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Convert .png to PVRTC * on * iPhone

Is there a standard mechanism or a well-known library that will convert .png images to compressed PVRTC textures on the iPhone itself (not during development using standard tools in OS X).

I have a number of .png textures in my application, but replacement is a problem. I would like to create PVRTC variants of .png on the device if the available memory is low when the application starts (or, possibly, when the application first loads).

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I did not see any information on the network about how to create PVRTC images manually, and as far as I know, support for this support built into the iPhone is not required (and it would not be necessary to read PVRTC files).

For most applications, it makes no sense to include or create both versions of files. Under optimal conditions, PVRTC versions should be practically indistinguishable from PNG versions and are truly “pre-processed” versions of files optimized for direct streaming to video memory.

As a rule, it’s best to look at all your images and make decisions about how to pack the image in the best way to balance storage and quality of memory for all users, and not just in special situations with limited memory.

A few things to consider (apologies if this is excess knowledge):

  • PVRTC files can have problems with complex alpha mixed images, as preprocessing can cause unsightly artifacts along mixed edges.
  • Opaque PNG files must have their own alpha channel in the original image (memory and overhead storage).
  • For images with a limited range of colors, reduce the image from PNG32 to PNG16 or PNG8 to save memory on disk.
  • If this is for OpenGL-based programs, consider using an advanced version of Texture2D (for example, Cocos2D) that supports alternative pixel formats such as 565 and 4444. This can significantly reduce the overhead of a graphics card with minimal impact on image quality, carefully choosing quality A pixel format that matches the color balance in the original image.
  • In addition, for OpenGL-based programs, avoid separate images (320x480) for the background, as this will result in a 512x512 texture in memory for each of them. Break the image into smaller parts or create a 512x512 image and fill the extra space with other images to load only one texture.
  • As with everything, first focus on the largest images to get the biggest bang for the buck.

It is also worth noting that since your application will only work (except for system applications), the only real memory overhead will be a limited amount of "disk space". Making a second copy of all image files will actually work against you, not help.

Barney

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I would be careful in believing that this will help you. Once you link to images once, that is, upload them to UIImage, the iPhone will start caching your png, whether you like them or not. Squeezing them will not serve you well to achieve what you are looking for here, in my opinion.

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If you want to compress images in PVR on iOS, you can consider the OpenSceneGraph pvr plugin:

http://www.openscenegraph.org/projects/osg/browser/OpenSceneGraph/branches/OpenSceneGraph-3.0/src/osgPlugins/pvr/ReaderWriterPVR.cpp .

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