Devices & Pixel Ratios
The idea of a 720p display on a phone is the norm, with 1080p probably coming over the next year or 2. With other devices like the iPad and iPhone with huge pixel counts, the use of images that exploit screens that have a pixel ratio of 2 is something everyone should look into doing.
In my device selection post a few months back, i only had 2 HD phones, no i am not going to use the term RETINA as a standard. These 2 phones were the iPhone and the Galaxy nexus, both had pixel ratios of 2. Since then, tablets and phones have appeared with similar specifications and more, such as “The New iPad”. In terms of device selection, if you have no plans to support HD images, then this is slightly less important, but for those that are, device selection can be slightly tricky.
The Samsung Galaxy Tab 7.7 for example, has a 1280x800 screen, yet uses a pixel ratio of 1. More content, but lack of HD images, so one to avoid. The iPad 3, clearly the favourite, but the big thing coming out is the Nexus device from Google. This device will be sold everywhere, use Chrome as the default browser and have a PR of 2, giving a good device to test those lovely images on.
For phones, the G Nexus, iPhone, HTC One X, Galaxy S3 are all good choices, though the iPhone has the highest PPI, followed closely but the Galaxy Nexus, so they could be your 2 bets choices.
Below we have a couple of images showing the difference in News Banner, this is a version of the site that has the enhancement and a version that doesn’t, the second image is the HD image.
If you are going to make you images HD, then picking the right device is important to test on, the pixel ratio is ultimately set by the manufacturer of the device, so high resolutions screens are not always going to be supported. For hybrid devices with strange ratios, it might be worth looking at your site traffic and seeing which devices are going to improve from getting HD images, only time what tell what frankenstein creations will be hitting the market soon with Windows 8 and Jelly Bean.