Patent ID: 8842145

Claim:
A method of calibrating a substrate marking apparatus comprising the steps of: providing a radiation source operable to produce radiation at two or more distinct wavelengths; and means for controlling emission of radiation from the radiation source so as to controllably irradiate selected areas of the substrate with desired quantities of radiation from the radiation source so as to mark said substrate in a desired manner wherein the radiation source is operable to emit radiation at a first wavelength to selectively activate irradiatable areas of the substrate for colour change and radiation at a second wavelength to effect a colour change of the previously irradiated areas of the substrate; and irradiating the substrate with a sequence of wavelengths and intensities to generate a test pattern; validating the test pattern by comparing it to a predefined calibration image; and if the test pattern is not substantially the same as the calibration image, adjusting the apparatus and generating a further test pattern by irradiating the substrate with an adjusted sequence of wavelengths and intensities to generate the further test pattern until the test pattern is substantially the same as the calibration image.