“Expose to the right” vs “JPEG Histogram to the right”

[Ray]

There are a couple of aspects of this concept of ETTR or 'optimal exposure' which I find very relevant for my own photography, which I'll list below.

(1) How much time does one have, before losing the shot, to employ techniques like taking a spot meter reading of the brightest part of the screen, then calculating an increase of exposure by 3 stops, or 2.75 stops, or 2.5 stops, depending on camera model, or examining the camera's histogram of a jpeg image and making a guess as to the optimal exposure?

(2) How anally retentive, or fanatical, does one need to be in order to get a satisfactory dynamic range which does not include blown highlights?

In answer to the first question, I decided years ago, when using Canon equipment, that it was much better to auto-bracket exposures for each shot, then later in Adobe Camera Raw select the shot that was best. Sometimes the best shot was not the one with the optimal exposure, but the underexposed shot which just happened to catch the best moment, when there was movement in the scene, and was the sharpest because of the faster shutter speed. That was a bonus. Also, if the scene was static, one could always merge to HDR in Photoshop.

In answer to the second question, there is less reason to be anally retentive now that recent models of DSLRs have significantly improved DR, especially if one is using Nikon cameras of course. 

Nevertheless, still being just a little bit fanatical myself, I do my best to avoid ruining shots with blown highlights which might contain detail relevant to the composition, such as amazing clouds in a bright sky.

The way I do this, which I've mentioned before, so I hope I'm not being too tedious, is to manually set exposure whilst viewing the camera's metering system at the bottom of the optical viewfinder.

On my D810, the exposure wheel is behind the shutter button and can be easily adjusted with my thumb without taking my eye away from the viewfinder.
I always use a single focusing square, which is also connected to the camera's metering system, and is activated with the AF-On button. The camera produces a meter reading which relates to whatever part of the scene is covered by the single focusing square, but this is not 'spot metering'.

On the D810, I don't even have to press a button to get a reading. I simply move the focusing square to any part of the scene in the composition, by swinging the camera rather than tediously moving the focusing square with the joystick. The exposure reading is shown at the bottom of the viewfinder.

The exposure reading scale in the viewfinder stretches from a minus sign on the extreme left, to a plus sign on the extreme right, and a zero in the center. If the exposure reading exceeds either extreme of plus or minus, a white arrow head appears at the extreme right or extreme left.

The issue that needs to be determined by anyone using such a method with a Nikon camera, is what reading at the foot of the viewfinder equates to an ETTR exposure, and also in relation to what RAW converter.

I use Adobe Camera Raw, and that's the only histogram I'm concerned with, at least initially. Consistency is the name of the game. Through basic, practical experiments, I have determined that an exposure reading to the far right of the D810's metering system, when the focusing square is positioned over the brightest part of the image (relevant to the composition, of course), is the correct exposure for an ETTR shot.

This is consistent for every shot, but only for my D810. When I use my Nikon D5300 with walk-around zoom lens, I have to adjust the exposure manually so that the meter reading in the viewfinder is only about 2/3rds of the way towards the extreme right. Also, the D5300 does not give a reading without pressing the AE-L/AE-F button, so one is actually refocusing whenever taking an exposure reading of the bright part of the scene.

However, I do understand that all this is not necessarily relevant for those who are not using Nikon cameras, except in so far as you do need to work out what is the best and/or quickest way of getting an optimal exposure with your particular model of camera, if you shoot in RAW mode.

The method I've outlined does cause a delay, compared with auto-focus in conjunction with auto-exposure, but a delay of only 3 or 4 seconds, and less when you've already made general adjustments for the lighting conditions of the environment.

[BJL]

Ray, you seeem to provide a second data point for a simple rule of thumb: “place the brightest relevant highlights at +3”. And also a strategy that makes a guideline like this – once adapted to particular camera – good enough in many cases: exposure bracketing, which can be automated and so done in a fraction of a second.

But let me check two things.
1) is the right end of that OVF light meter at +3? [UPDATE: yes, I checked, and the range on the D810's exposure indicator is the usual -3 to +3]
2) Is this at the D810’s minimum normal ISO dial setting, EI=64?

