed shots around the centre of your very precise measurements seems a good insurance measure and it would hardly add to the over all time of preparing the shot.

Time consuming?  If you've shot much outdoors you'll know that the light dictates how much time you're able to spend.  Ansel didn't spend much time on Moonrise, Hernandez, NM because he knew the light wasn't going to stay on the headstones for long.  I wouldn't either, in a similar situation.  The time I spend shooting depends on what kind of time I want to spend.  No one is going to make you take a lot of time.  If you do want to spend time, go for it, it's your time. Of course, as you hone any skillset, it takes less time.  I've been doing this since late 1998 when we got the first Philips sensor.

I like to think that most shooter's work visually communicates the time they spent.  Do you need to spend more time on your images?, or would less time be more appropriate?

>I agree in principle, if you are so absolutely sure of your methods and your vision, and you are not interested in changing those at a later stage, then following the tradition of Ansel Adams might serve you well.

It does and I won't change my workflow as long as I have the s/n that allows it.  You'd need to see some prints to find out if you agree as well.  Trouble is, you won't find a lot of shooters espousing the placement of highest value according to the paper's density range and highest separable value.  Most folks ritually give as much exposure as possible, and I do too, when I shoot with gear that doesn't allow less exposure.

>Your method seem to me to be the equivalent of shooting transparencies, but in digital mode. You've got a final result which inspires cofidence that that was what you envisioned. The hues and tones are right without relying upon memory.

We might find value in considering that a digital image isn't a negative, it's a positive.  Ansel taught us to expose for threshold and develop for the other end of the scale.  Threshold for digital, being a positive, is the start of density on the paper or monitor. I teach my customers that threshold is what we expose for and that shooting the number of tones (whenever possible) that match the measured DR of the paper will allow a perfect rendering.

>I understand that approach. But it wouldn't suit me because I rely just upon the camera (a 5D) with its in-built processes, and most of the time I don't have the luxury of hanging around to take precise measurements, even if I had the ancilliary equipment.

Maybe not, but it doesn't have to take a lot of time.  If I had a 5D, I'd test it by shooting a test scene; place the highest important value on zone IX, VIII, VII, VI, and V.  Use the spot function in the camera's reflected meter mode to choose your exposures.  As to precise measurments, I'll assume that you remember how to use an in-camera meter-- it reads only the reflectance in the metered area.  Open the pictures in CS2 and look at the results.  CS2's automatic function will do it's best to make the shot look the way Adobe thinks you want it.  Check out the highs, and the lows.  Depending you your camera's performance and the original scene contrast, the lows will be noisy, or they'll be OK.  The highs will be more textured, as you give less exposure.  Of course you may alter Adobe's notion with ACR's tools.

Even if you don't use the technique, it might be nice to quantify your camera's performance, handy for eval against future gear you obtain, if you standardize your test scene; I use sunlight and a 24 patch Colorchecker.

Whether you give this test a shot is up to you.  If you use the technique, that's up to you too.  You can objectively take a look at what the advantages and disadvantages engender, understanding that as the performance of the device improves, you gain the luxury of lower placment of highest important value.  It's my opinion that rendering a correct number of tones to our target is more emotive than rendering too many.  It why we like Velvia in flat light.  Tonal craft is what really good shooters manage.  Luckily, you can manage in more than one style, just choose the style that works for you and your equipment.

Richard Chang

[Schewe]

OK, Richard...I don't get it.

You say (and I very much agree) to expose to retain textural highlights in a digital capture. Fine. So, where does this "reduce the levels of tones captured" come into play?

If you properly expose to just maintain textural highlights with no clipping, I would consider that a "good exposure". It would be an "expose to the right" senario if the scene contrast range was within the dynamic range of the sensor...and it would be a best compromise for a scene outside of the range of the sensor.

I don't see where any "reduction of exposure" to "limit the tones captured" does you any good...it all comes down to getting a proper capture and setting the proper tone responce curve...doesn't it?

I would ALWAYS prefer to take tones down in post than trying to lighten tones in post. It's easy to make your 1/4 tones darker but bloody hard to get them lighter without getting into noise.

I also don't have a problem tweaking highlights to increase texture and contrast. So even if my exposure to maintain textural highlights clumps a lot of data in the upper levels capturered, there are good techniques to bring those textures out. Careful tone curves in Camera Raw, dual processing in Camera Raw, local contrast adjustment in Photoshop, etc.

