Patent ID: 7224377

Claim:
A method of controlling a thermal print head to print a digital image, the digital image being composed of lines of multi-bit pixels, the print head having a plurality of thermal resistors, adapted to be simultaneously addressed in parallel by a corresponding plurality of shift register elements, the print head being pulsed a plurality of times to print one line of the image, comprising the steps of: a) providing a table of additive complement values, one additive complement value for each of the possible values of a multi-bit pixel; b) successively adding a complement value to each of the pixel values in a line to obtain a number of sums corresponding to the number of pixels in the line, each sum having an overflow bit that is either “0” or “1”, depending on the respective pixel value; c) loading the overflow bits of each sum in the line to the shift register elements and applying a printing pulse to the print head; d) repeating steps b) and c) for each complement value in the table; and e) repeating steps b) to d) for each line of multi-bit pixels in the image.