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. Fromthis article <http://libregraphicsworld.org/blog/entry/richard-hughes-on-color-management-in-linux-and-gnome> (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 <https://en.wikipedia.org/wiki/Linux_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. ___________________________________________________________________________ darktable developer mailing list to unsubscribe send a mail to darktable-dev+unsubscr...@lists.darktable.org
