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Author Topic: exposing to the right  (Read 32513 times)
pco98
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« on: March 31, 2008, 09:05:49 AM »
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Hello all,

I'm in Hong Kong airport sitting with a scanner, scanning my last batch of film (hey do you remember those days?). But as of tomorrow I'm hitting downtown HK to finally go fully digital with a 5D, now at their cheapest ever. I put all my money into some L lenses, so there's been a financial delay in getting a high-end digital body until now :-)

I've been reading up about exposing to the right as the preferred shooting technique and had a question about the practicalities of this. Am I right in assuming you don't know if the highlights have been blown until after the image is taken and you check the histogram? If so is there a lot of checking and deleting because a channel has been clipped or because it's not as close to the clipping threshold as it could be. Or, after a while do you develop a feel for how much to expose to the right, getting non-clipped shots most of the time?

Thanks in advance,

Ross
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Steven Draper
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« Reply #1 on: March 31, 2008, 09:16:42 AM »
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Hello. Exposing to the right allows more data in the shadows to be collected. The danger, as you highlight!!! is blowing the highlights. IMO, a badly blown highlight is generally worse than a dark area. Hence in some cases I actually have to expose, using the same terminology,  left, and the push the shadows later.

The problem with the histogram is that you don't see it until after the image has been exposed, and then what you are seeing is based on the Jpeg, and also the WB set in the camera. Some people have produced "null" WB settings in order to combat this.

In most camera's there is the ability to pull back some highlight detail during RAW conversion, but this really becomes a Know your camera, convertor and scene style. 2/3 of a stop is about my working limit.

It does provide benefits, but on a "must have" shot only you can determine whether the slight improvements to shadows out-ways the risk of protecting any channel clipping.

There is a technique called "high-speed Bracketing" which is also worth exploring, where you set the camera to bracket either side of your exposure and then take the images in rapid fire mode.

Steven
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Mark D Segal
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« Reply #2 on: March 31, 2008, 09:27:19 AM »
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Hello all,

I'm in Hong Kong airport sitting with a scanner, scanning my last batch of film (hey do you remember those days?). But as of tomorrow I'm hitting downtown HK to finally go fully digital with a 5D, now at their cheapest ever. I put all my money into some L lenses, so there's been a financial delay in getting a high-end digital body until now :-)

I've been reading up about exposing to the right as the preferred shooting technique and had a question about the practicalities of this. Am I right in assuming you don't know if the highlights have been blown until after the image is taken and you check the histogram? If so is there a lot of checking and deleting because a channel has been clipped or because it's not as close to the clipping threshold as it could be. Or, after a while do you develop a feel for how much to expose to the right, getting non-clipped shots most of the time?

Thanks in advance,

Ross
[a href=\"index.php?act=findpost&pid=185686\"][{POST_SNAPBACK}][/a]

It's true - you don't know until after you've made the shot what the histogram looks like. There is no live preview of the histogram. Typically, I find Canon DSLRs (the two that I own) have a tendancy of under-exposing relative to what one wants using the ETTR approach. I don't know exactly why - could be how they calculate middle grey, how they accommodate specular highlights - a number of possibilities; but the outcome is that I often find after making the initial exposure, it is necessry to add some exposure compensation and make another shot to get the ETTR correctly positioned.

One develops a certain "feel" (aided by careful observation and experimentation) for how much compensation is needed relative to the amount of empty space on the right which needs to be "filled" with tones.

But it is also important to remember that the histogram and the preview are based on an in-camera JPEG rendition of the file, not the raw file itself. This in-camera JPEG may or may not be a fairly accurate predictor of how the raw file will emerge. So this is a second variable you need to mentally adjust - by experimenting a bit. You make several exposures with what looks like best ETTR practice on the camera's histogram, then open them in your raw converter to see any gaps between what the camera predicts and what emerges from the file on your computer display. I've found there is a bit of leeway - when the camera begins to show clipping the raw file may still be fine, but you'd need to check the extent of any such leeway with your camera.
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Mark D Segal (formerly MarkDS)
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joedecker
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« Reply #3 on: March 31, 2008, 09:27:20 AM »
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I've been reading up about exposing to the right as the preferred shooting technique and had a question about the practicalities of this. Am I right in assuming you don't know if the highlights have been blown until after the image is taken and you check the histogram? If so is there a lot of checking and deleting because a channel has been clipped or because it's not as close to the clipping threshold as it could be. Or, after a while do you develop a feel for how much to expose to the right, getting non-clipped shots most of the time?

Yep, you are right that you don't know until after the fact, and yes, I look at the (RGB, not luminance) histogram primarily to determine that.  I find that in most situations, autoexposure gives me something "pretty good", and that I'll tend to "shoot, glance at histogram, move on", and when that doesn't work it's more "shoot, glance at histogram, quickly sketch in some exposure compensation, shoot again, glance at histogram, move on".  

