Re: [darktable-dev] what happens with linux color management ?

[Aurélien Pierre]

Le 24/11/2018 à 04:51, David Houlder a écrit :
> On 24/11/18 3:22 am, Aurélien Pierre wrote:
>>
>> Hi everyone,
>>
>> my darktable is installed on Ubuntu Budgie (fork of Gnome 3), but it
>> was the same when I used Gnome Shell.  I have a custom screen ICC
>> profile installed in gnome-color-manager, and loaded in darktable
>> through colord.
>>
>> When I change the ICC profile on Gnome with darktable open, the
>> colors of the darkroom preview change too (no matter if darktable
>> uses the system display profile or one built-in profile, like Adobe
>> RGB). That is the contrast and white point of the picture, plus the
>> color of the UI.
>>
>> So that means that the OS is stacking another color transformation on
>> top of darktable's one.
>>
> Is it possible that you're just seeing the effects of the gamma ramps
> changing when they're loaded from the VCGT of the profile that you
> switch to?
>
When changing between D65 and D55 profiles, the colors take an amber
shift, so it's not just a problem of VCGT.
>
> If you can change the profile without loading the VCGT (or restore the
> gamma ramps manually after the change) and the supposedly
> non-colour-managed parts of the UI change, then I'd say that there's
> some kind of double-correction happening, otherwise it's probably
> working as intended.
>
>
I don't know if messing directly with the VCGT is even possible.
>>
>> Fromthis article
>> 
>> (2011), I get that gnome expects apps to take care of themselves :
>>
>> One of the things I tried to deliberately ignore designing colord
>> was actually flipping pixel values. Colord is a very high level
>> daemon that can say to apps like Krita or GIMP “Use this profile
>> for this device” rather than them supplying a 140Mb memory buffer
>> and an operation list. This means we can do the conversion on the
>> CPU using lcms2 for some programs and using the GPU using a
>> shader in things that use 3D. By not trying to wrap lcms we can
>> let the application do the pixel conversion in the right layer in
>> the right way.
>>
>> Of course, the downside of this is that you have to patch
>> applications to actually do the right thing. We can make this
>> easier by doing some framework code for Clutter and Cairo, but
>> sooner or later the application has to know about color
>> management in one form or another. This is going to be my main
>> focus for GNOME 3.4; now we have all the framework installed and
>> working and we can say to application authors “It's already
>> installed, so don't worry about the additional dependency, just
>> commit my patch and it'll just work”.
>>
>> But gnome-color-manager has no documentation, and even the Gnome
>> color dev documentation is pretty useless (a lot of "how to", no
>> "what's going on", but they found time to design a cheesy
>> kindergarten theme).
>>
>> Looking at GDK pixbuf doc, they don't have tags to explicitely say
>> "hey that's already color-corrected so bug off". The Wikipedia entry
>> ofLinux color management
>>  is as helpful
>> and factual as a marketing director motivational speech (let's
>> increase the leverage of color management by ensuring the quality of
>> good devices, with a pro-active method to supervise critical elements
>> in a proficent way — sure !).
>>
>> As of now, I have seen no block diagram to describe the full color
>> pipe in Linux, nor any way to ensure the quality of the transform.
>>
>> From the info I have gathered, the pipe I have put together is as follow:
>>
>> || darktable pipe -> LCMS/(Internal cmatrix color correction + TRC)
>> -> Cairo surface -> GDK pixbuff -> || -> Mutter compositor -> (OS
>> color correction ? TRC ?) -> Xorg -> Nvidia/Intel GPU driver ->
>> (Color correction ? VCGT ?) -> || -> HDMI DAC (gamma 2.2) -> Screen
>>
>> So my question is : does anyone have any idea of what's going on with
>> color on Linux, or are we stacking ICC on top of shit just to pretend
>> it's color-managed magically, somehow ?
>>
>> Thanks,
>>
>> Aurélien.
>>
>>
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>
>
> -- 
> David Houlder
> +61 2 6248 7463
> da...@davidhoulder.com
> https://davidhoulder.com
>
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Aw: [darktable-dev] what happens with linux color management ?

