Why EDID is not trustworthy for DPI

Adam Jackson ajax at redhat.com
Thu Oct 6 16:12:45 UTC 2011

On Thu, 2011-10-06 at 11:14 -0400, Jon Masters wrote:
> On Tue, 2011-10-04 at 13:54 -0400, Adam Jackson wrote:
> > EDID does not reliably give you the size of the display.
> How about "EDID as it exists today". Since you're able to so beautifully
> explain what the pitfalls are, I'd assume you've raised this with the
> VESA and asked that they revisit this in the future to accurately
> provide DPI information that Operating Systems can rely on?

Given that successive revisions of the spec have gone out of their way
to make it acceptable for displays to provide _less_ useful information,
on the grounds of manufacturing cost reduction, I think the momentum is
quite in the other direction.

More pragmatically, VESA are not the people with any influence here.
The only thing that matters to a monitor vendor is what Windows does
when you plug it in.  Linux can stamp its little foot all it wants.  No
one will care.  If you want to be a big enough player in that market to
have some influence, you have to start by playing in the sandbox that's
already built, and in that sandbox physical dimensions are just not
reliable and never will be.


- ajax
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