Luminous Landscape Forum
Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: Bill Jaynes on July 13, 2008, 01:50:56 am
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Shooting black and white negatives, I learned a good exposure technique, meter the shadows and stop down 2. This would ensure good shadow detail and leave highlight adjustment for printing when it could most often be handled.
Now, with digital, the larger horror is blown highlights. Has anyone worked out a scheme such as metering the highlights and opening up 1, 2, how many stops?
Thanks,
Bill
http://www.montanahi-line.net/ (http://www.montanahi-line.net/)
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You actually need to expose for the lights to maintain maximum dynamic range and protect shadow detail.
This is a good introduction into this matter:
http://www.luminous-landscape.com/tutorial...ose-right.shtml (http://www.luminous-landscape.com/tutorials/expose-right.shtml)
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I call my method BTYB.
Bracket till you blow.
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Just use your histogram and exposure compensation. In very little time you will know your camera (sensor) so well that the second exposure nails the ETTR.
Marc
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Just use your histogram and exposure compensation. In very little time you will know your camera (sensor) so well that the second exposure nails the ETTR.
Marc
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That's the soundest procedure to use, but FWIW...
If the OP desperately needs examples, my goodol'300d (yes, the original DRebel) blows about 2 and a third stop above metering - ie when the needle starts to blink in M mode, indicating a metering more than 2 stops above the choiced setting, I'll begin to be on the verge of blown HL.
Quite useful for the peculiar case of panoramas imho.
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Shooting black-and-white negatives, I learned a good exposure technique, meter the shadows and stop down 2. This would ensure good shadow detail and leave highlight adjustment for printing when it could most often be handled.[a href=\"index.php?act=findpost&pid=207760\"][{POST_SNAPBACK}][/a]
Exactly. This method is called "to expose for the shadows"---get the shadows right and let the highlights fall where they may. It's the proper way to shoot negative film (B/W and colour) ... but it is, and always was, wrong for slide film. With the latter, you would expose for the highlights which means---surprise, surprise---get the highlights right and let the shadows fall where they may.
When thinking about it, it's not too hard to understand why negative and positive (slide) films require different strategies of exposure. After all, the highlights in a slide film are the shadows in a negative.
Today, shooting digital is pretty close to shooting slide film. In particular, you have to expose for the highlights, not for the shadows.
Now, with digital, the larger horror is blown highlights.[a href=\"index.php?act=findpost&pid=207760\"][{POST_SNAPBACK}][/a]
This exactly also used to be the horror with slide film, too. However, slightly blown highlights in a slide never looked as terrible as they do in a digital file, as over-exposed areas on film would roll off fairly gently into saturation. With digital, brightness will rise linearly with exposure until it smashes into saturation abruptly; no gentle roll-off here.
Has anyone worked out a scheme such as metering the highlights and opening up 1, 2, how many stops?[a href=\"index.php?act=findpost&pid=207760\"][{POST_SNAPBACK}][/a]
No. Because with digital, there is a better method. Increase the exposure until the histogram just touches the right-hand border, or the highlight warning in the camera display starts flashing, then back off a quarter or a third of an f-stop. Basically that's just the same as "expose for the highlights" always jused to be---just the way how to know when exposure is fine has changed with modern technology. So the new name for a well-known thing is "expose to the right" (ETTR)---the right-hand side of the histogram, that is. (By the way, expose for the shadows today would be called ETTL, i. e. expose to the left. But with digital that's not a sensible thing to do.)
-- Olaf
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Just use your histogram and exposure compensation. In very little time you will know your camera (sensor) so well that the second exposure nails the ETTR.
Marc
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Only if you are using uni-WB and proper in-camera settings; otherwise you will always be leaving exposure latitude (that's potential extra DR) on the table. Besides that, bracketing and guessing is a guarantee of missing shots (they don't always wait for you to get the exposure right).
The answer to the OP's question depends on the camera. Presuming you can actually find the relevant highlight you want to retain detail for, then with my D300 I typically can get about 3 stops positive EC from that using the Spot meter; with the D200 it is closer to 2 stops. A better and quicker solution is to use Center-weighted metering and fully understand your camera's metering tendencies and true RAW latitude. Again referencing my D300, the answer is usually +.7 (plus or minus .3) using Center-weighted metering, and then I pull the density to where I want the scene's overall density during RAW conversion -- for high DR scenes there may be no pulling at all, for lower DR scenes I may pull the scene a full stop or more.
