The Optimum Digital Exposure

[Torbjörn Tapani]

What I demonstrated is that ISO is another tool to achieve ETTR on Canon sensors when aperture/shutter don't suffice because of the lighting conditions and DOF/motion blur requirements.

So yes, ETTR is about ISO as well, not only about collecting photons.

Regards

Ok. I think I can understand what you mean by that. But I think that is a different situation. Actually it is more like the situation I had in the discussion in the link about unity gain, trying to optimize ISO for when you could not raise exposure(shutter/aperture) due to other constraints.

But if the situation is that you benefit from raising ISO and expose less with aperture/shutter in some case, then I agree, then ETTR is about ISO as well. But in my mind ETTR is about collecting photons.

[Torbjörn Tapani]

Hi,

Guillermo's post illustrates what I was thinking about. The way I see it, ETTR is about maximising the number of electrons captured. But on Canons and some other cameras, increasing ISO will reduce readout noise, so increasing ISO and doing ETTR may make some sense.

On "isoless" cameras I would say that keeping base ISO and exposing as much as possible is the key to achieve maximum image quality.

Best regards
Erik

I think I can understand that view. Not conviced tho. Could you demonstrate a situation where you would raise ISO before you increase exposure (shutter/apterure) with that kind of sensor?

[Guillermo Luijk]

But if the situation is that you benefit from raising ISO and expose less with aperture/shutter in some case, then I agree, then ETTR is about ISO as well. But in my mind ETTR is about collecting photons.

It is not that situation. It is not when you DECIDE to expose less with aperture/shutter, but when you CANNOT capture more photons (e.g. you are using max aperture and slowest shutter to prevent motion blur, and that is still not enough to achieve ETTR).

[ErikKaffehr]

Hi,

I absolutely agree on that!

Best regards
Erik

But in my mind ETTR is about collecting photons.

[Guillermo Luijk]

Hi,

I absolutely agree on that!

Best regards
Erik

And I absolutely disagree. ETTR is about shifting the histogram to the right (maximise RAW levels before clipping). To achieve that on a digital camera there are three variables: aperture, shutter AND ISO, the last one has no connection to captured photons. As simple as that

[Torbjörn Tapani]

And I absolutely disagree. ETTR is about shifting the histogram to the right (maximise RAW levels before clipping). To achieve that on a digital camera there are three variables: aperture, shutter AND ISO, the last one has no connection to captured photons. As simple as that

Then we can agree to disagree about the definition of ETTR, that is fine by me. As long as we all expose as much as possible first. Then raise ISO.

I would optimize shadow detail with increased ISO in my Nikons as well up to a point. Not to shift the histogram but to take advantage of better shadow S/N ratio.

 

[deejjjaaaa]

I think I can understand that view. Not conviced tho. Could you demonstrate a situation where you would raise ISO before you increase exposure (shutter/apterure) with that kind of sensor?

his situation is = when your best /best = most possible light/ exposure (remember that ISO is not a part of exposure - it is part of your decision about exposure, along w/ other variables) in a particular situation (motion blur, DOF, shutter shock, etc, etc) does not lead to unacceptable clipping (in raw) then w/ some cameras (Canon for example) it makes sense to increase ISO settings as that leads to greater post exposure pre ADC amplification /analog gain/ that leads to better S/N (in /deep/ shadows)... to a certain extent of course /that's why people check their camera model to find out what is the reasonable limit in ISO/

[Guillermo Luijk]

Not to shift the histogram but to take advantage of better shadow S/N ratio.

Both are the same thing Torb, the purpose of ETTR is to reduce visible noise

[deejjjaaaa]

On "isoless" cameras I would say that keeping base ISO and exposing as much as possible is the key to achieve maximum image quality.

there is a school of thought that says that some raw converters (along with their "camera profiles" that drive the color transforms/etc) are not doing a good job in deep shadows... so sometimes your decisions (like w/ clipping - some converters are not good w/ inventing eye pleasing fake colors/transitions where you have clipping in raw) depend on your raw converter as well.

[Torbjörn Tapani]

deejjjaaaa, then we are doing the exact same thing. Only in a Canon you have lower read noise with increased ISO and analog gain to much higher ISOs. You would do the same thing with a D4. In other Nikons, I have a D7000 and D800 you would not gain much above where analog gain ends. About 800 and 1600 ISO respectively.

[Bart_van_der_Wolf]

It is not that situation. It is not when you DECIDE to expose less with aperture/shutter, but when you CANNOT capture more photons (e.g. you are using max aperture and slowest shutter to prevent motion blur, and that is still not enough to achieve ETTR).

