Color image-processing apparatus

• US 4,745,467 A
• Filed: 10/24/1986
• Issued: 05/17/1988
• Est. Priority Date: 10/28/1985
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Kawakami, Haruko, Yamamoto, Naofumi, Sekizawa, Hidekazu, Saito, Tutomu
• Primary Examiner(s): Britton, Howard W.
• Application Number:
  US06/923,045
• Time in Patent Office: 571 Days
• Field of Search: 358/80, 358/75, 358/78
• US Class Current: 358/523
• CPC Class Codes: H04N 1/401 Compensating positionally unequal response of the pick-up or reproducing head H04N1/403 takes precedence
• CPC Class Codes: H04N 1/6016 Conversion to subtractive colour signals

Abstract

A color copier comprises a color line-image sensor, a matrix circuit, and a color conversion circuit. The color line-image sensor reads a color document, to output a plurality of fundamental color signals. The matrix circuit converts the fundamental color signals into a brightness signal and two color-difference signals. The color-conversion circuit converts the brightness and color difference signals into ink-amount control signals for controlling the amounts of color inks used in a color printer. In order to decrease the memory capacity of the color conversion circuit and faithfully reproduce dark colors, a nonlinear conversion circuit is provided at the preceding stage of the matrix circuit. The nonlinear conversion circuit is arranged to increase a change in level of an input signal in a low-level range, to an extent greater than that in a high-level range.

Claims

1. A color copier comprising:

a color line image sensor for optically scanning, line by line, a color document to provide fundamental color signals for each line of the document;

matrix circuit means connected to receive the fundamental color signals for converting the fundamental color signals into a brightness signal and two color difference signals, said matrix circuit means having a set of matrix coefficients for obtaining the brightness signal and the two color difference signals;

a color printer for reproducing the color document by use of a plurality of color inks;

color conversion circuit means, coupled between said matrix circuit means and said color printer, including a read only memory table for storing ink amount control signals in a digitalized manner, which are adapted for controlling the amounts of the color inks used in said color printer, said read only memory table being accessed by the brightness signal and the color difference signals for outputting corresponding ink amount control signals; and

nonlinear conversion circuit means connected between said image sensor and said matrix circuit means for converting the fundamental color signals from said image sensor in a nonlinear fashion such that a change in level of an input signal in a low-level range is increased to an extent greater that that in a high-level range, whereby the degrees of data quantization of the ink amount control signals are made substantially uniform in said read only memory table of said color conversion circuit means.

2. A copier according to claim 1, wherein

said color line-image sensor is divided into a plurality of sensor sections along the line of the document;

and

said matrix circuit has a plurality of matrix conversion coefficient sets corresponding to said plurality of sensor sections of said color line-image sensor.

3. A copier according to claim 2, wherein said plurality of matrix conversion sets are determined such that a difference in color signals obtained from adjacent sensor sections can be minimized.

4. A copier according to claim 1, wherein said color line-image sensor comprises a charge-coupled device and a color filter array of fundamental colors.

5. A copier according to claim 4, wherein said color filter array comprises red, blue, and green filter elements arranged in a line.

6. A copier according to claim 1, wherein said nonlinear conversion circuit has a conversion characteristic given by

7. A copier according to claim 6, wherein D is about 0.05 and n is ranged from 1/2 to 1/3.

8. A copier accoridng to claim 2, wherein D=0.05 and n=1/3.

9. A copier according to claim 6, wherein D=0.01 and n=1/3.

10. A color copier comprising:

a color line image sensor for optically scanning, line by line, a color document to provide fundamental color signals representative of red, green, and blue for each line of the document;

matrix circuit means connected to receive the fundamental color signals for converting the fundamental color signals into a brightness signal I and two color difference signals C1 and C2, said matrix circuit means having a set of matrix coefficients for obtaining the brightness signal and the two color difference signals;

a color printer for reproducing the color document by use of a plurality of color inks including magneta, yellow, and cyana;

color conversion circuit means, coupled between said matrix circuit means and said color printer, including a read only memory table for storing ink amount control signals in a digitized manner, which are adapted for controlling the amounts of the color inks used in said color printer, said read only memory table being accessed by the brightness signal and the color difference signals for outputting corresponding ink amount control signals; and

nonlinear conversion circuit means connected between said image sensor and said matrix circuit means for converting the fundamental color signals from said image sensor in a nonlinear fashion such that a change in level of an input signal in a low-level range is increased to an extent greater than that in a high-level range, whereby the coordinates representing each of yellow, magneta, cyan, red, green, and blue are distributed at substantially the same distance from the origin on a plane defined by color difference axes in said read only memory table of said color conversion circuit means.