Re: Pixel, Points and Spatial Measures

Wayne wrote:
> In web jargon 12pt = 16px, a flexible measure... We will ultimately talk to web developers in pixels 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

That I certainly agree with, on the call last Tuesday someone made the mistake of saying points and meaning pixels, which are 25% off in terms of size. As pixels are the unit designers and devs use, they general mistake PT as meaning pixels anyway, which leads to mis-calculation of text size when doing colour contrast checks.


> what a person can see is determined by the angle it subtends on the retina. 

And worth noting that the CSS pixel is defined as an angle. [1]
    

> 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. 

It would be misleading to use spatial measures as the basis for the SC for web content. When a browser opens on a device, it decides what size a “CSS pixel” is.

*Every other measurement unit is based on that CSS pixel*. 

Inches, CMs, EMs, REMs, PT, everything is based on the CSS pixel. (Percentages and VW/VH are based on viewport size, in CSS pixels.) The browser and OS convert the CSS pixels to device pixels for display (which is why stuff doesn’t get smaller on high-res screens, and occasionally you can get rounding errors).

As I’ve said before [2,3,4] and I’ll repeat: CSS Pixels are the only relevant, semi-consistent measure for sizing web content across devices.

As Patrick said, you could convert the other way as a rough guide, but we have to test in CSS pixels.

-Alastair

    
1] https://www.w3.org/TR/CSS21/syndata.html#img-pixel1 
2] https://alastairc.ac/2012/04/relative-pixels/ 
3] https://alastairc.ac/2013/02/how-to-hold-your-ipad/

4] https://alastairc.ac/2012/11/in-defence-of-pixels/

Received on Friday, 13 January 2017 09:53:17 UTC