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Only if you are using uni-WB and proper in-camera settings; otherwise you will always be leaving exposure latitude (that's potential extra DR) on the table. [a href=\"index.php?act=findpost&pid=208929\"][{POST_SNAPBACK}][/a]
That's right.
I always get interesting comments on forums when I show examples of how a totally blown jpg can be saved (in the case where the raw data isn't blown). A lot of people without a proper understanding of how digital capture works, say things like "Well, you are just covering up for the fact that you didn't get exposure right in-camera". But I maintain that I DID get it right (as long as I haven't blown the raw data). Clearly I didn't get it right according to Johnny "the jpeg" Technician in the Canon factory, but I would much rather control my own images through a proper understanding of linear raw capture.
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No. Because with digital, there is a better method. Increase the exposure until the histogram just touches the right-hand border, or the highlight warning in the camera display starts flashing, then back off a quarter or a third of an f-stop. Basically that's just the same as "expose for the highlights" always jused to be---just the way how to know when exposure is fine has changed with modern technology. So the new name for a well-known thing is "expose to the right" (ETTR)---the right-hand side of the histogram, that is. (By the way, expose for the shadows today would be called ETTL, i. e. expose to the left. But with digital that's not a sensible thing to do.)
-- Olaf
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I would disagree mostly with what you wrote. It would be far better to:
1. Shoot raw.
2. Ascertain the primary element/s in your composition.
3. Apply EC until those elements are exposed just a bit over, with NO regard for possible blown highlights in the unimportant parts of the composition.
4. In post processing, "normalize" the exposure of the primary element/s.
5. Never judge exposure by the image displayed on the camera's LCD. It lies too much and too many factors like brightness level, and ambiant light effect how the display looks. Far better to use the histogram, although the blinkies that show on the image can be helpful.
There is this supersition that one must never blow highlights. This is wrong. They can be blown judiciously for the sake of the primary element/s in the composition.
It is also wrong to shoot in such a way as to try to effect a particular histogram shape. Every composition is different, and if a comp shows lots of shadow, then by golly the histo will show a profound lean left, and that is okay.
My method says to expose to the right, while always keeping the primary element/s in consideration. Often a great image will in fact show blown highlights. One must not necessarily expose until the histo is just touching the right border...this is not a good method at all, although there might be times when one should do this, but to make it a generalized blanket policy is not really good.
When shooting raw, the in-camera histogram will show blown highlights that are often not really blown until the highlights are more then 1/3rd blown, so there is lee way. This is why one must not back off 1/3 to 1/2 stop as you assert.
The in-camera histogram is based on the temporary tiny JPG that is created by the camera for the sake of providing an image to display on the camera's LCD. This image is severly res'd down and has a dynamic range that is at least 1/3 stop narrower then the corresponding raw. This small jpg gets created even if one shoots raw only.
In addition, it is best to get the white balance as close to perfect as possible even when shooting raw, as WB will effect exposure, even if it is changable during post processing.
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Only if you are using uni-WB and proper in-camera settings; otherwise you will always be leaving exposure latitude (that's potential extra DR) on the table. Besides that, bracketing and guessing is a guarantee of missing shots (they don't always wait for you to get the exposure right).
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This is not true if one shoots raw.
And since raw ignores the in-camera parameter values, the ETTR method is the best way to capture raw data, and insures the widest DR is achieved in one's image. Although WB is chanable with a raw image later in post processing, I like to get it as perfect as possible at the time the exposure is taken because the WB value will effect exposure.
I do agree with you, that bracketing is not a good way to shoot. Leave braketing primarily to film shooters, who don't have the benefit of an LCD histogram. Bracketing can make one miss shots, true what you wrote. Same for light meters....I've not used my since years ago when I shot film....histograms are king!
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Two points and a question:
1. Most (all?) RAW processors have the ability to bring back "blown" highlights. Just yesterday I was shooting in bright daylight and couldn't get ETTR exposure to acceptable levels without risking severe shadow noise. LR "Recovery" allowed me to pull back almost all the data in the blown clouds. I haven't done tests to see how "good" the data is, ie. how much color shift there is, yet, or how much leeway there is.