[61Dynamic]

Wow. Seven pages since I last visited this topic. Pardon me if I don't read it all but considering what I've read on page 6 and 7, not much new ground has been treaded since page 2.

Maybe I'm missing something obvious. Or perhaps some others are missing the obvious...?

With regard to the comments by Jeff Schewe:
[...]
>And while you may think post processing is less desirable, I would argue that an artist will do whatever it takes to get the image to look the way they want.

I never said that post processing is less desireable, I suggested that I don't appreciate the over processed look of some of the expose-to-the-right imagery.  I do post processing, layer adusts, masks and the like.  I even did the Schewe edge sharpen routine until the new Photoshop sharpening showed up.
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How could you possibly know someone used ETTR? Over-processed is over-processed regardless of the use of ETTR.

While PS RAW histograms display separate channels, do in-camera histograms do so also? If not, won't ETTR relying on histograms result in potential clipped channels?

Newer cameras are coming out with separate RGB histograms but many others display luminance histograms. So, yes, ETTR can lead to clipped channels if you aren't careful to consider the subject matter you are photographing.

[bjanes]

Rags' contention that less exposure may be better has it's roots in manufacturing a specific number of tones for a picture rendering.  While zone V is drastic for some scenes and targets, it's not all that unbelievable for some capture devices.  Why?  Let's compare the number of tones in 12 bits (4096) with the signal-to-noise ratio of a high end camera back (4000:1).  We've got approximately 4000 units in each comparative and the equation suggests that the noise in 12 bits is approximately 1 bit.  In 12 stops of range, zone I has noise (0 is black) and the others are noise free.

For a normal scene (for example, let's say it's a 6 stop scene), one could expose right, place the highest important value way high with the histogram and no zone in the scene has noise.  One could also expose the highest important on zone VII, and no zone in the scene has noise.

Richard Chang
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Your contention that your camera back, which I take to be the Megavision E5, has no noise above Zone I is not credible. That camera is based on a Kodak CCD, possibly the KAF 22000CE, which has 9 by 9 micron sensors. I do not have the specifications for that sensor, but for the following analysis I assume they are similar to the KAF-16801LE. If these specs are not representative for your sensor, please supply the correct specs, but the quoted specs should be close enough to demonstrate the principles.

[a href=\"http://www.kodak.com/global/en/digital/ccd/products/fullframe/KAF-16801E/specifications.jhtml?id=0.1.4.6.4.27.4&lc=en]http://www.kodak.com/global/en/digital/ccd....6.4.27.4&lc=en[/url]

All digital sensors have photon counting noise, which has a Poisson distribution and the standard deviation of this noise is equal to the square root of the number of photons collected. Another source of noise is the read noise. Dr. Roger Clark has done an analysis of noise for the Canon EOS 1D Mark II and the table shown is a similar analysis for the Kodak sensor, which has a full well capacity of 100,000 electrons and a read noise of 15 electrons at 1MHz.

http://www.clarkvision.com/imagedetail/eva...-1d2/index.html

For Zone 10 at base ISO, the sensor can utilize the full well electron count, and each of the other zones will have half the electrons of the preceeding as shown. For the darker zones, there must be considerable noise, better than the Canon because of the larger pixel size but only by a factor of 2 or so. If you shoot above base ISO, the full well will not be utilized and noise will be greater. In contrast to your statement that your camera is free of noise in Zone 10, the noise is actually greatest there, but because of the high S/N ration it is not evident.

[attachment=526:attachment]

In view of this analysis, I think that your shots could benefit from exposure to the right. If you disagree, please inform us why the laws of physics do not apply to your camera.

[Schewe]

All digital sensors have photon counting noise, which has a Poisson distribution and the standard deviation of this noise is equal to the square root of the number of photons collected.

"Poisson distribution"? I don't know what the heck that is, but I sure love the implication...noise because of POISSON!!!

Yeah, yeah, I found out it's called that because of Siméon-Denis Poisson who did a probability theory  and published Recherches sur la probabilité des jugements en matières criminelles et matière civile ("Research on the Probability of Judgments in Criminal and Civil Matters") in 1838. Interesting a theory about the Probability of Judgments in Criminal and Civil Matters has implications in 2006 digital capture...

