>> There is no such thing as a perceptually linear color space. None that
>> can be
>> represented in cartesian space at any rate.
>
> I've never really understood the big deal about perceptually uniform
> color spaces. Compare to sound compression. There it makes sense. You
> save disk space. But the color spaces try to muck things up. Whereas in
> music a F remains an F and a C remains a C.

It doesn't have anything to do with compression to save disk space. And 
when converting between colour spaces the colour remains physically the 
same, just like 1 inch is the same as 25.4 mm, two different ways to 
conceptually describe the same physical thing.

The idea of using a perceptually linear colour space is that then the 
"distance" between two colours looks the same "difference" to a human no 
matter what colours are used. This is not the case with sRGB, for 
example the difference between (0,0,0) and (0,128,0) looks much "bigger" 
than between (0,128,0) and (0,128,128), even though the distance is 128 
in both cases. So using a distance in sRGB space would be quite useless.

In fact, there's a metric called "delta-E" which is used extensively in 
many indsutries where colour is important (clothing, painting, make-up, 
plastics, food, printing etc) that is exactly the "distance" between two 
colours. However it is calculated in a (near) perceptually linear colour 
space, and scaled so that a delta-E of 1.0 is "just visible" by most 
humans. It is then a very useful number indeed.

Post a reply to this message