2. Bracketing is generally faster than tweaking an exposure using a histogram. Not as accurate of course, but faster.
Question: it seems that some are implying that white balance affects RAW - which I thought was not the case. I just checked my Canon's manual and it specifically says RAW allows me to change WB in post without degrading image quality.
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Question: it seems that some are implying that white balance affects RAW - which I thought was not the case. I just checked my Canon's manual and it specifically says RAW allows me to change WB in post without degrading image quality.
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WB (and other in camera settings) impact the histogram. So you might think you've blown a channel but haven't. (Or have.) Dunno if that is a universal truth.
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Dunno if that is a universal truth
Someone posted on another thread, that his MFDB displays raw histograms. I don't know which MFDB that was, but this appears logical, as those cameras don't have the multitude of settings, which are useful only for JPEG.
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Although WB is chanable with a raw image later in post processing, I like to get it as perfect as possible at the time the exposure is taken because the WB value will effect exposure
This has been posted already somewhere above. It is still nonsense.
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Only if you are using uni-WB and proper in-camera settings; otherwise you will always be leaving exposure latitude (that's potential extra DR) on the table.
This is not true if one shoots raw.
And since raw ignores the in-camera parameter values, the ETTR method is the best way to capture raw data, and insures the widest DR is achieved in one's image.[a href=\"index.php?act=findpost&pid=209800\"][{POST_SNAPBACK}][/a]
There is no RAW histogram per se in any DSLR I'm aware of; the histogram you are using to evaluate exposure is based on an embedded JPEG which is based on "in-camera parameter values" (contrast, saturation, sharpening, and especially WB gain settings). The native WB of my Nikon DSLRs are around 4350K with a -35 hue (yes, it's very green); that means any WB gain and correction of the hue to reflect accurate colors delivers an inaccurate histogram. You can get a reasonably accurate histogram that reflects the RAW data by using uni-WB (zeroing out the WB gain and adjusting the hue), and by using a linear curve with no added saturation or sharpening.
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There is this supersition that one must never blow highlights. This is wrong. They can be blown judiciously for the sake of the primary element/s in the composition.
In addition, it is best to get the white balance as close to perfect as possible even when shooting raw, as WB will effect exposure, even if it is changable during post processing.
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Both accurate but the second has caveats.
There are parts of some images that will blow no matter what, such as chrome on a car and other specular highlights with other types photography. It doesn't mean the image is bad.
WB does affect exposure at least in post processing with ACR and that is a good reason to get it where you want it before processing. However, if you only stick to the WB you shot, then you are giving up a LOT of creativity when post processing.
Let's say you shoot a night scene with city lights. You want the image to come off cool so the sky blues out instead of blacks out. Fair enough. you shoot cool or in tungsten mode. Now you get home and decide you like it better at daylight so the lights are yellow and warm. What are you going to do, leave it cool?
If you can figure out how you want the WB though, such as a commercial studio shoot, then yeah nail it.
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Question: it seems that some are implying that white balance affects RAW - which I thought was not the case. I just checked my Canon's manual and it specifically says RAW allows me to change WB in post without degrading image quality.
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It does in ACR. If you get your highlights just where you want them, then change the WB, sometimes the highlight blow again. Many times you can crank up recovery though and offset the change. If not, then you need to mess with your exposure again.
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It does in ACR. If you get your highlights just where you want them, then change the WB, sometimes the highlight blow again. Many times you can crank up recovery though and offset the change. If not, then you need to mess with your exposure again.
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That's a persuasive reason not to use ACR.
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That's a persuasive reason not to use ACR.
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It doesn't pose any problems really, unless ACR is doing something it should not be doing, which I doubt.
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That's a persuasive reason not to use ACR.
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No it's not. That's how white balance works. All raw converters will do the same thing.
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This is why setting WB in raw conversion should be your first step. It will impact how you adjust exposure, among other things. It's also why WB is listed as the first adjustment in the CR plug-in and in LR as well.
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Shooting black and white negatives, I learned a good exposure technique, meter the shadows and stop down 2. This would ensure good shadow detail and leave highlight adjustment for printing when it could most often be handled.
Now, with digital, the larger horror is blown highlights. Has anyone worked out a scheme such as metering the highlights and opening up 1, 2, how many stops?
