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Luminous Landscape has taught me to err on the side of over-exposure and not under-exposure.
Provided that one does not clip any highlight information that is desired, is it ever wrong to expose to the right?
Are there circumstances where one might get better results not doing ETTR (expose to the right)?
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Luminous Landscape has taught me to err on the side of over-exposure and not under-exposure.
Provided that one does not clip any highlight information that is desired, is it ever wrong to expose to the right?
Are there circumstances where one might get better results not doing ETTR (expose to the right)?
No - you are thinking analog, not digital. LULA would not teach you to "over-expose". In digital, over-expose means you clip highlights having detail you want to preserve. As long as you don't do that, you are not over-exposing. The image may LOOK brighter than you want it to be in the final analysis, but that's just a matter of adjusting it back down in post-capture processing; at least you will be starting with the maximum luminance information obtainable. That's what ETTR does for you.
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Are there circumstances where one might get better results not doing ETTR (expose to the right)?
There are several cases where ETTR is not the best option, for example:
- If your subject of interest is in the deep shadows, and the scene has a high dynamic range. For example you take a picture of your cat at home in a dark room with a window facing a sunny day outside. ETTR would mean to expose in such a way that the window is preserved, but your cat would be captured so dark that will display a lot of noise when lifting the shadows in post processing.
- If to achieve ETTR you are forced to use a shutter speed not quick enough to avoid motion blurring, or you are forced to use such an aperture that your DOF is insufficient. In these cases, some extra noise because of not-ETTR is desirable vs the lack of sharpness
- If the scene is so dynamic that you cannot do the calculations or trial&error to achieve proper ETTR. In that situation it is better not to ETTR and underexpose slightly in order to prevent highlight clipping.
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To add to Mark's comments that you should, if anything, err on the side of underexposing with digital since one can recover more from the shadows than with film. One has about two stops latitude on overexposure on negative film (and one under), depending on the scene.
Of course, ETTR's purpose (roughly speaking) is to maximize capture quality (w.r.t. noise and number of levels of luminosity distinguished) after applying exposure compensation in post while staying within the scene's dynamic range. But if what you want/need is not provided by ETTR, then it can be "wrong", just like trying to use any tool for something it wasn't intended for.
In addition to the examples from Guillermo, here are some more:
For instance, if you need to use unadjusted output from the camera (for example, to hand an out-of-camera JPEG to a client on the spot), then you don't have the option of adjusting exposure compensation in post; ETTR is not suitable here. Or, if you know you can afford to blow highlights, then you're not staying within the scene's dynamic range. For example, maybe you're going to crop your image to eliminate the part with blown out highlights. Here, you can increase exposure even more to maximize capture quality. But you really do need to make sure you can afford/want to have clipped highlights and/or will be removing those sections of the image later.
If you're shooting RAW and can adjust later, the exposure you would get from using ETTR should be the minimum and only to be exceeded if you know what you're doing!
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There are several cases where ETTR is not the best option, for example:
- If your subject of interest is in the deep shadows, and the scene has a high dynamic range. For example you take a picture of your cat at home in a dark room with a window facing a sunny day outside. ETTR would mean to expose in such a way that the window is preserved, but your cat would be captured so dark that will display a lot of noise when lifting the shadows in post processing.
- If to achieve ETTR you are forced to use a shutter speed not quick enough to avoid motion blurring, or you are forced to use such an aperture that your DOF is insufficient. In these cases, some extra noise because of not-ETTR is desirable vs the lack of sharpness
- If the scene is so dynamic that you cannot do the calculations or trial&error to achieve proper ETTR. In that situation it is better not to ETTR and underexpose slightly in order to prevent highlight clipping.
Guillermo, all of which adds-up to saying that we have capture situations where compromises are necessary, which of course is true; but one should perhaps emphasize this doesn't impair the general principle that ETTR make the most sense for those who want to retain the maximum possible amount of usable, high quality information in a raw capture.
On your first point, if the scene DR substantially exceeds that of the sensor and you want it all, it may be necessary to make several exposures and blend them - if the situation allows. However, if you intend to ignore or crop-out the areas where the extreme DR manifests itself worst, then of course concentrate the exposure on the material one will keep - and make it an ETTR capture. On your third point, I agree with the idea of being extra-cautious not to clip highlights in conditions of real uncertainty.
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In two situations: when shooting very high speed iso, and when shooting jpegs fomat that can't handle the data build up in the highlights.
Most of the pixels are in the high-end and in shooting in moderate to flat lighting it is a good method IF you are processing parametrically . Shooting in bright sunlight where the high values are extreme you have to be a little more careful, like in Tucson in the summer....
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Being a frequent visitor to this forum, I have gained great respect for Guillermo's knowledge and expertise in this (and other) areas; thus I should know better than to quibble with his response. However on this occasion I venture to do so because, even in this august assembly, I believe there are readers not sufficiently able to read between the lines and may misinterpret the answers provided here.
There are several cases where ETTR is not the best option, for example:
- If your subject of interest is in the deep shadows, and the scene has a high dynamic range. For example you take a picture of your cat at home in a dark room with a window facing a sunny day outside. ETTR would mean to expose in such a way that the window is preserved, but your cat would be captured so dark that will display a lot of noise when lifting the shadows in post processing.
I thought that we had reached a consensus on the meaning of ETTR. Expose in such a way that the highlights are preserved, only if those highlights contain detail which is important to your image. In this particular example I think the correct advise would be to forget the window and then expose as far to the right as the cat and the dark room will allow. In other words, ETTR and then ETTR some more.
- If to achieve ETTR you are forced to use a shutter speed not quick enough to avoid motion blurring, or you are forced to use such an aperture that your DOF is insufficient. In these cases, some extra noise because of not-ETTR is desirable vs the lack of sharpness
Here again the less knowledgable reader needs to know that in these circumstances (fixed shutter speed and/or aperture), employing ETTR through increasing the ISO (with many cameras) will produce a cleaner image, without sacrificing sharpness or desired DOF.
