Hi, Quick test showed that Castle Game Engine and view3dscene work OK with libpng 1.6. Various testing images (with colors encoded in different ways), as well as deliberately wrong images, are handled correctly.
Tested with libpng16-16 in current Debian testing (1.6.21-2). The necessary change in CGE is just a 2-line addition of if PngLibrary = nil then PngLibrary := TDynLib.Load('libpng16.so.16', false); to src/images/castlepng_dynamic.inc . Nothing else is needed. I committed this upstream (taking also the occasion to improve comments and search order there) in https://github.com/castle-engine/castle-engine/commit/3abd42911bd85bf3782d0fac16439d0ab301d11a . For testing, you can simply comment out loading other libpng versions, to make sure that only libpng 1.6 is picked up. (In engine version from GitHub, you would also undefine CASTLE_PNG_USING_FCL_IMAGE in src/base/castleconf.inc, to avoid using the native Pascal version.) Regards, Michalis