Cool!

Course, I still don't understand it.

:~)

[bjanes]

"Poisson distribution"? I don't know what the heck that is, but I sure love the implication...noise because of POISSON!!!

Yeah, yeah, I found out it's called that because of Siméon-Denis Poisson who did a probability theory  and published Recherches sur la probabilité des jugements en matières criminelles et matière civile ("Research on the Probability of Judgments in Criminal and Civil Matters") in 1838. Interesting a theory about the Probability of Judgments in Criminal and Civil Matters has implications in 2006 digital capture...

Cool!

Course, I still don't understand it.

:~)
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Jeff,

Look at any statistics book on sampling distributions. The major ones are binomial, Poisson, and normal. If you read on in Wikipedia, you will see the Poisson distribution  is also useful in assessing random events such as radioactive decay, road kill, and the number of soldiers killed by horse-kicks each year in each corps in the Prussian cavalry. It is not reassuring that a process for evaluating random events applies in court proceedings. In any event, the Poisson distribution also applies to photon sampling.

I can't tell if you are being sarcastic or not, but it is really interesting that all of these events can be evaluated by the Poisson process.

 

[Schewe]

I can't tell if you are being sarcastic or not, but it is really interesting that all of these events can be evaluated by the Poisson process.
 
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Not sarcastic at all...I just think it's interesting that if one wants to, one can delve deep into the math of so many aspects of photography and digital imaging. And yes, I had to look it up on Wikipedia...course my eyes glazzed over cause I don't have the math :~)

My wife is constantly amazed by the fact that I can even use a computer to run Photoshop because I am so math challenged. But I get along...thankfully, I rely on Thomas Knoll and a real good interface between the math and the functions of Camera Raw/Photoshop!

[bjanes]

Not sarcastic at all...I just think it's interesting that if one wants to, one can delve deep into the math of so many aspects of photography and digital imaging. And yes, I had to look it up on Wikipedia...course my eyes glazzed over cause I don't have the math :~)

My wife is constantly amazed by the fact that I can even use a computer to run Photoshop because I am so math challenged. But I get along...thankfully, I rely on Thomas Knoll and a real good interface between the math and the functions of Camera Raw/Photoshop!
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Yes, the math of the Poisson distribution can be a bit daunting when one has to calculate the mean, but fortunately one need not know the math to apply the concept. The nice thing about the Poisson distribution is that the mean and variance (square of the standard deviation) are the same. We measue the mean in Photoshop or stipulate it in the model and the square root function is available on our computers or calculators.

I am still waiting for Richard's response. I can't imagine how he can climb out of the hole into which he has dug, but it will be interesting. In any event, the math of noise justifies ETTR as much as does the number of levels, originally brought to our attention by Mr. Knoll's campfire side discussions with MR.

[Chris_T]

I haven't scanned any film since I went digital, so I have no experience recovering highlights in that situation and did not even know it was possible. Fortunately, you still have your original and can re do it.

The single histogram on most cameras is unfortunately a luminance histogram, not what Adobe calls an RGB histogram. In the luminance histogram, the RGB colors are weighted according to the sensitivity of the eye, and the red and blue channels do not get much weighting.

http://www.cambridgeincolour.com/tutorials/histograms2.htm

With a lumonsity histogram it is very easy to blow a blue or red channel. Here is an example from my own experience. I exposed this red flower to the right according to the lumonsity histogram on my D70. In Photoshop, the lumonsity histogram looks fine (look at the black and white histogram) and resembles what I saw on the camera. However, the RGB histogram shows clipping of the red channel. My new D200 has separate RGB histograms which would avoid this problem, as do the professional Nikons and Canons. If a camera had only one histogram, one would think that it should be what Adobe calls the RGB histogram so as to avoid this problem.

[attachment=522:attachment]
[attachment=523:attachment]

BTW, the camera histogram does not show the RAW channels, but those of the JPEG preview, which has been converted to the assigned color space with the current camera settings. If you use ProPhotoRGB in ACR, the red clipping does not occur in the wider color space. Unfortunately, this space is not available on most cameras. (These screnshots are posted as GIF to better show text, hence the posterization in the colors)

[attachment=524:attachment]
[attachment=525:attachment]
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I'll save my response to recovering a scan's highlights for another thread. This one is getting rather lengthy. (But please don't stop.)

