Help! Linear color space not working?

Sorry for totally newbie question :-/
I’m trying gimp2.9’s linear gamma space, which I thought can’t be hard. According Elle Stone’s great webpages I use one of his demo images, tested in partha gimp2.9.5, and krita. In krita it works perfectly well, but in gimp I just can’t get correct result, like this:

You can see my stroke all got ugly dark edges no matter what precision&color profile I choose

I’m confused, because haven’t heard anybody got this issue. Is there any tricky setting I could set wrong? Thanks

btw I tried another PC, no luck.

Which build of GIMP are you using? What OS? Where did you get GIMP? What commit # (Help/About)?

Hi thanks for answering.
I got gimp from, tried gimp2.9.5 64bit for windows, installed/portable, also gimp2.9.5 cce 64bit, installed/portable, commit 0c9d76d, it’s the only avaiable window version currently. Os is Win10 64bit

Default GIMP 2.9.5 code has changed a lot over the last few months. Old 2.9 tutorials are out of date.

I’m on Linux and not in a position to check how Partha’s current default GIMP 2.9 build works. For Partha’s cce build, for linear gamma painting, convert your image to this profile:

Thanks for your time! I already tried this profile in std and cce. it looks kinda weird in cce:

they look almost same but notice the weird colorful halo of the linear ones. I don know if it solves the problem, and this profile hugely lighten all colors

Don’t assign the linear gamma sRGB profile to a regular sRGB image. Convert from regular to linear sRGB. Make sure image is at >=16-bit precision and referably 32f.

Did you download the tutorial image? If so, why? Try making a new linear gamma sRGB image using CCE and painting. Then make a regular sRGB image and paint similar strokes. Compare.

Wow thanks for converting trick. I found that only way is: create or open a image in cce, without assign profile, then convert the built-in sRGB to sRGB-elle-v4-g10, then linear space works well. If I create a new image with sRGB-elle-v4-g10, it got weird colorful halo. and in gimp std it just wont work at all, either way.

Following your specifing profile&converting I blind guess some profiles in kirta folder. Turns out gimp std can also work well in linear space if I convert build-in sRGB to rec2020-elle-v4-g10 or CIERGB-elle-v4-g10, at least dark edges (almost)gone. It just won’t work with sRGB-elle-v4-g10. Thanks a lot

I can’t replicate this. What is your step-by-step procedure?

It shouldn’t work with default GIMP, at all, unless/until you trigger the making of an internal profile, but this process sometimes fails to work. With default GIMP you are better off only opening regular sRGB images and only using the built-in sRGB profile when making a new image.

Don’t do this. Just use the built-in sRGB profile with default GIMP. Otherwise you’ll run into issues with hard-coded sRGB primaries, even if GIMP is handling the TRC correctly.

My steps: gimp cce 64bit for window
2.create new image, space=rgb, precision=32 bit fp, profile=sRGB-elle-V4-g10.icc, click ok
3. fill a bg color, like red
4. paint with another color, got weird halo, like this:

My steps getting correct results:
when creating image, left profile blank
after created, menu image–color manage–convert profile to sRGB-elle-V4-g10.icc, as u suggested
like this:

yes I read about you specifically point out about hard coded sRGB thing, I indeed see some subtle but colorful halo with rec2020 or CIERGB. I just desperatly guess they are anyway better than sRGB profile :-//

You mean I just give up tring to use default gimp for linear space work? Bad news:-(( I will stick to cce then

@lancertaki the JPEG compression artifacts in your images are quite horrible to look at and somewhat obscure the problem. Could you increase the compression quality?

I tried using GIMP 2.9.4 (commit 60e9405):

  • RGB, 32-bit linear floating point, GIMP built-in Linear sRGB
  • RGB, 32-bit gamma floating point, GIMP built-in sRGB

I get this:

Perhaps there is an error in your procedure that you are overlooking? or perhaps in the Window’s build - @partha ? .

Painting using Normal blend is not affected by the sRGB primaries. LCH is affected, but most blend modes are not. Also, when you paint fully saturated Rec2020 colors, all you are seeing is the most saturated colors your monitor can display. So unless you are using a Rec2020 monitor, what you see is highly misleading.