Thanks,
Bill
http://www.montanahi-line.net/ (http://www.montanahi-line.net/)
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It's a viable technique. The exact number of stops will vary depending on the camera and the colors involved in the highlights. I took a series of progressively more overexposed images of various single-colored items to see at what point RAW was blown. With the 350D, between 2.5 and 3 stops is allowable before unfixable color changes appear. Thus you could use the technique of metering for the brightest part *that you don't want blown* and stopping down 2-3 stops depending on what you've found works for your camera and the colour of the highlights (I found less latitude in blues, unfortunately). While bracketing will work in some cases, this method will allow for a good preset exposure for those pictures that you don't get a second chance at. Different situations have different best methods.
-Lars
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No it's not. That's how white balance works. All raw converters will do the same thing.
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Not at all. NX can be set to apply WB gain from scratch, and I can change WB with Capture One LE with no overexposure penalty.
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I took a series of progressively more overexposed images of various single-colored items to see at what point RAW was blown. With the 350D, between 2.5 and 3 stops is allowable before unfixable color changes appear. Thus you could use the technique of metering for the brightest part *that you don't want blown* and stopping down 2-3 stops depending on what you've found works for your camera and the colour of the highlights...
-Lars
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I think you meant open it up 2 or 3 stops. The actual number varies depending on the light, the color, and the camera.
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Not at all. NX can be set to apply WB gain from scratch, and I can change WB with Capture One LE with no overexposure penalty.
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That's interesting. I'm not sure of the process you are describing with NX, can you expand?
To clarify the Capture One thing - you are saying that you can set exposure to just short of clipping and when you change white balance it won't ever show clipping as a result? That's an interesting feature, and one I have often thought from an academic point of view would be useful. So I am envisaging a case where say the blue channel was just shy of clipping and the R and G are not clipping. Then, change white balance such that it increases the blue multiplier, which would ordinarily cause the blue channel to clip. But in this case, instead of increasing the blue multiplier, it would actually decrease the R and G multipliers in the correct proportions. Is this what is happening in Capture?
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That's interesting. I'm not sure of the process you are describing with NX, can you expand?
To clarify the Capture One thing - you are saying that you can set exposure to just short of clipping and when you change white balance it won't ever show clipping as a result? That's an interesting feature, and one I have often thought from an academic point of view would be useful. So I am envisaging a case where say the blue channel was just shy of clipping and the R and G are not clipping. Then, change white balance such that it increases the blue multiplier, which would ordinarily cause the blue channel to clip. But in this case, instead of increasing the blue multiplier, it would actually decrease the R and G multipliers in the correct proportions. Is this what is happening in Capture?
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If that is the case, what is the trade off?
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If that is the case, what is the trade off?
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If you're working on the raw data, then there should be no trade off. Remember, a linear raw file is very dark and green. The colour channels have already undergone a lot of scaling upwards to get to the nice bright image you see on your screen. Sending them a little of the way backwards, shouldn't have any better or worse effect than shoving them around in the first place.
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That's interesting. I'm not sure of the process you are describing with NX, can you expand?[a href=\"index.php?act=findpost&pid=210086\"][{POST_SNAPBACK}][/a]
In NX you can select a WB target, then the program applies a multiplier to the red and blue channels (e.g., B=1.3, R=1.6), and you can be fine tune the amount of multiplication in each channel.
To clarify the Capture One thing - you are saying that you can set exposure to just short of clipping and when you change white balance it won't ever show clipping as a result? That's an interesting feature, and one I have often thought from an academic point of view would be useful. So I am envisaging a case where say the blue channel was just shy of clipping and the R and G are not clipping. Then, change white balance such that it increases the blue multiplier, which would ordinarily cause the blue channel to clip. But in this case, instead of increasing the blue multiplier, it would actually decrease the R and G multipliers in the correct proportions. Is this what is happening in Capture?
No, you can set WB and then adjust exposure compensation so that the individual channel does not clip; essentially, this is the same as what you are suggesting.
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In NX you can select a WB target, then the program applies a multiplier to the red and blue channels (e.g., B=1.3, R=1.6), and you can be fine tune the amount of multiplication in each channel.
No, you can set WB and then adjust exposure compensation so that the individual channel does not clip; essentially, this is the same as what you are suggesting.
