Method and apparatus for calibrated digital printing using a four by four ...

[54] METHOD AND APPARATUS FOR

CALIBRATED DIGITAL PRINTING USING A
FOUR BY FOUR TRANSFORMATION
MATRIX

[76] Inventors: William J. Lloyd, Court 5 #203

5-27-20 Koenji-Minami, Suginami-ku, Tokyo 166, Japan; John D. Meyer, 29360 Bird Rd., Tracy, Calif. 95376; King-Wah W. Yeung, 10129 Mello PL, Cupertino, Calif. 95014

[21] Appl. No.: 53,638

[22] Filed: Apr. 27,1993

[51] Int. CI.6 H04N 1/50; H04N 1/56;

H04N 1/60

[52] U.S. CI 358/501; 358/504; 358/518;

358/519; 358/523

[58] Field of Search 358/504, 406,

358/501, 401, 523, 518, 519, 296; 356/402, 405; 250/226; 395/109

[56] References Cited

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4,727,425 2/1988 Mayne et al ; 358/523

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OTHER PUBLICATIONS

"Low-Cost Color Hardcopy Now Possible", Machine Design, May 24, 1990, pp. 62-63. Clapper, F. R., "An Empirical Determination of Halftone Color-Reproduction Requirements", Technical Association of the Graphic Arts, Thirteenth Annual Meeting, Jun. 12-14, 1961, pp. 31-41.

Primary Examiner—Scott A. Rogers

[57] ABSTRACT

A Self Calibrating Color Printer. The present invention enables color printers to accurately reproduce color images despite variations in ink, paper or the printing system. The calibrated printer includes a movable optical sensor assembly which first calibrates itself by measuring an included known color gamut located within the movement range of the sensor assembly. Once calibrated, the sensor assembly measures a color print test pattern newly printed by a movable color print head of the printer. An analog-to-digital converter transforms electrical signals from the sensor assembly to sensor values in digital form, enabling a printer control processor to process the measured data, thereby producing two look-up tables stored in memory: first, a color correction look-up table which adjusts image color values to account for the ink/paper variations, and second, an error diffusion look-up table which spreads color value errors at a given pixel to its neighbors. Once the printer control processor creates these two look-up tables and, the printer is able to process image data, and control the print head via its associated print head electronics to faithfully reproduce the image onto paper. The moveable sensor and associated gamut and print test pattern of the present invention provide an accurate, inexpensive and durable apparatus for calibrating any digital color printer. The Self Calibrating Color Printer disclosed and claimed in this patent applications provides an advanced, accurate and relatively inexpensive instrument for true reproduction of detailed color images.

13 Claims, 5 Drawing Sheets