Patent ID: 8102591

Claim:
A display apparatus, including: at least one digital micro-mirror device having a plurality of micro-mirror elements; at least one electromagnetic radiation source arranged to illuminate each digital micro-mirror device and each digital micro-mirror device being arranged to generate a desired image and a test image; at least one micro-mirror element of the at least one digital micro-mirror device being arranged to reflect electromagnetic radiation within one of at least two pathways; at least one electromagnetic radiation measurement arrangement associated with at least one of the at least two pathways and arranged to measure electromagnetic radiation associated with the test image on that pathway; and at least one comparator arrangement associated with the electromagnetic radiation measurement arrangement arranged to compare a predetermined value for electromagnetic radiation associated with the test image on a pathway with a value of electromagnetic radiation associated with the test image measured by the electromagnetic radiation measurement arrangement wherein generation of the test image is arranged such that it is not perceived by an observer whilst viewing the desired image.