With much respect.
m
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There is a post by Ctein on TOP http://theonlinephotographer.typepad.com/the_online_photographer/2011/10/expose-to-the-right-is-a-bunch-of-bull.html which is typical of the misunderstanding of what ETTR is all about. The problem is that the ETTR is the third of three factors which must be considered:
1. Don't blow highlights that have detail you want to preserve.
2. Use the appropriate shutter speed, f stop and ISO
3. If, subject to 1 and 2 there is latitude to increase the exposure, do so.
The goal of ETTR is to provide as much flexibility in post as is practical. If that's not important to you (and for some it really isn't) then don't worry about ETTR.
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The goal of ETTR is to provide as much flexibility in post as is practical. If that's not important to you (and for some it really isn't) then don't worry about ETTR.
I would be more precise than talking about 'flexibility'. I would say:
If noise is not a problem in your application, you don't need to worry about ETTR.
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There is a post by Ctein on TOP http://theonlinephotographer.typepad.com/the_online_photographer/2011/10/expose-to-the-right-is-a-bunch-of-bull.html which is typical of the misunderstanding of what ETTR is all about. The problem is that the ETTR is the third of three factors which must be considered:
1. Don't blow highlights that have detail you want to preserve.
2. Use the appropriate shutter speed, f stop and ISO
3. If, subject to 1 and 2 there is latitude to increase the exposure, do so.
The goal of ETTR is to provide as much flexibility in post as is practical. If that's not important to you (and for some it really isn't) then don't worry about ETTR.
Hi Tim,
I think this is an excellent summary of good advice. The problem with Ctein's argument is that he focuses mainly on noise, dismisses it too easily in my opinion - regardless of the technical progress since 2003, and doesn't take into account that ETTR allows for capturing more information, resulting in more assurance of smooth tonal gradation, given the greater amount of tonal information the sensor captures further up the tone scale, (ref. Jeff Schewe in his ACR books). Some people think this is a theoretical consideration not seen in practice, but others have seen it in practice. Ctein makes a separate point that in-camera histograms are not necessarily a reliable indicator of clipping. I think this can be true and also well-known, but all it means is to be careful - understand what your camera is showing and perhaps allow a slight margin if in doubt. It doesn't vitiate the general principle.
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Some people think this is a theoretical consideration not seen in practice, but others have seen it in practice.
Unfortunately for us all, none of them wanted to show others what they saw.
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I should have said others claim to have seen it in practice. The smoothness of tonal gradations can be an elusive quality to observe unambiguously. Nonetheless it makes sense to me in principle that if you can safely expose in a manner that preserves more information rather than less, it makes sense to do so. What's the downside, noting that I used the word "safely" ?
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Nonetheless it makes sense to me in principle that if you can safely expose in a manner that preserves more information rather than less, it makes sense to do so. What's the downside, noting that I used the word "safely" ?
I don't think anyone says there is any downside in ETTR, I simply claim there is no advantage in it beyond SNR improvement. If that is true, talking about ETTR is talking about noise, being anything else a fallacy.
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Guillermo, The SNR improvement alone is a very good reason to retain this practice regardless of how good the sensors and noise reduction programs have become. I have noticed this even using a Canon 1Ds3 at 400ISO. Images with histograms further to the right display better noise properties than those with histograms further to left, all else roughly equal, and noise mitigation programs always involve at least some sacrifice of IQ, even if a little. So why not avoid this if possible? As for the benefit of conserving more luminance information, you may be "exposing yourself to the right a bit" :-) saying this a fallacy, unless you can demonstrate that there are no imaging conditions in which it may be useful.
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saying this a fallacy, unless you can demonstrate that there are no imaging conditions in which it may be useful.
It is impossible to prove a negative. There have been attempts at showing improvements in bright tones due to ETTR, but in my view they did not show benefit. I know of none that shows benefit.
That is no proof, but to me it is a strong indication.
-h
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I would expect most of the improvement to show in better gradation of dark tones, because that is where the purported information paucity would be greatest, absent deliberate exposure technique to optimize it.
Yes, indeed, hard to prove a negative and that's why I like the expression "never say never".
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I would expect most of the improvement to show in better gradation of dark tones
But dark tones are dithered by noise, so extra levels mean no practical advantage. Camera makers choose the number of bits of their ADC not to be the limiting factor for any posterization issues even in the dark shadows (where less differentiated levels are encoded per stop) at base ISO (where less dithering noise is present).
I am a fan of ETTR and I use it whenever possible, but I think the only advantage it provides is cleaner images thanks to SNR improvement. The fallacy begins with the having more tonal levels/more information bla bla bla claim, which has zero effect in practice, and nobody has shown any evidence of the opposite so far. The only thing we have are articles (like Michael's) claiming that ETTR is good because it adds extra tonal levels, and people repeating what they read in those articles.
Regards
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But dark tones are dithered by noise, so extra levels mean no practical advantage. Camera makers choose the number of bits of their ADC not to be the limiting factor for any posterization issues even in the dark shadows (where less differentiated levels are encoded per stop) at base ISO (where less dithering noise is present).
Unless I'm missing something, which is entirely possible, this seems to set aside the notion that through increased exposure of the darker scene tones, they become lighter captured tones as one is moving them rightward up the scale where there is a higher number of encoded levels, and the S/N is greater.
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Unless I'm missing something, which is entirely possible, this seems to set aside the notion that through increased exposure of the darker scene tones, they become lighter captured tones as one is moving them rightward up the scale where there is a higher number of encoded levels, and the S/N is greater.
The point of Guillermo is (I believe) that there is sufficient noise prior to the ADC that it is this noise that limits the performance, and not the ADC levels. Adding noise to a signal tends to "dither" it, meaning that the quantization noise is effectively decorrelated with the signal, and can be considered a noise source in itself. Going to 16 bits or 24 bits of true ADC resolution might only measure the sensor/electronics noise with higher precision, instead of having any more precise data about the desired (noiseless) "signal". Using a 24-bit audio ADC to digitize old worn-out tapes might not give any better audio compared to a 16-bit one, as the desired signal is mainly degraded by the noise and flaws of the tape.
