Re: [Gimp-developer] New Image/Color Management option

El dom, 05-06-2016 a las 09:26 +0200, Øyvind Kolås escribió:
Practical, applied color management is not that complicated.
Neither is
understanding the basics of radiometrically correct editing.

Most people - including people doing photography and graphic design
work for a living - prefer not to. I used to teach people becoming
such professionals at a university level. It should also be possible
to use GIMP for color scientists and color science geeks that care
more about color accuracy control than image composition.

That should come endorsed by a professional photographer or designer
saying she doesn't care about color management.
We can assume that the silence is because nobody cares. But there is
also a fat chance that there aren't many of those professionals around

It's also possible that many future professionals at university level
truly don't care, because they weren't taught about the importance and
influence of color management in their work.
I know that was the case with me. The quality of my work improved
substantially after I understood the basics of color management.
"just works" for most of the people means "I don't have to care about
that" and that's a huge mistake.

I do graphic design work for a living, and for ideological reasons I
chose to do it with free software. I do care about proper color
management because I know how doing it wrong degrades and limits the
quality of my work.

I know exactly when I want to use linear RGB and exactly when I
want to use
perceptually uniform RGB, as do other high end/professional users.

Maybe not, professional photographers might not know that they want
pre-multiplied alpha, linear light data for doing resampling, nor
goes wrong if the pixel data for some reason isn't pre-multiplied or
linearized, providing constraints that makes such misconfiguration
hard is a service to novice and professional user alike.


There is also flipping to/from formats with alpha. Pre-multiplied and
non-premultiplied alpha. As well as flips to/from higher and lower
bit-depths as well as to/from CIE Lab. By necessity of the operations
involved, working on linear data is another one of these constraints
that should be fulfilled. Whenever possible the developer/designer of
image processing algorithms should be burdened with reducing the
number of parameters, as well as sticking with good defaults - making
efficient work-flows possible. If you continue calling it "babl
I will start calling your non-flipping-babl a lobotomized babl - you
could also collapse "RaGaBaA float" into "RGBA float" along with
"R'G'B'A float" to make babl even less capable of providing internal
color / pixel-representation management for GEGL and thus GIMP and
other applications using GEGL. Before scaling or blurring an image a
user would then have to run a pre-multiply filter and after-wards
un-premultiply filter.

The fully automatic choice of alpha association is not always the best
way to go.
Sure, there are many documented cases where you know exactly what's the
most adequate association, but then there are also cases (which are not
corner cases at all) that completely fall apart with an automatic
For instance, take an EXR file with luminescent transparent pixels.
That's a perfectly valid case that is used extensively in VFX to
composite fire, light effects and any kind of emissive phenomena that
produce light but don't occlude light from the background.
It's important to note that what I mention is not a hack used by
artists at all. It's a valid alpha compositing situation described both
in the original porter-duff paper and the EXR specs.
If you feed that data to a program that decides a strategy of alpha
association, the most probable outcome is that the information in
pixels with zero alpha is discarded.
There is an infamous thread at Adobe Forums that had the most renowned
imagers ranting about how Photoshop was screwing image data because
programmers decided for users and made assumptions.

That's why it's important to know what artists will do with your
software before making such assumptions.
I'm not saying that every single option in a graphics program should
come with a toggle, but you can't choose for users if you don't know
what they need.


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