Re: [Gimp-developer] GIMP useability - choosing linear vs perceptually uniform RGB

El vie, 01-05-2015 a las 18:03 -0400, Elle Stone escribió:
On 05/01/2015 04:47 PM, Gez wrote:
El vie, 01-05-2015 a las 05:40 -0400, Elle Stone escribió:

This is a color managment issue. It's fundamentally important. GIMP
shouldn't make decisions like "use linear here and perceptual there",
other than to offer the user good defaults.
A color management issue? You're proposing to let users do whatever they
want with the trc,

Yes. I don't understand why this bothers you so much.

Because I'd expect better answers than "just because".
The tool should provide a reasonable range of tools and possibilities to
allow people do things.
And "let me do whatever I want with X" is not reasonable. If you don't
provide solid reasons backing why you would need some behavior, don't
expect the developers to implement it.
It's like asking the makers of a word processor to allow editing the
page upside down or mirrored and replying "because the program should
let me do whatever I want" when they ask you "why".

no matter if it's right or wrong.

There is no right or wrong with respect to whether any given editing 
operation is done using linear or perceptually uniform RGB. Right or 
wrong depend on what the user wants to accomplish. For example:

If the user wants to draw a gradient that drops off  like real light 
drops off, the user should use linear RGB. Using perceptually uniform 
RGB would be a mistake.

If the user really wants a gradient drawn using perceptually uniform RGB 
because she needs the tonality to not drop so quickly from white to 
black, that's the user's call to make. The developers aren't sitting in 
the right place to make that kind of decision for the user.

Why do you want to put roadblocks in the user's way?

There are certainly rights and wrongs when using a tool. If the tool is
designed to work some way and you don't respect that, you're doing it
Try taking a hammer upside-down and hammer nails with the handle.
That's wrong. 

You chose one of the few cases where both linear and perceptually
uniform could be valid options and none of them are right or wrong.
Of course I'm not against allowing two valid instances of the same
thing, like in this case.

But you're not proposing to add a toggle to gradients alone, you're
proposing to put them *everywhere*.

I'd like to see this discussion heading towards a real world list of
examples of real needs for such options that can't be satisfied with
anything else than these toggles.

That's a color
management issue!

Yes, it really is a color management issue. In PhotoShop, if the user 
wants to perform operation X on linear RGB, the user must do an ICC 
profile conversion and convert the entire layer stack to a linear 
version of the RGB working space. And when the user wants to perform 
operation Y on perceptually uniform RGB, the user must convert the layer 
stack back to the perceptually uniform version of the RGB working space.

The babl flips *could* make it possible for the user to easily choose 
linear vs perceptually uniform RGB without having to use an ICC profile 
conversion to convert the entire layer stack back and forth between 
linear and perceptually uniform RGB.

With GIMP right now, the user has no choice in whether linear or 
perceptually uniform RGB is used. Or rather choice is via the gamma 
hacks and precision changes, which leaves the user to play a guessing 
game about what's happening to the data. With GIMP as currently 
programmed, the user can't even resort to the PhotoShop option of 
converting the layer stack, because the babl flips presume the sRGB TRC.

I was with you when we both discussed these issues with the GEGL and
GIMP developers a few months ago.
They stated clearly that the immediate plan is to make GIMP 2.9 work
exactly as the current stable version with the new GEGL core.
Everything else is just a bonus. The minimum goal seems to be having a
GEGLized version of the current GIMP, which is still 8bpc sRGB.

If that's the goal and they are working towards that goal, why keep
insisting on what's wrong with high bit depth editing? 

How do you ensure correct results when the user can
change that at will on every single operation performed?

It's the user's job to make the right decisions regarding how to edit 
the user's image. It really isn't a developer responsibility.

It's a shared responsability. Developers have to design tools in order
to facilitate users making the right decisions.
A good tool makes it easy to do the job properly and allows extra
It's not the users job to dictate how a tool has to be designed, and
it's certainly not the designer's choice what users will do with the
tool. The designers have to address the users needs and give them
capable tools. 
This should be a collaboration and not a struggle.


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