If there are two noise sources, and one is a lot bigger than the other, then you often might as well forget about the smaller one (spectral characteristics might also play a part).
http://en.wikipedia.org/wiki/Dithering
http://www.sengpielaudio.com/calculator-spl.htm
-h
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this seems to set aside the notion that through increased exposure of the darker scene tones, they become lighter captured tones as one is moving them rightward up the scale where there is a higher number of encoded levels, and the S/N is greater.
There are extra levels thanks to ETTR, but as I said in the previous post: "extra levels mean no practical advantage" in this case, because noise dithers any possible posterization.
Left image is 8-bit, right is just 5-bit (8 times less encoded levels):
(http://www.guillermoluijk.com/article/ettr3/poster.gif)
Both look similar and are equally robust thanks to noise. The same thing happens in the lower stops of a RAW file.
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Possibly, but leaves questions in my mind about the level along the tonal range at which intentionally induced dithering is overcome by the correlation of S:N, and what degree of image enlargement one requires to see any of these effects at work.
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I think some of the quibble here is over semantics, or rather precision of language. There is a distinction between 'encoded levels' and 'information'. Having more levels does not necessarily mean more information. What photographers who employ ETTR understand intuitively is that by increasing exposure they get smoother tonal gradations, and that is indeed because there is more information in the image due to higher S/N. There are indeed more distinguishable levels because that number is governed by the S/N; and this number of distinguishable levels, it should be noted, is distinct from the number of encoded levels which is the number of raw values encompassing any given exposure zone in the image. One can play all sorts of tricks with the latter without changing the S/N and thus the image quality, as Guillermo's example shows.
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Unless I'm missing something, which is entirely possible, this seems to set aside the notion that through increased exposure of the darker scene tones, they become lighter captured tones as one is moving them rightward up the scale where there is a higher number of encoded levels, and the S/N is greater.
No...actually it dovetails fine. The bottom line is it's the increase of photons caused by ETTR that increases the SNR. The bit about "bits" or levels or tones originally written about by Mike is what's the confusing issue. ETTR works because it's the increase in the photon count that improves the signal-more photons = better signal-not more bits in the shadows.
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No...actually it dovetails fine. The bottom line is it's the increase of photons caused by ETTR that increases the SNR. The bit about "bits" or levels or tones originally written about by Mike is what's the confusing issue. ETTR works because it's the increase in the photon count that improves the signal-more photons = better signal-not more bits in the shadows.
OK, now taking this one step further. I have cases "A" and "B". In case "A" I don't care about ETTR, I make an exposure, the scene's dark tones emerge really dark - not many photons - the histogram is positioned relatively leftward. In case "B" I do care about ETTR, so I do it - safely - and those same scene dark tones are hitting the sensor at a higher photon count, because my ETTR is achieved either by a wider lens opening or a lower shutter speed. Absent further intervention they would look "over-exposed".
Now, when I open both images in LR and I want to optimize luminosity (brightness and contrast), in Case A I would find myself lightening up the shadow areas and revealing more of the latent noise in the image. In Case B I would be remapping the brightness of the shadow areas to darker values, but if ETTR is to be a useful recommendation at least with respect to quarter-tones, the Case B process should reveal less noise and perhaps have more refined tonal gradation than the Case A result. ??
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the Case B process should reveal less noise and perhaps have more refined tonal gradation than the Case A result. ??
The case B will have less noise and a more refined tonal gradation, but the only visible effect you will see is less visible noise. In other words, there is nothing about tonal gradation in Case B that you could be missing in Case A, because in case A the lower SNR dithered any lack of tonal gradation. Both shots A and B have the same robustness against posterization (so none of them is particularly lacking tonal gradation), but A is noisier.
Take a typical isoless camera such as the Pentax K5. Take a shot at ISO100 with 2 stops headroom in the highlights. Now take another shot at ISO400, a perfectly ETTR'ed RAW file. The ISO400 shot has a more refined gradation (the RAW file has 4 times more filled levels), but you will not notice it since SNR is the same on both shots. In brief, having more levels not always means a visible softer tonal gradation. For the same reason, having less levels not always means seeing a poorer tonal gradation (Case A vs Case B).
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In real world shooting, flare is a very good reason not to ETTR. Flare from a bright sky or other light sources will wash out more detail than you save by reducing noise. It does not take much overexposure for moderate flare to arrive.
Other reasons are motion blur and saving yourself time in post. There's splitting hairs about S/N, but these are things most people will never encounter, certainly not in a real world viewing and real world shooting.
The above are, however.
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In real world shooting, flare is a very good reason not to ETTR. Flare from a bright sky or other light sources will wash out more detail than you save by reducing noise. It does not take much overexposure for moderate flare to arrive.
I don't think your hypothesis is correct. Veiling flare is proportional to luminance and will be increased when you ETTR, but when you normalize the image by decreasing exposure in the raw converter, the flare will be proportionately reduced.
Regards,
Bill
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Hi,
In my view, ETTR is always OK if correctly done. On the other hand, a correctly exposed image can be a boring image. We can capture a lot of DR but mapping it down to screen may be very hard.
The image here shows an example of an image straight out of camera and the same image after some manipulation in CS5:
(http://echophoto.dnsalias.net/ekr/images/Psychadelic/FromHereToHere.jpg)
The interpretation may be a bit psychedelic but illustrates how much information is buried in a digital image. The workflow is described here: http://echophoto.dnsalias.net/ekr/index.php/photoarticles/61-hdr-tone-mapping-on-ordinary-image
Best regards
Erik
Luminous Landscape has taught me to err on the side of over-exposure and not under-exposure.
Provided that one does not clip any highlight information that is desired, is it ever wrong to expose to the right?
Are there circumstances where one might get better results not doing ETTR (expose to the right)?
