Re: [Gimp-developer] New Image/Color Management option

[Elle Stone <ellestone ninedegreesbelow com>]

On 05/12/2016 03:56 PM, Michael Natterer wrote:
> The option in Image -> New allows to disable color management
> and whatever color management transforms on a per-image base.

What specifically is included in "color management transforms"?

> This is mainly because almost nobody understands what this
> whole color stuff is about at all.

There is a difference between a deep theoretical understanding and a 
working understanding.

Here is everything a user needs for a basic working understanding of 
color management:

1. Make or find an accurate monitor profile. Select that profile in 
Preferences.
     In a worst-case scenario, set the monitor to the 
manufacturer-supplied sRGB preset and use sRGB as the monitor profile.

2. Open an image. If there's no embedded ICC profile, assign the right 
profile. For many (but not all) untagged images, sRGB is the right choice.

3. Convert the image to the user's chosen RGB working space.
     Sadly, in GIMP the RGB working space must be sRGB, or else too 
many editing operations won't work because of the hard-coded sRGB 
parameters in the code base.

4. When you are done editing, convert the image to the desired output 
color space, which for the web should be sRGB.

All (sic!) graphics artists
> I know and have asked switch off color management entirely
> in Photoshop because it's this confusing thing that changes
> colors in an unpredictable way  (which is not surprising
> given the cluelessness).

Well, see, PhotoShop doesn't actually provide an option to disable color 
management.

Under "Color Management Policies" there are several options, one of 
which is "Off". But choosing "Off" doesn't do what you might think it 
does. Instead, quoting from an Adobe forum post 
(https://forums.adobe.com/thread/1934844):

""Off" is an illusion, it's not really off. What happens is that the 
working space is assigned to the file no matter what color space the 
file was created in . . . And to top it off, the file is then saved 
without an icc profile, throwing everything completely to the wind even 
if it wasn't before."

I left out part of the quote because it was addressing an issue with a 
broken monitor profile, so see the forum post for the full quote.

What is said in the forum post coheres with what I remember to be the 
case for CS2.

So your confused PhotoShop users are just making a bad situation worse.

There used to be an option in PhotoShop to disable color management for 
*printing*. This option was very useful in advanced printing workflows. 
This option was removed to the great dismay of people trying to make and 
use custom print profiles with PhotoShop. But this is not what you are 
talking about.

There also has been much gnashing of teeth over the years among 
PhotoShop users trying to make CMYK files for printing. But this 
particular color management issue has nothing to do with GIMP, because 
GIMP doesn't support CMYK.

> The sane choice way to let users disable it, rather than
> forcing it upon them.

If you want to let users disable color management on a per image basis, 
then the per image option should do exactly what the global option in 
"Preferences/Color Management/Image display mode/No color management" 
does, which is "Send the RGB values directly to the screen without doing 
any conversion from the image profile to the monitor profile for display".

I can't think of a single use case for trying to edit a non-color-manged 
image in an ICC profile color-managed editing application such as GIMP.

Best,
Elle