1-channel is taken as Y 8 (greyscale) 2-channel is taken as YA 8:8 (greyscale and transparency) 3-channel is taken as RGB 8:8:8 4-channel is taken as RGBA 8:8:8:8 (colour with transparency) (y x channels), where channels is 1, 2, 3, or 4, as listed above. [#out] only : write PNG to file [#in] only : read PNG from file. supported number of channels are listed below.