Linux Color Management Hackfest Brno 2012 ended

Around a dozen people met inside the Red Hat offices in Brno last weekend. The attendees came from various distributions and projects to discuss and work on color management for Linux. Most people arrived at Thursday and we started immediately to brain storm ideas and share information.

I was quite shocked as I heard Dantii could not join us. Fortunately the last messages about him sound very encouraging. It is great that our community could in different ways help him and his family.

The basic concept we worked with during the hackfest, was the opt-out of colour management approach. That was visible in printing and in window manager colour management.

Printing people discussed the PDF/X OutputIntent. The concept was developed to overcome the current short commings in the cupsICCprofile, which is primarily a vendor solution for CUPS print servers and the colord user session hook inside CUPS server. The implementation of the concept was done inside libCmpx, which is basically a wrapper around Ghostscript, which does the majority of the work, and a interface to Oyranos. From the other side John Layt looked into that work and Krita new print colour management tab to understand the implications for the KDE/Qt print dialog. He discussed lively with Till Kamppeter, Richard Hughes, Chris Murphy and me on how to get forward with that. Richard wrote a proof of concept for on screen print simulation in GTK. Chris talked a lot about osX printing and did some testing there. His experience on other platforms than Linux helped us a lot to figure out, which path we want to go and way the make sense. I searched for some PDF’s showing the features we need. They can now be found on ColourWiki. Jaroslav Reznik printed them and Till tested them. Michael Vrhel from the Ghostscript project fixed already after the event all of the bugs, which Till worked on in Brno. We had the idea, that some PDF printers might be able to do the right thing with the OutputIntent themselves. While discussing on how to know about that capability, Till and Richard had a nice idea how to reduce code duplication inside the current set of Linux CUPS filters. In parts the Color Management Hackfest crossed over into a Printing Summit.

Jan Grulich started coding on KolorManager. He implemented a widget to show a 2D graph of a ICC profile inside the information tab. Sirko Kemter was not very happy about the colours inside the graph. So I adjusted them, but after the hackfest.

While working on that, Jan profiled his monitor using Dantii’s colord-kde. Yes, Lukáš Tinkl fixed it, so it can now create ICC profiles. We needed to hand massage the profile to get it into Taxi DB, and then thought, it would be good to download the fresh profile later through Oyranos. That worked fine on the command line. But inside KolorManager a selection that a profile is available for download from Taxi DB would be more appealing. Jan wanted to look into that, and I worked later on a API and code snippet for Oyranos.

By the way, the above screen shot is done using the new colour correction feature for KDE-4.10. You might see the strong colour cast in it. Dan Vrátil worked on undoing that cast inside KSnapshot using the actual monitor profile. The initial coding was fast. But he likes to get that working for multiple outputs too.

Casian Andrei, who did the KWin Color Correction project during this years GSoC, wrote some documentation about that newly added feature. While writing that and clarifying some points, we discussed the opt-out inside KWin and found that it is not yet present. Sig. But Casian had played with the idea already and said that per region opt-out would be trivial inside KWin and started to write on that feature during Sunday. In case that works out, it would be trivial to opt out inside existing applications. But we found as well, that for a perfect results only a blending in the correct colour space is needed during compositing. That can be implemented inside toolkits, which is not trivial, and can then be used together with the per window opt-out. That buys us some valuable time for the toolkits to become ready for full colour management support. Whether the same per region approach is easy enough to implement in Wayland needs to be seen.

Now back to profile distribution. Oyranos obtained a new backup tool for Taxi DB. And we counted already over 200 different ICC profiles in the online data base. Sirko Kemter and Daniel Jahre grabbed the taxi sources, installed MongoDB and worked on mostly basic stuff to add later more features. The online front end to the DB can be used on every platform for download and upload. Daniel and Sirko discussed how to temporarily store a ICC profile from the ColorHug LiveCD. We found that the data base can be used for very different things, e.g. distribution of spectral data sets for camera sensors.

Pippin worked since some time on improving the display of gradients on 8-bit driven monitors. He came up with a dithering approach and tested that using the Taxi DB profiles for the analysis of his implementation. That helped him to make the algorithm more robust even with strongly distorted monitor gamma curves. There is quite some interest inside the graphics designers community for his work to solve banding problems. We talked a bit about gegl and I found babl especially interesting. The small library does, what I call pixel layout conversions. Those are in part colour space conversions and encoding conversions. For better separating encoding, 8-bit versus 16-bit etc., from colour spaces, e.g. linear gamma + Rec709 primaries versus sRGB etc., we need better ICC profile analysis. Especially gamma analysis can be improved inside rendering pipelines. Beside discussing hardware stuff, spectral imaging, video processing and so on, he gave a small and very helpful introduction into colour theory, which was a eye opener for many of the colour management newcomers and thus very welcome.

We had a interesting discussion about financial implications of colour measurement hardware. My impression is the high costs and thus reduced availability for good colour measurement gear nags on the success and acceptance of ICC colour management in consumer and professional markets.

During the hackfest it was really a pleasure to have so many experts in the field in one room and work together in a highly productive atmosphere. Some of them I met the first time. So let me thank our sponsors Google, Red Hat and KDE for their generous support of the hackfest idea.

We all worked quite a lot and found such a event should not stay single. So we agreed already to arrange a one day track and one following day at LGM in Madrid / Spain 2013 under the OpenICC umbrella. I hope we will see then even more projects coming.