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I don't think your hypothesis is correct. Veiling flare is proportional to luminance and will be increased when you ETTR, but when you normalize the image by decreasing exposure in the raw converter, the flare will be proportionately reduced.
Regards,
Bill
Not necessarily. Shoot two series of images, one with a light source surrounded by a light colored background, and one by a dark colored (windows and curtains work nicely) The dark colored will have more noticeable bleed into it at moderate exposures.
Not sure why this is, though I suspect its because veiling glare, and its causes and solutions, are more complex than a linear relationship. Perception may play a part as well, which tends to cause havoc when debating merits of things like S/N :)
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Not necessarily. Shoot two series of images, one with a light source surrounded by a light colored background, and one by a dark colored (windows and curtains work nicely) The dark colored will have more noticeable bleed into it at moderate exposures.
And what do these conditions have to do with ETTR?
Regards,
Bill
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And what do these conditions have to do with ETTR?
Regards,
Bill
Hi Bill,
ETTR results in more noticeable glare in real world conditions. Modern cameras are fairly clean noise wise, even at fairly high ISO it's inoffensive, glare is more of a problem in reducing detail than noise is. Thus, the photographer will want to correct for glare that might be linear (veiling global glare), or non-linear (localized) in post. This all takes time.
At one time, when noise was a bigger issue, ETTR made sense, if you didn't have highlights to control. But now, ETTR as a general shooting rule is deprecated and, at best, a waste of time. Expose properly and be done with it. Move on to the next shot rather than worrying about whether you've saturated the pixels enough :)
I shoot a lot of architecture and glare is a frequent unwelcome guest. Here's a very interesting paper on (rather extreme) glare and various solutions: http://graphics.stanford.edu/papers/glare_removal/
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Hi Bill,
ETTR results in more noticeable glare in real world conditions. Modern cameras are fairly clean noise wise, even at fairly high ISO it's inoffensive, glare is more of a problem in reducing detail than noise is. Thus, the photographer will want to correct for glare that might be linear (veiling global glare), or non-linear (localized) in post. This all takes time.
At one time, when noise was a bigger issue, ETTR made sense, if you didn't have highlights to control. But now, ETTR as a general shooting rule is deprecated and, at best, a waste of time. Expose properly and be done with it. Move on to the next shot rather than worrying about whether you've saturated the pixels enough :)
I shoot a lot of architecture and glare is a frequent unwelcome guest. Here's a very interesting paper on (rather extreme) glare and various solutions: http://graphics.stanford.edu/papers/glare_removal/
I still see no evidence that you have brought forth that ETTR with proper normalization produces more veiling glare than an expose to the left strategy with no adjustment. The Stanford paper is interesting, but nowhere do they mention ETTL as a solution to this problem. Do you have any examples to support your thesis?
Regards,
Bill
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ETTR isn't 'deprecated' ... It is the axiomatic principle of digital exposure.
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Hi Bill and Jeremy,
I think you misunderstand my point. ETTR is a waste of time because its benefits are negligible, and may even be harmful to an image when in real world conditions. By 'harm' I mean degradation from non-linear glare that normalizing cannot fix, or as simple as motion blur from a longer exposure time. In laboratory conditions, where you don't have any glare and isolate all vibration... it may result in slightly better results in some pixels (would these be visible on a normal display or print?), but what benefit is this outside of there?
Glare is often non-linear in real-world shooting, which is partly why the deconvolution technique in the Stanford paper didn't work so well and why they came up with the method to deal with it physically. Normalizing an ETTR exposure will not always fix it. This is one reason why I consider glare to be a downside to ETTR. I find this glare to be more offensive than slight noise that is not viewable under real world conditions.
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Hi Bill,
ETTR results in more noticeable glare in real world conditions. Modern cameras are fairly clean noise wise, even at fairly high ISO it's inoffensive, glare is more of a problem in reducing detail than noise is. Thus, the photographer will want to correct for glare that might be linear (veiling global glare), or non-linear (localized) in post. This all takes time.
Hi Craig,
I agree that global veiling glare (very low spatial frequency due to outside-of-FOV) and more localized glare/flare (due to bright light sources, or bright reflective surfaces, within the FOV) can be a pain. However, I'm undecided about it's non-linearity in its contribution to the final exposure. Given an amount of flare for a given scene with a given optical path and exposure level, only increasing the exposure level would result in a linear contribution of all elements that add to the exposure, assuming that the sensor has a linear response (which CCDs an CMOS devices do in general, save for provisions for draining overexposure), or so it would seem.
Yet John McCann also suggests (http://web.mac.com/mccanns/HDR/Glare_Limits_HDRI_files/07EI%206492-41_1.pdf) that the veiling glare contribution is non-linear. I can imagine that being the case for intra-occular glare, because the change of the pupil diameter of our eyes is a function of the brightness, and thus of the optical and thus glare performance. However, when only the exposure time is a variable, I sofar fail to see the non-linear contributing component(s).
I shoot a lot of architecture and glare is a frequent unwelcome guest. Here's a very interesting paper on (rather extreme) glare and various solutions: http://graphics.stanford.edu/papers/glare_removal/
Indeed, architecture is a more obvious scenario in which I also encounter the detrimental effects of veiling glare (which can be minimized on a given lens by using a good adjustable lens hood, and in general by using lenses with few lens-groups, good coating, and proper internal lens edge and barrel blackening). Some lenses even use multiple apertures to suppress internal reflections.
The only reason for non-linearity that I can identify sofar, is that it's spatially variant (i.e. subject to local brightness), but I don't see the non-linear aspect of a uniform change in exposure level (by varying exposure time, not by changing aperture (which is a no-no in HDR photography)) for a given scene.
Given John McCann's examples, I feel that I'm overlooking something obvious ..., but sofar I'm unable to pin-point it.
