Method and apparatus for controlling color image reproduction

• US 6,057,931 A
• Filed: 03/22/1996
• Issued: 05/02/2000
• Est. Priority Date: 07/12/1993
• Status: Expired due to Term

• Current Assignee: Verizon Patent and Licensing Incorporated (Verizon Communications Inc.)
• Original Assignee: MCI Incorporated (Verizon Communications Inc.)
• Inventors: McConnell, Troy, Reitz, Allan C.
• Primary Examiner(s): VU, KIM Y
• Application Number:
  US08/620,480
• Time in Patent Office: 1,502 Days
• Field of Search: 358/518, 358/520, 358/529, 358/530, 358/1.9, 382/167, 395/109
• US Class Current: 358/1.9
• CPC Class Codes: H04N 1/6022 Generating a fourth subtractive colour signal, e.g. under colour removal, black masking
• CPC Class Codes: H04N 1/62 Retouching, i.e. modification of isolated colours only or in isolated picture areas only

Abstract

The present invention provides a color-control method for use in an image reproducing process where the image is reduced to a plurality of pixels, with each pixel having a color value. The color control method uses a color control program in the image reproduction process. The color control program includes a color correction module and a color separation module. The color correction program provides a method for using HSL values to select which pixels will be color corrected. The color-separation program is used to convert RGB color values to YMCK color values and provides for undercolor removal and black generation. Undercolor removal removes gray components from the hue pixel data and replaces it with black pixel data. The black generation routine provides for the selection of pixels for which black will be added by the input of selected parameter of an HSL slice range.

Claims

1. A color control method for use in an image reproducing process where a color image is reduced to a plurality of pixels having different colors with each pixel having a color value, comprising the steps of:

(a) assigning to each pixel an HSL value corresponding to the color of the pixel, wherein each color value falls within an HSL color space and includes a hue component falling within a hue range, a saturation component falling within a saturation range, and a level component falling within a level range;

(b) defining an HSL slice range, the step of defining the HSL slice range including the steps of;

(1) defining a minimum and a maximum hue value;

(2) defining a minimum and a maximum saturation value;

(3) defining a minimum and maximum level value;

(c) forming an HSL slice by selecting at least one pixel which falls within the HSL slice range, wherein said slice range is defined by outwardly scanning pixels in all directions beginning at a user-selected reference pixel to form a like-colored sector of pixels surrounded by a discontinuity border of differently colored pixels;

(d) using the HSL range to determine which of the pixels of the color image are to be color corrected; and

(e) color correcting the HSL slice such that the colors of the pixels contained within the HSL slice are altered.

2. The method of claim 1 further including the step of identifying the colors of the pixels with cubic color values located in a cubic color space where each cubic color value includes a first color component, a second color component, and a third color component, and wherein the step of color correcting the HSL slice includes adjusting the cubic color values of the pixels contained within the HSL slice.

3. The method of claim 2 wherein the cubic color values are RGB values where each RGB value includes a red component, a green component, and a blue component.

4. The method of claim 1 wherein the step of defining an HSL slice range includes the step of providing for the manual input of HSL slice parameters.

5. The method of claim 4 wherein the step of defining an HSL slice range includes the step of prompting a user for HSL slice parameters.

6. The method of claim 1 wherein the step of defining an HSL slice range is automated and includes the step of forming the HSL slice parameters based on the HSL value of a mouse-selected pixel, wherein the HSL value of the mouse-selected pixel falls within the HSL slice parameters.

7. The method of claim 6 wherein the automated method of defining the HSL slice range further includes the steps of:

(a) defining a color discontinuity limit for selecting when two pixels are of sufficiently different colors to indicate a color discontinuity in the color image;

(b) evaluating pixels beginning at the selected pixel and extending outwardly in all directions from the mouse-selected pixel so as to establish a sector in the color image containing like-colored pixels, the step of scanning pixels comprising the steps of;

(1) comparing color values of the selected pixels with the color values of other pixels in the color image to determine color discontinuity values between scanned pixels,

(2) comparing the color discontinuity values with the color discontinuity limit to establish the like-colored sector; and

(c) forming the HSL slice range based on the color values of the pixels within the like-colored sector.

