High Resolution and the iPad

Or Vector versus Raster and why you shouldn’t always take the easy option.

This week has seen a number of articles criticising reading apps including this one from Business Insider, relating to the iPad (and in their case) looking at problems with Adobe’s Digital Publishing Suite (which is a good product if you have the resources to create new editions from scratch specifically for the mobile tablets). Business Insider are essentially saying that either you end up with ‘pixelated junk’ (their words), or when you update to the newer version, you end up downloading a huge amount of extra content (in the case of the WIRED App from Conde Nast, using Adobe DPS), 200 MB more to download *per edition*.

Although that particular post talks about the Adobe product specifically, this problem affects a lot of digital publishing solutions.

There are two ways to store and display digital pages. The first is as a raster image. For those unfamiliar with rastering, this is your garden variety image on the web (jpegs, gifs, pngs, etc), with nearly all web images outside of Flash being raster based – they essentially have a fixed resolution, and represent an image with a grid of pixels.

So, when the new iPad came out, the improved screen resolution made the pixels more visible, giving the text in particular a blurry or a more jagged look. This can be fixed making the image higher resolution – but this quadruples the number of pixels in the page image, and so makes it much larger to download.

The second way is to store the page text in vector format. This stores the information about what the text is, and works out how to display that as pixels at a later point. Because it can render the text to match the screen resolution, it can display it with perfect sharpness, no matter how high or low resolution the screen is.

Creating these images on the device means more work for the device to do, and hence, could potentially be too slow for the user – but as it turns out, that’s not a problem. Each generation of the iPad (and other devices) get faster and faster, so, while the images they generate are much larger in the case of the iPad 3, it’s also a much faster device than the iPad 1, for instance, and can render the images without performance issues.

This is harder to set up – handling vector-based content is more difficult than using simple images throughout. But as screen resolutions continue to improve, and users’ patience for download times continues to shorten, we’re increasingly glad of having made this design choice!


Categories: Apps, Experts, iPad

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