Question on ETTR

Started 2 months ago | Discussions thread
bobn2 Forum Pro • Posts: 56,291
Re: JPEG vs. Raw

Vincent_Ledvina wrote:

bobn2 wrote:

Vincent_Ledvina wrote:

Mark Scott Abeln wrote:

If you are shooting JPEG, then the histograms are likely to be completely reliable. What you see is what you get, and so expose them to the right, and adjust on the computer if needed.

But you can actually do better, even with JPEG. If you use a wider color space such as Adobe RGB, and lower the image contrast, lower the saturation, or use a flat camera profile, you actually can expose your JPEGs more than if you use the typical “cooked” images that are output by consumer-grade cameras.

Also, always using a neutral white balance will help greatly: many photographers, myself included, will set my white balance to ‘Daylight’ to retain the warm colors of sunset, but using a neutral balance will allow you to expose your images even more.

These tricks are used in digital cinema, and while they produce flat, tepid, dull-looking images, this is easily corrected on the computer, and you get a cleaner image, too, maybe one or two extra stops of exposure, depending on a number of factors. You also get better shadow detail and all of your color channels are more likely to contain usable information for processing.

The advantage of these methods is that you can still rely on your histogram for JPEG images, and you can still expose to the right and get better results, with however, more processing on the computer. Typically, when you boost contrast and saturation on the computer, you’ll have to lower the image brightness a bit to avoid blowing the brightest colors, but you’ll have a cleaner image. Lowering brightness digitally is preferable to lowering exposure.

Finally, some photographers use UniWB, which keeps the camera white balance fixed to its native color sensitivity (typically, all images will turn out green), but this gives you a much better idea of how much exposure the red and blue color channels actually get. But this isn’t a good option for JPEG shooters.

In raw, things like contrast, saturation, white balance, camera profile, and color space have no effect. So you can pretty much always blow your JPEG histograms and still preserve all of the data in your theee color channels.

RawDigger will let you see your actual raw data histograms, and you may be surprised at how small of a signal the red and blue channels actually get under many circumstances. DxOMark camera data also tells you how much the raw channels are manipulated under daylight and incandescent lighting, and typically your red and blue color channels are boosted considerably. Eventually, you’ll get a feel for how much headroom is present in your raw files, and you can confidently know how much you can overexpose your histograms.

That's insane. I never realized that my histogram was lying to me. If I teach ETTR, I will also have to go over these principles.

I really do suggest that you give up any ambition of teaching ETTR until you have overcome this tendency to kick back against anyone that tries to explain it to you.

I'm not trying to kick back, but I'm also not going to blindly accept everything I have been told, by you, and by others.

That is a good attitude, in which case, you ask for further explanation until you have been told enough to judge the matter on its merits.

If I encounter information that is in opposition with "status quo," which everything in this article has been (against my preconceived and cemented misconceptions), I think it's more than acceptable to question that information.

Indeed, all information should be taken with a degree of scepticism. There is, however a way of being sceptical, which is to accept what people say as being well intentioned even if possibly not well informed, and if you need more explained, to ask for that, and to raise further questions if the responses don't seem satisfactory.

I understand exposure vs. brightening, SNR, etc.,

I'm not sure what you mean when you say you 'understand exposure vs brightening'. Even putting it that way doesn't seem to indicate that you do. It seems as though you have read gollywop's rather nice article and failed to fully understand it. In the end, you should know what exposure is, because that is a basic part of photographic knowledge. You should also understand what lightness is, because that is also important. I don't know where the 'vs' comes in, except as part of gollywop's explanation of why what some people incorrectly call 'exposure' isn't.

so it was surprising to find that ETTR is an invalid way to teach someone about crafting an optimal exposure.

Now you're beginning to use strange language again, which doesn't give much confidence that you have reached the level of knowledge where you should be aspiring to teach others. Saying that you 'craft' an exposure is like saying that you 'craft' a temperature. The choice of the word speaks volumes about the extent to which the subject of exposure has become mystified. As explained, the 'optimal' exposure is simply the largest exposure that your pictorial constraints and your camera will allow. The problem with ETTR is that in general it does not set that exposure because it is based on the two false premises that I gave you. It will often result in a larger exposure than ISO based metering, so is to that extent 'more' optimal, but it's also more complex than simply setting the largest aperture and longest shutter speed that your pictorial and equipment constraints allow.

I must admit, I approached the discussion with my own opinions, but I have been taught incorrectly before and reserve skepticism when I encounter such new and radical principles. I appreciate you trying to help me loosen my grip on the false information I cling to.

Just wondering... what made you think I was kicking back in what you quoted above? I was expressing genuine surprise at this discovery since I often use my histogram to check if any RGB/luminance data is being clipped.

Your previous answers to me made me think that you had approached that post in the same vein. If not, my apologies for misjudging the situation.

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Tinkety tonk old fruit, & down with the Nazis!

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