Automatic convergence system for color video projector

A method for correcting convergence of a plurality of light images projected on a screen in mutual superposition from a plurality of image projectors comprising the steps of:

• causing each projector, in sequence, to project an identical test pattern comprising a plurality of discrete pattern units, said tests pattern being substantially coextensive with the light images projected on the screen and comprising an array of discrete pattern illumination units each of which is characterized by a substantially uniform variation of light intensity over the unit, successively define on said array a plurality of sensor patterns respectively representing said projected test patterns, said sensor patterns each comprising a plurality of discrete sensor pattern units,
• locating and storing positions of predetermined points on each unit of each of said sensor patterns,
• comparing positions of the predetermined points on each unit of a first one of said sensor patterns with positions of the predetermined points on corresponding units of a second one of said sensor patterns, and
• determining convergence correction error values based upon said comparing of positions.

A color projecting system comprising:

• first, second and third cathode ray tube projectors,
• a screen,
• lens means for projecting converging images of mutually different colors from said projectors in mutual superposition on said screen,
• means for generating a test pattern comprising an array of mutually discrete test pattern units wherein each said pattern unit comprises an area of light having an intensity that smoothly varies across the area,
• means for causing said projectors to sequentially project said test pattern on said screen as first, second and third mutually identical and sequentially projected patterns,
• means including sensor means fixedly mounted with respect to said projectors for finding the locations of the centroid of each unit of each said first, second and third projected patterns,
• means for comparing locations of the centroids of units of said first projected pattern with locations of corresponding centroids of units of each of said second and third projected patterns to develop error signals, and
• means responsive to said error signals for displacing the projected images of two of said projectors in a sense to decrease said error signals.