1. An image processing method for processing a pixelised image, the method comprising the steps of: analyzing pixel data representative of said pixelised image in a colour space and based thereon determining a gray axis defined as a straight line connecting a white point with a black point; determining for each pixel of said pixelised image the shortest distance to said gray axis; forming a cumulative histogram by plotting for the pixels of said pixelised image a value of said shortest distance versus a cumulative pixel count being the number of associated pixels having at least said value of said shortest distance; and analyzing a relationship between the pixels in said cumulative histogram and based thereon judging whether said pixelised image is to be processed as a monochrome image or a colour image.