Enhanced color correction

• US 6,594,387 B1
• Filed: 04/28/2000
• Issued: 07/15/2003
• Est. Priority Date: 04/30/1999
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Pettitt, Gregory S., Walker, Bradley W.
• Primary Examiner(s): Wu, Jingge
• Application Number:
  US09/561,160
• Time in Patent Office: 1,173 Days
• Field of Search: 382/162-167, 358/515-540, 345/598-609
• US Class Current: 382/167
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence
• CPC Class Codes: H04N 1/6016 Conversion to subtractive colour signals
• CPC Class Codes: H04N 23/86 for controlling the colour saturation of colour signals, e.g. automatic chroma control circuits
• CPC Class Codes: H04N 9/68 for controlling the amplitude of colour signals, e.g. automatic chroma control circuits H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86

Abstract

A method and apparatus for correcting the color of an image signal. Data in a first color space such as RGB is converted (502) to primary/secondary/neutral color space by setting neutral color word equal to the minimum of the input values, the primary color word equal to the maximum of the input values minus the neutral color word, and the secondary color word equal to the median of the input values minus the neutral color word. A set of three coefficients is selected (506) for each of the primary color word, the secondary color word, and the neutral color word. The primary, secondary, and neutral color words are then multiplied by the coefficients by a matrix multiplier (504) to yield color-corrected data in the first color space.

Claims

1. A method of correcting color image data for a pixel, the method comprising the steps of:

providing intensity data for three primary colors, three secondary colors, and a neutral color for said pixel;

providing a set of matrix coefficients for each output primary color, one said coefficient for describing the contribution said output primary color makes to each of the primary, secondary, and neutral colors; and

summing the products of said matrix coefficients and corresponding said intensity data to provide a corrected intensity data value for each output primary.

2. The method of claim 1, further comprising the step of storing said corrected intensity data values.

3. The method of claim 1, further comprising the step of forming an image pixel using said corrected intensity data values.

4. The method of claim 1, further comprising the step of printing an image pixel using said corrected intensity data values.

5. A method of correcting color image data for a pixel, the method comprising the steps of:

providing image data for said pixel, said image data comprising a maximum input intensity value, a median input intensity value, and a minimum input intensity value, each said input intensity value corresponding to one of three primary colors;

converting said image data to a color space having a primary, secondary, and neutral color component, said neutral color component equal to said minimum input intensity value, said primary color component equal to the difference between said maximum input intensity value and said minimum input intensity value, and said secondary color component equal to the difference between said maximum input intensity value and said median input intensity value;

providing coefficients describing the contribution made each of three output primary colors to the formation of said primary, secondary, and neutral color components, said coefficients dependent on which of said three primary colors corresponds to said maximum, median, and minimum input intensity values;

summing the products of said coefficients and said primary, secondary, and neutral color components to provide a corrected intensity data value for each output primary.

6. The method of claim 5, further comprising the step of storing said corrected intensity data values.

7. The method of claim 5, further comprising the step of forming an image pixel using said corrected intensity data values.

8. The method of claim 5, wherein said step of providing coefficients further comprises the step of providing coefficients describing the contribution made each of three output primary colors to the formation of said primary, secondary, and neutral color components, said coefficients dependent on which of said three primary colors corresponds to said maximum, median, and minimum input intensity values and operable to compensate for a gamma correction applied to said image data.

9. A method of correcting color image data for a pixel, the method comprising the steps of:

providing image data for said pixel, said image data comprising a maximum input intensity value, and median input intensity value, and a minimum input intensity value, each said input intensity value corresponding to one of three primary colors;

converting said image data to a color space having a primary (P), secondary (S), and neutral (N) color component, said neutral color component equal to said minimum input intensity value, said primary color component equal to the difference between said maximum input intensity value and said minimum input intensity value, and said secondary color component equal to the difference between said maximum input intensity value and said median input intensity value;

providing a dynamic coefficient (X_RP) describing the contribution of said primary color component to a first output primary (R′

);

providing a dynamic coefficient (X_RS) describing the contribution of said secondary color component to said first output primary (R′

);

providing a dynamic coefficient (X_RN) describing the contribution of said neutral color component to said first output primary (R′

);

providing a dynamic coefficient (Y_GP) describing the contribution of said primary color component to a second output primary (G′

);

providing a dynamic coefficient (Y_GS) describing the contribution of said secondary color component to said second output primary (G′

);

providing a dynamic coefficient (Y_GN) describing the contribution of said neutral color component to said second output primary (G′

);

providing a dynamic coefficient (Z_BP) describing the contribution of said primary color component to a third output primary (B′

);

providing a dynamic coefficient (Z_BS) describing the contribution of said secondary color component to said third output primary (B′

);

providing a dynamic coefficient (Z_BN) describing the contribution of said neutral color component to said third output primary (B′

);

calculating a corrected output value for each said output primary according to the following equation;

$[\text{\hspace{1em}<br><br>}<br><br>\begin{array}{c}{R}^{\mathrm{\prime <br><br>}}\\ G^{\mathrm{\prime <br><br>}}\\ B^{\mathrm{\prime <br><br>}}\end{array}<br><br>\text{\hspace{1em}<br><br>}]=[\text{\hspace{1em}<br><br>}<br><br>\begin{array}{ccc}{X}_{\mathrm{RP}}& X_{\mathrm{RS}}& X_{\mathrm{RN}}\\ Y_{\mathrm{GP}}& Y_{\mathrm{GS}}& Y_{\mathrm{GN}}\\ Z_{\mathrm{BP}}& Z_{\mathrm{BS}}& Z_{\mathrm{BN}}\end{array}<br><br>\text{\hspace{1em}<br><br>}]<br><br>\text{\hspace{1em}<br><br>}[\text{\hspace{1em}<br><br>}<br><br>\begin{array}{c}P\\ S\\ N\end{array}<br><br>\text{\hspace{1em}<br><br>}].$

10. The method of claim 9, further comprising the step of storing said corrected intensity data values.

11. The method of claim 9, further comprising the step of forming an image pixel using said corrected intensity data values.

12. The method of claim 9, said steps of providing a dynamic coefficient further comprising the step of providing a dynamic coefficient compensating for a gamma correction applied to said image data.