Cheers,
Bart
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Hi Craig,
I agree that global veiling glare (very low spatial frequency due to outside-of-FOV) and more localized glare/flare (due to bright light sources, or bright reflective surfaces, within the FOV) can be a pain. However, I'm undecided about it's non-linearity in its contribution to the final exposure. Given an amount of flare for a given scene with a given optical path and exposure level, only increasing the exposure level would result in a linear contribution of all elements that add to the exposure, assuming that the sensor has a linear response (which CCDs an CMOS devices do in general, save for provisions for draining overexposure), or so it would seem.
Yet John McCann also suggests (http://web.mac.com/mccanns/HDR/Glare_Limits_HDRI_files/07EI%206492-41_1.pdf) that the veiling glare contribution is non-linear. I can imagine that being the case for intra-occular glare, because the change of the pupil diameter of our eyes is a function of the brightness, and thus of the optical and thus glare performance. However, when only the exposure time is a variable, I sofar fail to see the non-linear contributing component(s).
Indeed, architecture is a more obvious scenario in which I also encounter the detrimental effects of veiling glare (which can be minimized on a given lens by using a good adjustable lens hood, and in general by using lenses with few lens-groups, good coating, and proper internal lens edge and barrel blackening). Some lenses even use multiple apertures to suppress internal reflections.
The only reason for non-linearity that I can identify sofar, is that it's spatially variant (i.e. subject to local brightness), but I don't see the non-linear aspect of a uniform change in exposure level (by varying exposure time, not by changing aperture (which is a no-no in HDR photography)) for a given scene.
Given John McCann's examples, I feel that I'm overlooking something obvious ..., but sofar I'm unable to pin-point it.
Cheers,
Bart
I am not sure about the non-linear glare either. A google search on non-linear veiling glare brings back some interesting papers, but they seem to be for very specific situations, such as reducing the reflection of a car dash off a windshield, where geometry makes a difference.
W/ respect to photography I can think of a couple of issues involving human perception. Most raw files are processed with a curve applied to them because human vision isn't linear. This will cause some issues. And then of course if the flare is saturating a color channel. One source of glare that is behind the shutter is the sensor itself causing reflections, I would also assume some mirrorbox features and geometry would also contribute. The Stanford paper mentions this, but doesn't go into detail. It seems like this would be highly dependent on source position and intensity and some other factors.
In real world shooting, glare tends to be noticeably worse when a source is surrounded by a dark feature rather than a light one. A bright light against a white ceiling is less problematic that one against a dark. It may simply be a matter of perception, which is what is really important here, but I bet the default curve applied to raw images contributes.
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In real world shooting, glare tends to be noticeably worse when a source is surrounded by a dark feature rather than a light one. A bright light against a white ceiling is less problematic that one against a dark. It may simply be a matter of perception, which is what is really important here, but I bet the default curve applied to raw images contributes.
I still don't understand how all of this talk about human perception applies to ETTR and veiling glare. Whether or not we ETTR a given scene, the background and other factors do not change and the overall image is the same except for exposure.
Shown below are some shots of a Stouffer wedge with and without masking off glare from the light table. The images are rendered in ACR with a linear tone curve. The image marked 08 has the surrounding brightness of the light table masked off to reduce veiling glare. The image marked 01 Nominal is without masking and is exposed so that step 1 has an sRGB value of 193. Image 03 is exposed to the right so that step 1 has a value of 252. Exposure of image 03 is decreased in ACR so that step one has a value of 193 (the same as image 1 exposed to the left). The shadow values are virtually the same, showing in this case that ETTR does not affect veiling glare.
Regards,
Bill
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or as simple as motion blur from a longer exposure time.
I think that ETTR should be defined as "increase exposure until you have objectional highlight clipping, or objectional motion blur or objectional lack of DOF". In other words: expose hot, but not too hot and not if it makes the image look bad. Then motion blur should not be a problem either?
-h
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I still don't understand how all of this talk about human perception applies to ETTR and veiling glare. Whether or not we ETTR a given scene, the background and other factors do not change and the overall image is the same except for exposure.
Me neither.
Exposure is about how much time you spend collecting photons. As long as your sensor doesn't get saturated (i.e. as long as you do proper ETTR), the only difference between shots taken at different shutter speeds, once their exposures are matched in post processing, is SNR. Proper ETTR has zero influence in the harmful effects of glare.
Regards
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I still don't understand how all of this talk about human perception applies to ETTR and veiling glare. Whether or not we ETTR a given scene, the background and other factors do not change and the overall image is the same except for exposure.
Shown below are some shots of a Stouffer wedge with and without masking off glare from the light table. The images are rendered in ACR with a linear tone curve. The image marked 08 has the surrounding brightness of the light table masked off to reduce veiling glare. The image marked 01 Nominal is without masking and is exposed so that step 1 has an sRGB value of 193. Image 03 is exposed to the right so that step 1 has a value of 252. Exposure of image 03 is decreased in ACR so that step one has a value of 193 (the same as image 1 exposed to the left). The shadow values are virtually the same, showing in this case that ETTR does not affect veiling glare.
Regards,
Bill
As I said before, in laboratory-like conditions, ETTR may have a modest benefit in the numbers, but in the real world, this bears out differently.
With your wedge on a light table, you have just about replicated a standard way of measuring global veiling glare in a lens. McCann does something similar to show that veiling glare limits information available in an image - this actually furthers my point a bit, that ETTR has no benefits and in general shooting, increases chances of a subpar image w/ respect to motion blur and glare.
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I think that ETTR should be defined as "increase exposure until you have objectional highlight clipping, or objectional motion blur or objectional lack of DOF". In other words: expose hot, but not too hot and not if it makes the image look bad. Then motion blur should not be a problem either?
-h
This is how I think of it:
In circumstances where:
- There is no undesired motion, from either camera or subject, that a longer exposure would exacerbate.
- There is no localized veiling glare
- Highlights are controlled
- You're using an ugly-noise camera
- You want to spend time correcting the exposure later
ETTR may provide a slight benefit in numbers. Even then, I have doubts as to whether this is visible on screen or in print.
