Screenshots of an iPhone showing the broken background and the working background
Updated: 22nd Feb 2010
I experienced a slightly odd bug in the latest version of mobile Safari on iPhone where it was shrinking large background images applied via CSS to fit within the confines of the screen. Not finding anyone else who has written about this problem I thought I’d share my findings.

Firstly a bit of background, the company I am working for at the moment recently released a real-time CSS editor (of sorts) which I built that allows customers to style their sites using nothing more than uploaded images and some UI controls – for more details on that you can see a video of it in action on this blog post and some of the amazing results that customers have been able to achieve with it.

Yesterday one customer reported an issue where a large background image (1800×2520) was being shrunk on the iPhone. I did quite a lot of investigation and to cut a long-ish story short I discovered that there is a tipping point where the total pixel-area of an image causes mobile Safari to resize the image. This tipping point appears to be at 2,000,001 pixels.

Read on for a bit more of a breakdown of my experiment results.
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