first cs depend case: brighness,contrast

[Grzegorz Borowiak]

On Tue, 7 Jun 2005, Casper Boemann wrote:

> Personally I think that say brighness filter should produce the exact same
> visual effect in every colorspace.
> doing:
> RGB >> change brightness+5
> should equal exactly (except for rounding errors)
> RGB >> CMYK >> change brightness+5 >> RGB

I don't think so, i.e. I, as a user, do not expect an image manipulation
program to change brightness with _exactly_ the same effect on each
colorspace.

Changing brightness is rather a fuzzy concept. When we want the filter to
increase brightness, we do not choose brightening factor as an exact, a
priori number, but we move slider left and right to produce result which
satisfies us. If in another colorspace brightness works slightly
differently, it's no problem since we just move that slider slightly
differently to get what we want.

The problem could be with reproduction of exactly the same effect on many
similar images, e.g. subsequent frames of a movie. But it's hardly
probable that subsequent frames will be in different colorspaces, and
within one colorspace brightness/contrast is perfectly reproducible.

-- 
Grzes