Method and system for color matching between digital display devices

• US 6,072,902 A
• Filed: 10/14/1997
• Issued: 06/06/2000
• Est. Priority Date: 05/03/1995
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Myers, Robin D.
• Primary Examiner(s): Chang, Jon
• Assistant Examiner(s): Patel, Jayanti K.
• Application Number:
  US08/949,330
• Time in Patent Office: 966 Days
• Field of Search: 358/518, 358/520, 358/523, 382/100, 382/162, 382/163-167, 345/154, 348/661
• US Class Current: 382/167
• CPC Class Codes: G06K 15/02 using printers
• CPC Class Codes: G06K 2215/0094 Colour printing
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: H04N 1/54 Conversion of colour picture signals to a plurality of signals some of which represent particular mixed colours, e.g. for textile printing
• CPC Class Codes: H04N 1/6055 using test pattern analysis
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut

Abstract

A method and system for matching color displayed by source and destination display devices and particularly for providing color matching between a computer monitor and an ink printer. The technique of the present invention initially determines the combination and color value ratios of single destination color components that will cause the destination device to display a color that essentially matches each of fully saturated single and dual colors of a source display device. These combinations of single destination color components and their corresponding color value ratios determine the best available blends of destination device color components for printing source device colors. A color matching algorithm is employed to derive the color value ratios--one for each of the single destination color components. Each color component ratio is then scaled and linearly interpolated over a range defined by the color matching algorithm to generate a set of look-up tables (LUTs)--one for each single destination color component. Color matching is performed by 1) performing a first series of computational steps to translate the source color value into an intermediate color value which is expressed in terms of single destination color components, 2) accessing the set of LUTs with the intermediate color value obtained in step 1 to obtain a second color value composed of the scaled linearly interpolated color values stored in the LUTs, and 3) optionally performing a second series of computational steps to translate the second color value into a color value which is expressed in terms of the original source color components.

Claims

1. A method of displaying a first color on a source display device that essentially matches a second color displayed on a destination display device, wherein said source device is a monitor and said destination device is a printer, and wherein said first color has an associated first color value composed of red, green, and blue (RGB) source color components and said second color has an associated second color value composed of red, green, blue, cyan, magenta, yellow and black (R,G,B,C,M,Y,K) single destination color components, said method comprising the steps of:

determining a combination and ratio of color values of single destination color components corresponding to each of fully saturated single and dual source component color values, each of said combination and ratio of color values of said destination components corresponding to a color displayed by said destination device that provides the closest color match with respect to hue and saturation to said each fully saturated source single and dual component color values displayed on said source device;

generating a set of look-up tables (LUTs), one LUT corresponding to each of said single destination color components using said ratio of color values, by;

scaling each of said ratio of color values to a given range, said range having an associated maximum color value and minimum value;

linearly interpolating each of said ratio of color values over said given range to generate a set of linearly interpolated color values, each of said set of interpolated color values corresponding to one of said single destination color components;

storing said each set of interpolated color values into a storage means;

using said set of LUTs to perform color matching between said first color and said second color by;

translating said first color value so as to express it in terms of an intermediate color value composed of single destination color components, wherein said intermediate color value is composed of said single destination color components r,g,b,c,m,y,k, and w each having corresponding color values;

accessing said storage means with said intermediate color value, wherein said storage means outputs said second color value, said second color value being composed of said linearly interpolated color values;

wherein said step of translating said first color value so as to express it in terms of said intermediate color value comprises the following steps;

evaluating said first color value to determine a minimum source component color value (Min(RGB)) and a maximum source component color value (Max(RGB)) wherein, Min (RGB) is equal to a white component color value (w), and wherein said white component color value is a first component of said intermediate color value;

determining a black component color value (k) in said first color value wherein, k is equal to a fully saturated source single component color value minus Max(RGB), wherein said black component color value is a second component of said intermediate color value;

determining color values r'"'"', g'"'"', and b'"'"' wherein,

space="preserve" listing-type="equation">r'"'"' =R-w

space="preserve" listing-type="equation">g'"'"' =G-w

space="preserve" listing-type="equation">b'"'"' =B-w;

determining a maximum r'"'"', g'"'"' and b'"'"' (Max(r'"'"',g'"'"',b'"'"')) value and a minimum r'"'"', g'"'"', and b'"'"' value (Min(r'"'"',g'"'"',b'"'"'));

determining remaining components of said intermediate color value wherein,

if Max(r'"'"',g'"'"',b'"'"')=r'"'"', then;

space="preserve" listing-type="equation">m=b'"'"'

space="preserve" listing-type="equation">y=g'"'"'

space="preserve" listing-type="equation">r=r'"'"'-Max(g'"'"',b'"'"')=r'"'"'-(g'"'"'+b'"'"')

space="preserve" listing-type="equation">c=0

space="preserve" listing-type="equation">g=0

space="preserve" listing-type="equation">b=0

else if Max(r'"'"'g'"'"'b'"'"')=g'"'"', then;

space="preserve" listing-type="equation">m=0

space="preserve" listing-type="equation">y=r'"'"'

space="preserve" listing-type="equation">r=0

space="preserve" listing-type="equation">c=b'"'"'

space="preserve" listing-type="equation">g=g'"'"'-Max(r,b)=g'"'"'-(r'"'"'+b'"'"')

space="preserve" listing-type="equation">b=0

else if Max(r'"'"'g'"'"'b'"'"')=b'"'"', then;

space="preserve" listing-type="equation">m=r'"'"'

space="preserve" listing-type="equation">y=0

space="preserve" listing-type="equation">r=0

space="preserve" listing-type="equation">c=g'"'"'

space="preserve" listing-type="equation">g=0

space="preserve" listing-type="equation">b=b'"'"'-Max(r,g)=b'"'"'-(r'"'"'+g'"'"').

2.

2. The method as described in claim 1 wherein further including the step of translating said second color value to express it in terms of RGB color components.

3. A system for implementing the method as described in claim 2 comprising:

a first logic means for translating said first color value so as to express it in terms of said intermediate color value;

said storage means for storing said set of scaled interpolated color values, said intermediate color value for accessing said linearly interpolated color values;

a second logic means for translating said second color value so as to express it in terms of said RGB color components.

4. The system as described in claim 3 wherein the method of translating said second color value so as to express it in terms of said RGB color components comprises the following steps:

1) determining said RGB color component values in each of said linearly interpolated color values;

2) adding said red color component color values corresponding to said each linearly interpolated color values;

3) adding said blue color component color values corresponding to said each linearly interpolated color values;

4) adding said green color component color values corresponding to said each linearly interpolated color values;

5) adding said white color component to the added red color components from steps 2-4 to obtain said red color component value of said translated second color value, adding said white color component to the added blue color components from steps 2-4 to obtain said blue color component value of said translated second color value, and adding said white color component to the added green color components from steps 2-4 to obtain said green color component value of said translated second color value.