Color picture processing apparatus for reproducing a color picture having a smoothly changed gradation

• US 5,696,611 A
• Filed: 06/05/1995
• Issued: 12/09/1997
• Est. Priority Date: 11/08/1994
• Status: Expired due to Fees

• Current Assignee: Panasonic Communications Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Graphic Communication Systems, Inc. (Panasonic Holdings Corporation)
• Inventors: Sato, Shinichi, Nishimura, Kazuyuki
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): WALLERSON, MARK E
• Application Number:
  US08/463,531
• Time in Patent Office: 918 Days
• Field of Search: 358/518, 358/515, 358/520, 358/462, 358/465, 358/470, 358/529, 358/517, 358/530, 358/447, 358/456, 358/523, 382/162, 382/270
• US Class Current: 358/518
• CPC Class Codes: G01J 3/462 Computing operations in or between colour spaces; Colour management systems
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening
• CPC Class Codes: H04N 1/6022 Generating a fourth subtractive colour signal, e.g. under colour removal, black masking

Abstract

An achromatic color judging region is determined in a red-green-blue (RGB) color system, and it is judged in an achromatic color judging unit whether or not a color picture at a remarked pixel designated by a R multi-valued digital input signal, a G multi-valued digital input signal and a B multi-valued digital input signal is placed within the achromatic color judging region. Also, the RGB multi-valued digital input signals are converted into pieces of RGB binary data in an error dispersion processing unit while dispersing errors occurring in the RGB binary data. In case where it is judged that the color picture is an achromatic color because the color picture is placed within the achromatic color judging region, a piece of achromatic color data is generated from the RGB binary data in an achromatic color reproducing and color transforming unit and is output to reproduce the color picture at the remarked pixel. In contrast, in case where it is judged that the color picture is a chromatic color because the color picture is not placed within the achromatic color judging region, the RGB binary data are output to reproduce the color picture at the remarked pixel. Therefore, the color picture can be reproduced in a smoothly changed gradation in a small sized color picture processing apparatus.

Claims

1. A color picture processing apparatus, comprising:

achromatic color judging means for judging whether a color picture at a remarked pixel has an achromatic color or a chromatic color according to a piece of first multi-valued primary color data, a piece of second multi-valued primary color data and a piece of third multi-valued primary color data indicating three primary color components of the color picture;

binary data converting means for converting the first, second and third multi-valued primary color data into three pieces of binary primary color data indicating the three primary color components of the color picture; and

achromatic color reproducing means for generating and outputting a piece of achromatic color data indicating an achromatic color component of the color picture to reproduce the color picture of the remarked pixel according to the binary primary color data converted by the binary data converting means in cases where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the achromatic color and outputting the binary primary color data to reproduce the color picture of the remarked pixel in cases where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the chromatic color,

wherein a first binary value of the achromatic color data output from the achromatic color reproducing means in case where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the achromatic color is set to a second binary value of one of the binary primary color data converted by the binary data converting means, and third binary values of the other binary primary color data are set to the second binary value, the achromatic color of the color picture being reproduced by the three binary primary color data having the same binary value.

2. A color picture processing apparatus, comprising:

achromatic color judging means for judging whether a color picture at a remarked pixel has an achromatic color or a chromatic color according to a piece of first multi-valued primary color data, a piece of second multi-valued primary color data and a piece of third multi-valued primary color data indicating three primary color components of the color picture;

the achromatic color judging means comprising

a maximum value detecting circuit for detecting a maximum value A from among three digital values of the first, second and third multi-valued primary color data,

a minimum value detecting circuit for detecting a minimum value B from among the three digital values of the first, second and third multi-valued primary color data,

a difference calculating circuit for calculating a differential value A-B between the maximum value A detected by the maximum value detecting circuit and the minimum value B detected by the minimum value detecting circuit,

a dividing circuit for dividing the differential value A-B calculated by the difference calculating circuit by the maximum value A detected by the maximum value detecting circuit to obtain a divided value (A-B)/A,

a selector for selecting an achromatic judging threshold value from a plurality of threshold values,

a comparator for comparing the divided value (A-B)/A obtained in the dividing circuit with the achromatic judging threshold value, and

a judging signal producing circuit for producing an achromatic color judging signal indicating that the color picture at the remarked pixel has the achromatic color in case where the divided value (A-B)/A compared by the comparator is equal to or lower than the achromatic judging threshold value and an achromatic color judging signal indicating that the color picture at the remarked pixel has the chromatic color in case where the divided value (A-B)/A compared by the comparator is higher than the achromatic judging threshold value;

