# US 2014/0193067 A1 · Method for converting a full colour image to a monochrome image

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- Number: US 2014/0193067 A1
- Document ID: US20140193067A1
- Status: Published application
- Kind: A1
- Application number: 14/204,134
- Filed: 2014-03-11
- Published: 2014-07-10
- Earliest claimed: 2011-09-12
- Assignees: Oce-Technologies B.V.
- Applicants: Oce-Technologies B.V.
- Inventors: Johannes H.M. JANSSEN
- Web page: https://patentgrep.com/patent/US20140193067A1

## CPC

- H04N 1/56: Processing of colour picture signals (H04N1/52 takes precedence)
- H04N 1/40012: {Conversion of colour to monochrome}
- H04N 9/646: {for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters}
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A method for converting a full color image to a monochrome image is provided, wherein the color values of pixels are decomposed in a luminance and a chrominance component. Both components are converted to a grayscale value representing an intensity of a pixel. The luminance grayscale value is in a limited range close to a light end of the available grayscale. The chrominance grayscale value is closer to the dark end of the available grayscale when the chrominance component of the color value is larger. The darkest value of the two converted values is selected for a corresponding pixel. The effect of this conversion is that colored pixels are darker than colorless pixels, which is useful to highlight parts of a monochrome image that stand out because of their color in a full color image. It is particularly useful to help color blind people recognize colored parts of an image.

## Claims

### Claim 1

A method for converting a full color image into a monochrome image, the full color image comprising pixels that have a color value and the monochrome image comprising pixels that have a grayscale value within a full range from dark to light, the method comprising the steps of:
a) selecting a pixel of the full color image;
b) decomposing the color value of the pixel into a luminance and a chrominance component;
c) converting the luminance component into a first grayscale value within a first range that is substantially smaller than the full range from dark to light and substantially on the light side of the full range;
d) converting the chrominance component into a second grayscale value within a second range that extends beyond the first range in the direction of the dark side of the full range;
e) selecting the darkest value from the first and second grayscale values as the grayscale value of a corresponding pixel within the monochrome image, and f) repeating steps a) to e) until all pixels have been selected.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the first grayscale value is within a range that is one quarter of the full range from dark to light on the light side of the full range.

### Claim 3 (depends on 1)

The method according to claim 1, wherein the step of converting the chrominance component into a second grayscale value comprises the steps of
d1) projecting the chrominence component onto a number of predetermined color directions to obtain a number of colorscale values;
d2) converting the colorscale values into grayscale values according into a number of predetermined transfer functions; and
d3) selecting the darkest grayscale value as the second grayscale value.

### Claim 4 (depends on 1)

The method according to claim 1, wherein the color value of pixels in the full color image is defined in R, G and B components and the luminance and chrominance components are calculated by linear combinations of the R, G and B components.

### Claim 5 (depends on 4)

The method according to claim 4, wherein the chrominance component is projected onto three predetermined color directions to obtain three colorscale values, the colorscale values are converted into grayscale values according to a number of predetermined transfer functions and the darkest grayscale value is selected as the second grayscale value.

### Claim 6 (depends on 1)

The method according to claim 1, wherein the color value of the pixels are converted into conventional L*, a* and b* components from which the luminance and chrominance components are derived.

### Claim 7 (depends on 6)

The method according to claim 6, wherein the luminance component is derived from the conventional L* component and the chrominance component comprises the conventional a* and b* components.

### Claim 8 (depends on 7)

The method according to claim 7, wherein the chrominance component is projected onto a number of predetermined color directions in the a*,b*-plane to obtain an equal number of colorscale values, the colorscale values are converted into grayscale values according to predetermined transfer functions and the darkest grayscale value is selected as the second grayscale value.

### Claim 9 (depends on 8)

The method according to claim 8, wherein the number of predetermined color directions is three.

### Claim 10 (depends on 9)

The method according to claim 9, wherein the three color directions comprise a first direction that makes an angle of about 20 degrees with the positive a*-direction, a second direction that is parallel to the negative a*-direction, and a third direction that is parallel to the negative b*-direction.

### Claim 11 (depends on 1)

A print system, comprising an image processing unit for converting digital image data into print data, and a print engine for applying marking material on a medium according to print data to make a hard copy of an image, characterised in that the image processing unit is configured to apply the method according to claim 1.