I don't delete in the field.  My shooting style tries to keep my brain as much as possible aimed at "seeing", and less time (but not less than necessary) on "intellectual thinking".  

How much?  It depends a little, but if I think the highlights will be visible in the histogram (this can be tricky when you only have a couple tiny highlights in a darker scene, but that's a rarer case), I tend to aim  to put them about, oh, I dunno, an tenth of the visual width of the histogram from the right hand side.      

A lot of times I will accept a capture with wider spacing if I know that the exposure I eventually want in the print is darker or about the same as the exposure I captured, I'll worry about ETTR more if I feel like I'm going to pull up the shadows, or if my histogram has pegged or nearly-pegged shadows I'd like some level of detail in.

This all sounds like a lot of work, but it becomes, for me, very intuitive and quick after a while.
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Joe Decker
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« Reply #4 on: March 31, 2008, 10:18:50 AM »
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ERRT, the good, the bad and the ugly:
http://www.digitalphotopro.com/tech/exposing-for-raw.html
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Andrew Rodney
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« Reply #5 on: March 31, 2008, 12:53:23 PM »
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Also note that with recent cameras you have the option of Live View which does show a live histogram.

Same limitation of the histogram being generated from the in-camera JPEG applies, however.
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bjanes
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« Reply #6 on: March 31, 2008, 12:58:40 PM »
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ERRT, the good, the bad and the ugly:
http://www.digitalphotopro.com/tech/exposing-for-raw.html
[a href=\"index.php?act=findpost&pid=185720\"][{POST_SNAPBACK}][/a]

This is a good article on exposure to the right, but I would take exception with the use of Adobe Lightroom (or the equivalent Adobe Camera Raw) to evaluate clipping in the raw file. The tone curve can affect the results and it is best to look directly and avoid these complications.

I recently did some tests with the Nikon D3, taking bracketed shots of a Stouffer step wedge and splitting out the green channel of the raw file in Iris (a free ware astronomical program) and analyzing it in ImageJ (a free ware program from the US National Institutes of Health). I used 14 bit NEFs with lossless compression.

Here is a plot of an image with step one of the wedge just short of clipping.



And here is a histogram of step one, confirming the absence of clipping.



Here is the image in Adobe Camera Raw (which uses the same raw conversion engine as Lightroom). ACR indicates clipping through step 3 (each step is 0.3 EV or 1/3 stop).



To elilminate the clipping, it is necessary to use negative exposure compensation of -0.6 EV.



The camera histogram with the camera set to the Standard Picture Control (normal contrast, normal saturation) also shows come clipping:



Decreasing exposure by 0.3 EV removes the clipping in the camera histogram, confirming that the camera histogram is slightly conservative in its treatment of highlights, but is within 1/3 stop, which is a reasonable amount of headroom.



My conclusion is that the camera histogram is useful in ETTR but that the result of the ACR histogram can be misleading as ACR by default places the highlights too high with this particular camera.

Bill
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Mark D Segal
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« Reply #7 on: March 31, 2008, 02:13:12 PM »
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Also note that with recent cameras you have the option of Live View which does show a live histogram.

Same limitation of the histogram being generated from the in-camera JPEG applies, however.
[a href=\"index.php?act=findpost&pid=185781\"][{POST_SNAPBACK}][/a]

Hi Eric,

As far as I'm aware the only recent cameras with live histograms are non-DSLRs. Even my 1DsMk3, which has live-view, does NOT (much to my chagrin) have a live histogram. I wish..........

Mark
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Mark D Segal (formerly MarkDS)
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« Reply #8 on: March 31, 2008, 02:20:24 PM »
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This is a good article on exposure to the right, but I would take exception with the use of Adobe Lightroom (or the equivalent Adobe Camera Raw) to evaluate clipping in the raw file. The tone curve can affect the results and it is best to look directly and avoid these complications.

I recently did some tests with the Nikon D3, taking bracketed shots of a Stouffer step wedge and splitting out the green channel of the raw file in Iris (a free ware astronomical program) and analyzing it in ImageJ (a free ware program from the US National Institutes of Health). I used 14 bit NEFs with lossless compression.

Here is a plot of an image with step one of the wedge just short of clipping.



And here is a histogram of step one, confirming the absence of clipping.



Here is the image in Adobe Camera Raw (which uses the same raw conversion engine as Lightroom). ACR indicates clipping through step 3 (each step is 0.3 EV or 1/3 stop).



To elilminate the clipping, it is necessary to use negative exposure compensation of -0.6 EV.



