# US 7,411,696 B2 · Smooth gray component replacement strategy that utilizes the full device gamut

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- Number: US 7,411,696 B2
- Document ID: US7411696B2
- Status: Granted
- Kind: B2
- Application number: 10/342,355
- Filed: 2003-01-15
- Published: 2004-07-15
- Granted: 2008-08-12
- Earliest claimed: 2003-01-15
- Assignees: Xerox Corporation
- Inventors: Martin S. Maltz
- Web page: https://patentgrep.com/patent/US7411696B2

## CPC

- G06K 15/00: Arrangements for producing a permanent visual presentation of the output data {, e.g. computer output printers}(printing or plotting combined with another operation, e.g. with conveying, G06K17/00)
- H04N 1/6025: {using look-up tables}
- H04N 1/6058: {Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut}
- G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

Systems and methods are disclosed of a smooth gray component replacement strategy which utilizes the full gamut of a printer device. A CMY to CMYK gray component replacement transform is disclosed which inherently exploits the full gamut of the printer, by transforming points in CMY cube to L*a*b* color space, scaling the obtained values so they fill the maximum gamut obtainable with the printer device and calculating the CMYK values needed to obtain the scaled L*a*b* values. The CMY to CMYK transform is then smoothed with an averaging filter that does not change CMYK values at the corners. The entire color gamut is adequately sampled and small changes in CMY do not produce large jumps in L*a*b*.

## Claims

### Claim 1

A method of gray component replacement usable to obtain an expanded color gamut for a color reproduction device, comprising:
transforming colorant values in a color reproduction device colorant space to color values in a color independent color space;
scaling the values in the color independent color space to fill the maximum gamut obtainable with the colorant values in the device colorant space; and
determining the colorant space values which correspond to the scaled values in the color independent space, wherein
the colorant space values which correspond to the scaled values in the color independent space are usable to control a printing device to produce an image.

### Claim 2 (depends on 1)

The method of claim 1, further comprising smoothing the determined colorant space values.

### Claim 3 (depends on 2)

The method of claim 2, wherein smoothing the colorant space values is done without changing values at the boundaries of the colorant space.

### Claim 4 (depends on 1)

The method of claim 1, wherein determining the colorant space values comprises determining the colorant space values using tetrahedral interpolation.

### Claim 5 (depends on 4)

The method of claim 4, further comprising smoothing discontinuities resulting from the tetrahedral interpolation on at least one tetrahedral face.

### Claim 6

A gray component replacement device usable to obtain an expanded color gamut for a color reproduction device, comprising:
a first transformer that transforms colorant values in a color-reproduction device colorant space to color values in a color-independent color space;
a warper that scales the values in the color-independent color space to fill a maximum gamut obtainable with the colorant values in the device-colorant space; and
a second transformer that determines the colorant space values which correspond to the scaled values in the color-independent color space; wherein the colorant space values which correspond to the scaled values in the color independent space are usable to control a printing device to produce an image.

### Claim 7 (depends on 6)

The device of claim 6, further comprising a smoother that smoothes the determined colorant space values.

### Claim 8 (depends on 7)

The device of claim 7, wherein the smoother smoothes the colorant space values without changing the colorant space values at the boundaries of the colorant space.

### Claim 9 (depends on 6)

The device of claim 6, wherein the second transformer determines the colorant space values using tetrahedral interpolation.

### Claim 10 (depends on 9)

The device of claim 9, further comprising a smoother to smooth discontinuities resulting from the tetrahedral interpolation on at least one tetrahedral face.