How much support for PNG does GraphApp have?
GraphApp’s support for PNG is not complete. It can load PNG images in any format, but it can only represent 8 or 32 bits per pixel in the GraphApp Image structure. Therefore, if the PNG image you are loading contains 16 bits in any one data channel (such as 16 bit greyscale, or 48 bit colour) you will only see the top 8 bits in those data channels.