The camera histogram with the camera set to the Standard Picture Control (normal contrast, normal saturation) also shows come clipping:



Decreasing exposure by 0.3 EV removes the clipping in the camera histogram, confirming that the camera histogram is slightly conservative in its treatment of highlights, but is within 1/3 stop, which is a reasonable amount of headroom.



My conclusion is that the camera histogram is useful in ETTR but that the result of the ACR histogram can be misleading as ACR by default places the highlights too high with this particular camera.

Bill
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Bill, a couple of points: Firstly, I believe, based on my experience with the Canon 1Ds and 1DsMk3, plus discussion with a Nuikon D3 owner, that the Canons have a tendancy to under-expose and the Nikon D3 tends to expose more toward the right. The OP is in the Canon "world". Secondly, when I examine an image in ACR, I start out with totally neutral conditions" W/B "As Shot", all the rest of the front panel are zeros and both tone curves are linear. This way you see what's coming from the camera without any tinkering. Non-linearity in either of the tone curves or any positive saturation values, or a warming of the white balance, depending on the image, could generate some highlight clipping which isn't a product of what emerged from the camera.
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Mark D Segal (formerly MarkDS)
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douglasf13
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« Reply #9 on: March 31, 2008, 03:20:46 PM »
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Lightroom was doing this to my A700 RAW files, but I've since set the default import settings of Contrast, Brightness, and Black level to zero, as well as the linear tone curve, and this seems to be more indicative of the actual RAW.
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NikoJorj
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« Reply #10 on: March 31, 2008, 03:32:45 PM »
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This is a good article on exposure to the right, but I would take exception with the use of Adobe Lightroom (or the equivalent Adobe Camera Raw) to evaluate clipping in the raw file.
[...]
Here is the image in Adobe Camera Raw (which uses the same raw conversion engine as Lightroom). ACR indicates clipping through step 3 (each step is 0.3 EV or 1/3 stop).


[a href=\"index.php?act=findpost&pid=185786\"][{POST_SNAPBACK}][/a]
Mmmmmm, it seems that your default preset for that shot has a Contrast of +25... I'd say, better to set it at 0 for that particular purpose?
Ditto for the Blacks : +5 should mean clipping, shouldn't it?
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Nicolas from Grenoble
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« Reply #11 on: March 31, 2008, 03:52:06 PM »
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Bill, a couple of points: Firstly, I believe, based on my experience with the Canon 1Ds and 1DsMk3, plus discussion with a Nuikon D3 owner, that the Canons have a tendancy to under-expose and the Nikon D3 tends to expose more toward the right. The OP is in the Canon "world". Secondly, when I examine an image in ACR, I start out with totally neutral conditions" W/B "As Shot", all the rest of the front panel are zeros and both tone curves are linear. This way you see what's coming from the camera without any tinkering. Non-linearity in either of the tone curves or any positive saturation values, or a warming of the white balance, depending on the image, could generate some highlight clipping which isn't a product of what emerged from the camera.
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Mark,

Thanks for your comments. A contrast curve (S-curve) affects the three quarter tones much more than the highlights themselves. Here are my results with the settings you suggest. The point curve was also set to linear.





Negative exposure compensation is still necessary to bring step 1 below clipping.

Bill
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bjanes
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« Reply #12 on: March 31, 2008, 03:56:11 PM »
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Mmmmmm, it seems that your default preset for that shot has a Contrast of +25... I'd say, better to set it at 0 for that particular purpose?
Ditto for the Blacks : +5 should mean clipping, shouldn't it?
[a href=\"index.php?act=findpost&pid=185851\"][{POST_SNAPBACK}][/a]

That is the default ACR for the D3 and other Nikon cameras that I have. See my reply to MarkDS for a linear tone curve. It does not affect the highlights very much, but does affect the three quarter tones. The Black setting does not affect the highlights.

Bill
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Mark D Segal
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« Reply #13 on: March 31, 2008, 04:27:37 PM »
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Mark,

Thanks for your comments. A contrast curve (S-curve) affects the three quarter tones much more than the highlights themselves. Here are my results with the settings you suggest. The point curve was also set to linear.

Negative exposure compensation is still necessary to bring step 1 below clipping.

Bill
[a href=\"index.php?act=findpost&pid=185857\"][{POST_SNAPBACK}][/a]

Bill,

Thanks for taking the trouble to test that and illustrate it. Most interesting. Yes of course - what you say about the S-Curve is mainly correct, what it is supposed to do - and does; but depending on the image it (especially combined with boosted brightness and contrast in the Basic Tab) can have the unwanted side-effect of clipping some of the highlights. That is why it's safer to start in ACR with zeroed Basics and linear curves, as your own results show. The extent of clipping with my suggested (flat) settings is far less than it was with the previous settings - only about half a stop. In the example you show here, the preferred correction for the slight highlight loss would be to increase Recovery till those highlights just recover. This will work as long as it is not all three channels that are clipped.