8. The method of claim 1 further including the steps of:

(a) providing for the selection of a plurality of different HSL slice ranges defining a plurality of HSL slices; and

(b) forming a plurality of HSL slices, the step of forming a plurality of HSL slices including the steps of;

(1) testing to determine whether the pixels of the color image overlap a plurality of different HSL slice ranges so as to fall within a plurality of HSL ranges,

(2) placing a pixel falling within a plurality of HSL slice ranges in only one HSL slice range where the HSL slice range in which an overlapping pixel is placed is based on the order in which the HSL slice ranges were defined.

9. A color control method as claimed in claim 1 further comprising the preliminary step of storing the minimum and maximum hue, saturation and level values to be used and the defining step includes retrieving the stored values for use in the defining step.

10. A color control method as claimed in claim 1 further comprising the steps of:

(a) identifying the colors of the pixels with cubic color values located in a cubic color space where each cubic color value includes a first color component, a second color component, and a third color component;

(b) generating a black color component removed from the first, second and third color components in an amount equal to a proportion of the least of them;

(c) reducing each of the first, second and third color components by an amount equal to the black color component; and

(d) printing the pixels of the image with inks of the first, second, third and black color components.

11. The method of claim 10 wherein the first, second and third color components are yellow, cyan and magenta.

12. A color control method as claimed in claim 1 further comprising the steps of:

(a) identifying the colors of the pixels with color values located in a color space where each cubic color value includes a first color component, a second color component, a third color component and a black color component;

(b) evaluating the first second and third color components of each pixel in HSL space including hue, saturation and level values to determine if the pixel is located in a neutral window of HSL space and, if so, adding to the black color component, and

(c) printing the pixels of the image with inks of the first, second, third and black color components.

13. A color control method as claimed in claim 12 wherein the HSL space is a polar coordinate system and the neutral window is a cylinder coaxial with pole of HSL space.

14. A color control method as claimed in claim 12 further comprising the preliminary step of storing parameters defining the neutral window and wherein the evaluating step includes retrieving the stored values for use in the evaluating step.

15. A color control method as claimed in claim 12 wherein the HSL space is a polar coordinate system including darker and lighter hemispheres, the neutral window is located coaxial with the pole of HSL space and the majority of the neutral window is in the darker hemisphere.

16. The method of claim 1 wherein step (c) further comprises the steps of:

(1) scanning in a first direction a target pixel located adjacent to the reference pixel;

(2) if the target is similar to the reference pixel, then it is included in a sector of like-colored pixels and its HSL values are used for comparing with a subsequently scanned pixel, wherein the target pixel is treated as a reference pixel and the most recently scanned pixel adjacent and to the left of the target pixel is considered as a target pixel; and

(3) iterating steps (1) and (2) until either the edge of the image or a discontinuity in the image is encountered.

17. The method of claim 16 further comprises the steps of:

(4) scanning in a second direction, that is opposite to said first direction, a target pixel located adjacent to the reference pixel upon encountering the edge of the image or a discontinuity in the image;

(5) if the target pixel is similar to the reference pixel, then it is included in a sector of like-colored pixels and its HSL values are used for comparing with a subsequently scanned pixel, wherein the target pixel is treated as a reference pixel and the most recently scanned pixel is considered as a target pixel; and

(6) iterating steps (4) and (5) until either the edge of the image or a discontinuity in the image is encountered.

18. The color control method of claim 1 further comprises the steps of:

(a) identifying the colors of the pixels with color values located in a color space where each cubic color value includes a first color component, a second color component, a third color component and a black color component;

(b) evaluating the first, second, and third color components of each pixel in HSL space including hue, saturation and level values to determine if the pixel is located in a neutral window of HSL space and, if so, adding to the black color component following the iterative steps of;

if nww is zero, then

add K=(%bg/100)*(255-L) (make sure we don'"'"'t divide by zero)

else

add K=(%bg/100)*(255-L)*(1-(S/255)*(100/nww))

endif

K=K+add K

If K>

255 then

K=255

endif

endif;

where nww=neutral window width;

%bg=percent black generation;

L=luminance;

S=saturation, and

(c) printing the pixels of the image with inks of the first, second, third and black color components.

