# Pixel, Points and Spatial Measures

• From: Wayne Dick <wayneedick@gmail.com>
• Date: Fri, 13 Jan 2017 00:03:47 -0800
• To: GLWAI Guidelines WG org <w3c-wai-gl@w3.org>
• Message-ID: <CAJeQ8SDew=eucvv1KNuHXHorkpB9ZGskh8UHjyk+V2PjybbRQw@mail.gmail.com>
```In web jargon 12pt = 16px, a flexible measure. To the rest of the
publishing world, 12pt = 1/6 inch= 5/24 cm, a spatial measure. We will
ultimately talk to web developers in pixel because pixel is the unit
of web measurement. I propose omitting the use of point size as a
measure in our discussions and speak only in pixels for screens size
and centimeters and inches for spatial size. It is sad, but point has
become ambiguous.

There is a serious but solvable problem when we apply pixel measures
to low vision accessibility. People with low vision need real spatial
measures for their font sizes. A person with low vision cannot read
print with 0.139in= 0.347cm font size (newspaper font) from 16in=
40-cm (comfortable distance). I cannot give a pixel statement like
that, because what a person can see is determined by the angle it
subtends on the retina. The same pixel count will have different
spatial sizes and subtend different angles on the retina for different
screen sizes and resolutions.

I propose that in font size issues for low vision we use spatial
measures, and give conversion tables for developers. We can give our
developers conversion tables in the techniques.  I can do it with
centimeters and inches. The problem isn't that difficult, at least for
me, a resident mathematician.

if we do not state our SCs in spacial measurements we will have not
way of knowing if they work.
```

Received on Friday, 13 January 2017 08:05:00 UTC