Use case for high-DPI zoom

In PPK’s much needed research into how browsers handle media queries, he suggests that there isn’t a use case for increasing the DPI when zooming in. I think I have one. When talking about people zooming in:

I doubt whether such a user would be able to appreciate the crispness of images and canvas elements. He doesn’t see these details very well anyway, witness his decision to zoom in. So we can as well forget about the extra crispness that the new DPR settings make possible.

It is counter-intuitive, but actually the higher the DPI the better for people with mild/moderate visual impairments (VIPs from here).

For example, I heard from several VIPs that they found the iPhone 4 a big improvement in clarity. Googling just now I found someone post about that.

Wikipedia also mentions high-DPI as beneficial (although I’d love to find some more concrete research references), and Zoomtext lists xFont as a key feature:

With ZoomText’s revolutionary ‘xFont’ technology, you’ll see amazingly clear text at all magnification levels. All types and sizes of text are displayed with high-definition clarity, in all of your applications. Once you’ve seen xFont, no other screen magnifier will do.

That maybe on the hyperbolic side, but I’ve heard VIPs mention that as the reason they pay for a magnifier.

Overall though, a robust zoom feature that triggers media queries is much more valuable than a crisp canvas view, and I tend to agree with the points about not downloading more resources as you zoom.

Zoom requirements

I’m not sure I understood all the details of the article (although I’m very glad it’s there!), but there are a couple of accessibility requirements I hope are improved, or at least not made worse by the proposals.

Firstly, I assume that zoom on desktop would still triggers media queries in responsive designs? I think that’s the case but I’m not entirely sure.

Secondly, could we improve on mobile zoom?

Currently mobile zoom works like a desktop magnifier: the layout stays the same and you zoom-in on a part of the content. This could be improved though, as you often end up scrolling back and forth across the screen trying to read text that won’t fit in the screen.

Assuming a responsive design, could it work like desktop until you hit a minimum width? (E.g. 320px) In that way the content would fit to the screen until you really cannot cram in any-more.

It would reduce horizontal scrolling, especially on mid-size devices between 5-8″ (e.g. the Nexus 7″ tablet), so you could use a larger tablet and get the smallest mobile view of the content (thus making the text larger).