[jrsforums]

There are a couple of aspects of this concept of ETTR or 'optimal exposure' which I find very relevant for my own photography, which I'll list below.

(1) How much time does one have, before losing the shot, to employ techniques like taking a spot meter reading of the brightest part of the screen, then calculating an increase of exposure by 3 stops, or 2.75 stops, or 2.5 stops, depending on camera model, or examining the camera's histogram of a jpeg image and making a guess as to the optimal exposure?

Common sense says you always take one or more shots to capture a scene before optimizing.  This would be true whether the optimization was for exposure or taking from a different viewpoint.

[jrsforums]

ACR and Lightroom histogram will show actually blown highlights as not being blown.  That is, it will attempt to “recover” highlights that have blown channels in them.  This often works, but often doesn’t. 

Ray, I would suggest you use a RAW histogram to prove this for yourself.

[digitaldog]

There are a couple of aspects of this concept of ETTR or 'optimal exposure' which I find very relevant for my own photography, which I'll list below.

(1) How much time does one have, before losing the shot, to employ techniques like taking a spot meter reading of the brightest part of the screen, then calculating an increase of exposure by 3 stops, or 2.75 stops, or 2.5 stops, depending on camera model, or examining the camera's histogram of a jpeg image and making a guess as to the optimal exposure

The answer is of course it depends. 
You're shooting something that warrants the time to bracket and the subject is stationary/fixed (not a portrait etc), no reason not to bracket. Or take time to perhaps spot meter.
There are times when that's impossible and you'd lose the shot. For example sports, wildlife, street photography etc. Case in point, as someone who shot the 1984 Olympics on film (transparency), in all kinds of differing settings, no such luxury. And no, 100% of what I captured (30-50 rolls a day) where not perfectly exposed. But transparency like digital or any other capture, requires (demands?) the photographer understand how his meter(s) work in conjunction with the film/ASA just as he/she does with digital. If you know you can move, say +1/3 to 1/2 over the meter's recommendation without blowing out highlights you don't wish to blow out, (even if 'optimal' exposure from spot metering based on your understanding of how your camera/meter works suggests more), you're +1/3 to 1/2 closer to that goal of optimal exposure for the data.

When I'm shooting fast and loose, I have my 5DMII set to compensate +1/3 to +1/2 KNOWING I'm closer to the so called 'right' (of a Histogram I totally ignore) and years of doing so have not produced issues, I'm simply getting better data doing so.

What I recommend is understanding the limitations of your sensor by viewing brackets under differing situations with RawDigger. There's absolutely no reason IMHO to view a camera Histogram that isn't raw as was the case before cameras had Histograms! And the media (transparency) needed to be exposed without perhaps 1/3 to 1/4 a stop. Snip tests, push/pull processing helped to a degree but only a tiny degree. IF this could be accomplished with transparency film, I can't fathom why it can't be done with digital. The first step is to ignore the camera Histogram when shooting raw or, as suggested for Canon shooters, Magic Lantern if you really, really HAVE to view a Histogram while shooting. 

[digitaldog]

ACR and Lightroom histogram will show actually blown highlights as not being blown.  That is, it will attempt to “recover” highlights that have blown channels in them.  This often works, but often doesn’t. 

Absolutely! And it only tells you about ProPhoto RGB linear and rendered data along with that highlight recovery. Only a raw Histogram actually tells you about the facts of exposure on the raw data.
ACR will attempt to rebuild highlights if one or two channels have clipped but one hasn't. And yes, how well this works is often iffy. Those channels did clip and RawDigger will show you this. Also, it has a really awesome feature where say you were over exposed by 1 stop. You see this with their clipping overlay. You can set it to show you what would clip had you exposed differently! It shows you what the result would be if say you were actually over exposed 1/2 stop or under exposed by the same amount or more. Super useful.
WHY all raw converters can't do this is beyond me. I've asked Adobe for a raw Histogram for many, many years.

[BJL]

You're shooting something that warrants the time to bracket and the subject is stationary/fixed (not a portrait etc), no reason not to bracket. Or take time to perhaps spot meter.
There are times when that's impossible and you'd lose the shot. For example sports, wildlife, street photography etc.

