# US 7,612,915 B2 · Determining composite grays

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- Number: US 7,612,915 B2
- Document ID: US7612915B2
- Status: Granted
- Kind: B2
- Application number: 11/254,628
- Filed: 2005-10-20
- Published: 2007-04-26
- Granted: 2009-11-03
- Earliest claimed: 2005-10-20
- Assignees: Hewlett-Packard Development Company, L.P.
- Inventors: Huanzhao Zeng; Mary Nielsen
- Web page: https://patentgrep.com/patent/US7612915B2

## CPC

- H04N 1/6027: {Correction or control of colour gradation or colour contrast (H04N1/6058 takes precedence)}
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A system and method for determining composite grays using device values. Device values are received from image data on which color separation was performed. Gray component replacement are determined on black point device values by using target lightness values, target chromaticity values, and target black device values. A printing device and a computer readable media having computer instructions for implementing the method of determining composite grays are also provided.

## Claims

### Claim 1

A computer-readable medium having instructions stored thereon such that execution of the instructions by a processing device causes a method for determining composite grays to be performed, the method comprising:
defining target lightness values by performing a black point adjustment on lightness values of black device values, where performing the black point adjustment comprises evaluating:
Lcrv=Lcbp+(Linp−Lpbp)*(Lwp−Lcbp)/(Lwp−Lpbp),
where Lcrv is a target lightness value being defined, Lcbp is a lightness value of a composite gray black point for a device, Linp is an input lightness value for a black device point, Lpbp is a lightness value of a process black point for the device, and Lwp is a lightness value of a media white point;
defining target chromaticity values corresponding with a chromaticity curve of neutral grays;
defining target black device values by performing gray component replacement on black device values, where performing the gray component replacement comprises evaluating:
Kgcr=Kmax*((Kinp−Kstr)/(UPPER−Kstr))^EF,
where Kgcr is a linearized black device value being defined and having a replaced gray component, Kmax is an upper black device value for the device, Kinp is an input linearized black device value having a gray component to be replaced, Kstr is a starting value for gray component replacement, UPPER is an upper device value for the device, and EF is an exponential shaping factor; and
determining composite gray device values by using the target lightness values, the target chromaticity values, and the target black device values.

### Claim 2 (depends on 1)

The computer-readable medium of claim 1, wherein defining the target lightness values includes defining target lightness values by performing the black point adjustment on the lightness values of black device values, wherein the black point adjustment is based on a black point, at which:
a black device value equals the upper device value for the device; and
each non-black device value equals a lower device value for the device.

### Claim 3 (depends on 2)

The computer-readable medium of claim 2, wherein defining the target lightness values includes using a black point adjustment formula, which includes a white point, at which, a device value for each color of the output device, equals a lower device value for the device.

### Claim 4 (depends on 1)

The computer-readable medium of claim 1, wherein defining the target chromaticity values includes defining target chromaticity values corresponding with a chromaticity curve, which includes:
a white point, with zero chromaticity; and
a black point, with a non-zero chromaticity.

### Claim 5 (depends on 1)

The computer-readable medium of claim 1, wherein defining the target chromaticity values includes defining target chromaticity values, corresponding with a chromaticity curve, which includes a black point with a highest chromaticity of the chromaticity curve.

### Claim 6 (depends on 1)

The computer-readable medium of claim 1, wherein defining the target chromaticity values includes defining target chromaticity values corresponding with a chromaticity curve, which smoothly transitions from a white point to a black point.

