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

[Elle Stone <ellestone ninedegreesbelow com>]

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.

> 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?

> 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.

> 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.

If the default is linear RGB, and the default is clearly indicated, and 
the user chooses to perform the edit on perceptually uniform RGB instead 
(or vice versa), why should GIMP stand in the user's way?

My apologies, I didn't understand some of the rest of your email, and 
some of it seemed to cover already covered territory.

Elle