In the real world of photography and not lab tests, some or all of these criteria are not met. Plus, you'd need a stout tripod, mirror lockup and a remote release to eliminate all vibration to eliminate any pixel-level blurring. Obviously, with a lot of subject matter this just isn't practical.
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As I said before, in laboratory-like conditions, ETTR may have a modest benefit in the numbers, but in the real world, this bears out differently.
With your wedge on a light table, you have just about replicated a standard way of measuring global veiling glare in a lens. McCann does something similar to show that veiling glare limits information available in an image - this actually furthers my point a bit, that ETTR has no benefits and in general shooting, increases chances of a subpar image w/ respect to motion blur and glare.
Again, you are making assertions without any data to back them up. My experiment does show that increasing the camera exposure (ETTR) has no effect on veiling glare when the image is normalized to what would be obtained with an ETTL exposure, contrary to your assertion that it increases glare even when one normalizes the ETTR exposure. Your comments about motion blur are correct, but if one is shooting from a tripod and photographing a static scene, motion blur would not be a factor.
Regards,
Bill
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Again, you are making assertions without any data to back them up. My experiment does show that increasing the camera exposure (ETTR) has no effect on veiling glare when the image is normalized to what would be obtained with an ETTL exposure, contrary to your assertion that it increases glare even when one normalizes the ETTR exposure. Your comments about motion blur are correct, but if one is shooting from a tripod and photographing a static scene, motion blur would not be a factor.
Regards,
Bill
Hi Bill,
Veiling glare limits information. It puts values into pixels which are unrelated to the scene. You might think of it as a type of noise that originates from the optical path and not the sensor. McCann demonstrates this, so does the Stanford paper. Normalizing does not add information that does not exist. Shooting at a proper exposure won't either in a linear glare situation, non-linear it might improve things.
The purpose of ETTR is to improve your SN ratio (with dubious results), but veiling glare puts a limit to this. So your ETTR isn't accomplishing its purpose, and in the real world, increases the chance of noticeable degradation from the other factors I mentioned.
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I think some of the quibble here is over semantics, or rather precision of language. There is a distinction between 'encoded levels' and 'information'. Having more levels does not necessarily mean more information. What photographers who employ ETTR understand intuitively is that by increasing exposure they get smoother tonal gradations, and that is indeed because there is more information in the image due to higher S/N. There are indeed more distinguishable levels because that number is governed by the S/N; and this number of distinguishable levels, it should be noted, is distinct from the number of encoded levels which is the number of raw values encompassing any given exposure zone in the image. One can play all sorts of tricks with the latter without changing the S/N and thus the image quality, as Guillermo's example shows.
DXO does quantify the number of distinguishable levels in an image with their Tonal Range (http://www.dxomark.com/index.php/About/In-depth-measurements/Measurements/Noise) measurement. They state "The standard deviation of noise can be viewed as the smallest difference between two distinguishable gray levels."
The tonal range for the Pentax K5 (an ISO less camera) is shown along with an Excel spreadsheet showing the actual number of levels. With an ISO-less sensor, the tonal range with increasing ISO can represent exposure to the left, since each doubling of ISO halves the number of photons collected by the sensor and the read noise does not change. One may not be using the full scale of the ADC with higher ISO, but this does not make much difference, since the quantization is limited by noise and not the number of ADC steps.
Regards,
Bill
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This is how I think of it:
In circumstances where:
- There is no undesired motion, from either camera or subject, that a longer exposure would exacerbate.
- There is no localized veiling glare
- Highlights are controlled
- You're using an ugly-noise camera
- You want to spend time correcting the exposure later
ETTR may provide a slight benefit in numbers. Even then, I have doubts as to whether this is visible on screen or in print.
In the real world of photography and not lab tests, some or all of these criteria are not met. Plus, you'd need a stout tripod, mirror lockup and a remote release to eliminate all vibration to eliminate any pixel-level blurring. Obviously, with a lot of subject matter this just isn't practical.
I have no doubt whatsoever. Properly used, the technique works fine and helps produce cleaner images. As for the "conditions" you specify:
- Bill Janes has amply demonstrated that "veiling glare" is a red-herring.
- It goes without saying that one would select a high enough shutter speed to elimimate undesired motion blur. Exposure is always about compromises, so don't try invalidating a generally valid proposition by confusing it with the issue of compromises often needed in any exposure situation.
- Controlling highlights is part of ETTR technique, not an obstacle to it. Another red-herring.
- All cameras have a background level of noise that becomes more apparent the lower the exposure. This is still an inescapable fact of digital imaging regardless of the camera and all the technical progress to date.
- "Spending time correcting the exposure later" is also a red-herring, because any one who shoots raw is editing the images in post-capture software anyhow.
It's been an interesting discussion, but I think this argument has run its course.
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Hi Bill,
Veiling glare limits information. It puts values into pixels which are unrelated to the scene. You might think of it as a type of noise that originates from the optical path and not the sensor. McCann demonstrates this, so does the Stanford paper. Normalizing does not add information that does not exist. Shooting at a proper exposure won't either in a linear glare situation, non-linear it might improve things.
The purpose of ETTR is to improve your SN ratio (with dubious results), but veiling glare puts a limit to this. So your ETTR isn't accomplishing its purpose, and in the real world, increases the chance of noticeable degradation from the other factors I mentioned.
Veiling glare affects predominantly the shadows. The ETTR will improve SNR in the highlights as shown in my previous post. Overall DR will be limited by the effect of veiling glare diluting the shadows, but the ETTR will still improve SNR in the highlights. You have yet to demonstrate that the veiling glare is non-linear. For my shooting, I will continue to use ETTR, taking care not to blow important highlights. Veiling glare does not enter into the equation.
Regards,
Bill
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It's been an interesting discussion, but I think this argument has run its course.
+1
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I have no doubt whatsoever. Properly used, the technique works fine and helps produce cleaner images. As for the "conditions" you specify:
- Bill Janes has amply demonstrated that "veiling glare" is a red-herring.
