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Author Topic: Exposing to the Right  (Read 14956 times)
maenol
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« on: August 19, 2009, 07:15:36 AM »
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Hi,
I am sorry if this is a stupid question. But being new I would like some advice. I read a lot about exposure to the right and understand that not doing so underuses the capabilities of modern sensors. However, what should I do if presented with a subject that contains no highlights? If say there are no whites in the object should I shoot correct exposure manually using some nearby reference, or overexpose, using histogram as guide? The latter seems wrong to me but I would like guidance. Correct exposure would seem more logical. I am sorry if I am barking up the wrong tree here.
Peter
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Blendenteufel
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« Reply #1 on: August 19, 2009, 08:47:35 AM »
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Hi,

from my point of view, it makes sense to use Expose to the right only if you shoot in RAW. Also, I would always recommend to bracket your exposure, so you always have a fall-back option in case highlight details are missing.

There are several good articles in the www that elaborate on the costs and benefit of that matter. You should draw your on conclusions based on some sample shots of your normal subjects.

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digitaldog
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« Reply #2 on: August 19, 2009, 08:48:05 AM »
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Quote from: maenol
If say there are no whites in the object should I shoot correct exposure manually using some nearby reference, or overexpose, using histogram as guide? The latter seems wrong to me but I would like guidance. Correct exposure would seem more logical. I am sorry if I am barking up the wrong tree here.

First off, ETTR is correct exposure for Raw data.

Next, just attempt to expose based on the scene, putting as much data as possible in that first stop of the tone scale that ETTR usually reserves for "highlights".
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Andrew Rodney
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Guillermo Luijk
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« Reply #3 on: August 19, 2009, 09:22:32 AM »
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Quote from: maenol
what should I do if presented with a subject that contains no highlights? If say there are no whites in the object should I shoot correct exposure manually using some nearby reference, or overexpose, using histogram as guide?
Correct me if I am wrong Peter, but reading your thoughts about the subject's highlights I have a feeling you are trying to understand ETTR from a film photography point of view, where camera exposure was linked to the desired final printed exposure.

If you want to maximise the quality (basically signal to noise ratio) of your captures shooting RAW, forget about that link. Capture exposure is not linked to the printed exposure anymore since in digital exposure can be adjusted without any loss or change in the image information.

No matter how the lights are in the scene, ETTR means exposing as much as possible so that the highest luminosity area of your scene gets the maximum RAW values right before clipping. Afterwards, in the RAW development process you will adjust exposure to your desire, being now certain that noise was minimised in your shadows.

BR
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PeterAit
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« Reply #4 on: August 19, 2009, 09:27:52 AM »
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Quote from: maenol
Hi,
I am sorry if this is a stupid question. But being new I would like some advice. I read a lot about exposure to the right and understand that not doing so underuses the capabilities of modern sensors. However, what should I do if presented with a subject that contains no highlights? If say there are no whites in the object should I shoot correct exposure manually using some nearby reference, or overexpose, using histogram as guide? The latter seems wrong to me but I would like guidance. Correct exposure would seem more logical. I am sorry if I am barking up the wrong tree here.
Peter

Actually, when there are no whites in the subject is when ETTR is most appropriate. If there are whites (and what I mean is near-whites that contain some detail, such as snow), then ETTR has the potential to blow them out so the detail is lost - although shooting RAW lessens the change of this happening.

Peter
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Peter
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walter.sk
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« Reply #5 on: August 19, 2009, 09:30:50 AM »
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Quote from: GLuijk
Correct me if I am wrong Peter, but reading your thoughts about the subject's highlights I have a feeling you are trying to understand ETTR from a film photography point of view, where camera exposure was linked to the desired final printed exposure.

If you want to maximise the quality (basically signal to noise ratio) of your captures shooting RAW, forget about that link. Capture exposure is not linked to the printed exposure anymore since in digital exposure can be adjusted without any loss or change in the image information.

No matter how the lights are in the scene, ETTR means exposing as much as possible so that the highest luminosity area of your scene gets the maximum RAW values right before clipping. Afterwards, in the RAW development process you will adjust exposure to your desire, being now certain that noise was minimised in your shadows.

BR
Your explanation is very clear.  I've been exposing to the right for years now, and it just occurred to me as I read your description that it should be fairly simple for the camera manufacturers to program their pro cameras' exposure systems to automatically put the brightest part of the scene right at the limit before clipping occurs, tailored for the specific model's sensor.  While some people might object to more automation it certainly would not have to preclude the possibility of exposure compensation or purely manual exposure.  It could even operate only when the camera is in RAW mode.

I for one would really like such a setup.
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Guillermo Luijk
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« Reply #6 on: August 19, 2009, 09:38:14 AM »
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Quote from: walter.sk
Your explanation is very clear.  I've been exposing to the right for years now, and it just occurred to me as I read your description that it should be fairly simple for the camera manufacturers to program their pro cameras' exposure systems to automatically put the brightest part of the scene right at the limit before clipping occurs, tailored for the specific model's sensor.  While some people might object to more automation it certainly would not have to preclude the possibility of exposure compensation or purely manual exposure.  It could even operate only when the camera is in RAW mode.

