To ETTR or not to ETTR...?

Started 3 months ago | Discussions thread
timo Veteran Member • Posts: 5,435
Re: Have I got it right?

FingerPainter wrote:

timo wrote:

This thread seems to have got super-complicated. Have I misunderstood ETTR?

My understanding is that the further up the histogram you go (i.e. to the brighter end), the more useful data the file can contain, and that includes finer distinctions of tonal values.

Yes, as long as you move to he right by increasing exposure - the amount of light per unit area falling on the sensor.

In many cameras, you can also make a (usually much) smaller improvement by moving up the histogram by increasing the ISO setting for the first few stops above base ISO.

So for the purposes of taking the photo, you push the exposure up as far as you can SHORT OF blowing the highlights to the point where they are unrecoverable.


The image will look overexposed at that point.

The image will probably look too light. It won't actually be exposed too much. It is useful to avoid calling an image "overexposed" when it might be too light for a reason other than too much exposure. The mis-use of the term "overexposed" is a holdover from roll-film, where there was often a close to one-to-one mapping between lightness and exposure. This is not the case for digital images.

Then in post-processing, you bring the 'exposure', or 'brightness', or whatever you want to call it,

Call it "lightness". "Exposure" is the amount of light that fell on the sensor per unit area. You cannot change that after capture. "Brightness" is a property of an image displayed by a light-emitting device, like a monitor or television. You can increase the brightness of an image displayed on your computer monitor by increasing the brightness setting of the monitor without affecting the image file. Prints do not, AFAIK, have a brightness, Just a lightness.

back down to whatever reflects you visual intentions. That way you will get more subtle, more accurate, shadow tones. And better S/N ratio,


provided you haven't had to adjust the ISO upwards, which would have defeated the purpose.

Adjusting ISO upward only defeats the purpose if it is done instead of increasing exposure. If you got the maximum exposure you can tolerate (not too much motion blur, too shallow DoF or too much lens aberration blur), then incrasiog ISO can make a samll improvement to SNR on many cameras, at least for the first few stops above base ISO.

If, using the camera's metering system and with your EV dial set to 0, your shot is already just about triggering blinkies, you are already 'exposing to the right', and you don't have to adjust anything.

In fact, when desired highlights are blown at the metered exposure, ETTR requires negative EC.

ETTR is most relevant in situations where there are no important extreme highlights, and you have a lot of shadow detail that you want to maintain.

Hmm, given that ETTR is essentially exposing for the hightlights, I don't think it becomes less relevant in situation where there are no important extreme highlights. It just doesn't give as much SNR improvement. It is still relevant because ETTR is as much about preserving desired highlight detail as it is about increasing SNR. Fundamentally it is about maximizing usable data. It does this both by trying to increase light capture and also by trying to avoid throwing away data in highlights.

What have I missed?

See above?

Yes, that all makes sense. Like many of a certain age, I'm conditioned by hauling nearly transparent slides out of the plastic box, holding them up to the light and saying 'wow that's over-exposed' ... Another factor is the use of the term 'exposure' for a slider in Lightroom. But sure, 'lightness' does express what one means.

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