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

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.


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