Color editing with simple encoded images

• US 5,204,665 A
• Filed: 12/09/1991
• Issued: 04/20/1993
• Est. Priority Date: 05/02/1990
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Van Inwegen, Myra E., Bollman, James E.
• Primary Examiner(s): Weldon, Ulysses
• Assistant Examiner(s): Liang, Regina
• Application Number:
  US07/805,358
• Time in Patent Office: 498 Days
• Field of Search: 340/701, 340/703, 340/793, 358/31, 358/75, 358/80
• US Class Current: 345/605
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607

Abstract

In an original image in red, green, blue color space (RGB) defined by a large number of colors, color variety of the original image is accomplished by displaying a reduced representative color set. The reduced representative color set is produced by initially treating each color separation individually, to reduce the number of levels defining the image, in a manner which retains much of the image information. Subsequently, the separations are combined into an index into color set in a look up table (LUT) having between about 27 and 120 RGB triplets. Each RGB triplet defined by one of the LUT triplets is converted to a luminance/chrominance value. Modifications are made to the image in luminance/chrominance, and converted back to RGB space to reload the LUT for real time color variation of the image. Upon establishing a desirable color set in luminance/chrominance space, the luminance/chrominance values selected, which define the new position of the image in luminance/chrominance space, are used to change the colors in the original in a single step. The new original image is then again displayed with a new reduced representative color set derived in the same manner as described.

Claims

1. A method of modifying color in an n-bit system, wherein a digitally encoded representation of an original image in red-green-blue color space, the original image composed of pixels defined by the level of red, green and blue therein, each pixel defined by one of a number of encoded values of levels of red, green and blue, such number relatively large with respect to a desired number of levels for modifying the color of the original image, comprising the steps of:

a) separating the original image into red, green and blue color separations, whereby for each separation, each pixel in the original image is defined by one of N different levels of red or green or blue at that pixel position;

b) for each of the red, green and blue color separations, reducing the number of levels N defining pixels in each separation, to a value N_R, N_B, and N_G, respectively, where N_R ×

N_B ×

N_G is less than 2ⁿ ;

c) producing a look up table having a number of entries equal to N_R ×

N_B ×

N_G, each entry of the look up table consisting of one RGB triplet;

d) combining the reduced number of levels N_R, N_B, and N_G together to form an index for each pixel for which an RGB triplet in the look up table is selected;

e) displaying the original image in terms of the reduced number of levels N_R, N_B, and N_G on a display device;

f) converting each RGB triplet in the look up table to a set of luminance and chrominance values, whereby each pixel identified as an RGB triplet is defined by a set of luminance and chrominance values;

g) modifying the of each RGB triplet in the look up table, whereby each pixel identified as an RGB triplet is identified as a modified RGB triplet, whereby the overall appearance of the image is changed; and

h) modifying each pixel of the original image defined by one of a relatively large number of encoded values of levels of red, green and blue, in accordance with the modifications to the set of luminance and chrominance values of each combination of N_R, N_B, and N_G in the look up table.

2. The method as defined in claim 1, wherein the relatively large number of encoded values of levels of red, green and blue, is approximately (256)³.

3. The method as defined in claim 1, wherein the number of levels N defining pixels in each separation is 256.

4. The method as defined in claim 1, wherein the number n is equal to 8.

5. The method as defined in claim 4, wherein N_R, N_B, and N_G, are not necessarily equal, and 3≦

N_R, N_B, or N_G ≦

8.

6. The method as defined in claim 4, wherein for an N_x of the group N_R, N_B, and N_G, 3≦

N_x ≦

8.

7. The method as defined in claim 4, wherein 27≦

N_R ×

N_B ×

N_G ≦

120.

8. The method as defined in claim 4, wherein N_R ×

N_B ×

N_G is between 90 and 100.

9. The method as defined in claim 4, wherein N_R ×

N_B ×

N_G equals 96.

10. The method as defined in claim 1 wherein the step of reducing the number of levels N defining pixels in each separation, to the reduced number of levels N_R, N_B, and N_G, respectively, where N_R ×

N_B ×

N_G ≦

2ⁿ, uses error diffusion among neighboring pixels to smooth artifacts arising from the reduction in levels from N to N_R, N_B, or N_G.