   Camera manufacturers PLEASE: when RAW histograms and an ETTR mode?  
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evogel99
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« Reply #7 on: August 19, 2009, 02:42:32 PM »
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Quote from: GLuijk

It is ironic that given all the EEs working on the design of these things, such an obvious design optimization has never been included. Perhaps they tried too hard to mimic film cameras as a design spec, and there is nothing like that even possible in a film camera. In digital, you know everything there is to know about the "film" (sensor). You surely should leverage that information!
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bjanes
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« Reply #8 on: August 20, 2009, 08:11:29 AM »
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Quote from: digitaldog
First off, ETTR is correct exposure for Raw data.

Next, just attempt to expose based on the scene, putting as much data as possible in that first stop of the tone scale that ETTR usually reserves for "highlights".

What exposure is correct is debatable, depending on the definition of correct. My understanding of ETTR is that the highlights containing important detail should be placed just short of clipping and no headroom is reserved for the highlights. A perfect ETTR exposure would have the highlights at but not above clipping, and IMHO, this would be the correct esposure. In practice, exposures not quite meeting this goal can be corrected with the exposure control and highlight recovery in the raw converter. With advances in sensor design with low noise and high full well electron capacity, overexposure is more harmful than under exposure, since clipping with overerxposure results in permanent loss of data. Shadow clipping can occur with underexposure, but shadow detail is usually limited by noise.

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walter.sk
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« Reply #9 on: August 20, 2009, 08:14:56 AM »
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Quote from: evogel99
It is ironic that given all the EEs working on the design of these things, such an obvious design optimization has never been included. Perhaps they tried too hard to mimic film cameras as a design spec, and there is nothing like that even possible in a film camera. In digital, you know everything there is to know about the "film" (sensor). You surely should leverage that information!
I'm afraid that the reasoning is more like this:  "Yes, we are selling a professional DSLR, for between $4000 and $8000.  But there may be some rich beginners moving up from their $200 point-and-shoot cameras who will shoot jpegs and complain that they have 'blinkies' in them, worse than in their P&S camera."  I think fear of losing such customers rather than the pros who are a "captive audience" might be behind the reluctance.
« Last Edit: August 20, 2009, 08:16:51 AM by walter.sk » Logged
digitaldog
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« Reply #10 on: August 20, 2009, 08:35:56 AM »
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Quote from: bjanes
What exposure is correct is debatable, depending on the definition of correct. My understanding of ETTR is that the highlights containing important detail should be placed just short of clipping and no headroom is reserved for the highlights. A perfect ETTR exposure would have the highlights at but not above clipping, and IMHO, this would be the correct esposure.

I wouldn't debate that definition of correct although the bit about "no headroom reserved for highlights" I'm not clear on. I'd say you'd be reserving this assuming there's something in the highlight you wish to record (not clip). As image creators, we have to view the scene and decide what we hope to record. A shot of a black cat on coal is going to be treated differently than a white on white shot composed of chrome objects with highlight detail we may or may not wish to capture.
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Andrew Rodney
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bjanes
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« Reply #11 on: August 20, 2009, 09:11:25 AM »
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Quote from: digitaldog
I wouldn't debate that definition of correct although the bit about "no headroom reserved for highlights" I'm not clear on. I'd say you'd be reserving this assuming there's something in the highlight you wish to record (not clip).
I am assuming that the highlights that need to be recorded are at or just short of clipping and anything above this would be allowed to clip. Leaving a half stop of "head room" is reasonable, but then you are not really exposing fully to the right, IMHO. However, if your intention is to leave a half stop of highlight headroom, then the exposure would be correct. One really needs to know how much headroom is reserved by the camera exposure system. If your camera metering allows a half stop of headroom and uses a hot TRC (such as many current Nikons), you might not want to add another half stop according to the histogram.
« Last Edit: August 20, 2009, 09:19:21 AM by bjanes » Logged
PeterAit
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« Reply #12 on: August 20, 2009, 09:59:13 AM »
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Quote from: GLuijk
Correct me if I am wrong Peter, but reading your thoughts about the subject's highlights I have a feeling you are trying to understand ETTR from a film photography point of view, where camera exposure was linked to the desired final printed exposure.

If you want to maximise the quality (basically signal to noise ratio) of your captures shooting RAW, forget about that link. Capture exposure is not linked to the printed exposure anymore since in digital exposure can be adjusted without any loss or change in the image information.

No matter how the lights are in the scene, ETTR means exposing as much as possible so that the highest luminosity area of your scene gets the maximum RAW values right before clipping. Afterwards, in the RAW development process you will adjust exposure to your desire, being now certain that noise was minimised in your shadows.

BR

I think we are in agreement. What I meant is that a scene that does not have highlights can be exposed MORE to the right than a scene with highlights (again, I mean very light areas with detail) simply because you can increase the exposure more in the former without blowing out the lightest areas.