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I don't know that it is. As far as I know the process you are describing for Capture One is exactly the same for ACR and all the others I have played with. You can adjust the exposure slider any time you want and it will change the amount of clipping. This is totally independant of white balance.
The idea I am talking about is similar to what Dave Coffin does with DCRaw when you can opt to have multipliers greater than or less than one. I would like to take it a step further and have it so that the multipliers are scaled so that the most saturated channel can't clip. If I could find the time to revisit my 'C' skills I would probably do it.
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It does in ACR. If you get your highlights just where you want them, then change the WB, sometimes the highlight blow again. Many times you can crank up recovery though and offset the change. If not, then you need to mess with your exposure again.
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White balance is obtained by multiplying the red and blue channels by a coefficient greater than unity. Typical RGB values for the Canon 350D are 1.392498, 1.000000, 2.375114 for tungsten and 2.132483, 1.000000, 1.480864 for daylight. Normally the red and green channels are considerably to the left of the green, but if the image contains strong reds or greens, these channels can get blown when the multiplier is applied. The green channel would never be blown, since the multiplier is 1.0.
As [a href=\"http://www.guillermoluijk.com/tutorial/dcraw/index_en.htm]Guillermo Luijk [/url] explains in his post on DCRaw, this can be avoided by using multipliers that are all equal to or less than one. For example, in daylight balancing one could use 1.00000, 0.46894, and 0.694436; the ratios between the multipliers are unchanged but no channel would be blown. With these multipliers, the image would be too dark, and one would have to apply a scaling factor of 2.132483 (about 1 f/stop) to the image after white balance. This can be accomplished by use of the exposure control. The same principles apply to conversion with ACR.
If the channels are blown with ACR during white balance, one can use the exposure control to apply a uniform scaling factor to restore the integrity of the channels (i.e use a negative exposure value). Depending on the image, the exposure control would be better than the recovery control, which is nonlinear and affects mainly the highlights. If you want to tone down the highlights, then the recovery control would be preferable.
Bill
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White balance is obtained by multiplying the red and blue channels by a coefficient greater than unity. Typical RGB values for the Canon 350D are 1.392498, 1.000000, 2.375114 for tungsten and 2.132483, 1.000000, 1.480864 for daylight.
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What you are saying is would correspond to a WB matrix where off-diagonal elements are zero.
In typical implementations there are inter-channel dependencies. Therefore, off-diagonal elements are not zero (typically they are negative) to properly offset the R,G, and B channels.
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What you are saying is would correspond to a WB matrix where off-diagonal elements are zero.
In typical implementations there are inter-channel dependencies. Therefore, off-diagonal elements are not zero (typically they are negative) to properly offset the R,G, and B channels.
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What you say may or may not be true--I don't know. However, the multiplication factors are what are used in DCRaw and Iris with good results. What do you make of that?
Bill
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What you are saying is would correspond to a WB matrix where off-diagonal elements are zero.
In typical implementations there are inter-channel dependencies. Therefore, off-diagonal elements are not zero (typically they are negative) to properly offset the R,G, and B channels.
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Depends on how you think about it. For pure WB you just need a diagonal matrix (which performs a non-uniform scaling operation, which is what Bill described). This produces neutral grays, as desired, but also produces awful colors because camera color response doesn't match human visual response. That's where camera color profiles come into play. If you want to characterize a RGB camera using a simple 3x3 matrix, then in general the off-diagonal elements of the matrix would be non-zero. You can either think of the color mapping as two steps: first a WB diagonal matrix applied, followed by a color matrix ... or as a single step where the WB and color matrix have been pre-multiplied together.
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Bill, the source code for dcraw also has the color matrices for several cameras. They are not necessary for white balance but they are needed to get respectable-looking color.
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Two points and a question:
1. Most (all?) RAW processors have the ability to bring back "blown" highlights. Just yesterday I was shooting in bright daylight and couldn't get ETTR exposure to acceptable levels without risking severe shadow noise. LR "Recovery" allowed me to pull back almost all the data in the blown clouds. I haven't done tests to see how "good" the data is, ie. how much color shift there is, yet, or how much leeway there is.