19. A color correction apparatus for correcting stored, scanned pixel color data comprising,

a data input device,

a memory for storing pixel color data,

a video display for displaying stored pixel color data to depict a color image, and

a processing unit for converting stored pixel color data from a cubic color value to an HSL color value and for receiving data input for a color correction of selected pixels falling within a defined HSL slice, said HSL slice is formed by selecting at least one pixel which falls within the HSL slice and wherein said slice is defined by outwardly scanning pixels in all directions beginning at a user-selected reference pixel to form a like-colored sector of pixels surrounded by a discontinuity border of differently colored pixels.

20. A color correction apparatus as claimed in claim 19 further comprising a scanner to raster scan a view and generate signals representative of cubic color values of pixels of the scanned view.

21. A color correction apparatus as claimed in claim 19 further comprising a memory for storing the minimum and maximum hue, saturation and level values to be used and the processing unit is adapted to retrieve the stored values for use in color correction.

22. A color correction apparatus as claimed in claim 19 further comprising an undercolor removal apparatus for removing gray components from stored, scanned pixel color data and printing the resultant image comprising,

said memory for storing pixel color data including storing cubic color values located in a cubic color space where each cubic color value includes a first color component, a second color component, and a third color component,

said processing unit including for generating a black color component removed from the first, second and third color components in an amount equal to a proportion of the least of them and for reducing each of the first, second and third color components by an amount equal to the black color component;

and

a printer to print the pixels of the image with inks of the first, second, third and black color components.

23. A color correction apparatus as claimed in claim 19 further comprising a black addition apparatus for adding black components to stored, scanned pixel color data and printing the resultant image comprising,

said memory for storing pixel color data including storing color values located in a color space where each color value includes a first color component, a second color component, and a third color component, and a black color component,

said processing unit including for evaluating the first second and third color components of each pixel in HSL space includign hue, saturation and level values to determine if the pixel is located in a neutral window of HSL space and, if so, adding to the black color component, and

a printer to print the pixels of the image with inks of the first, second, third and black color components.

24. A color correction apparatus as claimed in claim 23 further comprising a memory for storing parameters defining the neutral window and the processing unit is adapted to retrieve the stored parameters for use in color correction.

25. A color correction apparatus as claimed in claim 19 wherein the processing unit is also capable of converting pixels to YMC space and performing an undercolor removal data operation.

26. A color correction apparatus as claimed in claim 19 wherein the processing unit is also capable of converting pixels to YMC space and performing a black generation data operation.

27. A color correction apparatus as claimed in claim 19 further comprising a four color printer capable of printing black, yellow, cyan and magenta.

28. A color control method for use in an image reproducing process where a color image is reduced to a plurality of pixels having different colors with each pixel having a color value, comprising the steps of:

(a) assigning to each pixel an HSL value corresponding to the color of the pixel, wherein each color value falls within an HSL color space and includes a hue component falling within a hue range, a saturation component falling within a saturation range, and a level component falling within a level range;

(b) defining an HSL slice range, the step of defining the HSL slice range comprises the steps of;

(1) defining a minimum and a maximum hue value;

(2) defining a minimum and a maximum saturation value;

(3) defining a minimum and maximum level value;

(4) defining a color discontinuity limit for selecting when two pixels are of sufficiently different colors to indicate a color discontinuity in the color image;

(5) evaluating pixels beginning at the selected pixel of step (4) and extending outwardly in all directions from the selected pixel so as to establish a sector in the color image containing like-colored pixels, the step of scanning pixels further comprising the steps of;

(i) comparing color values of the selected pixels with the color values of other pixels in the color image to determine color discontinuity values between scanned pixels,

(ii) comparing the color discontinuity values with the color discontinuity limit to establish the like-colored sector; and

(6) forming the HSL slice range based on the color values of the pixels within the like-colored sector;

(c) forming an HSL slice by selecting at least one pixel which falls within the HSL slice range;

(d) using the HSL range to determine which of the pixels of the color image are to be color corrected; and

(e) color correcting the HSL slice such that the colors of the pixels contained within the HSL slice are altered.

