ios - Xcode blowing up PNG size and ignoring Compress PNG = NO flag?

Question

Currently, my Assets.xcassets folder is ~13MB with all images for my application. However, when I archive my app the Assets.car that results is closer to 33MB. When using iOSAssetExtractor as described here: What contributes to the size of assets in an IOS App and how can I shrink this? the issue appears to be that the PNGs are blowing up in size when they are "compressed" by Xcode. Many PNGs are 2-3x the size they were before going through the archiving process. This is a common problem that is referenced in multiple places.

The usual solution as referenced here: XCode png compression issue and here: https://imageoptim.com/xcode.html appears to be setting "Compress PNG Files" to No in build settings. This skips Xcode's unpacking and recompression of assets to avoid the asset size bloat that can be experienced. However, this doesn't appear to be working currently and might have stopped working in Xcode 7.3. There is a thread on this in the Apple forums here: https://forums.developer.apple.com/thread/43372 . However, the accepted solution appears to be changing the file type in the inspector to data which works for PNGs in a resources folder but does not appear to be an option for PNGs stored in an xcassets folder.

Note: I've also tried setting "Remove Text Metadata from PNG Files" to no as well with no success.

Can anyone recommend a solution for how to fix this issue in the current (7.3) version of Xcode so that my Assets.car file does not end up 2-3x larger than expected?

Answer 1

The specific problem of PNG sizes getting much larger seems to have been an Apple bug which appears to be addressed now. But, the more general problem of shrinking down each PNG to the smallest possible size is something that can still be solved more effectively. If you are interested in reading about a new delivery codec that can squeeze every last byte out of each PNG, then please have a look at this iOS framework.