CgBI

CgBI is the informal name of a PNG-like image file format developed by Apple. It is also called iOS optimized PNG, and other similar names.

It is not compatible with PNG. PNG decoders that don't support it should fail completely, due to an unknown "critical chunk".

Identification
Files begin with the standard 8-byte PNG signature. A private "CgBI" chunk appears before the "IHDR" chunk. Usually or always, ASCII "" appears at offset 12.

Software

 * XnView
 * Farbfeld Utilities: pngff
 * pngdefry (C)
 * https://github.com/briancollins/PNGNormalizer (C)
 * https://github.com/jongwook/libpng (libpng patch)
 * https://github.com/jakubknejzlik/cgbi-to-png (CoffeeScript)
 * https://github.com/swcai/iphone-png-normalizer (Ruby)
 * Pincrush (encoder)