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(12) United States Patent
Biernath et al.
(io) Patent No.: (45) Date of Patent:
US 7,418,202 B2 Aug. 26, 2008
(54) ARTICLE HAVING A BIREFRINGENT SURFACE AND MICROSTRUCTURED FEATURES HAVING A VARIABLE PITCH OR ANGLES FOR USE AS A BLUR FILTER
(75) Inventors: Rolf W. Biernath, Wyoming, MN (US);
Robert L. Brott, Woodbury, MN (US);
William Ward Merrill, White Bear
Lake, MN (US); John S. Huizinga,
Dellwood, MN (US); William B. Black,
Eagan, MN (US)
(73) Assignee: 3M Innovative Properties Company,
Saint Paul, MN (US)
( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 479 days.
(21) Appl.No.: 11/196,887
(22) Filed: Aug. 4, 2005
(65) Prior Publication Data
US 2007/0031140 Al Feb. 8, 2007
An optical low pass filter or blur filter, and method of making the filters, using an article having a birefringent surface for refracting incoming light when used with an image sensor. The birefringent surface of the article, such as a film, is structured or tilted such that, when the blur filter is placed within an optical path between a lens and the image sensor, the birefringent surface causes refraction of a light signal in the optical path into multiple light signals each being incident upon different sub-pixels within the pixels in the image sensor to prevent or reduce artifacts, such as undesirable color moire effects, in the resulting digital image. The structures on the surface have a variable pitch or angles. The variable pitch can include a periodic, aperiodic, or quasi-aperiodic pitch, to reduce diffractive artifacts in the resulting image.
19 Claims, 16 Drawing Sheets
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* cited by examiner