Peter
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Peter
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Panopeeper
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« Reply #13 on: August 20, 2009, 10:34:08 AM »
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I often see the debate about "headroom" in conjunction with raw and ETTR. I don't understand the issue at all. ETTR is not reasonable without the photog knowing the effect (instead of judging it). This can be achieved only if the histograms and/or the clipping indication reflect the state of the raw data. If this is so, then any headroom is a waste of DR capacity. If the "raw exposure" is not reliably shown by the camera, then ETTR is simply lottery.
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« Reply #14 on: August 20, 2009, 02:57:03 PM »
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Quote from: bjanes
Shadow clipping can occur with underexposure, but shadow detail is usually limited by noise.

But exposing to the right will collect more photons in those shadows, and that's always a good thing as far as noise is concerned. Of course, if one wants really deep shadows... ;-)
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digitaldog
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« Reply #15 on: August 20, 2009, 03:05:16 PM »
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Quote from: PierreVandevenne
Of course, if one wants really deep shadows... ;-)

Then clip them in post (in the converter). I agree with you, get less noise in shadows, even if you later decide to clip there, which is something many find an appealing color appearance.
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Andrew Rodney
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Daniel Browning
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« Reply #16 on: August 20, 2009, 03:58:48 PM »
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Is flare (veiling or otherwise) ever a downside to ETTR? For example, +3 EC by using a slower shutter, printed down -3 linear EC in raw conversion.
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bjanes
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« Reply #17 on: August 20, 2009, 05:12:21 PM »
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Quote from: PierreVandevenne
But exposing to the right will collect more photons in those shadows, and that's always a good thing as far as noise is concerned. Of course, if one wants really deep shadows... ;-)
Increased exposure as a result of exposing to the right will linearly increase the pixel values of all parts of the image--from shadows to highlights. If the shadows are too bright as a result of increased exposure, then the midtones and highlights will also be too light. The remedy is to decrease exposure with the raw converter.
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JeffKohn
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« Reply #18 on: August 20, 2009, 10:35:35 PM »
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What I've found for real-world shooting, is that ETTR works best with lower-contrast scenes where you don't really have any whites. For scenes where there are highlight tones that I care about maintaining discernible detail, I get better results by placing them 1/3 to 1/2 stop below clipping, rather than right under the clipping limit. Even if that means having to add a small boost to the shadows or darker midtones, noise is pretty much a non-issue at base ISO and this approach gives me more natural-looking results with less fiddling around in the raw converter.
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bjanes
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« Reply #19 on: August 21, 2009, 08:36:22 AM »
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Quote from: JeffKohn
What I've found for real-world shooting, is that ETTR works best with lower-contrast scenes where you don't really have any whites. For scenes where there are highlight tones that I care about maintaining discernible detail, I get better results by placing them 1/3 to 1/2 stop below clipping, rather than right under the clipping limit. Even if that means having to add a small boost to the shadows or darker midtones, noise is pretty much a non-issue at base ISO and this approach gives me more natural-looking results with less fiddling around in the raw converter.
Since the original post by Michael on ETTR, it has become almost a religion for some photographers. However, the originally stated rationale for ETTR concerning the number of levels in the brightest f/stop of the image is incorrect and the naming of the process is based on the appearance of the the histogram, and the appearance of the histogram can be misleading. The basic concept of ETTR is to give as much exposure as practicable in order to collect the maximum number of photons, therey increasing the signal to noise ratio and maximizing dynamic range. An image taken at high ISO with the histogram fully to the right may have captured fewer photons than an image taken at a lower ISO and showing a histogram fully to the right. These principles are explained in great detail by Emil Martinec.

Some purists (such as Panopeeper) allow no headroom and place the highlights at clipping, while Jeff and others allow some headroom for protection of the highlights. If the sensor is linear up to clipping, headroom should not improve the image but can help prevent inadvertent clipping of the highlights. The advangtages of ETTR can be overblown. Since signal to noise varies as the square root of exposure, doubling of the exposure will improve S:N only by a factor of 1.4. With current sensors, this may not make much difference.

Maximizing the number of photons collected requires the use of base ISO, so the principles of ETTR can only be fully realized at base ISO. If shutter speed/aperture considerations prevent fully exposing to the right at base ISO, then one can use a higher ISO. Under these conditions, shadow S:N will be improved only to a certain point by increasing the ISO and having a histogram with data on the right. Above a certain ISO (often 1600 on many cameras), the histogram will look better with a higher ISO but the signal to noise ratio in the shadows will not be better than would be obtained at ISO 1600 with a histogram to the left. At this point, it is best to increase exposure in the raw converter. The higher ISO under these conditions will limit headroom and dynamic range. This is explained in detail in Emil's paper.

While these concepts are beyond the beginner lever, the take home message is to give as much exposure (shutter speed and f/stop) as possible. Signal to noise is largely deterined by exposure. A high ISO image will have more noise because of less exposure rather than the use of a high ISO per se.
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