29. A color method for use in an image reproducing process where a color image is reduced to a plurality of pixels having different colors with each pixel having a color value, comprising the steps of:

(a) assigning to each pixel an HSL value corresponding to the color of the pixel, wherein each color value falls within an HSL color space and includes a hue component falling within a hue range, a saturation component falling within a saturation range, and a level component falling within a level range;

(b) defining an HSL slice range, the step of defining the HSL slice range is automated and includes steps of;

(1) defining a minimum and a maximum hue value;

(2) defining a minimum and a maximum saturation value;

(3) defining a minimum and maximum level value;

(c) providing for the selection of a plurality of different HSL slice ranges defining a plurality of HSL slices;

(d) forming at least one HSL slice by selecting at least one pixel which falls within the HSL slice range, the step of forming the HSL slice including the steps of;

(1) testing to determine whether the pixels of the color image overlap a plurality of different HSL slice ranges so as to fall within a plurality of HSL ranges;

(2) placing a pixel falling within a plurality of HSL slice ranges in only one HSL slice range where the HSL slice range in which an overlapping pixel is placed is based on the order in which the HSL slice ranges were defined;

(e) using the HSL range to determine which of the pixels of the color image are to be color corrected; and

(e) color correcting the HSL slice such that the colors of the pixels contained within the HSL slice are altered.

30. A color correction apparatus for use in an image reproducing process where a color image is reduced to a plurality of pixels having different colors with each pixel having a color value, comprises:

a data input device;

a memory for storing pixel color data;

a video display for displaying stored pixel color data to depict a color image;

means for assigning to each pixel an HSL value corresponding to the color of the pixel, wherein each color value falls within an HSL color space and includes a hue component falling within a hue range, a saturation component falling within a saturation range, and a level component falling with a level range;

means for defining an HSL slice range, wherein defining said slice range comprises the steps of;

(1) defining a minimum and a maximum hue value;

(2) defining a minimum and a maximum saturation value;

(3) defining a minimum and maximum level value;

(4) defining a color discontinuity limit for selecting when two pixels are of sufficiently different colors to indicate a color discontinuity in the color image;

(5) evaluating pixels beginning at the selected pixel of step (4) and extending outwardly in all directions from the selected pixel so as to establish a sector in the color image containing like-colored pixels, the step of scanning pixels further comprising the steps of;

(i) comparing color values of the selected pixels with the color values of other pixels in the color image to determine color discontinuity values between scanned pixels,

(ii) comparing the color discontinuity values with the color discontinuity limit to establish the like-colored sector; and

(6) forming the HSL slice range based on the color values of the pixels within the like-colored sector;

means for forming an HSL slice by selecting at least one pixel which falls within the HSL slice range; and

means for color correcting images by using the HSL range to determine which of the pixels of the color image need color correction.

31. An apparatus for color correcting an image reduced to a plurality of pixels having different colors with each pixel having a color value, comprises:

means for assigning to each pixel an HSL value corresponding to the color of the pixel, wherein each color value falls within an HSL color space and includes a hue component falling with a hue range, a saturation falling within a saturation range, and a level component falling with a level range;

means for defining an HSL slice range which includes defining a minimum and a maximum hue value, defining a minimum and a maximum saturation value, and defining a minimum and maximum level value;

means for selecting a plurality of different HSL slice ranges defining a plurality of HSL slices;

means for forming at least one HSL slice, said slice being formed by selecting at least one pixel falling within the HSL slice range;

means for testing to determine whether the pixels of the color image overlap a plurality of different HSL slice ranges so as to fall within a plurality of HSL ranges; and

means for color correcting the pixels contained within the HSL slice.