binary data converting means for converting the first, second and third multi-valued primary color data into three pieces of binary primary color data indicating the three primary color components of the color picture; and

achromatic color reproducing means for generating and outputting a piece of achromatic color data indicating an achromatic color component of the color picture to reproduce the color picture of the remarked pixel according to the binary primary color data converted by the binary data converting means in cases where the judging signal producing circuit of the achromatic color judging means produces the achromatic color judging signal indicating that the color picture at the remarked pixel has the achromatic color and outputting the binary primary color data to reproduce the color picture of the remarked pixel in cases where the judging signal producing circuit of the achromatic color judging means produces the achromatic color judging signal indicating that the color picture at the remarked pixel has the chromatic color.

3. A color picture processing apparatus, comprising:

achromatic color judging means for judging whether a color picture at a remarked pixel has an achromatic color or a chromatic color according to a piece of first multi-valued primary color data, a piece of second multi-valued primary color data and a piece of third multi-valued primary color data indicating three primary color components of the color picture,

the achromatic color judging means judging that the color picture at the remarked pixel has an achromatic color in case where the primary color components of the color picture are placed within an achromatic color region widened on a high lightness side in a primary color space;

binary data converting means for converting the first, second and third multi-valued primary color data into three pieces of binary primary color data indicating the three primary color components of the color picture; and

achromatic color reproducing means for generating and outputting a piece of achromatic color data indicating an achromatic color component of the color picture to reproduce the color picture of the remarked pixel according to the binary primary color data converted by the binary data converting means in cases where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the achromatic color and outputting the binary primary color data to reproduce the color picture of the remarked pixel in cases where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the chromatic color.

4. A color picture processing apparatus according to claim 3 in which the achromatic color region is formed in a hexagonal pyramid in which a central line connects a black point and a white point, a vertex is placed at the black point and a hexagonal bottom plane is placed near to the white point.

5. A color picture processing apparatus, comprising:

achromatic color judging means for judging whether a color picture at a remarked pixel has an achromatic color or a chromatic color according to a piece of first multi-valued primary color data, a piece of second multi-valued primary color data and a piece of third multi-valued primary color data indicating three primary color components of the color picture,

the achromatic color judging means comprising

a color difference calculating circuit for calculating a piece of first multi-valued color difference data defined as a first difference between the first and second multi-valued primary color data, a piece of second multi-valued color difference data defined as a second difference between the first and third multi-valued primary color data and a piece of third multi-valued color difference data defined as a third difference between the second and third multi-valued primary color data,

an absolute value calculating circuit for calculating three absolute values of the first, second and third multi-valued color difference data calculated by the color difference calculating circuit,

a maximum value detecting circuit for detecting a maximum value from among three digital values of the first, second and third multi-valued primary color data,

a multiplying circuit for multiplying the maximum value detected by the maximum value detecting circuit by an achromatic color judging threshold value to produce a multiplied value,

a comparator for comparing each of the absolute values calculated in the absolute value calculating circuit with the multiplied value produced in the multiplying circuit, and

a judging signal producing circuit for producing an achromatic color judging signal indicating that the color picture at the remarked pixel has the achromatic color in case where the absolute values compared with the multiplied value in the comparator are respectively equal to or lower than the multiplied value and producing an achromatic color judging signal indicating that the color picture at the remarked pixel has the chromatic color in case where one of the absolute values compared with the multiplied value in the comparator is higher than the multiplied value,

binary data converting means for converting the first, second and third multi-valued primary color data into three pieces of binary primary color data indicating the three primary color components of the color picture; and

achromatic color reproducing means for generating and outputting a piece of achromatic color data indicating an achromatic color component of the color picture to reproduce the color picture of the remarked pixel according to the binary primary color data converted by the binary data converting means in cases where the achromatic color judging signal indicating that the color picture at the remarked pixel has the achromatic color is produced by the judging signal producing circuit of the achromatic color judging means and outputting the binary primary color data to reproduce the color picture of the remarked pixel in cases where the achromatic color judging signal indicating that the color picture at the remarked pixel has the chromatic color is produced by the judging signal producing circuit of the achromatic color judging means.

6. A color picture processing apparatus according to claim 5 in which the achromatic color judging means further comprises a selector for selecting the achromatic judging threshold value utilized in the multiplying circuit from a plurality of threshold values.