[Alexander Rabtchevich]

Hello

And there is no colord in Mate desktop, at least on Linux Mint. So I have to 
select correct profile from the list manually each time I load Darktable. Could 
the last selection be saved and restored? Or could the settings include 
preferred monitor profile to be loaded if darktable failed to find system one?

With respect,
Alexander Rabtchevich
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Re: [darktable-dev] what happens with linux color management ?

[David Houlder]

On 24/11/18 3:22 am, Aurélien Pierre wrote:


Hi everyone,

my darktable is installed on Ubuntu Budgie (fork of Gnome 3), but it 
was the same when I used Gnome Shell.  I have a custom screen ICC 
profile installed in gnome-color-manager, and loaded in darktable 
through colord.


When I change the ICC profile on Gnome with darktable open, the colors 
of the darkroom preview change too (no matter if darktable uses the 
system display profile or one built-in profile, like Adobe RGB). That 
is the contrast and white point of the picture, plus the color of the UI.


So that means that the OS is stacking another color transformation on 
top of darktable's one.


Is it possible that you're just seeing the effects of the gamma ramps 
changing when they're loaded from the VCGT of the profile that you 
switch to?


If you can change the profile without loading the VCGT (or restore the 
gamma ramps manually after the change) and the supposedly 
non-colour-managed parts of the UI change, then I'd say that there's 
some kind of double-correction happening, otherwise it's probably 
working as intended.



Fromthis article 
 
(2011), I get that gnome expects apps to take care of themselves :


One of the things I tried to deliberately ignore designing colord
was actually flipping pixel values. Colord is a very high level
daemon that can say to apps like Krita or GIMP “Use this profile
for this device” rather than them supplying a 140Mb memory buffer
and an operation list. This means we can do the conversion on the
CPU using lcms2 for some programs and using the GPU using a shader
in things that use 3D. By not trying to wrap lcms we can let the
application do the pixel conversion in the right layer in the
right way.

Of course, the downside of this is that you have to patch
applications to actually do the right thing. We can make this
easier by doing some framework code for Clutter and Cairo, but
sooner or later the application has to know about color management
in one form or another. This is going to be my main focus for
GNOME 3.4; now we have all the framework installed and working and
we can say to application authors “It's already installed, so
don't worry about the additional dependency, just commit my patch
and it'll just work”.

But gnome-color-manager has no documentation, and even the Gnome color 
dev documentation is pretty useless (a lot of "how to", no "what's 
going on", but they found time to design a cheesy kindergarten theme).


Looking at GDK pixbuf doc, they don't have tags to explicitely say 
"hey that's already color-corrected so bug off". The Wikipedia entry 
ofLinux color management 
 is as helpful 
and factual as a marketing director motivational speech (let's 
increase the leverage of color management by ensuring the quality of 
good devices, with a pro-active method to supervise critical elements 
in a proficent way — sure !).


As of now, I have seen no block diagram to describe the full color 
pipe in Linux, nor any way to ensure the quality of the transform.


From the info I have gathered, the pipe I have put together is as follow:

|| darktable pipe -> LCMS/(Internal cmatrix color correction + TRC) -> 
Cairo surface -> GDK pixbuff -> || -> Mutter compositor -> (OS color 
correction ? TRC ?) -> Xorg -> Nvidia/Intel GPU driver -> (Color 
correction ? VCGT ?) -> || -> HDMI DAC (gamma 2.2) -> Screen


So my question is : does anyone have any idea of what's going on with 
color on Linux, or are we stacking ICC on top of shit just to pretend 
it's color-managed magically, somehow ?


Thanks,

Aurélien.


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--
David Houlder
+61 2 6248 7463
da...@davidhoulder.com
https://davidhoulder.com


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