The referred article about histograms is very educational and well written, thanks. So ETTR is not as simple as just gauging by the histogram. One must also take into consideration a histogram's clippability (!?) and color space . More questions:

When is a camera's histogram available for viewing: before or after taking the shot?

If a camera's histogram can display separate rgb channels, will you ETTR so that no channel is clipped?

Of course, when in doubt, bracket, just like in the "good old" film days. The difference is burning storage rathen than film. How well do the higher end digital cameras support bracketing?

[Ray]

Sorry, Ray, but I don't get your point. [a href=\"index.php?act=findpost&pid=64098\"][{POST_SNAPBACK}][/a]

Well, what can I say, bjanes! I don't understand why you don't get my point.

Let me re-phrase it. If you unintentionally overexpose a blue sky, which you might well do when attempting to expose to the right, or even when simply using the camera's evaluative meter mode, there is a hue shift towards cyan which is not pleasant. This, I surmise, is due to the blue channel clipping more than the green channel.

If you unintentionally overexpose a grey, cloudy sky, or even a blue sky with clouds, the clouds usually retain their neutral greyness, although of course there is some loss of detail.

Now since I'm not in the habit of overexposing skies, I have trouble finding appropriate examples. However, on my way to the pub this afternoon, I stopped by the roadside to take a few shots just to confirm that I was not just imagining this effect.

[attachment=528:attachment]

[bjanes]

Well, what can I say, bjanes! I don't understand why you don't get my point.

Let me re-phrase it. If you unintentionally overexpose a blue sky, which you might well do when attempting to expose to the right, or even when simply using the camera's evaluative meter mode, there is a hue shift towards cyan which is not pleasant. This, I surmise, is due to the blue channel clipping more than the green channel.

If you unintentionally overexpose a grey, cloudy sky, or even a blue sky with clouds, the clouds usually retain their neutral greyness, although of course there is some loss of detail.

Now since I'm not in the habit of overexposing skies, I have trouble finding appropriate examples. However, on my way to the pub this afternoon, I stopped by the roadside to take a few shots just to confirm that I was not just imagining this effect.

[attachment=528:attachment]
[a href=\"index.php?act=findpost&pid=64168\"][{POST_SNAPBACK}][/a]

With all due respect, Ray, the overexposure of the clear blue sky in your demonstration was hardly unintentional, and the fact that you could find no good example in your archives proves that it is not common in your experience. What did your meter, evaluative or spot, read for the overexposed sky and the rest of the scene? Would that degree of overexposure likely result from anything other than carelessness or deliberate attempt?

Since the sky is predominately blue, of course the blue channel will clip first. Minus 2 EV is beyond ACR's limits for highlight recovery. If you overexposed a red flower, the red channel would clip first. However, with a neutral scene, the channel that clips first is usually determined by the spectral response of the RGB channels. In the case I demonstrated, it is the green channel that clips first. So, again, what is your point?

[Ray]

So, again, what is your point?

Well now you've got me going back to page 6 to find out what the point of all this is. I think the point in general is that you surprised me by arguing with a common experience I had when I first started using the D60 with evaluative metering, several years ago.

You also made the following statement which doesn't accord with my experience.

It takes quite a bit of overexposure to blow out blue sky, since neither the luminance nor saturation of clear blue sky is that high. Much more likely, is blowing out of the clouds in a blue sky as shown in the shot of the Golden Gate Bridge in Bruce Fraser's article.

In the examples I've shown, both clouds and blue sky have partially blown with 2 stops overexposure. With one stop overexposure, which I would consider an ETTR situation for this shot, but which wasn't really necessary anyway, all detail has been recovered with -1 EC in ACR. Both clouds and sky seem to be equally susceptible to blowing, but the sky is more of a problem subjectively because of the hue shift.

[bjanes]

Well now you've got me going back to page 6 to find out what the point of all this is. I think the point in general is that you surprised me by arguing with a common experience I had when I first started using the D60 with evaluative metering, several years ago.

You also made the following statement which doesn't accord with my experience.
In the examples I've shown, both clouds and blue sky have partially blown with 2 stops overexposure. With one stop overexposure, which I would consider an ETTR situation for this shot, but which wasn't really necessary anyway, all detail has been recovered with -1 EC in ACR. Both clouds and sky seem to be equally susceptible to blowing, but the sky is more of a problem subjectively because of the hue shift.
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Arguing with a common experience? If the experience is so common, why couldn't you recover an example in your archives? Why does Ansel Adams list clear northern sky as Zone V?