### Claim 7

A computer readable medium, having instructions stored thereon for
causing a device to perform a method, comprising:
sampling black device values to obtain linearized black device values;
calculating lightness values of the linearized black device values, by evaluating:
Lcrv=Lcbp+(Linp−Lpbp)*(Lwp−Lcbp)/(Lwp−Lpbp),
where Lcrv is a target lightness value being calculated, Lcbp is a lightness value of a composite gray black point for a device, Linp is an input lightness value for a black device point, Lpbp is a lightness value of a process black point for the device, and Lwp is a lightness value of a media white point;
digitizing the linearized black device values to form digitized black device values;
determining black device values for composite gray device values by performing a gray component replacement on the digitized black device values, where performing the gray component replacement comprises evaluating:
Kgcr=Kmax*(Kinp−Kstr)/(UPPER−Kstr))^EF,
where Kgcr is a linearized black device value being determined and having a replaced gray component, Kmax is an upper black device value for the device, Kinp is an input linearized black device value having a gray component to be replaced, Kstr is a starting value for gray component replacement, UPPER is an upper device value for the device, and EF is an exponential shaping factor; and
determining lightness values of the non-black device values of the composite gray device values by using the calculated lightness values.

### Claim 8 (depends on 7)

The medium of claim 7, wherein the sampling includes sampling a digital-to-linear look-up-table for black device values.

### Claim 9 (depends on 8)

The medium of claim 8, wherein the digitizing includes digitizing the linearized black device values by using a linear-to-digital look-up-table that is an inverse of the digital-to-linear look-up-table.

### Claim 10 (depends on 7)

The medium of claim 7, wherein the sampling includes:
sampling a first black device value that is a lower device value of the device; and
sampling a second black device value that is an upper device value of the device.

### Claim 11 (depends on 10)

The medium of claim 10, wherein the determining black device values includes using a gray component replacement formula, which includes the second black device value.

### Claim 12 (depends on 10)

The medium of claim 10, wherein the sampling includes uniformly sampling black device values of the device, between the first black device value and the second black device value.

### Claim 13

A printing device, comprising:
a processor;
a memory coupled to the processor; and
an ASIC, the ASIC including instructions executable to:
generate a conversion look-up-table that relates device values of a device to color exchange space values;
generate a digital-to-linear look-up-table for black device values of the device;
sample a black device value from the digital-to-linear look-up table and by employing gray component replacement, where performing the gray component replacement comprises evaluating:
Kgcr=Kmax*((Kinp−Kstr)/(UPPER−KstrY))^EF,
where Kgcr is a linearized black device value being defined and having a replaced gray component, Kmax is an upper black device value for the device, Kinp is an input linearized black device value having a gray component to be replaced, Kstr is a starting value for gray component replacement, UPPER is an upper device value for the device, and EF is an exponential shaping factor; and
determine at least a portion of a composite gray color for the output device by using the sampled black device value.

### Claim 14 (depends on 13)

The printing device of claim 13, the ASIC including instructions executable to determine a black device color of the composite gray color by using the sampled black device value with a replaced gray component.

### Claim 15 (depends on 13)

The printing device of claim 13, the ASIC including instructions executable to define a lightness of the composite gray color, by matching nonblack device colors in the look-up-table with a lightness value of the sampled black device value.

### Claim 16 (depends on 15)

The printing device of claim 15, the ASIC including instructions executable to define a chromaticity of the composite gray color, by matching non-black device values in the look-up-table with a chromaticity value corresponding with a chromaticity curve.

### Claim 17 (depends on 16)

The printing device of claim 16, the ASIC including instructions executable to repeat the program instructions to determine a set of N composite gray colors.

### Claim 18

A device, comprising:
a processor;
a memory coupled to the processor; and
means for generating balanced composite grays suitable for mapping to a device gamut without adjusting a neutral balance of the grays, by performing color matching during a color separation process wherein the means for generating includes instructions executable to generate the balanced composite gray components by at least performing gray component replacement, where performing the gray component replacement comprises evaluating
Kgcr=Kmax*((Kinp−Kstr)/(UPPER−Kstr))^EF,
where Kgcr is a linearized black device value being defined and having a replaced gray component, Kmax is an upper black device value for the device, Kinp is an input linearized black device value having a gray component to be replaced, Kstr is a starting value for gray component replacement, UPPER is an upper device value for the device, and EF is an exponential shaping factor.

### Claim 19 (depends on 18)

The device of claim 18, wherein the means for generating includes instructions executable to generate the balanced composite grays by using a target produced by a device associated with the device gamut.