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

Hi Elle -

Seeing your e-mail give the same kind of "and what can I do about it"
feeling I have when talking to Americo (he should also be reading
this mailing  list by now).

There are obvious lots of improvements that _could_ be done so that
GIMP would be a killer application.
What you do on the high-depth, color management field, Americo is
doing on the painting tools/dynamics/presets

The problem is: currently there is not enough colaborator time to put
these suggestions together. There are barely collaborator resources
to read in full what you and Americo write (though the later have been
writing mostly to me in private due to language barriers) .

So, I hope that with the previous e-mail you could get to a good
summary of what would be needed for GIMP not only to be vaibale, but
to surpass current photoshop U.I. when dealing with these issues . I hope so.

Now help us think on the next steps. For example get that e-mail
worked into a feasible specification: If you can, refine it, then
maybe try to get someone with UI expertise that could fine tune that
your suggestions into specifications that could be really great -  now
we don't have Peter helping the project anymore.
(could be someone from your area, to whom you could get face to face
meetings) - (I'd rather have another switch along the layer modes than
to duplicate all layer modes in the UI, for example) -

And use having more people who could help with development. :-)

At least I can see the suggested features as great. And I can't think
of a way to even begin takling them without an enormous amount of
weekly hours to dedicate to it (or Americo's issues for the matter)

Best regards,


On 29 April 2015 at 08:55, Elle Stone <ellestone ninedegreesbelow com> wrote:
On 04/19/2015 06:44 AM, Elle Stone wrote:

The single biggest useability issue with GIMP 2.9 is the mechanism for
allowing the user to switch between linear and perceptually uniform RGB.

On 04/19/2015 03:40 PM, Liam R. E. Quin wrote:
In the meantime in my own workflow the lack of "repeat last filter
used" is a much bigger usability issue than anything to do with gamma
or clipping. So phrases like "everyone" and "the biggest usability
problen" don't carry as much weight as specific use cases, I think.

I will guess that most current GIMP users, just like most current PhotoShop
users, don't have any notion of whether any given RGB operation should be
done on linear vs perceptually uniform RGB. They rely on what they see on
the screen, and they are used to seeing wrong results.

Anyone who understands and intends to take advantage of high bit depth
linear gamma image editing needs *control* over whether an operation is done
using linear or perceptually uniform RGB:

* The user shouldn't have to guess whether the RGB values have been
linearized or not.

* The user shouldn't be forced to rely on the developer's "decisions from
afar" regarding whether any given RGB operation should be done using linear
or perceptually uniform RGB.

* The GIMP UI should provide easy user choice for all RGB editing
operations, with good default settings. For example the default for gaussian
blur should be linear RGB and the default for adding RGB noise should be
perceptually uniform RGB. But the user needs the ability to *easily* make
the other choice.

Back when I used PhotoShop for linear gamma image editing I encountered
three useability issues, which apparently still exist in the latest version
of PhotoShop:

1. PhotoShop couldn't display a true linear gamma image without causing
posterization in the shadows, at least until the image was zoomed in to
nearly 100%.

2. PhotoShop Curves and Levels provided far too few tonal steps in the
shadows to allow good control over edits made in linear gamma color spaces.

3. Switching between linear gamma and perceptually uniform RGB required
doing an ICC profile conversion.

GIMP 2.9 from git used to have (but doesn't any longer have) the first two
problems (well, there seems to be some kind of problem with Curves/Levels
shadow adjustments, but it's not related to having too few tonal steps).

The babl flips are a brilliant solution to the third problem. But the
current User Interface for switching between linear gamma and perceptually
uniform RGB is a useability nightmare.

Currently the only way a use could know how to get an operation to operate
on linear vs perceptually uniform RGB is if someone supplied a table that
includes all operations, with a column for how to get linear RGB and another
column for how to get perceptually uniform RGB. For examples of how very
inconsistent the current UI is, see this table:
The table explains how to get selected operations to work on linear RGB.

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