7. A color picture processing apparatus, comprising:

achromatic color judging means for judging whether a color picture at a remarked pixel has an achromatic color or a chromatic color according to a piece of first multi-valued primary color data, a piece of second multi-valued primary color data and a piece of third multi-valued primary color data indicating three primary color components of the color picture,

the achromatic color judging means comprising

a color transforming circuit for transforming the first, second and third multi-valued primary color data defined in a first primary color system into a piece of first multi-valued transformed color data, a piece of second multi-valued transformed color data and a piece of third multi-valued transformed color data defined in a second primary color system which has a complementary relationship with the first primary color system,

a color difference calculating circuit for calculating a piece of first multi-valued color difference data defined as a first difference between the first and second multi-valued transformed color data obtained in the color transforming circuit, a piece of second multi-valued color difference data defined as a second difference between the first and third multi-valued transformed color data obtained in the color transforming circuit and a piece of third multi-valued color difference data defined as a third difference between the second and third multi-valued transformed color data,

an absolute value calculating circuit for calculating three absolute values of the first, second and third multi-valued color difference data calculated by the color difference calculating circuit,

a maximum value detecting circuit for detecting a maximum value from among three digital values of the first, second and third multi-valued transformed color data obtained in the color transforming circuit,

a multiplying circuit for multiplying the maximum value detected by the maximum value detecting circuit by an achromatic color judging threshold value to produce a multiplied value,

a comparator for comparing each of the absolute values calculated in the absolute value calculating circuit with the multiplied value produced in the multiplying circuit, and

a judging signal producing circuit for producing an achromatic color judging signal indicating that the color picture at the remarked pixel has the achromatic color in case where the absolute values compared with the multiplied value in the comparator are respectively equal to or lower than the multiplied value and producing an achromatic color judging signal indicating that the color picture at the remarked pixel has the chromatic color in case where one of the absolute values compared with the multiplied value in the comparator is higher than the multiplied value,

binary data converting means for converting the first, second and third multi-valued primary color data into three pieces of binary primary color data indicating the three primary color components of the color picture; and

achromatic color reproducing means for generating and outputting a piece of achromatic color data indicating an achromatic color component of the color picture to reproduce the color picture of the remarked pixel according to the binary primary color data converted by the binary data converting means in cases where the achromatic color judging signal indicating that the color picture at the remarked pixel has the achromatic color is produced by the judging signal producing circuit of the achromatic color judging means and outputting the binary primary color data to reproduce the color picture of the remarked pixel in cases where the achromatic color judging signal indicating that the color picture at the remarked pixel has the chromatic color is produced by the judging signal producing circuit of the achromatic color judging means.

8. A color picture processing apparatus according to claim 7 in which the first multi-valued primary color data indicates a red component of the color picture, the second multi-valued primary color data indicates a green component of the color picture, the third multi-valued primary color data indicates a blue component of the color picture, the first multi-valued transformed color data indicates a cyan component of the color picture, the second multi-valued transformed color data indicates a magenta component of the color picture, and the third multi-valued transformed color data indicates a yellow component of the color picture.

9. A color picture processing apparatus, comprising:

color difference calculating means for receiving a piece of first multi-valued primary color data, a piece of second multi-valued primary color data and a piece of third multi-valued primary color data indicating three primary color components of a color picture at a remarked pixel and calculating a piece of first multi-valued color difference data defined as a first difference between the first and second multi-valued primary color data, a piece of second multi-valued color difference data defined as a second difference between the first and third multi-valued primary color data and a piece of third multi-valued color difference data defined as a third difference between the second and third multi-valued primary color data;

matrix color correcting means for correcting the first, second and third multi-valued primary color data to a piece of first multi-valued corrected color data, a piece of second multi-valued corrected color data and a piece of third multi-valued corrected color data;

achromatic color judging means for judging whether the color picture at the remarked pixel has an achromatic color or a chromatic color according to the first, second and third multi-valued color difference data calculated by the color difference calculating means;

binary data converting means for converting the first, second and third multi-valued corrected color data obtained in the matrix color correcting means into three pieces of binary corrected color data; and

achromatic color reproducing means for generating and outputting a piece of achromatic color data indicating an achromatic color component of the color picture to reproduce the color picture of the remarked pixel according to the binary primary color data converted by the binary data converting means in cases where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the achromatic color and outputting the binary primary color data to reproduce the color picture of the remarked pixel in cases where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the chromatic color,

wherein a first binary value of the achromatic color data output from the achromatic color reproducing means in case where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the achromatic color is set to a second binary value of one of the binary corrected color data converted by the binary data converting means, and third binary values of the other binary corrected color data are set to the second binary value, the achromatic color of the color picture being reproduced by the three binary corrected color data having the same binary value.

