Why EDID is not trustworthy for DPI

Tomasz Torcz tomek at pipebreaker.pl
Thu Oct 6 20:36:52 UTC 2011

On Thu, Oct 06, 2011 at 12:00:26PM -0700, Adam Williamson wrote:
> On Thu, 2011-10-06 at 13:36 -0500, Chris Adams wrote:
> > Once upon a time, Bill Nottingham <notting at redhat.com> said:
> > > Obviously you embed radar in every projector.
> > 
> > Projectors with auto-focus already detect the distance to the screen (I
> > think they use IR).  I don't expect that they change the EDID screen
> > size reporting though.
> But you don't (only) need to know the distance between the projector and
> the screen, you need to know the distance between the *audience* and the
> screen.
> So, logically, what we need to do is make projectors capable of using
> Bluetooth to figure out what cellphones are nearby, and Facebook and
> Foursquare to check on their GPS locations...

  Every time DPI discussion begins, sooner or later projectors and points-per-arc
are appear.  They are like Godwin Law for DPI Discussions.
  I think everybody agrees that true DPI cannot be found.  But true DPI is
only needed if we want PERFECT setup.  Perfect isn't possible. Can
we just give up on perfect setup and instead just go with GOOD ENOUGH?

  Good Enough is getting real DPI for main screen and not really caring
about secondary screens.  Just read DPI from laptop panel (or first
detected output on desktops) and use it instead of 96.  Let's not care
about not-so-common case of wildly different DPI on connected screens.
  (hey, my 300 DPI cellphone has HDMI output. I can connect it to 70" TV
which gives 32 DPI.  Let's don't even try to accomodate real DPI of TV!)

Tomasz Torcz                        To co nierealne -- tutaj jest normalne.
xmpp: zdzichubg at chrome.pl          Ziomale na życie mają tu patenty specjalne.

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