To apply this filter to a colour image img we call. sepia_img = img.dot(sepia_matrix.T) Since sepia matrix rows do not have unit sums, once the full sepia image is constructed, we need to rescale the ...

Therefore, using RGB vectors to represent colour, one could view an image as 3 matrices, each one corresponding to an RGB channel. It may also help to view them as stacked in the 3rd dimension. Since ...