- It goes without saying that one would select a high enough shutter speed to elimimate undesired motion blur. Exposure is always about compromises, so don't try invalidating a generally valid proposition by confusing it with the issue of compromises often needed in any exposure situation.
- Controlling highlights is part of ETTR technique, not an obstacle to it. Another red-herring.
- All cameras have a background level of noise that becomes more apparent the lower the exposure. This is still an inescapable fact of digital imaging regardless of the camera and all the technical progress to date.
- "Spending time correcting the exposure later" is also a red-herring, because any one who shoots raw is editing the images in post-capture software anyhow.
It's been an interesting discussion, but I think this argument has run its course.
Hi Mark, I agree that it's run its course, but if veiling glare is a red herring then why are there research papers devoted to its effects and limitations? Have you read and understood the two papers linked to here? IMO, the loss of information negates ETTR benefits.
I believe ETTR has a very limited usefulness and is not 'generally valid' today for anyone interested in real world photography. Especially when the discussion has no alternative but to turn to various charts and graphs that do not represent real world ink hitting paper.
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Veiling glare limits information.
Yes, veiling glare limits information, BUT...
ETTR DOESN'T INCREASE THE EFFECT OF VEILING GLARE
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Yes, veiling glare limits information, BUT...
ETTR DOESN'T INCREASE THE EFFECT OF VEILING GLARE
Lol, nice. That's debatable. However, it seems few in this thread have read and understood the papers and other things presented here. Who knew this was such a touchy subject?
Enjoy the holiday folks :)
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Hi Mark, I agree that it's run its course, but if veiling glare is a red herring then why are there research papers devoted to its effects and limitations? Have you read and understood the two papers linked to here? IMO, the loss of information negates ETTR benefits.
I believe ETTR has a very limited usefulness and is not 'generally valid' today for anyone interested in real world photography. Especially when the discussion has no alternative but to turn to various charts and graphs that do not represent real world ink hitting paper.
All kinds of research papers are devoted to all kinds of stuff and that in itself proves nothing. You've had two highly respected researchers on this forum telling you that veiled glare is a non-issue in respect of ETTR. As for real world ink hitting paper, I think my Epson 4900 and previous incarnations qualify. I've been making high quality inkjet prints from a range of top-of-the-line cameras for years, and if I tell you I can perceive noise differences in those prints as a function of exposure - and we're talking real-word photos, not charts - I'm not inviting you to tell me I don't know what I'm looking at, unless you've seen what I've seen yourself. This is not a "touchy subject" - it's simply s debate about facts, and not everyone here agrees with your view of the facts. That happens - no hard feelings. As I said, this has run its course.
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Lol, nice. That's debatable. However, it seems few in this thread have read and understood the papers and other things presented here.
I don't think any of those papers state that ETTR increases veiling glare since a sensor is just a linear photon counter. If you expose more by increasing exposure time, you'll just have higher levels defining your veiling glare areas, but not more veiling glare.
If I am wrong, I'd be pleased that you explain why, or in which precise point of any link this is explained. If you cannot do that I'd simply request you stop saying ETTR is a bad idea because of veiling glare.
All this in a friendly Christmas atmosphere ;D
(http://www.guillermoluijk.com/title_en.gif)
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I don't think any of those papers state that ETTR increases veiling glare since a sensor is just a photon counter. If you expose more by increasing exposure time, you'll just have higher levels defining your veiling glare areas, but not more veiling glare.
If I am wrong, I'd be pleased that you explain why, or in which precise point of any link this is explained. If you cannot do that, I'd simply request you stop saying ETTR is a bad idea because of veiling glare.
All this in a friendly Christmas atmosphere ;D
(http://www.guillermoluijk.com/title_en.gif)
Hi Guillermo,
The papers suggest that some glare is not linear. Yes, a sensor is a linear source - although with all the variables that go between photo capture and ink hitting paper, the final result might not be. The Stanford paper for example, finds that deconvolution does not work so great. It could be their implementation, or, some of the glare does not follow linearly before their algorithm is applied, or a combination thereof. Some glare, for example, is behind the shutter and off the sensor, or there could be other hardware/software interactions with the data. Remember the good ol' days of sensor blooming?
My own experience of thousands of images, which I am sad to say does not come with attendant charts and graphs :), shows that some glare is worse to deal with than others, and simply normalizing the data does not provide the same benefit as a shorter exposure time. Not all glare follows this, but it happens often enough, usually when a bright source is against a darker background. But, even as this case is rare, the non benefits of ETTR plus the increased risk of motion blur and such detail killing artifacts make it a poor choice as a general rule.
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My own experience of thousands of images, which I am sad to say does not come with attendant charts and graphs :), shows that some glare is worse to deal with than others, and simply normalizing the data does not provide the same benefit as a shorter exposure time.
In thousands of images you'll surely have one that demonstrates what you say. Why not use it?
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In thousands of images you'll surely have one that demonstrates what you say. Why not use it?
Chalk me up to the latest ETTR debater too lazy to bother digging one up from the archive. That is why until now I've tried to avoid the "you haven't seen what i've seen!" argument. Hence the papers that show the information limitations caused by glare, and also, simply the threat of pixel level motion blur or highlight detail loss in real world photography that undoes any benefit from ETTR.
The next time I come across the non-linear issue I'll post it, but until then, feel free to focus on that rather than the other more concrete issues with ETTR. :)
But to bring this back full circle to the original post of "Is expose to the right ever wrong?" Yes. I believe it is wrong in most situations that a typical photographer will encounter, despite all the apparently well-meaning charts and graphs that don't tell the whole story.
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Chalk me up to the latest ETTR debater too lazy to bother digging one up from the archive. That is why until now I've tried to avoid the "you haven't seen what i've seen!" argument. Hence the papers that show the information limitations caused by glare, and also, simply the threat of pixel level motion blur or highlight detail loss in real world photography that undoes any benefit from ETTR.
