A method for generating an image signal of an object by way of a display device including a display screen including light-emitting diodes arranged in rows and columns, the method including displaying a series of images each representing one respective pattern leading to the emission of a light beam that may be identical or different to the preceding light beam depending on whether the displayed pattern is identical or different to the pattern of the preceding image, acquiring a plurality of measurements of the power consumption of the display device during the display of each image while each light beam scans a surface of the object, acquiring a plurality of measurements of the variations in the power consumption of the display device and delivering an image signal of the object.