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List:       gimp-developer
Subject:    Re: [Gimp-developer] the blur/smudge was better in 2.8
From:       Ell via gimp-developer-list <gimp-developer-list () gnome ! org>
Date:       2019-06-22 16:55:54
Message-ID: e963cf31-26e6-44f7-a25a-880779b5ef1c () email ! android ! com
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On June 20, 2019 8:12:32 AM GMT+02:00, Natalie Baldwin via gimp-developer-list \
<gimp-developer-list@gnome.org> wrote:
> I've redownloaded version 2.8 because i've found no way to emulate the
> mathematical precision that the blur/smudge tools give me.
> 
> [...]
> 
> Making a transition with blur/smudge from 255-0-0 to 0-255-0 (red to
> green)
> i do not expect to get any colours where red+green > 255. I expect to
> find
> 254-1-0 followed by 253-2-0 followed by 252-3-0 etc. This feature is
> extremely important to me because of a shader i wrote that reads colour
> values mathematically. So, if i get a vote, please reintroduce the old
> way
> to blur.

In 2.10, many operations, especially ones involving color blending, transitioned from \
working in perceptual RGB, to linear RGB. This is the physically-correct way to blend \
colors, as, in perceptual RGB, the component intensities are compressed using a \
nonlinear gamma function. In other words, this change is intentional, and is \
generally the Right Thing to do.

That being said, there are still valid reasons to want to keep working in perceptual \
RGB, as in your case. Unfortunately, while some parts of GIMP provide this choice, \
others (like the smudge and blur tools) don't: it's a balancing act between allowing \
enough control, while not cluttering the UI with too many options, which we haven't \
fully nailed down yet. That's not to say we don't want to get there eventually, just \
that we don't have a general solution that feels quite *right* yet.

While there are workarounds for working perceptually in 2.10, even when GIMP doesn't \
provide this option otherwise, they're so terrible that I'd rather not mention them \
:)

Lastly, just to reiterate, the smudge and blur tools *do* still have the properties \
you're looking for, they just apply to the *linear* component values, rather than to \
the perceptual ones (which can be checked by converting the image precision to 32-bit \
linear float, and using the color picker tool in "pixel" mode). So, another option is \
to switch your shaders from working in perceptual RGB to linear RGB, if that's \
applicable.

> The gradient
> tool with perceptual RGB works almost as expected, somehow the blue
> value
> goes up even though i'm trying to gradient between pure red and pure
> green.

Oof, good catch! That's a bug. You can take care of that by disabling dithering in \
the gradient-tool options, but it shouldn't happen with dithering enabled either.

--
Ell
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.
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