EDID decoding in libXrandr?

Kai-Uwe Behrmann ku.b at gmx.de
Sun Nov 18 01:00:53 PST 2007

> Date: Fri, 16 Nov 2007 15:24:58 -0800
> From: Keith Packard <keithp at keithp.com>
> On Thu, 2007-11-15 at 18:59 +0100, Soeren Sandmann wrote:
> > The monitor name displayed to the user should be computed based on
> > both the display descriptor strings, and on the vendor ID, depending
> > on what information is available. 

Oyranos parses EDID 1 information for monitor identification. It uses the 
18 byte blocks starting from 54 for a monitor manufacturer, model and 
serial ID string. In case the manufacturer was omitted, it switches back 
to scan the 2 byte ID's starting at position 8. The later could be 
extended to model(10) and serial(12).
> All I was suggesting was that the server should probably provide much of
> what you want in a EDID-indepenent fashion, so that the same tools will
> work with non-EDID monitors.

Yes, this is a good point.

> If you've got a list of identifying information that you'll be pulling
> out of EDID, we can see which make sense to have as output properties.
> > I also need the ability to compute an identifier that will allow the
> > client to recognize whether a monitor we have seen before, or a
> > sufficiently similar one, is plugged in so that the mode can be set
> > with no user interaction required at all.

A md5 or the like of a broken EDID block can possibly be used as a 
substitution for a serial number? The parser may not be able 
to identify manufacturer or model in such case.

> RandR 1.3 will have a fairly long list of 'standard' properties to try
> and make user interfaces more consistent across different video drivers
> and monitors; if you've got information you're interested in, having us
> standardize the content and format will help not only your application,
> but video driver developers as well.
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.

Hope this email provides some helpful information.

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

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