10. A color picture processing apparatus, comprising:

color difference calculating means for receiving a piece of first multi-valued primary color data, a piece of second multi-valued primary color data and a piece of third multi-valued primary color data indicating three primary color components of a color picture at a remarked pixel and calculating a piece of first multi-valued color difference data defined as a first difference between the first and second multi-valued primary color data, a piece of second multi-valued color difference data defined as a second difference between the first and third multi-valued primary color data and a piece of third multi-valued color difference data defined as a third difference between the second and third multi-valued primary color data;

matrix color correcting means for correcting the first, second and third multi-valued primary color data to a piece of first multi-valued corrected color data, a piece of second multi-valued corrected color data and a piece of third multi-valued corrected color data;

achromatic color judging means for judging whether the color picture at the remarked pixel has an achromatic color or a chromatic color according to the first, second and third multi-valued color difference data calculated by the color difference calculating means,

the achromatic color judging means comprising

an absolute value calculating circuit for calculating three absolute values of the first, second and third multi-valued color difference data,

a comparator for comparing each of the absolute values calculated in the absolute value calculating circuit with an achromatic judging threshold value,

a judging signal producing circuit for producing an achromatic color judging signal indicating that the color picture at the remarked pixel has the achromatic color in case where the absolute values compared with the achromatic judging threshold value in the comparator are respectively equal to or lower than the achromatic judging threshold value and producing an achromatic color judging signal indicating that the color picture at the remarked pixel has the chromatic color in case where one of the absolute values compared with the achromatic judging threshold value in the comparator is higher than the achromatic judging threshold value, and

a selector for selecting the achromatic judging threshold value compared in the comparator from a plurality of threshold values;

binary data converting means for converting the first, second and third multi-valued corrected color data obtained in the matrix color correcting means into three pieces of binary corrected color data; and

achromatic color reproducing means for generating and outputting a piece of achromatic color data indicating an achromatic color component of the color picture to reproduce the color picture of the remarked pixel according to the binary primary color data converted by the binary data converting means in cases where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the achromatic color and outputting the binary primary color data to reproduce the color picture of the remarked pixel in cases where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the chromatic color.

11. A color picture processing apparatus, comprising:

matrix correcting factor storing means for storing a plurality of first values of a first matrix correcting factor varying with a piece of first multi-valued color difference data defined as a first difference between pieces of first and second multi-valued primary color data, a plurality of second values of a second matrix correcting factor varying with a piece of second multi-valued color difference data defined as a second difference between pieces of first and third multi-valued primary color data and a plurality of third values of a third matrix correcting factor varying with a piece of third multi-valued color difference data defined as a third difference between pieces of second and third multi-valued primary color data;

color difference calculating means for receiving a piece of particular first multi-valued primary color data, a piece of particular second multi-valued primary color data, a piece of particular third multi-valued primary color data indicating three primary color components of a color picture at a remarked pixel and calculating a particular first difference value of a piece of particular first multi-valued color difference data defined as a first difference between the particular first and second multi-valued primary color data, a particular second difference value of a piece of particular second multi-valued color difference data defined as a second difference between the particular first and third multi-valued primary color data and a particular third difference value of a piece of particular third multi-valued color difference data defined as a third difference between the particular second and third multi-valued primary color data;

control means for controlling the selection of a particular first value of the first matrix correcting factor corresponding to the particular first difference value of the particular first multi-valued color difference data calculated in the color difference calculating means from among the first values stored in the matrix correcting factor storing means, the selection of a particular second value of the second matrix correcting factor corresponding to the particular second difference value of the particular second multi-valued color difference data calculated in the color difference calculating means from among the second values stored in the matrix correcting factor storing means, and the selection of a particular third value of the third matrix correcting factor corresponding to the particular third difference value of the particular third multi-valued color difference data calculated in the color difference calculating means from among the third values stored in the matrix correcting factor storing means;

corrected color data producing means for producing a piece of first multi-valued corrected color data from the particular first value of the first matrix correcting factor selected under the control of the control means and the particular first difference value of the first multi-valued color difference data calculated in the color difference calculating means, a piece of second multi-valued corrected color data from the particular second value of the second matrix correcting factor selected under the control of the control means and the particular second difference value of the second multi-valued color difference data calculated in the color difference calculating means, and a piece of third multi-valued corrected color data from the particular third value of the third matrix correcting factor selected under the control of the control means and the particular third difference value of the third multi-valued color difference data calculated in the color difference calculating means;

