A method of generating a map for use in a laser engraving process using a laser engraving apparatus , the method comprising the steps of: providing a plurality of calibration images having mutually different, uniform grayscale values between a minimum grayscale value and a maximum grayscale value, engraving the plurality of calibration images on a predefined substrate surface of a substrate by varying only a single laser parameter of the laser engraving apparatus , measuring a colour value of each of the engraved calibration images and of the predefined substrate surface in a colour space, the method being characterized in that it comprises the steps of: calculating a plurality of colour space distances between each of the colour values of the engraved calibration images and the colour value of the substrate surface , associating each of the colour space distances with one of a plurality of predefined laser parameter values between a minimum laser parameter value and a maximum laser parameter value, in accordance with the grayscale values and/or the colour distances of the corresponding calibration images, determining a relationship between the colour space distance and the laser parameter value based on the association, and generating the map by determining a colour space distance for a grayscale value of an input image, determining a corresponding laser parameter value based on the determined relationship, determining a grayscale value of an output image based on a predefined relationship between the determined laser parameter value and the grayscale value of the output image, and mapping the grayscale value of the input image to the grayscale value of the output image. providing a plurality of calibration images having mutually different, uniform grayscale values between a minimum grayscale value and a maximum grayscale value, engraving the plurality of calibration images on a predefined substrate surface of a substrate by varying only a single laser parameter of the laser engraving apparatus , measuring a colour value of each of the engraved calibration images and of the predefined substrate surface in a colour space, calculating a plurality of colour space distances between each of the colour values of the engraved calibration images and the colour value of the substrate surface , associating each of the colour space distances with one of a plurality of predefined laser parameter values between a minimum laser parameter value and a maximum laser parameter value, in accordance with the grayscale values and/or the colour distances of the corresponding calibration images, determining a relationship between the colour space distance and the laser parameter value based on the association, and generating the map by determining a colour space distance for a grayscale value of an input image, determining a corresponding laser parameter value based on the determined relationship, determining a grayscale value of an output image based on a predefined relationship between the determined laser parameter value and the grayscale value of the output image, and mapping the grayscale value of the input image to the grayscale value of the output image. <EOS>