EDID decoding in libXrandr?

Kai-Uwe Behrmann ku.b at gmx.de
Mon Nov 19 06:46:40 PST 2007

> Date: Sun, 18 Nov 2007 09:29:30 -0800
> From: "Hal V. Engel" <hvengel at astound.net>
> On Sunday 18 November 2007 01:00:53 Kai-Uwe Behrmann wrote:
> snip
> > Not shure if the colorimetry information will make sense for some people.
> > I mean the RGB primaries and the witepoint from position 25 till 34 and
> > gamma in 23.
> > As I see, this information is dangerous for broken monitor EDID's and of
> > not much value for most of the others. Still it is there.
> Assuming that this info is (partly) valid for cases were the EDID is not 
> broken then this could be useful.  For example LProfs visually based monitor 
> profiler could use the RGB primaries and maybe the whitepoint information.  
> But that also means that as a consumer of this information I also need to be 
> able to query X as to how broken EDID is for the device in question.  

Agreed with the EDID borken status to be asked first before use. Just the 
EDID colorimetry information may be broken in that sense that most monitor 
manufacturers, or who else provides the EDID blob, dont much care about 
that information. That said, even in a otherwise valid EDID block can 
stand garbage or simply sRGB coordinates in the colorimetry section of 
That may be the reason why it is not much used on other platforms. I 
remember a small little application, which parsed the EDID block to create 
a profile. 
... ddc2xdccc.c  Interesstingly it creates a deprecated XDCCC block.

If you can render say 90% of the monitors have a better than nothing 
colorimetry in EDID, then the according buttons in LProf may have 
technical value. At least you should check for swapping and non relevant 

Last but not least some users may be irritated to get the inbuild 
colorimetry straight from the monitor without a mesurement device - huh.
Will be difficult to explain later why they should by a colorimeter, which 
may cost more than the complete monitor if they have the inbuild data 
already ;-)

kind regards
Kai-Uwe Behrmann
developing for colour management 
www.behrmann.name + www.oyranos.org

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