Re: [Gimp-developer] [Gimp-user] Time to fork BABL and GEGL

[Elle Stone <ellestone ninedegreesbelow com>]

On 11/18/2014 03:05 AM, Michael Henning wrote:
> On Mon, Nov 17, 2014 at 11:39 PM, Gez <listas ohweb com ar> wrote:
> > P.s.: If you think this discussion is a waste of your time and my time,
> > feel free to skip an answer. I don't think it's a waste of time at all,
> > it's developer/user interaction regarding important aspects of the tool.
> > Do you really think that discussing this is counterproductive?
>
> Yes, I think that discussing this is counterproductive because it is
> premature. If I had spent the time I spent responding to color-related
> emails on coding this system instead, it would easily be working right
> now.

If I had not spent time and effort explaining the problems *before* you 
got around to implementing unbounded sRGB image editing, you would have 
coded up a "working" high bit depth GIMP that was steadily churning out 
wrong results. And I'd be filing a whole lot of bug reports.

> Then, we could be discussing the details of a system that
> actually existed, instead of the details of a system that does not
> exist, and if current rates of coding continue, will never exist.

And the discussion would be exactly the same. You would still need to 
use UserRGB chromaticities instead of sRGB chromaticities. But you'd 
have to undo a lot of new code to get there.

Convincing the babl/GEGL/GIMP devs of anything regarding color 
management has never been easy. For example, in 2013 I tried to explain 
why there is a difference between device Y vs ICC profile D50-adapted Y:

* 
https://mail.gnome.org/archives/gimp-developer-list/2013-September/msg00113.html 
and eight follow-up messages
* http://ninedegreesbelow.com/photography/srgb-luminance.html.

Michael Henning did understand and did make appropriate changes to 
babl's hard-coded sRGB Y values. But I doubt whether any of the other 
devs understood; if they did, babl wouldn't still use D65 device sRGB to 
convert to XYZ before converting to LAB, and GIMP wouldn't still be full 
of hard-coded D65 device sRGB Y values. See:

GIMP really does need someone on the team who understands ICC profile 
color management. But it doesn't do any good to have such a person 
around unless you actually listen.

To listen *intelligently* so you can ask the right questions when your 
color management person seems to be giving wrong advice (I'm just as 
capable as the next person when it comes to giving wrong advice), you 
need to understand a little bit about ICC profile color management. I've 
done my best to make this task easier:

Completely Painless Programmer's Guide to XYZ, RGB, ICC, xyY, and TRCs
http://ninedegreesbelow.com/photography/xyz-rgb.html

I've learned a lot while trying to explain where babl/GEGL/GIMP has gone 
off track regarding one or another color management issue. Hopefully the 
exchange of knowledge has been a two-way street.

> You say I should stop responding, but it's hard to stop responding
> when novels are being written about how wrong you are, but you believe
> you are right. It's hard to stop responding when an article portraying
> you as incompetent appears on hacker news. It's hard to stop
> responding when you genuinely want people to understand.
>
>    -- drawoc

I agree with you that it's hard to stop responding when you want people 
to understand something that you care about. I doubt whether any of you 
have a clue just how much I value GIMP as an RGB image editor. But GIMP 
is critically important to free/libre artists and therefore GIMP color 
management needs to be right.

> Now, please explain this to me with a straight answer: Why is it so
> insanely important to know what color space an operation happens in,
> in a situation where it*by definition*  does not matter, that you are
> willing to waste hours of your time and hours of developers' time
> arguing about it?

This is exactly the right question. It will me take a bit of time to put 
together a straight answer that is also not one of my "walls of words". 
I'll try to post the answer today or at least by tomorrow morning.

Elle