Hi Guillermo,

Let's not get too deep into semantics, but EXPOSE to the right (ETTR) is all about photons, exposure, and allows to optimize Dynamic Range. Boosting gain on a limited given amount of photons may be beneficial, but IMHO it's something else.

Cheers,
Bart

[Fine_Art]

Thanks for your comments Bob.

I'm just waiting for one of the companies to file a patent for it. I have emails going back at least 10 years that would count as "prior art".

Cheers,

Michael

I believe, from having gone through the patent process, that "prior art" would be prior patents or physical objects that have been made. Without question you have copyright, which is some ways is more powerful, as it does not expire so fast. For example, I went to do a wall patent. A complex set of materials with a method of fast placement. My lawyer, a MSc in engineering, said yes it works, it is novel, etc. All is a go. The problem became a big company, and they are really big in construction, would bury me in a legal fight that forces my abandonment of the patent. So I have building designs that I submit in permits for building. The copyright on the design is more powerful than if I tried for a patent. Anyone submitting a permit worldwide can automatically be in copyright infringement, while an international patent is a whole new process with more fees.

[Bart_van_der_Wolf]

Then we can agree to disagree about the definition of ETTR, that is fine by me. As long as we all expose as much as possible first. Then raise ISO.

Yes, that's the idea. More photons will reduce shot noise, and if there are enough to almost saturate the sensor wells we have done well. In case there are restrictions to the number of photons, then there are some camera models that benefit in the Photon starved shadows by making sure that the read noise doesn't start contributing to the total noise more than necessary, and boosting amplification/gain with the ISO setting can help (more on some cameras than others).

I would optimize shadow detail with increased ISO in my Nikons as well up to a point. Not to shift the histogram but to take advantage of better shadow S/N ratio.

Yep.

Cheers,
Bart

[Guillermo Luijk]

I am being practical. I have zero interest to find out why the first guy who used the term ETTR (was Michael BTW?) didn't call it HTTR (Histogram To The Right), for instance.

The true is that on many cameras (Canons, many Nikons,...) there is a way to improve a lot image quality when exposure cannot be increased but we can still push RAW levels through ISO without clipping.

If that is not ETTR for you, ok take the term HTTR as a more general rule that covers ETTR and takes it beyond!

In fact in Spanish the term ETTR is usually translated as a terrific expression: "Derecheo del histograma", i.e. "Histogram rightization" or simply... HTTR. It's ugly but I believe it makes sense.

[telyt]

The article makes perfect sense.

Why don't our cameras, especially any over $500, have an ETTR exposure mode built in? Surely it is just a software addition to the metering reading?

People should be able to specify 100% within the matrix or 99.5% within the matrix in ETTR mode. The manufacturers should understand exposure enough to build this in.

Another automated feature to ignore and/or disable.  Unless the software knows what highlights are not important and can go to 255/255/255 it will take some user intervention.  Might as well use manual exposure.

[duane_bolland]

I think I found a minor mistake in the article.  Under method #2: "The exposure that shows no red clipping in highlight detail areas is the optimum exposure of the set. In this case EV+1.3."  No, I think that should be the EV+.6 exposure.  It goes on to say that either (+1.3 or +.6) would work in this case.  But clearly the +.6 has the least clipping.

Nice article.  It was insightful.  I push my exposure to the right often and essentially never toast it beyond salvage.   

[Fine_Art]

I think I found a minor mistake in the article.  Under method #2: "The exposure that shows no red clipping in highlight detail areas is the optimum exposure of the set. In this case EV+1.3."  No, I think that should be the EV+.6 exposure.  It goes on to say that either (+1.3 or +.6) would work in this case.  But clearly the +.6 has the least clipping.

Nice article.  It was insightful.  I push my exposure to the right often and essentially never toast it beyond salvage.   

You cant see the details so you do not know why he picks +1.3. Is it a wet roof? He is talking about specular highlights. We all agree the central idea is right.

[bjanes]

Hi Guillermo,

Let's not get too deep into semantics, but EXPOSE to the right (ETTR) is all about photons, exposure, and allows to optimize Dynamic Range. Boosting gain on a limited given amount of photons may be beneficial, but IMHO it's something else.