11. A method of modifying color in a digitally encoded representation of an original image in red-green-blue color space, the original image composed of pixels defined by the level of red, green and blue therein, each pixel defined by one of a number of encoded values of levels of red, green and blue, such number relatively large with respect to a desired number of levels for modifying the color of the original image, the modifications to be performed on a digital computer, with a processor, a display, a display memory suitable for storing a set of values defining pixels in each separation representing 256 colors, and data entry arrangement, comprising the steps of:

a) at the processor, separating the original image into red, green and blue color separations, whereby for each separation, each pixel in the original image is defined by one of N different values of red or green or blue at that pixel position;

b) at the processor, for each of the red, green and blue color separations, reducing the number of values N defining pixels in each separation, to a value N_R, N_B, and N_G, respectively, where 27≦

N_R ×

N_B ×

N_G ≦

120;

c) in the display memory, producing a look up table having a number of entries equal to N_R ×

N_B ×

N_G, each entry of the look up table consisting of one RGB triplet;

d) in the processor, combining the reduced number of levels together to form an index for each pixel for which an RGB triplet is selected from the reduced color set;

e) at the display, displaying the original image in terms of the reduced number of levels N_R, N_B, and N_G ;

f) with the processor, converting each RGB triplet in the look up table in the display memory to a set of luminance and chrominance values, whereby each pixel identified as an RGB triplet is defined by a set of luminance and chrominance values;

g) with the data entry arrangement, entering modifications, to the set of luminance and chrominance values of each combination of N_R, N_B, and N_G in the look up table, whereby each pixel identified as a combination of N_R, N_B, and N_G is also modified, and entering the modifications into the look up table in the display memory, whereby the overall appearance of the displayed image is changed; and

h) modifying each pixel of the original image defined by one of a relatively large number of encoded values of levels of red, green and blue, in accordance with the modifications to the set of luminance and chrominance values of each combination of N_R, N_B, and N_G in the look up table.

12. The method as defined in claim 11, wherein the relatively large number of encoded values of levels of red, green and blue, is approximately (256)³.

13. The method as defined in claim 11, wherein the number of levels defining pixels in each separation is 256.

14. The method as defined in claim 11, wherein N_R, N_B, and N_G, are not necessarily equal, and 3≦

N_R, N_B, or N_G ≦

8.

15. The method as defined in claim 11, wherein for each N of N_R, N_B, and N_G, 3≦

N≦

8.

16. The method as defined in claim 11, wherein N_R ×

N_B ×

N_G is between 90 and 100.

17. The method as defined in claim 16, including the step of:

displaying the modified original image, on the display device, by repeating steps a-d, for the modified original image.

18. The method as defined in claim 11, wherein N_R ×

N_B ×

N_G equals 96.

19. The method as defined in claim 11 wherein the step of reducing the number of levels N defining pixels in each separation, to N_R, N_B, and N_G, respectively, where 27<

N_R ×

N_B ×

N_G <

120, uses error diffusion among neighboring pixels to smooth artifacts arising from the reduction in levels from N to N_R, N_B, or N_G.

20. The method as defined in claim 11, including the step of:

with the processor, modifying each pixel of the original image defined by one of the relatively large number of encoded values of levels of red, green and blue, in accordance with the modifications to the set of luminance and chrominance values of each combination of N_R, N_B, and N_G in the look up table in the display memory.

21. A method of modifying color in a digitally encoded representation of an original image in red-green-blue color space, the original image composed of pixels defined by the level of red, green and blue therein, each pixel defined by one of a number of encoded values of levels of red, green and blue, such number relatively large with respect to a desired number of levels for modifying the color of the original image, the modifications to be performed on a digital computer, with a processor, a display, a display memory suitable for storing a set of values representing 256 colors, and data entry arrangement, comprising the steps of:

a) at the processor, separating the original image into red, green and blue color separations, whereby for each separation, each pixel in the original image is defined by one of N different values of red or green or blue at that pixel position;

b) at the processor, for each of the red, green and blue color separations, reducing the number of values N defining pixels in each separation, to a value N_R, N_B, and N_G, respectively, where 27≦

N_R ×

N_B ×

N_G ≦

120;

c) in the display memory, producing a look up table having a number of entries equal to N_R ×

N_B ×

N_G, each entry of the look up table consisting of one RGB triplet;

d) in the processor, combining the reduced number of levels together to form an index for each pixel for which an RGB triplet is selected from the reduced color set;

e) at the display, displaying the original image in terms of the reduced number of levels N_R, N_B, and N_G ;

f) with the processor, converting each RGB triplet in the look up table in the display memory to a set of luminance and chrominance values, whereby each pixel identified as an RGB triplet is defined by a set of luminance and chrominance values;

g) with the data entry arrangement, selecting a portion of the image;

h) in the display memory, producing a look up table having a number of entries equal to N_R ×

N_B ×

N_G for the selected area, each entry of the look up table consisting of one RGB triplet;

i) in the processor, combining the reduced number of levels together to form an index for each pixel in the selected area for which an RGB triplet is selected from the reduced color set;

j) with the data entry arrangement, entering modifications to the set of luminance and chrominance values of each combination of N_R, N_B, and N_G in the second look up table, whereby each pixel in the selected area identified as a combination of N_R, N_B, and N_G is also modified, and entering the modifications into the look up table in the display memory, whereby the appearance of the selected area of the displayed image is changed;

k) modifying each pixel of the original image defined by one of a relatively large number of encoded values of levels of red, green and blue, in accordance with the modifications, if any, to the set of luminance and chrominance values of each combination of N_R, N_B, and N_G in the look up table.