GSoC’12 Update – Week 4

Hey everyone.

Week four of the libCmpx/Krita GSoC printer color management project is now coming to a close.

So far I have reached some important milestones in development this week. The libCmpx ‘Renderer’ module (which I talked about last week) has been worked on to the point that all of its major components are functioning, and that PDF rendering is now available for sampling in the test dialog. When both a PDF file and ICC profile is selected from the dialog, the “Print” button will be enabled — Printing in this case simply means that a profile-embedded PDF spool file will be created in your tmp directory. (Remember that only a *copy* of the selected PDF will be created and processed, not the original!)

In addition to finalizing the PDF rendering module, I have improved libCmpx ‘Selector’ so that the “bond” between the module and the printer settings is further tightened. If you recall from my earlier GSoC’12 posting, I had mentioned that a “simulated” printer was actually used in the test dialog, and not the printer(s) installed on your machine. Since printer color management has just started to appear in Linux, printer drivers with color-related attributes are not yet widely available. These attributes – called ColorKeyWords – are used to separate general printing settings (page orientation, number of pages to print, etc.) and color-specific printing settings (color or grayscale, resolution, gamma level, etc.). For automatic ICC profile selection to work inside a print dialog, the color-specific settings would need to parsed and mapped with libCmpx in order to obtain a “best fit” ICC profile.

The custom printer driver file included with the libCmpx test dialog (testprinter.ppd) just so happens to contain these ColorKeyWords attributes, and is used to provide critical color-related settings in the dialog. When you select ‘Automatic’ in the ICC color profile combobox, libCmpx Selector will attempt to find the best ICC profile based on the chosen color settings. If a best fit profile isn’t found from those settings, then libCmpx Selector will obtain fallback profiles from either the printer driver or Oyranos.

Since most of the work done this week was in putting the final touches in libCmpx Renderer, the automatic profile-selection mechanism needs some more tweaks (in most cases, selecting Automatic will simply return sRGB as a best fit profile). So libCmpx Selector will again be put back into the spotlight for week five — and from there, some prospecting on possible integration points in Krita.



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