binary data converting means for converting the first, second and third multi-valued corrected color data produced in the corrected color data producing means into three pieces of binary color data;

achromatic color judging means for judging whether the color picture at the remarked pixel has an achromatic color or a chromatic color according to the particular first, second and third multi-valued color difference data calculated by the color difference calculating means; and

achromatic color reproducing means for outputting a piece of achromatic color data to reproduce an achromatic color of the color picture in case where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the achromatic color and outputting the binary color data converted by the binary data converting means to reproduce a chromatic color of the color picture in case where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the chromatic color.

12. A color picture processing apparatus according to claim 11 in which the first multi-valued primary color data indicates a red component of the color picture, the second multi-valued primary color data indicates a green component of the color picture and the third multi-valued primary color data indicates a blue component of the color picture.

13. A color picture processing apparatus according to claim 11 in which the first multi-valued corrected color data produced in the corrected color data producing means is obtained by adding the particular first value of the first matrix correcting factor and the particular first difference value of the particular first multi-valued color difference data, the second multi-valued corrected color data produced in the corrected color data producing means is obtained by adding the particular second value of the second matrix correcting factor and the particular second difference value of the particular second multi-valued color difference data, and the third multi-valued corrected color data produced in the corrected color data producing means is obtained by adding the particular third value of the third matrix correcting factor and the particular third difference value of the particular third multi-valued color difference data.

14. A color picture processing apparatus, comprising:

matrix element storing means for storing a first matrix element, a second matrix element and a third matrix element of a color transforming matrix;

color difference calculating means for receiving a piece of first multi-valued primary color data, a piece of second multi-valued primary color data and a piece of third multi-valued primary color data indicating three primary color components of a color picture at a remarked pixel and calculating a piece of first multi-valued color difference data defined as a first difference between the first and second multi-valued primary color data, a piece of second multi-valued color difference data defined as a second difference between the first and third multi-valued primary color data and a piece of third multi-valued color difference data defined as a third difference between the second and third multi-valued primary color data;

multiplying means for multiplying the first multi-valued color difference data calculated in the color difference calculating means by the first matrix element stored in the matrix element storing means to produce a first matrix correcting factor, multiplying the second multi-valued color difference data calculated in the color difference calculating means by the second matrix element stored in the matrix element storing means to produce a second matrix correcting factor, and multiplying the third multi-valued color difference data calculated in the color difference calculating means by the third matrix element stored in the matrix element storing means to produce a third matrix correcting factor;

corrected color data producing means for producing a piece of first multi-valued corrected color data from the first matrix correcting factor obtained in the multiplying means and the first multi-valued color difference data calculated in the color difference calculating means, a piece of second multi-valued corrected color data from the second matrix correcting factor obtained in the multiplying means and the second multi-valued color difference data calculated in the color difference calculating means and a piece of third multi-valued corrected color data from the third matrix correcting factor obtained in the multiplying means and the third multi-valued color difference data calculated in the color difference calculating means;

binary data converting means for converting the first, second and third multi-valued corrected color data produced in the corrected color data producing means into three pieces of binary color data;

achromatic color judging means for judging whether the color picture at the remarked pixel has an achromatic color or a chromatic color according to the first, second and third multi-valued color difference data calculated by the color difference calculating means; and

achromatic color reproducing means for outputting a piece of achromatic color data to reproduce an achromatic color of the color picture in case where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the achromatic color and outputting the binary color data converted by the binary data converting means to reproduce a chromatic color of the color picture in case where it is judged by the achromatic color judging means that the color picture at the remarked pixel has the chromatic color.

15. A color picture processing apparatus according to claim 14 in which the first multi-valued primary color data indicates a red component of the color picture, the second multi-valued primary color data indicates a green component of the color picture and the third multi-valued primary color data indicates a blue component of the color picture.

16. A color picture processing apparatus according to claim 15 in which the first multi-valued corrected color data produced in the corrected color data producing means is obtained by adding the first matrix correcting factor and the first multi-valued color difference data, the second multi-valued corrected color data produced in the corrected color data producing means is obtained by adding the second matrix correcting factor and the second multi-valued color difference data, and the third multi-valued corrected color data produced in the corrected color data producing means is obtained by adding the third matrix correcting factor and the third multi-valued color difference data.