Hi
You could modify the buffered image so that it uses a supported pixel format. Which kind of PNG do you use? "BytesPerPixel 8" is weird.
Edit.: You're probably using grayscale or truecolor PNGs with 2 bytes per sample. You can simply drop the least significant byte so that it uses 1 byte per sample, i.e 4 bytes per pixel which is supported by JOGL.