The next time I come across the non-linear issue I'll post it, but until then, feel free to focus on that rather than the other more concrete issues with ETTR. :)
But to bring this back full circle to the original post of "Is expose to the right ever wrong?" Yes. I believe it is wrong in most situations that a typical photographer will encounter, despite all the apparently well-meaning charts and graphs that don't tell the whole story.
If ETTR is wrong in most situations, then you should have no problem to take a few minutes TODAY to make a few captures to illustrate your point. This will not involve any searching at all...only picking up a camera and pushing a button. Otherwise, your points are....well....you do not have any.
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If ETTR is wrong in most situations, then you should have no problem to take a few minutes TODAY to make a few captures to illustrate your point. This will not involve any searching at all...only picking up a camera and pushing a button. Otherwise, your points are....well....you do not have any.
Is it not obvious that potential motion blur and non-linear veiling glare is a significant downside to ETTR, especially when ETTR provides zero-to-few benefits in the end? This is the entire point.
I find photography forums to be frustrating. Please read all of the above posts and papers before commenting.
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Is it not obvious that potential motion blur and non-linear veiling glare is a significant downside to ETTR, especially when ETTR provides zero-to-few benefits in the end? This is the entire point.
I find photography forums to be frustrating. Please read all of the above posts and papers before commenting.
I have read every post. I have not read every paper. I do not need to. I have incorporated ETTR (and tried to avoid ETFTTR) into my knowledge base and use it all of the time. I expose as far to the right as I can while retaining wanted highlight information, avoiding non-linear veiling glare, utilizing a high enough shutter speed to prevent unwanted motion blur, a low enough iso number, and my desired f stop. By doing so, I definitely have seen a reduction in the noise level in most of my images when compared to my images back in the days of exposing to the middle only. ETTR does not require the shooter to use a slow shutter speed thereby causing motion blur! There is also a potential for motion blur when under-exposing. It is a theory that the shooter can take into consideration when setting the parameters before tripping the shutter.
It does not matter if the problem is non-linear veiling glare or motion blur. I will set my camera settings to avoid both. In other words, I practice ETTR, not ETFTTR (Expose Too Far To The Right).
It is ok if you feel that ETTR provides zero-to-few benefits in the end. In my photographic world, I definitely see the benefits provided...no question.
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- It goes without saying that one would select a high enough shutter speed to elimimate undesired motion blur. Exposure is always about compromises, so don't try invalidating a generally valid proposition by confusing it with the issue of compromises often needed in any exposure situation.
It does go without saying, unless you are in a forum discussion about ETTR when some have to come up with reasons it is not going to work well. But you and I both know that we are not always in ideal conditions. No one in their right mind would invoke motion blur when not wanted just to provide more photons to the sensor! IF the conditions can be met, using ETTR, a Tripod, Mirror lock up, the best lens etc will produce the best (better) data than not using these techniques. And as image creators who understand the processes, I can’t see why we’d ignore better quality data if we can produce it. But there are all kinds of situations where I can’t use a tripod, or lock the mirror, or even ETTR to get an acceptable if not idelized data.
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Plus, you'd need a stout tripod, mirror lockup and a remote release to eliminate all vibration to eliminate any pixel-level blurring.
Which is something you need to consider doing regardless of whether or not you use ETTR...if you want max image quality, photographers need to exercise proper technique on a whole host of technical issues...ETTR is simply one factor in a range of factors to deploy. But claiming it has little or no benefit is short changing your arsenal for no good reason.
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Which is something you need to consider doing regardless of whether or not you use ETTR...if you want max image quality, photographers need to exercise proper technique on a whole host of technical issues...ETTR is simply one factor in a range of factors to deploy. But claiming it has little or no benefit is short changing your arsenal for no good reason.
Exactly.
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It does go without saying, unless you are in a forum discussion about ETTR when some have to come up with reasons it is not going to work well. But you and I both know that we are not always in ideal conditions. No one in their right mind would invoke motion blur when not wanted just to provide more photons to the sensor! IF the conditions can be met, using ETTR, a Tripod, Mirror lock up, the best lens etc will produce the best (better) data than not using these techniques. And as image creators who understand the processes, I can’t see why we’d ignore better quality data if we can produce it. But there are all kinds of situations where I can’t use a tripod, or lock the mirror, or even ETTR to get an acceptable if not idelized data.
Yes of course - the key point in the context of this thread being that having conditions where ETTR can't be used to advantage isn't a valid argument for asserting that it shouldn't be used altogether or only under unreasonably limited conditions.
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The paper that is referenced by Craig is a bit of a problem in that it deals with the direct cause of flare by extreme lighting conditions (mostly backlit) which any photographer who has captured images in nature with strong back lighting realizes how bad flare can get and how difficult it can be to adequately deal with it. I'm old enough to remember the old Kodak leaflets that accompanied their film that noted best images can be produced with the direct light source in back of the photographer. As others have pointed out the extreme case does not prove generally applicable nor does it invalidate ETTR. ETTR is extremely valuable as long as we understand how to apply it and what the limitations are. In the end the laws of physics are immutable (the confirmation of the pending discovery of the Higgs boson not withstanding).
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Yes of course - the key point in the context of this thread being that having conditions where ETTR can't be used to advantage isn't a valid argument for asserting that it shouldn't be used altogether or only under unreasonably limited conditions.
A point that was understood by many of us before the last 3 pages of contentious discourse.
I wonder some times if the OP has any idea what they're in for when asking seemingly innocent questions.
Sheesh.
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A point that was understood by many of us before the last 3 pages of contentious discourse.
I wonder some times if the OP has any idea what they're in for when asking seemingly innocent questions.
Sheesh.
Well, if you're the anonymous self-appointed keyboard warrior representing all those who got the point three pages ago, let me simply apologize here and now for boring you all - especially as I suggested many posts back that this discussion had run its course; my remark was directed at those who obviously don't get it or don't agree. Others are of course most welcome to ignore it.