Originally posted by robgo2 The theoretical reason for exposing to the right is that you get more tonal levels in a fully exposed image than in an uderexposed one. However, the human eye/brain may not be able to perceive the tonal differences, according to GordonBGood over on the dpreview forum.
This is an often quoted reason by many to dismiss ETTR. However, ETTR as promoted by the late Bruce Fraser (which is where I learnt about it) was meant as a way to expose for RAW files, not JPGs. During processing the exposure level of these RAW files needs to be adjusted to what's visually perceived as correct exposure, resulting in a better tonality compared to a RAW that was exposed as you would a JPG for straigh out of the camera use.
The required adjustment can be positive as well as negative BTW. ETTR could mean:
- underexposing to get detail in otherwise blown out highlights (requiring exposure push in PP). Here Gordon's remark may hold true for near white colours as the PP will render invisible some of the gained highlight detail, while potentially losing detail in shadows.
- overexposing to get better details in shadows of a scene without (relevant) highlights (requiring exposure pull in PP). Here PP may bring partially blown (one or two colour channels) part of the image back with a slightly off colour.
In either case the trade-off needs to be considered, and the application of ETTR to be applied with the necessary care, taking into account all colour channels.
Thinking a bit out of the box, ETTR doesn't even need to apply to the histogram of the entire scene you're photographing. If a bright background will be overexposed anyway, you may want to overexpose yet a little more to get a better distributed histogram for your foreground subject. In this case you will ignore the peak at the right of the histogram but will try to bunch up the Gaussian curve left to this peak as much as possible to the right without merging it with the peak. Be careful of sensor bleeding however...
In my book, the science behind ETTR holds, it's just the understanding and application by many that fails IMHO...
just a few random thoughs.
Wim