Does anyone know if there exists any code for PNG image compression in OpenCL?
AFAIK not.
But libPNG depends on zlibs deflate algorithm which is also used for zip compression and if you look here http://www.donanimhaber.com/ekran-karti/haberleri/AMD-GPUlar-ve-Fusion-icin-WinZip-165de-donanimsal-...
They are working on a OpenCL accelerated DEFLATE implementation.
I think after this you will find several OpenCL DEFLATE libs, which you then can use instead of zlib.
edit: but there is already a libjpeg built on opencl https://code.google.com/p/jpeg-opencl/