Cheers,
Bart

Bart, I agree entirely with you here. However, those of us who have been following the ETTR issue over the years will recall that the rationale for ETTR was initially based on the false premise that moving the histogram to the right made use of the greater number of theoretical levels in the upper ranges of the file: half of the levels are in the brightest f/stop of a linearly encoded raw file. I recall many heated exchanges on online forums regarding this topic. Emil Martinec debunked this rationale in his marvelous treatise posted on the University of Chicago web site. Increasing the ISO moves the histogram to the right, but does not change the exposure and has little effect with an ISO-less camera. With many older Nikons and many Canons where the electronics downstream to sensor limit dynamic range at low ISO, increasing the ISO will reduce the read noise and improve the SNR but this benefit maxes out at ISO 1600 or thereabouts (see Emil's Fig 12a for the Canon 1D3). Further increases in ISO will move the histogram further to the right and brighten the LCD image preview, but will limit highlight headroom with no improvement in image quality.

The concept of maximizing SNR by increasing exposure is an important concept, but the acronym ETTR is somewhat misleading; however, it has become so firmly established in the photography lexicon that I doubt that it will be renamed.

Bill

[Fine_Art]

Bart, I agree entirely with you here. However, those of us who have been following the ETTR issue over the years will recall that the rationale for ETTR was initially based on the false premise that moving the histogram to the right made use of the greater number of theoretical levels in the upper ranges of the file: half of the levels are in the brightest f/stop of a linearly encoded raw file. I recall many heated exchanges on online forums regarding this topic. Emil Martinec debunked this rationale in his marvelous treatise posted on the University of Chicago web site. Increasing the ISO moves the histogram to the right, but does not change the exposure and has little effect with an ISO-less camera. With many older Nikons and many Canons where the electronics downstream to sensor limit dynamic range at low ISO, increasing the ISO will reduce the read noise and improve the SNR but this benefit maxes out at ISO 1600 or thereabouts (see Emil's Fig 12a for the Canon 1D3). Further increases in ISO will move the histogram further to the right and brighten the LCD image preview, but will limit highlight headroom with no improvement in image quality.

The concept of maximizing exposure by increasing exposure is an important concept, but the acronym ETTR is somewhat misleading; however, it has become so firmly established in the photography lexicon that I doubt that it will be renamed.

Bill

So lets talk about what limits exposure. The need to control the look of motion. If not for that, we would all shoot base ISO, long exposure, capturing as many photons as possible. Is there anything else? What about several shots stacked? If you can mask moving areas, hopefully adding the captures of dark areas, you are further ahead. That assumes you need to bother. Low ambient light conditions can still be a problem.

[jpegman]

I think a lot of people are getting lost in the trees here.  Seems to me the premise is pretty simple.

1. If you are 2 stops underexposed (90%) you are using only 25% of your sensor data and effectively have thrown away 75% of your data; If you want to stop at the 97% level and don't want to go to the 99% level because it too risky you have discarded 50% of your sensor data - your choice! George Jardine documented this in his article referenced in the DiNatale's LuLa post (http://mulita.com/blog/?p=3358#Tonal-Compression) -it's real no matter what camera or sensor or raw converter one chooses - it's the nature of current digital capture technology!

2. The article was written for someone using Adobe ACR and works fine with my Canon 6D. If you use something else your mileage may vary and you will have to work it out for yourself with your specific software and tools.

3. Can you get a "full range image with only 25%-50% of your data - sure if you are willing to accept the 25%-50% loss in YOUR shadow data areas. If no one pixel peeps in the shadows - they may never know what they are missing.

4. Before this article, I would have never thought that pushing the white rabbit in snow even further than classic compensation recommended would result in a better image, and shooting the black cat in a coal bin image so the image was medium grey or LIGHTER would have been total heresy - yet our modern raw converters can bring it back in spades!

5. As Mark absolutely correctly noted (reply #20): "For the modern RAW "digital negative" workflow this classic rule can be stated as just the reverse, i.e.,  "Expose for the highlights and develop for the shadows". "ETTR" is just another way of saying the same thing, and it's also how we had to expose color reversal film except that we had no real control over the development of the shadows with color reversal film. With todays RAW image editors we do." As

6. How you get there is just a technique and the methodology presented seems both technically correct and even if it appears somewhat simplistic, it is doable (With no additional equipment than what you already have) and very easy to automate using camera custom functions and Lightroom stacks where the only cost is 2 extra exposures using extra digital card storage space. One doesn't have to do it for every shot just the ones you want to have both maximum data and maximum preserved shadow quality.

7. I have spent the last 2 days going over the calibrations and field testing and all I can say is IT WORKS!

8. As they say, the proof is in the results.

Jpegman