Of course, ETTR is also usually irrelevant to such situations for the simple reason that they require an elevated EI ("ISO speed") setting on the camera, and so one is usually not going to have any photosites receiving anything close to full well capacity. Let me say again that EXPOSING to the right is only relevant when the camera's lowest [normal] EI setting can be used. It is nothing to do with even the raw histogram at higher EI settings where the signal is amplified more, sending far less than full wells to maximum raw level. Maybe I will later post my take on the importance (or not) of worrying about raw histogram placement when at higher EI settings and with unavoidably suboptimal exposure of the photosites.

When I'm shooting fast and loose, I have my 5DMII set to compensate +1/3 to +1/2 KNOWING I'm closer to the so called 'right' (of a Histogram I totally ignore) and years of doing so have not produced issues, I'm simply getting better data doing so.

Yet another experienced photographer in this thread who has come to a similar rule of thumb to what I suggested for getting roughly optimal sensor exposure level, at least when "shooting fast and loose"!

What I recommend is understanding the limitations of your sensor by viewing brackets under differing situations with RawDigger.

Yes, probably one good way to calibrate the information that one is able to get in the field when no "raw histogram" is available.

There's absolutely no reason IMHO to view a camera Histogram that isn't raw as was the case before cameras had Histograms!

Here I disagree: subject to further testing and evidence, I am rather confident that there is a simple and easily-determined approximate relationship between the camera's JPEG histogram (at default settings for contrast etc.) and what the raw histogram would tell you, so the camera's histogram can probably get you within 1/2 stop of perfection once one adds a suitable shift to what that histogram suggests. Not perfect due to issue like one color being blown out while the JPEG luminosity, but a good approximation. (And maybe even the camera's overexposure "zebras" or "blinkies" convey enough information about the right end of the JPEG histogram, if one knows how to interpret them.)
Of course, I sometimes forget that not everyone has access to either a JPEG histogram or overexposure blinkies in the viewfinder while composing; increasing the need for spot metering or such.

And the media (transparency) needed to be exposed without perhaps 1/3 to 1/4 a stop. Snip tests, push/pull processing helped to a degree but only a tiny degree. IF this could be accomplished with transparency film, I can't fathom why it can't be done with digital.

Fortunately, good modern sensors are vastly more tolerant than transparency film, with its DR as low as five stops in the case of Velvia, so I see no practical reason to worry about getting within 1/3 stop or less of "optimal", as far as visual IQ is concerned.

[digitaldog]

Of course, ETTR is also usually irrelevant to such situations for the simple reason that they require an elevated EI ("ISO speed") setting on the camera, and so one is usually not going to have any photosites receiving anything close to full well capacity. Let me say again that EXPOSING to the right is only relevant when the camera's lowest [normal] EI setting can be used.

The key word is usually. Depends on the camera no? Case in point, higher ISO produces less noise:

Here I disagree: subject to further testing and evidence, I am rather confident that there is a simple and easily-determined approximate relationship between the camera's JPEG histogram (at default settings for contrast etc.) and what the raw histogram would tell you, so the camera's histogram can probably get you within 1/2 stop of perfection once one adds a suitable shift to what that histogram suggests.

That may be very true. My point is, it's not necessary to have any Histogram to produce optimal exposure. Wasn't with film which it appears some agree here was more demanding in terms of nailing exposure. Don't get me wrong, I'd LOVE a raw Histogram on the camera in some cases. I'd love one in the raw converter. I don't need one in the former. I was classically trained to expose transparency film many years before cameras had Histograms.

Fortunately, good modern sensors are vastly more tolerant than transparency film, with its DR as low as five stops in the case of Velvia, so I see no practical reason to worry about getting within 1/3 stop or less of "optimal", as far as visual IQ is concerned.

Unless there is zero visible difference between optimal exposure for raw and an exposure that is (x amount off), and I'd love to see demonstrations of this, it isn't the case with my old 5DMII (time for a Sony?), then I'll strive for optimal exposure and image quality.