Mark
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Mark D Segal (formerly MarkDS)
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« Reply #14 on: March 31, 2008, 08:40:58 PM »
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IMO, any test about ETTR to analyse if a RAW file was clipped, needs neutral (1.0) white balance multipliers. Since ACR and any other commercial developer don't allow them, I would not take too much seriously precise results obtained using them.

DCRAW achieves neutral WB by -r 1 1 1 1

Regards.
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« Reply #15 on: March 31, 2008, 09:57:47 PM »
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Also note that with recent cameras you have the option of Live View which does show a live histogram.

Same limitation of the histogram being generated from the in-camera JPEG applies, however.
[a href=\"index.php?act=findpost&pid=185781\"][{POST_SNAPBACK}][/a]

Hmmm .... not on my D300 it would appear.  Live histogram could be useful.
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« Reply #16 on: April 01, 2008, 03:20:00 AM »
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Hi Ross. With the size of cf cards now, I don't bother deleting until the images are in the raw converter. Seeing how much leeway I have or haven't got has taught me a lot. And yes, you quickly get used to checking the back of the camera and getting a feel for how to set it up.
I set the exposure to manual most of the time, take a shot and check the histogram, and then only check it every half hour or so. On the 40D, if the clipping warnings are just starting, then it's usually about right when opened in the raw converter. If I'm photographing birds, I take a reading off the sky and add about 1 to 1 1/2 stops. You'll have a lot of fun finding out what works for you. I hope you really enjoy your new gear. Cheers, David
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« Reply #17 on: April 01, 2008, 05:16:09 AM »
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It does not affect the highlights very much, but does affect the three quarter tones.
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Surprinsing, but well proven! Thanks to have taken the time for it.

Like Mark, I had the experience of the Contrast setting leading to clipping with borderline exposures (Canon 300d for me).


Side note : as my camera shows only a luminance jpeg-based histogram, I took the (bad) habit to consider that ETTR was OK as long as I had :
- on one hand, at least a bit of information in the upper stop,
- on the other hand, no jpeg clipping, and the more saturated colors in the hightlights the more margin I take with it (needs a well-tuned ouija board to be precise   ).

Matter of tastes, but I prefer the Scylla of noise to the Charybdis of clipping-related hue shifts in the highlights.
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Nicolas from Grenoble
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« Reply #18 on: April 01, 2008, 07:33:13 AM »
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In the example you show here, the preferred correction for the slight highlight loss would be to increase Recovery till those highlights just recover. This will work as long as it is not all three channels that are clipped.
[a href=\"index.php?act=findpost&pid=185870\"][{POST_SNAPBACK}][/a]

Mark,

Recovery is for the purpose you suggest, but in the case of global overexposure where all tones are lifted by say 0.5 EV, it may be better to use the exposure slider and bring down all tones by 0.5 EV. Recovery is useful in high dynamic range situations where you want to recover the highlights and not affect the three quarter tones and mid tones.

As an example, here are the characteristic curves for the stepchart images. On the left, negative exposure was used and highlight correction on the right, both in ACR using the previously posted example.

[attachment=5860:attachment]

In the recovery example, the slope of the curve is too flat, and the mid tones and highlight tones are not well separated
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Mark D Segal
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« Reply #19 on: April 01, 2008, 08:08:17 AM »
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Mark,

Recovery is for the purpose you suggest, but in the case of global overexposure where all tones are lifted by say 0.5 EV, it may be better to use the exposure slider and bring down all tones by 0.5 EV. Recovery is useful in high dynamic range situations where you want to recover the highlights and not affect the three quarter tones and mid tones.

As an example, here are the characteristic curves for the stepchart images. On the left, negative exposure was used and highlight correction on the right, both in ACR using the previously posted example.


In the recovery example, the slope of the curve is too flat, and the mid tones and highlight tones are not well separated
[a href=\"index.php?act=findpost&pid=186076\"][{POST_SNAPBACK}][/a]

Bill, yes, if all three channels are clipped there is nothing to recover, why I suggested one needs some information to make use of it. Your second sentence is the point I was trying to make.

While the charts are interesting for confirming what one observes on the image itself, the nice thing about ACR and a well-calibrated and profiled display is that we can try any combination of adjustments and see how they play-out on the image - an embarassment of riches really. Pushed too far on certain images, I agree Recovery can flatten the highlights too much - as your charts show, in which case use of the tone curves becomes more appropriate. Fortunately, once we've finished doing all this stuff, ACR implements it all in optimal sequence for us.
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Mark D Segal (formerly MarkDS)
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