Color imager bar based spectrophotometer for color printer color control system

• US 20020191183A1
• Filed: 05/22/2001
• Published: 12/19/2002
• Est. Priority Date: 05/22/2001
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Tandon, Jagdish C., Mestha, Lingappa K.
• Granted Patent: US 6,621,576 B2
• Time in Patent Office: Days
• US Class Current: 356/320
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0208 using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• CPC Class Codes: G01J 3/501 Colorimeters using spectrally-selective light sources, e.g. LEDs
• CPC Class Codes: G01J 3/51 using colour filters
• CPC Class Codes: G01J 3/513 having fixed filter-detector pairs
• CPC Class Codes: G01J 3/52 using colour charts
• CPC Class Codes: G01J 3/524 Calibration of colorimeters
• CPC Class Codes: G03G 15/01 for producing multicoloured copies colour correction in photography G03C; colour correction in printing plate production
• CPC Class Codes: G03G 2215/00063 Colour
• CPC Class Codes: G03G 2215/00067 on recording medium
• CPC Class Codes: H04N 1/6033 using test pattern analysis H04N1/6055 takes precedence

Abstract

An improved and lower cost color spectrophotometer, especially suitable for on-line color printer color control systems, incorporating a low cost commercial imaging chip, which normally only forms part of a three row, three color, document imaging bar used for imaging documents in scanners, digital copiers, or multifunction products, having multiple photo-sites with at least three different color filters in three rows. This multiple photo-sites chip may be modified to also provide unfiltered photo-sites. This spectrophotometer may have a substantially reduced number of different LED or other spectral illumination sources, one of which may be for white light, yet provide multiple spectral data outputs from the differently filtered photo-sites being simultaneous illuminated by the light reflected from a color test target area which is being sequentially illuminated by the respective limited number of LEDs, enabling broad spectrum information and color control.

Claims

1. A color correction system for a color printer having an output path for moving printed color sheets, including printed test sheets with printed color test patches, in which a spectrophotometer is mounted adjacent to said printer output path for sensing the colors printed on said printed color test patches on said printed test sheets as said printed test sheets are moving past said spectrophotometer in said output path, and in which a limited plurality of illumination sources are provided for sequentially illuminating said color test patches with different illumination spectra, and a photodetector system for providing electrical output signals in response to the color of said test patches from said sequential illumination of said test patches by reflection of said illumination of said color test patches by said illumination sources, to illuminate said photodetector system;

said photodetector system having a multiplicity of simultaneously illuminated photo-sites including at least three different sets of simultaneously illuminated photo-sites having at least three different spectral responses providing at least three different said electrical output signals.

2. The color correction system of claim 1, wherein said photodetector system comprises at least one low cost commercial photodetector chip designed for a part of a document color imaging bar and having at least three rows of small closely spaced photo-sites with integral red, green and blue color filters respectively, to provide said at least three different spectral responses with at least three different said electrical output signals in parallel.

3. The color correction system of claim 2, wherein said photodetector chip is modified to add a plurality of said simultaneously illuminated photo-sites which are broad spectral responsive photo-sites providing a fourth spectral response different from that of said photo-sites with integral red, green and blue color filters, and wherein at least one of said limited plurality of illumination sources produces white light.

4. The color correction system of claim 2, wherein said limited plurality of illumination sources comprises less than approximately five LEDs providing a corresponding limited number of different spectral illuminations, and a sequential actuation circuit for said LEDs.

5. A low cost broad spectrum spectrophotometer including a limited plural number of illumination sources with different spectral illuminations arranged to illuminate a color test target area, a sequential actuation circuit for sequentially actuation of said limited plural number of illumination sources, and at least one low cost commercially available photodetector chip at least a portion of which is arranged to receive reflected light from said illuminated color test target area, said photodetector chip being a component part for a document color imaging bar, and said photodetector chip having at least three rows of. small and closely spaced multiple photo-sites with different respective color filters, of which at least a portion of each of said three rows of multiple photo-sites are simultaneously exposed to said reflected light from said illuminated color test target to provide said at least three different spectral responses with at least three different electrical output signals.

6. The low cost broad spectrum spectrophotometer of claim 5, wherein said limited plurality of illumination sources comprises less than approximately five LEDs providing a corresponding limited number of different spectral illuminations.

7. The low cost broad spectrum spectrophotometer of claim 5, wherein said limited plurality of illumination sources includes one broad spectrum white light illumination source.

