A two dimensional spatial radiation modulator rotated about a rotation axis to modulate components of an incident radiation beam to encode the beam. The modulator includes sub-regions in a first annular segment being patterned to form a pair of radiation filters having substantially complementary modulation functions. The pair of radiation filters produces a first encoded component with a characteristic determined by the relative intensities of radiation from the beam incident on the pair of filters. The modulator also includes sub-regions in a second annular segment being patterned to form a filter that produces a second encoded component with a characteristic determined by the total intensity of radiation from the beam incident on the filter.