Re: [Gimp-user] color management -- basic question

[Casey Connor <gimp-user-list caseyconnor org>]

Thanks very much, Elle, for the detailed reply!

Firstly: I've been studying up on color theory for the last month or two 
and your website is amazing and very helpful, so thanks for the huge 
amount of work you have put in to it. There are not many (possibly no) 
resources like it, at least as far as I've found, for the color curious. 
We all owe a big debt of gratitude.

The only reason I was playing with the output profile and monitor 
profiles was mainly to test my understanding of it, not because I was 
developing a particular workflow.

The "colorful image" I was using was one of the test images here: 
http://joco.name/2014/03/02/all-rgb-colors-in-one-image/
I used one of the 4096x4096 8-bit-per-channel images, which I scaled to 
1024x1024 -- I just wanted an image to play with that I could be sure 
would show me a shift when/if it happened -- in other words, it's just a 
test image and I just assigned a randomly-chosen larger-than-sRGB gamut 
to it so I could see how the rendering intents looked --  so it has no 
associated color space, afaik, it's just "all the values" (or was, until 
I scaled it down.)

I now understand that with the generic sRGB profile I was using I 
shouldn't expect the rendering intents to look any different from each 
other.

Longer-term, I was interested to work in wider color spaces for the sake 
of photography. I'd just be exporting to Wide Gamut (or whatever larger 
space) and opening that up in gimp. The hope was to possibly retain some 
more detail, soft-proof to check what's out-of-gamut, experiment, and 
otherwise possibly get better results with certain transformations in 
Gimp. From what you said it sounds like the CCE is the version to use if 
I'm going to go through with that plan, since it amends certain tools to 
not assume sRGB under the hood, but maybe the default version of gimp 
would still be useful just to get a feel for what's out-of-gamut, and I 
could still use g'mic tools if they work in Lab/Lch/etc, right?

(Also, I hope to profile my monitor soon.)

> There are many versions of the sRGB ICC profile 
> (http://ninedegreesbelow.com/photography/srgb-profile-comparison.html). 
> Most of these versions are matrix profiles. Where did you get the sRGB 
> profile that you are using as the monitor profile, and what's its 
> exact file name?

From color.org, I think, judging by metadata? Not actually sure where 
it came from -- sRGB_IEC61966-2-1_black_scaled.icc

But yeah, nothing carefully-chosen, whatever it is -- I did read up a 
bit on the variety of sRGB profiles (thanks again to your site) and I 
know that I shouldn't trust or use or speak to any of them before 
checking ninedegreesbelow.com. :-)

> If you need ICC profiles, I provide a suite of well-behaved ICC 
> profiles here: https://github.com/ellelstone/elles_icc_profiles - 
> click the "Clone or download" button to download the zip file, just 
> ignore the code folder (unless you feel like compiling your own set of 
> profiles), and look in the "profiles" folder to find the already made 
> ICC profiles. This profile: "sRGB-elle-V4-srgbtrc.icc" is exactly 
> equivalent to the GIMP built-in sRGB profile.

I'm sorta curious why GIMP's built-in sRGB profile rarely appears in 
menu lists of available profiles -- e.g. the monitor profile choice, or 
the soft-proofing profile choices? I only see it when converting an 
image to a new color profile, and that makes me wonder if I'm still 
misunderstanding something fundamental about profile types.

> I absolutely agree with you that LCH is amazing, and now that it's 
> available, I can't imagine ever trying to edit without LCH. Default 
> GIMP and CCE both provide the LCH blend modes. In addition CCE 
> provides LCH color pickers and an LCH Hue-Chroma tool. So if even if 
> you only ever edit sRGB images, you might find CCE worth using until 
> these capabilities are added to default GIMP 2.9.

Yeah, those overlay modes are great (and thanks once again to your 
website for cluing me in to them). Are your LCH tools in the roadmap for 
2.9 or 2.10? That'd be super. I was about to file a FR for Lch mode in 
the native gimp levels dialog... is that already planned? (I've been 
using g'mic's colors->curves in Lch mode and it works great to boost 
shadows without altering colors.)

Thanks so much!
-c