Tip: Using zoom to target images to high density displays

I found this several days ago when I was looking for a way to scale images on an iPhone inside of a fluid layout such that they would display at a 1:1 pixel ratio. If you didn’t already know, the iPhone 4 and 4S displays everything as if the screen was the same size as a normal iPhone when it measures and does the layout. The result is that all the text looks extremely crisp, and any sites already designed for the original iPhone don’t break or look weird. With images this means that a 300 x 300 pixel image displays the correct size in the layout, but is essentially scaled up to fit over 600×600 “physical pixels”. As I was poking around I found an old CSS zoom property here: http://reference.sitepoint.com/css/zoom that for some reason works on mobile safari. Add a media query for 2x density screens, and viola! Your images now display at physical pixel dimensions on the iPhone 4 and 4S.

Here’s what the CSS looks like:

@media screen and (-webkit-min-device-pixel-ratio: 2) {
     img {
          zoom: 50%;
     }
}

Awesome hacks.

Happy img scaling.