8. The low cost broad spectrum spectrophotometer of claim 5, wherein said spectrophotometer is a part of a color control system of a color printer with a printed sheets output path and is mounted adjacent to at least one side of the printed sheets output path of said color printer and said illuminated color test target area is printed on a printed color test sheet printed by said printer and moving past said spectrophotometer in said printed sheets output path of said color printer.

9. The low cost broad spectrum spectrophotometer of claim 5, wherein said limited plurality of illumination sources comprises less than approximately five LEDs providing a corresponding limited number of different spectral illuminations, which LEDs are mounted arrayed around said photodetector chip and spaced from said color test target area to angularly illuminate said color test target area at substantially the same angle from opposing directions.

10. The low cost broad spectrum spectrophotometer of claim 5, wherein said limited plurality of illumination sources are mounted in a substantially circular pattern surrounding said photodetector chip to define a central axis and are spaced from said color test target area to angularly illuminate said color test target area at substantially the same angle from opposing directions, and wherein said photodetector chip is aligned with said central axis, and wherein a lens system is mounted on said central axis for transmitting said illumination reflected from said color test target area to a limited area of said photodetector chip containing at least a portion of each of said three rows of said multiple photo-sites.

11. The low cost broad spectrum spectrophotometer of claim 5, wherein said at least one low cost commercially available photodetector chip is normally a component part for a document color imaging bar, having at least three rows of small closely spaced photo-sites with integral red, green and blue color filters respectively to provide said at least three different spectral responses with at least three different electrical output signals thereof in parallel.

13. The method of broad spectrum color measurement of a color test area of claim 12, wherein said limited plural number of different spectra illuminations is provided by less than approximately five LEDs providing a corresponding limited number of different spectral illuminations of said color test area.

14. The method of broad spectrum color measurement of a color test area of claim 12, wherein one of said limited plural number of different spectra illuminations is broad spectrum white light.

16. The low cost broad spectrum spectrophotometer of claim 15, wherein said limited plural number of different spectra illuminations is provided by three to four different LEDs providing a corresponding limited number of different spectral illuminations, and a sequential actuation circuit for said LEDs.

17. The low cost broad spectrum spectrophotometer of claim 15, wherein said multi-photo-site photodetector is a low cost commercial photodetector chip which is normally a component part of a document color imaging bar, having at least three rows of small closely spaced photo-sites with integral red, green and blue color filters respectively to provide said at least three different spectral responses with at least three different electrical output signals thereof in parallel.

18. The low cost broad spectrum spectrophotometer of claim 15, further including color test area displacement insensitive optics means.

20. The low cost spectrophotometer of claim 19, further including plural different spectra LED illuminators and a sequential LED actuating circuit.

21. The low cost spectrophotometer of claim 15, further including a lens system and wherein said photodetector chip is oriented substantially in the plane of the image of said reflected light through said lens system.

12. A method of broad spectrum color measurement of a color test area comprising sequentially illuminating said color test area with a limited plural number of different spectra illuminations and sequentially measuring the reflected illumination from said sequentially illuminated color test area by applying said reflected illumination simultaneously to multiple photo-sites of a multi-photo-site photodetector, which simultaneously exposed multiple photo-sites comprise at least three different sets of photo-sites with three different illumination responsive spectral responses and at least three different illumination responsive signal outputs thereof.

15. A low cost broad spectrum spectrophotometer comprising means for sequentially illuminating a color test area with a limited plural number of different spectra illuminations, and means for sequentially measuring the reflected illumination from said sequentially illuminated color test area by applying said reflected illumination simultaneously to multiple photo-sites of a multi-photo-site photodetector, which simultaneously exposed multiple photo-sites comprise at least three different sets of photo-sites with at least three different illumination responsive spectral responses and three different parallel illumination responsive signal outputs thereof.

19. A low cost spectrophotometer comprising a broad spectrum white light illuminator for illuminating a color test target area and at least one multi-photo-site photodetector, wherein said multi-photo-site photodetector is a low cost commercial photodetector chip which is normally a component part of a document color imaging bar having at least three rows of small closely spaced photo-sites with respective red, green and blue color filters to provide at least three different spectral responses of at least three different electrical output signals, said multi-photo-site photodetector being optically positioned to receive reflected light from said color test target area illuminated by said broad spectrum white light illuminator.