png_set_dither() shall set transformation to dither file to 8-bit. For the given palette with num_palette number of colors, the number of colors in the palette shall be reduced to fit in "maximum_colors" if the palette is larger than maximum_colors. If supplied, the histogram is used to get better results of the reduced palette. For reducing the number of colors in palette, full_dither must be set to 0. If full_dither is set to 1, dithering cube shall be setup for RGB images to reduce the RGB file to a paletted file.