Last Updated Jun 14, 2010 1:03 PM EDT
In the past, print and screen have had significantly different resolutions. Photo printers, for example, have high enough resolution that most people will aim for 300 dot-per-inch (dpi) images. When the image prints, you have something that looks more or less like a photo. Will the quality stand up to magnified scrutiny? No, but an unaided eye will see relatively smooth tones and sharp edges.
Regular computer displays, on the other hand, typically came in at either 72 or 96 pixels-per-inch (ppi). It doesn't look like print, but it's been good enough for most people who didn't expect more. That provided a big advantage to developers and designers. They could reduce the resolution of images and, therefore, the image file sizes, because the screen won't display the extra visual information. For example, I took a digital photo I had on hand and saved two versions: one at 300 dpi and the other at 96 dpi, both with the same print size and little compression. They were indistinguishable. However, there was one big difference: the latter was 213KB in size, while the higher resolution one was 1.3MB -- a six-fold increase. You can see below how the two versions compare when displayed the same way:
On a desktop or laptop with hundreds of gigabytes of storage, that's relatively unimportant. But when you're talking about downloading apps with image files over a 3G network, especially if the carriers is AT&T (T) in the U.S. or O2 in the U.K., which have both scrapped so-called unlimited data packages (even though AT&T, at least, already had a 5GB cap in practice), size matters.
The small screen of the iPhone 4 means that images are displayed physically smaller. So I cropped the image appropriately and set it for the associated 326 ppi resolution. The JPEG was now 233KB, or about 3 inches by 2 inches. For a similar size screen at 96 ppi, the image file would be about 51KB. For an occasional image, this may not be a problem. Applications such as games and electronic magazines could require many such images, multiplying the size effect. All this gets bundled into the app, which now becomes bigger and whose download takes up more of the allowed monthly total.
It's a visually spectacular change for consumers, but developers will have to reexamine how many images they use and the amount of compression they can get away with. Also, it's not just about apps. Web sites that want to appeal to iOS users will have to consider creating separate sites with higher resolution graphics on everything -- not just images, but all graphic elements, including buttons, navigation tools, banners. Advertisers will have to create new resolution versions of banner and display ads. Advertising networks will need to distribute the appropriate type for the user's display resolution.
That's a lot of work on the part of many to shift to higher resolution displays. Given that the new iPhone is due out at the end of the month, a lot of high tech and media companies will have to move quickly.
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