>As to why, there's a reason behind the prevailing wisdom. >There are in fact a couple reasons. > >Light is a geometric scale, mapped by our cameras into a >linear scale. 1 stop of light is a doubling of the amount of >light. Converted to a numeric value by analog to digital >conversion, that means the difference between 16 and 32 is one >stop, 32 to 64 is one more stop, and 64 to 128 is one more >stop, etc. In a 12-bit conversion, the numeric value can range >from 0-(2^12-1) or 0-4095. The brightest stop of light that >can be recorded therefore contains a numeric range of >2048-4095. That's a full half of the numeric scale! The next >stop has a range of 1024-2047. Your brightest 2 stops contain >3/4 of your numeric range! Now consider the numeric range of >all 12 stops: >...... > >So, on a 12-bit capture, your brightest stop has the ability >to contain 2048 gradations, and your darkest stop only 1. This >is why you expose to the right, because let's say your data >spans 8 stops.
nice explanation but it has been demonstrated that the real reason to ETTR is what you said below
>Another aspect to ETTR is signal-to-noise ratio. If your >sensor produces a fixed amount of noise, you get improved SNR >by giving the sensor more data (light) to the fixed noise,
here is the reason that noise eliminates our perception of banding and quantization in the darker tones