Something critically important is missing from the roadmap: http://wiki.gimp.org/wiki/Roadmap

There is no mention of supporting RGB working spaces other than sRGB.

Also there is no mention of supporting gamma-encodings other than the sRGB TRC.

Elle

http://ninedegreesbelow.com
Color management and free/libre photography

On 01/11/2016 01:19 PM, Alexandre Prokoudine wrote:

The roadmap was never intended to mention every single thng we want adding

Maybe not. But leaving support for RGB working spaces other than sRGB altogether off the roadmap gives the impression that support for RGB working spaces other than sRGB isn't considered to be of very high importance, and therefore might not happen until some unspecified time well after "Future" (the roadmap lists items planned for 3.0, 3.2, and "Future").

I'm aware that support for RGB working spaces other than sRGB won't happen for 2.10 and isn't too likely to happen for 3.0, as 3.0 will be about converting from GTK2 to GTK3.

It would be nice if support for RGB working spaces other than sRGB, and also for "gamma" encodings other than the sRGB TRC, could be put on the roadmap for GIMP 3.2 as actual listed goals.

Elle

On 01/12/2016 01:26 AM, Sven Claussner wrote:

Hi,

just for a better understanding: - Is it for something that goes beyond assigning and converting to other color spaces?

Yes.

I think of native support of larger gamut color spaces than sRGB in Babl, GEGL and GIMP, am I right?

Yes. Different RGB working spaces have different RGB primaries (different XYZ locations for the color space's "reddest red, greenest green, and bluest blue" -
http://ninedegreesbelow.com/photography/xyz-rgb.html#RGB).

Many of GIMP's editing operations make use of the color space's RGB primaries (for example, converting to black and white using Luma or Luminance, decomposing to LAB/LCH/YCbCr, the LCH blend modes, some of the noise reduction algorithms). These operations give wrong results for images in color spaces other than sRGB.

Many other editing operations *don't* make use of the color space primaries (for example, Levels, Curves, USM, Gaussian blur, scaling and other transforms). However, for radiometrically correct results, many of these "independent of the primaries" editing operations require being done on linearized RGB. So as explained below, in GIMP these operations also produce incorrect results for images other than sRGB images:

- What exactly means 'supporting gamma-encodings other than the sRGB TRC'

Different RGB working spaces have different Tone Reproduction Curves (TRCs, http://ninedegreesbelow.com/photography/xyz-rgb.html#TRCs), and many RGB working spaces have TRCS that are more or less perceptually uniform (for example, gamma=2.2, gamma=1.8, and the sRGB TRC).

To produce radiometrically correct editing results, many GEGL and GIMP editing operations will request that the operation be done on linearized RGB.

Code in babl does the actual linearization and this babl code is hard-coded to linearize the sRGB TRC. So the only time the resulting "linearized" RGB values are actually linear is if the user really is editing an image that's encoded using the sRGB TRC.

sRGB is the only standardly-used RGB working space that uses the sRGB TRC. So results for images in other color spaces will be wrong.

There is code in GIMP that partially mitigates this problem by trying to make an RGB working space that has the user's RGB primaries and the sRGB or linear gamma TRC as required. But this code only works with images that were originally in RGB working spaces that already use the linear gamma TRC.

- Is it something that happens only in GEGL and Babl or would also GIMP's code need to be touched?

As explained in the babl roadmap (https://git.gnome.org/browse/babl/tree/docs/roadmap.txt), currently babl is hard-coded only to support the sRGB primaries and the sRGB TRC.

To support other RGB working spaces, new babl formatters will need to be written.

Also new GEGL and GIMP code will need to be written that will call on the new babl formatters.

Elle

On 01/12/2016 01:26 AM, Sven Claussner wrote:

- What exactly means 'supporting gamma-encodings other than the sRGB TRC' for intense GIMP users (artists and scientists)?

On the one hand, one goal for high bit depth GIMP is to make it easy for users to produce radiometrically correct editing results without having to know a lot (or anything) about color management, color science, and the mathematics of editing algorithms.

This important goal has been implemented pretty well (a handful of editing operations still use perceptually uniform RGB when they should use linearized RGB, and vice versa).

On the other hand, intense GIMP users - that is GIMP users who do have a working understanding of color management, color science, and the mathematics of editing algorithms - need control over their RGB working space primaries and TRC.

Control over the TRC:

The following bug report: https://bugzilla.gnome.org/show_bug.cgi?id=758001 provides a partial list of reasons why some users will want complete control over the TRC that's used to encode their RGB data. This bug report requests a GIMP GUI option to completely disable the babl code that linearizes the sRGB TRC.

A user option to disable the babl flips would go a long way towards making GIMP 2.10/3.0 much more friendly to intense users, and could probably be implemented more easily than providing full support for arbitrary user-chosen TRCs.

Control over the RGB primaries:

sRGB has a very small color gamut. Full support for arbitrary user-chosen RGB working spaces for babl/GEGL/GIMP might not happen very quickly, rather might take several years.

In the meantime, having at least one hard-coded wider gamut RGB working space made available through the GIMP UI would go a long way towards making GIMP 2.10/3.0 more friendly to intense users. Rec.2020 or ACEScg would both be excellent choices. Both of these color spaces are widely used by people working with VFX/CGI/Film, and both seem to produce better editing results than the print-based/Adobe-centric ProPhotoRGB:

http://colour-science.org/posts/about-rgb-colourspace-models-performance/ https://www.freelists.org/post/argyllcms/White-Point,45.

I would recommend Rec.2020 over ACEScg because ACEScg uses an imaginary primary.

Hard-coded RGB working spaces for GIMP would be nice to have:

Even if high bit depth GIMP already provided support for arbitrary user-chosen RGB working spaces, a selection of hard-coded built-in RGB working spaces is a solution to a problem that I believe Pippin mentioned awhile back: There are an awful lot of poorly-made RGB working space ICC profiles floating around out there. Providing users with a small selection of well-chosen and properly made built-in RGB working spaces seems to me to be a good thing to do. So providing at least one wider gamut RGB working space for GIMP 2.10/3.0 wouldn't be wasted coding effort.

Elle

On 01/12/2016 04:35 PM, Alexandre Prokoudine wrote:

On Wed, Jan 13, 2016 at 12:16 AM, Michael Natterer wrote:

So yes, that coulld be put into 'Future', then get rescheduled once changes land to babl and GEGL.

That seems like the right course of action.

Roadmap updated.

Thanks! for putting on the roadmap support for RGB working spaces other than sRGB and "gamma" encodings other than the sRGB TRC.

Elle