Since today is overcast and I don't have any examples of blown blue skies in my archives either, I did an experiment with a MacBeth color checker exposed under daylight (more or less, light entering my window on an overcast day) with proper exposure and with +2 EV exposure.

Here is the properly exposed target. Note the values for sky (3rd column, 1st row)

[attachment=529:attachment]

Here is the target with +2EV exposure:

[attachment=532:attachment]

Here is raw file with +2 EV as shown with DCRaw. Note that in the sky panel, no channels are blown and green exhibits the highest value.

[attachment=530:attachment]

Here is the +2EV exposure with -2EV in ACR. Since the sky patch had no blown channels, highlight recovery was possible for the sky, but other colors are clipped as shown in the histogram.

[attachment=531:attachment]

Again, it is not reasonable to expect to recover 2 stops of overexposure with ACR's highlight recovery. The example I gave with a Nikon camera may not apply to your Canon if it has different RGB filters. You should really look at your raw files without white balance and see what is going on. ETTR is NOT overexposure. It is exposure to the right of the histogram, not blowing highlights. Highlight recovery is for when you err in exposing to the right.

[BJL]

BJL,
Yes I have. It's probably a consequence of living in a sunny clime where brightness levels are greater than in northern Europe.
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I presume that by "brightness levels" you mean high "subject brightness range", or scenes of "high contrast", or in the Ansel Adam's jargon above, "long scale subjects". Because high overall brightness of a scene is not a problem in itself: just use sufficiently high shutter speeds to avoid over-exposure.

The issue I see a range of many stops from highlights to significant shadow details, or from an overall meter reading to far brighter highlights. In my experience those are also out of the range of the "straight" prints that I was asking about, into the territory needing tonal compression with low contrast settings, tone curve fiddling, or with film, printing with low contrast grades and perhaps developing for low contrast.

Anyway those sunny scenes are probably easily handled at base ISO speed like 100; the case I am worrying about is when base ISO speed will force one into underexposure due to shutter speed (and DOF) needs.


P. S. As an Australian who has lived and done much photography in the southern parts of the US, I know the problems of high subject brightness range!

[Ray]

I presume that by "brightness levels" you mean high "subject brightness range", or scenes of "high contrast", or in the Ansel Adam's jargon above, "long scale subjects". Because high overall brightness of a scene is not a problem in itself: just use sufficiently high shutter speeds to avoid over-exposure.

Yes. That's what I mean, high subject brightness range, which I believe is related to higher brightness levels in general because the parts of the scene in direct light will be brighter to a greater degree than the shadows will be, which rely upon indirect light.

The issue I see a range of many stops from highlights to significant shadow details, or from an overall meter reading to far brighter highlights. In my experience those are also out of the range of the "straight" prints that I was asking about, into the territory needing tonal compression with low contrast settings, tone curve fiddling, or with film, printing with low contrast grades and perhaps developing for low contrast.

I agree that such a wide DR will be out of the range of 'straight' prints, but aren't we all into some degree of digital processing of images before printing. I use the shadow/highlight tool in Photoshop a lot; also dual conversion. It's now possible to create a sort of composite image of parts from the one shot by isolating each significant part of the image in PS and processing that part as though it was a separate image.

Since most of my images are archived on DVD in a different location to where I am writing this, I can't drag out an image which would illustrate this well, but I have in mind a particular shot of a waterfall in a rainforest taken after a few rare weeks of good rainfall. The water was splashing over rocks near the top, creating an impressive spray of droplets which I wanted to capture (rather than the usual silky smooth flow that most people aim for). The sun was on part of the fall, but the foot of the fall, where there were interesting moss-covered boulders, pools and foliage, was in deep shadow. This was clearly a very high DR scene. I'd exposed for the highlights at ISO 100 and captured the spray clearly and sharply without blowing highlights significantly, but failed to get a decent rendering in post processing of the rocks in the shade. Neither Neat Image nor dual conversion was of much help. The image was therefore spoiled in my view; an experiment which didn't work because the Camera (the D60) had insufficient DR.