Am 01.12.2010 03:30, schrieb Stephen Klebs:

>> As a result, a truly linear gradient doesn't /appear/ linear to us: The
>> "distance" between 10% and 20%, for instance, is percieved as roughly
>> equal to that between 50% and 100%. Go figure.
>>
> What you are missing here is that this ability for the brain to retain a
> constant relation between widely varying changes in size, shape, colors or
> perspective is not something you need to correct in the picture. The brain does
> it. It works in a photograph as well, which is just a neutral recording device.

You'd be surprised how non-neutral photographic paper can be.

Fact is: A grey tone that looks like halfway between black and white 
does /not/ reflect half as much light as a pure white, but a lot less, 
and this fact causes a lot of problems wherever you try to compute the 
addition of light intensities (which is a pretty common task in 
raytracing), as you'll find out that "50%" perceptual brightness plus 
"50%" perceptual brightness does not add up to "100%" perceptual 
brightness in reality. So if you try to do your math with perceptual 
brightness rather than physical, you'll end up getting nonsense in the 
output image that your brain cannot fully compensate; sometimes you'll 
not even be able to pinpoint them because your brain does its best, but 
you'll still be able to "feel" that the image is CG).

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