[BJL]

The key word is usually. Depends on the camera no? Case in point, higher ISO produces less noise:

Ah yes, that was a significant issue with the earlier generations of CMOS sensors as in that Canon 5D Mk II. This seems to be vastly less significant with the newer on-chip column-parallel ADC technology. Briefly, because now virtually all noise enters _before_ analog gain is applied, at least once the camera is more than one or two stops above minimum EI setting, so that the noise in the analog signal is being amplified to well above the noise floor of the ADC process. Anyway, the strategy is different from EXPOSE TTR then: one is not adjusting exposure, but accepting the limits on how much exposure can be delivered to the photosites, and adjusting the ISO speed setting on the camera (adjusting the analog gain) to get a desirable raw histogram placement.

That may be very true. My point is, it's not necessary to have any Histogram to produce optimal exposure. Wasn't with film which it appears some agree here was more demanding in terms of nailing exposure. ... I was classically trained to expose transparency film many years before cameras had Histograms.

I agree on not needing a histogram! It is just one option for measuring where the highlights are, so you can then using knowledge about what that says where they will be "placed" on the sensor, relative to full well capacity. (I am happy with blinkies; Ray with spot metering on highlights and placing them at +3.)
One thing is actually easier with transparency film than with the pursuit of "maximum exposure without blown highlights": the goal with film is to meter a certain part of the scene and select the exposure that places that part of the scene where you want it in the developed film. That is more akin to choosing JPEG placement, and is dealing only with things that you or the light meter can directly see. There are no "invisible targets", as there are when people want to minimize the amount of raw file highlight headroom is being "left on the table".

[Ray]

Ray, you seeem to provide a second data point for a simple rule of thumb: “place the brightest relevant highlights at +3”. And also a strategy that makes a guideline like this – once adapted to particular camera – good enough in many cases: exposure bracketing, which can be automated and so done in a fraction of a second.

But let me check two things.
1) is the right end of that OVF light meter at +3? [UPDATE: yes, I checked, and the range on the D810's exposure indicator is the usual -3 to +3]
2) Is this at the D810’s minimum normal ISO dial setting, EI=64?

+3 from what base, BJL? Do you mean, from the zero point in the middle of the metering scale, or from an average exposure of the scene when the camera is in autoexposure mode?

Such considerations are of no practical significance with my method. My camera is set to manual exposure. I adjust the shutter speed by turning a wheel with my thumb until the camera's meter reading reaches the far right of the metering scale when the single focusing square covers (what I estimate to be) the brightest part of the scene in which I want to retain detail or color. In a landscape scene, that part of the composition which is the brightest is usually the clear blue sky or clouds. No calculations are required.

However, if the sky has many similarly bright patches of clouds, or white walls in sunlight, and I don't have the time to swing the focusing square from one bright patch to another to measure which is the brightest patch, because there are kangaroos in the foreground which might soon hop away (for example), then I'll use a shutter speed which is slightly faster than required for a far right meter reading.

If the scene does not have a high brightness range, and/or the situation calls for an appropriately fast  shutter speed which is of more concern than an ETTR exposure, then I will often take advantage of the 'close to ISO-invariant' nature of the Nikon D810, and other Nikon models. Instead of raising ISO a stop or two, I'll just underexpose. The loss of DR is very minimal.

For example, if one underexposes 2 stops at ISO 100, instead of using the same exposure at ISO 400, on the D810, one loses approximately 1/4th of a stop of DR. If one underexposes by 4 stops at ISO 100, instead of raising ISO to 1600 to produce an ETTR shot with the same exposure, one loses approximately 1/3rd of a stop of DR. No big deal, except for the anally retentive. 

Out of curiosity, I've just tested the range of the metering scale in the viewfinder of my D810. It's always 4 stops from the extreme left to the extreme right with the zero point in the middle, whatever the ISO setting.

[digitaldog]

For example, if one underexposes 2 stops at ISO 100, instead of using the same exposure at ISO 400, on the D810, one loses approximately 1/4th of a stop of DR.
 If one underexposes by 4 stops at ISO 100, instead of raising ISO to 1600 to produce an ETTR shot with the same exposure, one loses approximately 1/3rd of a stop of DR. No big deal, except for the anally retentive. 

