Re: Pixels Per Inch needs to be standardized 🔍

[Jasper St. Pierre]

What are the dimensions of a projector, whose pixels-per-inch or
dots-per-inch value is a distance of how far away the projector is for
the wall, or, in a keystoned case, isn't even constant across the
display?

For limited scenarios, you can make it work (with caution, see [0]).
But we cannot calculate a sensible DPI value in the general case.

[0] https://lists.fedoraproject.org/pipermail/devel/2011-October/157671.html

On Wed, May 4, 2016 at 10:45 AM, Mattias Andrée <maandree at member.fsf.org> wrote:
> On Wed, 4 May 2016 19:01:09 +0200
> Alberto Salvia Novella <es20490446e at gmail.com> wrote:
>
>> Mattias Andrée:
>> > What's wrong with dots per inch?
>>
>> How can an application reliably know which is the current
>> pixel density of the desktop?
>>
>>
>
> Well, you cannot know anything reliably. The EDID
> does contain all information you need for DPI, however
> with limited precision. X.org reports a bogus DPI. But
> if pretend that all monitors' dimensions are in whole
> centimetres, than the number of pixels per centimetre
> can be calculated
>
>   ppc_x = output_width_px(monitor) / output_width_cm(monitor);
>   ppc_y = output_height_px(monitor) / output_height_cm(monitor);
>
> Notice that this is easier to calculate than the pixels per inch.
>
>   ppi_x = output_width_px(monitor) / output_width_cm(monitor) * 2.540;
>   ppi_y = output_height_px(monitor) / output_height_cm(monitor) * 2.540;
>
> But why is pixels preferred over dots?
>
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-- 
  Jasper