CODEWITHSUNDEEP
iosimageretina-display
soleil
soleil

Reputation: 13135

iOS apps - why include both @2x and low-res images?

This has been bugging me for a while. I don't understand why one should include low-res images. If a 3GS, for example, can't find the low-res image, it just uses the @2x version anyway and displays it at it's native resolution. So why add to the filesize of your app by including all the half-res images?

Upvotes: 14

Views: 9724

Answers (5)

Duncan C
Duncan C

Reputation: 131503

Halley had it right. The system does not automatically downsample @2x images to non-retina size, and it shouldn't. The 3Gs does not have enough memory to load retina images. It will likely choke your app and cause it to exit with an out of memory error.

The problem gets even worse with the iPad 1. The iPad 1 has very low memory relative to it's screen size, and if you tried to make it load retina sized images, it would choke and die very quickly.

To scale an image the system has to load it at full size and do a complex scaling operation each time it draws it. It's the worst of all possible worlds - slower, 4x as much memory, and the images don't look as good.

Upvotes: 19

Chad Schultz
Chad Schultz

Reputation: 7860

The other posters mentioned some excellent points, but here's one more for posterity: as mentioned several times in http://developer.apple.com/library/ios/#DOCUMENTATION/UserExperience/Conceptual/MobileHIG/IconsImages/IconsImages.html#//apple_ref/doc/uid/TP40006556-CH14-SW1, a 2x image may be more detailed. In other words, the low-res image isn't simply a scaled-down version of the 2x image; the 2x image may contain details not present in the smaller image.

Upvotes: 1

Jason Fuerstenberg
Jason Fuerstenberg

Reputation: 1351

@2x filenames are intended for Retina Display enabled devices.

If you intend to use them for display on the iPhone 3GS make sure to properly test that they look as acceptable as the low-res image Apple wants you to use.

Upvotes: 0

CStreel
CStreel

Reputation: 2642

The reason being, is when images are scaled up if there is no @2x available, they can become pixelated and blurry, so you would prob think that making the original image twice as big would solve the problem.

But no, because the retina devices would still scale it up (in my experience) and non retina devices would display the image incorrectly.

It's got a lot to do with the quality standards Apple wants for the Apps on their app store

Upvotes: -1

Greg Hewgill
Greg Hewgill

Reputation: 994857

In most cases, you can make an icon look better when created at the low-res resolution, instead of having the system scale it. If you don't care too much about how your icons look when scaled, then using the @2x version only is probably fine.

Upvotes: 4

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