I understand the first sentence but not the second, specifically: instead of raising ISO to 1600 to produce an ETTR shot.

[Ray]

I understand the first sentence but not the second, specifically: instead of raising ISO to 1600 to produce an ETTR shot.

The meaning of ETTR is 'Expose To The Right' of the histogram. The letter R in ETTR must relate to a histogram, not to a full well situation in the original exposure before the camera has applied analogue gain. If you want to exclude the use of the expression ETTR from high ISO situations, then a different acronym should be chosen, such as ETFWCABISO (Expose To Full Well Capacity At Base ISO). 

[Ray]

Common sense says you always take one or more shots to capture a scene before optimizing.  This would be true whether the optimization was for exposure or taking from a different viewpoint.

The procedure I've described above, which might apply only to certain Nikon cameras, removes the need to take more than one shot and fuss around examining histograms.

As I mentioned, on the D810 one doesn't even need to press a button to get an exposure reading in the viewfinder. One can just swing the camera around until the single focusing square has covered every bright area in the composition that one has noticed. It takes just a few seconds.

If one discovers that a particular bright patch (of clouds for example) causes the meter reading to exceed the far right, one simply increases the shutter speed by another 1/3rd stop or whatever. It works every time for me.

[digitaldog]

The meaning of ETTR is 'Expose To The Right' of the histogram. The letter R in ETTR must relate to a histogram, not to a full well situation in the original exposure before the camera has applied analogue gain. If you want to exclude the use of the expression ETTR from high ISO situations, then a different acronym should be chosen, such as ETFWCABISO (Expose To Full Well Capacity At Base ISO). 

I understand what ETTR means. How was the first exposure different from the second other than 2 vs. 4 stops under? Raising ISO for ETTR?

[Ray]

I understand what ETTR means. How was the first exposure different from the second other than 2 vs. 4 stops under? Raising ISO for ETTR?

The difference is in the appearance of the histogram. An underexposure at any ISO setting results in the histogram, whether the camera's histogram or Adobe Camera Raw's histogram, being more to the left. This situation is not advisable when using Canon cameras. An ETTR at ISO 200 or 400 always has significantly better dynamic range than the same exposure used at ISO 100. This is where the Nikon cameras have an advantage.

However, at much higher ISOs, such as 1600, 3200 and 6400, the loss of DR resulting from a 2 stop underexposure at ISO 1600, as opposed to an ETTR exposure at ISO 6400, is of little significance with both Canon and Nikon cameras.

[Ray]

ACR and Lightroom histogram will show actually blown highlights as not being blown.  That is, it will attempt to “recover” highlights that have blown channels in them.  This often works, but often doesn’t. 

Ray, I would suggest you use a RAW histogram to prove this for yourself.

The only histogram I use is the one in Adobe Camera Raw. Before adjustments are made, an ETTR shot will usually appear to have blown highlights, especially if the composition includes a bright and cloudy sky. However, moving the 'highlights' slider to the left, and/or the 'whites' slider to the left, and/or the 'exposure' slider to the left, will always fix that appearance of blown highlights, except when the right of the histogram has a significant spike or 'cliff edge', which means one has really overexposed.

My method of exposing to the right of the camera's meter, does not result in significant spikes or cliff edges at the right of Adobe's histogram.

Photographs are all about appearance. If the adjusted image in Photoshop doesn't look as though it has any blown highlights, then that's all that matters for me. The fact that some other more accurate RAW histogram reveals that one or more channels are in fact clipped, is of little practical significance for me, although I understand it might be very significant for those who design cameras and software.

[BJL]

The meaning of ETTR is 'Expose To The Right' of the histogram. The letter R

Yes, but which histogram? Not any JPEG histogram of course, but also not any raw histogram at an elevated EI setting. The primary rationale for the method is adjusting exposure in the sense of how much light is received by the sensor, and thus the histogram referred to is the one reporting the level of exposure received by the photosites, with the right being the line corresponding to a full well. That is, it is about choosing the maximum Exposure Index that avoids overfilling any photosite.