@Morgan_Hardwood - good call. @lancertaki - are you saving linear gamma images as jpegs? Jpeg compression assumes perceptually uniform encoding.

Since 2.9.4, default GIMP has changed a lot. The old tutorials apply to 2.9.4, but not to @partha 's latest build. Maybe @partha can explain how to get linear blending from his latest build. Or maybe @lancertaki can download and use a 2.9.4 build and follow the tutorials.

Current default GIMP is even more different from 2.9.4 than Partha’s latest build. It’s getting close to being more intuitive to use, but still has some remaining rough edges. I can explain how to set up current GIMP for linear painting/blending, but @lancertaki isn’t using latest default GIMP.

@lancertaki mentioned Krita. CCE handles RGB color management more or less like Krita, and I’m completely clueless as to how/why @lancertaki is producing/getting odd results with CCE.

I tried cce again, now both assigning icc when creating and converting icc get correct results, I must did sth wrong in former test, sorry for that.

btw I didn’t use “export” or “save as”. I use a screenshot software, that’s supposed to capture what I see I guess?

Hi Morgan_hardwood. Do u use std or cce?. My gimp std is garantee NOT behaving correctly :-/ and I found a very very weird thing in gimp std 0c9d76d. here’s linear sRGB I got:

definitly not good.
now the weird thing: I create a regular sRGB image, but forcefully convert to a linear icc sRGB-elle-v4-g10.icc, now it, I’d say, looks like correct

I don know if I’m allowed set a icc profile except for built-in one to gimp std, Elle told me it’s hard coded with sRGB. I guess the icc I used is a sRGB profile? really no idea,

Thankfully I got cce to stick to so not big deal. And I’m doing game textures for window games so can’t try linux latest gimp version. hope partha will give us newer windows gimp to try later (Thank him a lot)


@lancertaki the important thing if you found a bug is to report it to the GIMP devs:

funny is I don know if it’s a bug. I read Elle’s articles again, and wildly guess maybe gimp std is now doing similiar to gimp cce? which means user just forget about switching between regular and linear rgb, let gimp stay in sRGB, all they need is assign a icc profile? Just guess. I will do some more test like blur and layer blend, to see if it just look like correct or really correct

And I’m quite sure that my gimp is relatively old (download in Feb.27), don know how current gimp behaves.

@lancertaki you don’t have to be 100% certain to report a bug. Open a bug report, clearly describe the steps to reproduce and the version of GIMP std you reproduced it on (the commit hash which you get from Help > About), and let them decide whether it’s a bug or not.

Sure will do

Hi @lancertaki,

With latest default GIMP on Linux, I can’t replicate what you show:

In Partha’s last build, the relevant code is very different. Everything has changed recently, so instead of filing a bug report now, it might be good to wait for the next build.

Actually in latest default GIMP it’s easy to produce what you get, but it’s done via a user choice in the UI: To get gamma artifacts while painting, deliberately choose Legacy blend mode for the brush, instead of using Default blend mode.

In default GIMP as of yesterday’s code, it’s best to only paint in the GIMP built-in sRGB color space.

Default GIMP doesn’t handle color management like CCE. Rather default GIMP separates the profile TRC from the profile Primaries. Currently TRC and Primaries are both hard-coded to sRGB, but eventually this will change.

Since the latest default GIMP code changes (not in Partha’s latest build), increasingly if I’m editing an sRGB image, many times I’ll use default GIMP instead of CCE, precisely to avoid avoid having to make profile conversions between regular sRGB and linear gamma sRGB.

Yea nice to see gimp actually behaves well, I think I can get a sweet latest version sooner or later.
My gimp std has no difference switching brush’s blend mode to legacy or not, maybe it proves my version is out of date?

Here’s the practical question: I did my stupid steps with my gimp std, and got a so-called correct linear work, now I tried the images in game engine. my exporting method is copy visible to a new built-in sRGB image then export a regular tga. I’d say it works at least visually great, I even think it IS the right linear work. image below shows them, gimp std default work(left), and my weird steps work(right)

and lots of my work is about grayscale images ONLY, I can safely edit them in default gimp build-in sRGB right?