Systems and methods that determine an image processing system tone reproduction curve

• US 6,842,266 B1
• Filed: 02/25/2000
• Issued: 01/11/2005
• Est. Priority Date: 02/25/2000
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Fisher, Julie A., Loverde, Regina M., Farnung, Charles E., Nagarajan, Ramesh, Tse, Francis
• Primary Examiner(s): Lee, Thomas D.
• Assistant Examiner(s): Thompson, James A.
• Application Number:
  US09/512,889
• Time in Patent Office: 1,782 Days
• Field of Search: 382/169, 358/1.9, 358/2.1, 358/3.01, 358/3.21, 358/448, 358/461, 358/518, 358/520, 358/521, 358/523, 358/525, 358/3.06, 358/3.1, 358/3.24
• US Class Current: 358/1.9
• CPC Class Codes: H04N 1/407 Control or modification of tonal gradation or of extreme levels, e.g. background level

Abstract

An image processing system receives image input terminal information and image output terminal information. Based on the content of the image input terminal information and the image output terminal information a new system tone reproduction curve is determined. This device independent methodology allows system tone reproduction curves to be generated as needed, and allows the additional flexibility for changes in the image input terminal or the image output terminal.

Claims

1. A system that determines an image processing system tone reproduction curve comprising:

an image processing system that dynamically adjusts an image processing system tone reproduction curve for a reproduction curve gray level value based on at least one of an image source identification and an image sink identification, the image processing system comprising;

a reflectance determination device that determines a reflectance value based on a system tone reproduction curve within a bounded-domain piecewise-continuous relation, and

a gray level determination device that determines a system gray level value, determines the reproduction curve gray level value, and aligns the system gray level value with a system tone reproduction curve gain value to produce an updated reproduction gray level value.

2. The system of claim 1, wherein the reflectance determination device converts a system tone reproduction curve to a reflectance value by the bounded-domain piecewise-continuous relation defined by:

R_in=L*_in/903.3 for L*_in<

8, and

R_in={(L*_in+16)/116}³ for L*_in>

8.

3. The system of claim 1, further comprising a controller that cascades the determined reflectance value with an image source tone reproduction curve to obtain the system gray level value.

4. The system of claim 1, further comprising wherein the gray level determination devices aligns the system gray level value with the system tone reproduction curve gain value to produce the updated image processing system tone reproduction gray level value by a linear interpretation defined by:

g′

={(g_h−

g_l)×

(R−

R_l)}/(R_h−

R_l), where

g′

is the updated image processing system tone reproduction gray level value,

g_l and g_h are lower and higher gray level values on the image processing system tone reproduction curve, respectively,

R is the system reflectance value, and

R_l, and R_h are lower and higher reflectance values on the image processing system tone reproduction curve, respectively.

5. The system of claim 4, wherein an adjusted image processing system gray level is determined from the updated image processing system gray level determination by an adjustment relation:

g″

=gain×

g′

+offset, where

g″ and

g′

are the adjusted and updated image processing system gray levels, and

gain is a coefficient and offset is a bias, both calculated from the system tone reproductive curve.

6. The system of claim 1, further comprising wherein the gray level determination device determines the image processing system tone reproduction curve gray level based on the image sink identification.

7. The system of claim 6, wherein if the image processing system tone reproduction curve is equal to the image processing system tone reproduction curve gray level, then the image processing system tone reproduction curve is used.

8. The system of claim 6, wherein if the image processing system tone reproduction curve is not equal to the image processing system tone reproduction curve gray level, then an updated image processing system tone reproduction curve gray level is determined by a linear interpretation defined by:

g′

={(g_h−

g_l)×

(R−

R_l)}/(R_h−

R_l), where

g′

is the updated image processing system tone reproduction gray level value,

g_l and g_h, are lower and higher gray level values on the image processing system tone reproduction curve, respectively,

R is the system reflectance value, and

R_l and R_h are lower and higher reflectance values on the image processing system tone reproduction curve, respectively.

9. The system of claim 1, further comprising a data file that adjusts image data to match the input source identification and the output source identification specified by image processing system tone reproduction curve for a mode of processing.

10. The system of claim 9, wherein the mode of processing is at least one of photo, halftone, fine halftone, course halftone, text and line art.

11. A method for determining an image processing system tone reproduction curve for a reproduction curve gray level value comprising:

dynamically adjusting an image processing system tone reproduction curve based on at least one of an image source identification and an image sink identification;

determining a reflectance value based on a system tone reproduction curve within a bounded-domain piecewise-continuous relation; and

determining a system gray level value, determining the reproduction curve gray level value, and aligning the system gray level value with a system tone reproduction curve gain value to produce an updated reproduction gray level value.

12. The method of claim 11, wherein determining the reflectance value based on the system tone reproduction curve uses the bounded-domain piecewise-continuous relation defined by:

R_in=L*_in/903.3 for L*_in<

8, and

R_in={(L*_in+16)/116}³ for L*_in>

8.

13. The method of claim 11, further comprising cascading the determined reflectance value with an image source tone reproduction curve to obtains the system gray level value.

14. The method of claim 11, further comprising aligning a system gray level value with a system tone reproduction curve gain value to produce an updated image processing system tone reproduction gray level value by a linear interpretation defined by:

g′

={(g_h−

g_l)×

(R−

R_l)}/(R_h−

R_l), where

g′

is the updated image processing system tone reproduction gray level value,

g_l and g_h are lower and higher gray level values on the image processing system tone reproduction curve, respectively,

R is the system reflectance value, and

R_l and R_h are lower and higher reflectance values on the image processing system tone reproduction curve, respectively.

15. The method of claim 14, wherein an adjusted image processing system gray level is determined from the updated image processing system gray level by an adjustment relation:

g″

=gain×

g′

+offset, where

g″ and

g′

are the adjusted and updated image processing system gray levels, and

gain is a coefficient and offset is a bias, both calculated from the system tone reproductive curve.

16. The method of claim 11, further comprising wherein determining the image processing system tone reproduction curve gray level is based on the image sink identification.

17. The method of claim 16, wherein if the image processing system tone reproduction curve is equal to the image processing system tone reproduction curve gray level, then the image processing system tone reproduction curve is used.

18. The method of claim 16, wherein if the image processing system tone reproduction curve is not equal to the image processing system tone reproduction curve gray level, then an updated image processing system tone reproduction curve gray level is determined by a linear interpretation defined by:

g′

={(g_h−

g_l)×

(R−

R_l)}/(R_h−

R_l), where

g′

is the updated image processing system tone reproduction gray level value,

g_l and g_h are lower and higher gray level values on the image processing system tone reproduction curve, respectively,

R is the system reflectance value, and

R_l and R_h are lower and higher reflectance values on the image processing system tone reproduction curve, respectively.

19. The method of claim 11, further comprising adjusting image data to match the input source identification and the output source identification specified by image processing system tone reproduction curve for a mode of processing.

20. The method of claim 19, wherein the mode of processing is at least one of photo, halftone, fine halftone, course halftone, text and line art.