Why EDID is not trustworthy for DPI

Martin Langhoff martin.langhoff at gmail.com
Tue Oct 4 20:17:08 UTC 2011

On Tue, Oct 4, 2011 at 4:03 PM, Camilo Mesias <camilo at mesias.co.uk> wrote:
> Thanks for the explanation... There is an alternative to endless
> explanation - roll out your best effort at a heuristic and let the
> crowd contribute to an ever growing set of exceptions.

Well, actually, people complain a lot more than what the code ;-)

> To play the devil's advocate, I'm asking why the monitor situation is
> different from any other bit of hardware.

And he just explained -- fairly well I would say.

On my part, I say thanks Adam -- even being familiar with some of the
vagaries of manufacturing data for general hardware, monitor's EDID
sounds like an extra-deep nightmare.

For fedora users, as others have mentioned, perhaps a UI that lets
users test a couple of possible dpi values might be useful (for those
users so inclined). It does have to cross a good chunk of the stack to
work well, and seems like a lot of work to get right; but the xrandr
improvements are a start.

For distributors -- such as OLPC -- that are know what HW they are
shipping, it is important to be able to override the guesswork and
state /this/ is my dpi. As far as I can see, Daniel has a way to do it
-- in other cases (ie: mozilla's xulrunner) we've had to patch some
versions so that they'd accept a configured dpi.


 martin.langhoff at gmail.com
 martin at laptop.org -- Software Architect - OLPC
 - ask interesting questions
 - don't get distracted with shiny stuff  - working code first
 - http://wiki.laptop.org/go/User:Martinlanghoff

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