This function converts the image to a duochrome palette image. Duochrome images are similar to monochrome images, since they are displayed only in two colours. Therefore you will be asked before the conversion whether the image is to be rasterized or dithered.
During conversion from a colour or greyscale image to a duochrome palette image some image information will be lost.
After the conversion of the raster image frame you can replace both palette colours used in the duochrome palette image by any other colours.