2. Bracketing is generally faster than tweaking an exposure using a histogram. Not as accurate of course, but faster.
Question: it seems that some are implying that white balance affects RAW - which I thought was not the case. I just checked my Canon's manual and it specifically says RAW allows me to change WB in post without degrading image quality.
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If you did recover "blown highlights" from your raw image, then they were not blown to begin with. Once the tonal value reaches 255, or in the case of 12 bit/channel 4,095, then it it blown and blown for good and forever. No amount of post processing is going to recover that tone, and how could it? Perhaps the in-camera histo showed "blown" but it actually may not have been. By the way, when shooting raw, WB and other settings don't effect raw directly, however WB will influence the exposure as shown on the histogram. One doesn't have to get it perfect when shooting raw, but getting it close would show benefit.
As to WB and the Canon manual, you misunderstand my comments. I never said shooting raw and with the wrong WB is detrimental to the image, nope never said that. What I did say is that if you shoot with the wrong WB, it WILL EFFECT EXPOSURE, and that might mean an EV that is not beneficial to your particular picture. For example, if you take the same exact shot 5 times with 5 different WB settings, the resulting 5 histograms will be different. So your Canon manual and what I wrote are both correct.
Bracketing is not that much faster, and if it is faster and less accurate then why even do it?...if you practice, you can adjust exposure on the fly and very fast. I've never blown a shot by applying EC. Applying EC per the histogram is a lot more accurate, and a shot worth taking is a shot worth that accuracy, yea?
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This has been posted already somewhere above. It is still nonsense.
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Let me be more accurate....WB will effect the histogram. Take the same exact shot with the same exact exposure values but different WB settings and you'll get a different histogram for each WB setting used.
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I think you meant open it up 2 or 3 stops. The actual number varies depending on the light, the color, and the camera.
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Yes, you're right, open up. I don't know that the exact number will really depend on the light (assuming raw), but certainly color and camera, maybe even lens.
-Lars
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Bill, the source code for dcraw also has the color matrices for several cameras. They are not necessary for white balance but they are needed to get respectable-looking color.
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Eric,
Yes, on looking at the source code for DCRaw, I came across a list of color matrices for various camera and noted that Dave Coffin thanked Adobe for supplying them. I presume Thomas Knoll uses these or something similar in Camera Raw. Are these matirx operations commutative (IOW, can they be applied in any order)?
Bill
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Let me be more accurate....WB will effect the histogram
Well, you need to be much more accurate, but before that you need to gain a better understanding the subject. You posted just above
What I did say is that if you shoot with the wrong WB, it WILL EFFECT EXPOSURE, and that might mean an EV that is not beneficial to your particular picture
NO, it WILL NOT affect the exposure, and that is good so.
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Yes, on looking at the source code for DCRaw, I came across a list of color matrices for various camera and noted that Dave Coffin thanked Adobe for supplying them. I presume Thomas Knoll uses these or something similar in Camera Raw. Are these matirx operations commutative (IOW, can they be applied in any order)?
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White balance, then apply the camera matrix. Matrix multiplication isn't commutative (generally) so the order is important in this case.
Example: you take a picture of a gray card. The actual camera R, G, B values are, say, 0.4, 0.7, 0.3. So you do white balance by applying scale factors of 7/4, 1, 7/3. This can be written as a diagonal matrix W = {{7/4, 0, 0}, {0, 1, 0}, {0, 0, 7/3}}. Then apply the camera color matrix C. So the combined operation is XYZ = C * W * (camera RGB). Once you're in XYZ space you now have colorimetrically-defined values and you can convert to whatever color space you want to work in (e.g., ProPhoto RGB with linear gamma, in the case of CR).
The DNG 1.2 spec has a more complete description of this process in one of its appendices.
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Depends on how you think about it. For pure WB you just need a diagonal matrix (which performs a non-uniform scaling operation, which is what Bill described). This produces neutral grays, as desired, but also produces awful colors because camera color response doesn't match human visual response. That's where camera color profiles come into play. If you want to characterize a RGB camera using a simple 3x3 matrix, then in general the off-diagonal elements of the matrix would be non-zero. You can either think of the color mapping as two steps: first a WB diagonal matrix applied, followed by a color matrix ... or as a single step where the WB and color matrix have been pre-multiplied together.
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Yes, you are right. Thanks for taking the time to explain it in detail.