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

[Elle Stone <ellestone ninedegreesbelow com>]

On 01/08/2017 09:13 PM, Casey Connor wrote:
> Thanks again, Partha! As a recent convert to LCH, Elle's version looks
> pretty amazing. I'm a little nervous to mess with my gimp install, as a
> non-sysadmin expert, but if Elle has the time to respond maybe she can
> let me know if there'd be value in trying her version. (I get the
> impression from her page on the subject that 2.9.5 has all the same
> color management stuff in it that her version does.)
>
> It's not at all crucial to my workflow that the rendering intent be
> obeyed, I was just curious what was going on, because I thought I
> understood it and the results seemed to imply that I didn't. I wasn't
> sure if this was a flaw in my thinking or gimp.

Hi Casey,

I sent an answer to your previous email regarding rendering intents to 
the gimp user's list (and to also directly to you and Partha). But it 
might not reach the list for awhile because I hadn't yet resubscribed to 
the GIMP users mailing list when I sent the email. So the post is in 
moderation "awaiting approval".

Anyway, if you only ever edit sRGB images, then default GIMP 2.9 will 
work just fine for your editing needs. The only exception would be if 
you want complete control over the TRC encoding for specific operations. 
For example, default GIMP doesn't yet provide for linearized RGB for 
Curves and Levels. Whereas in CCE, if you want to make a Curves or 
Levels adjustment using linear RGB, you can convert the image to a 
linear gamma ICC profile.

But if you edit in RGB working spaces other than sRGB, it's better to 
use CCE 
(http://ninedegreesbelow.com/photography/patched-gimp-compared-to-default-gimp.html) 
because of the hard-coded sRGB parameters in default GIMP 2.9.

Just keep in mind that CCE has a fair number of quirks and gotchas, for 
example in CCE the LCH operations, Luminance conversions to black and 
white, proper linear gamma down-scaling, and so forth only work as 
expected when the image is in a linear gamma RGB working space. Also CCE 
doesn't provide any decompose/compose operations, default GIMP supports 
importing many more file types than CCE, exchanging XCF files between 
default GIMP and CCE is tricky, and so forth.

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.

To avoid issues with installing two versions of GIMP on the same 
computer (which requires using prefixes and compiling from source), you 
can use a CCE AppImage, which are made by the author of the PhotoFlow 
raw processor and are available for download from here: 
https://pixls.us/files/

Best,
Elle