It is time to discuss the big difference between moving this "exposure histogram" to the right (by increasing exposure time, reducing aperture ratio, or adding light to the scene) versus moving the raw histogram by increasing the "ISO speed" and thus the analog gain applied before ADC. It helps to break noise sources into three main parts:
1) Photon shot noise in the light reaching the sensor: "shot noise".
2) Noise produced in the sensor before any amplification is applied, such as dark current noise: "pre-amp noise".
3) Noise introduced after analog gain is applied; I believe that these days this is mostly quantization noise in the ADC:  "post-amp noise".
There might also be something intermediate:
2.5) Noise introduced during the amplification stage.

How is the local signal to noise ratio at any part of the image affected by increasing actual sensor exposure (Exposure Index) versus changing the gain, as done by increasing the ISO speed setting?
- A one stop increase in exposure doubles the signal (photo-electron count), which increases photon shot noise by sqrt(2), and does not change the other noise sources. In all but the darkest parts of the image, photon shot noise dominates noise, so SNR improves by 2/sqrt(2) = sqrt(2): a half stop gain. In very underexposed parts of the image, where the sensor illumination is say ten stops or twelve or more stops below FWC, noise produced in the camera might become dominant, so there the SNR improvements can be more, sliding up to a full stop. This is what "engineering dynamic range measures", so gains in that measure can be misleadingly good, compared to the SNR improvements in most parts of the image.

- a one stop increase in analog gain (same exposure to the sensor) doubles the numerical values of the signal, the photon shot noise, and the pre-amp noise. These sources are again dominant in all but the darkest parts of the image, so there is no improvement in SNR there. However, in the darkest parts, that post-amp noise (mostly ADC quantization noise?) might be a significant part of all noise, at least until the "ISO gain" is enough to bring the shot plus pre-amp noise enough above that post-amp noise. So there can be a deep shadow SNR gain in the first few steps up the ISO speed range. Further up the scale, modern sensors enter an "ISO-less" range of EI settings (which I have seen starting at law as 400 or less and as high as 800 or even 1600) and then further analog gain has no significant SNR benefit, even if it moves the raw histogram further to the right.

- By the way, in some cameras ISO speed increases beyond some high setting apply further "ISO gain" digitally without increasing analog gain, using bit shifting or such. This of course has no SNR benefit at all; it just simplifies some steps in producing JPEGs.

I started some experiments today with my OM-D E-M5, comparing two images of the same subject, both at f/4 and 1/2000s, one "on meter" at EI=1600, the other at EI=200, so underexposed four stops and giving an almost totally black default JPEG conversion. After equalizing levels from the raw files in Lightroom, the noise levels were visibly indistinguishable. However, I need next to test on scenes with a wider subject brightness range, to check out the shadow handling.

[BJL]

An underexposure at any ISO setting results in the histogram, whether the camera's histogram or Adobe Camera Raw's histogram, being more to the left. This situation is not advisable when using Canon cameras.

That certainly used to be true, back when you were using Canon cameras. Is it still true now that Canon has adopted column-parallel ADC?

I agree with the rest of your post, except that when say "Nikon cameras", you probably mean more or less all cameras except (some) Canon ones.

[BJL]

+3 from what base, BJL? Do you mean, from the zero point in the middle of the metering scale, or from an average exposure of the scene when the camera is in autoexposure mode?

I mean that in manual mode, the exposure indicator scale at the bottom of the viewfinder is at its right limit, so the camera is suggesting that you are overexposing by three stops because it does not know that you are metering on the highlights, not the mid-tones.

Such considerations are of no practical significance with my method.

Quite so: all you need to know is that you have determined a predictable relationship between what that exposure indicator says and your desired exposure placement. I only ask so that I can use your evidence to test and refine my understanding of how the various measurements and outcomes are related. Partly because I am refining a similar approach, based instead on using highlight blinkies or the JPEG histogram in the EVF, so that I do not have to spot meter.

[digitaldog]

An ETTR at ISO 200 or 400 always has significantly better dynamic range than the same exposure used at ISO 100.

Considering that exposure is Aperture and Shutter alone, what has ISO and ETTR got to do with this? Sorry, I still don't understand what you are suggesting. Amplification in the processing?