Method of and apparatus for image processing

• US 20060023939A1
• Filed: 09/28/2005
• Published: 02/02/2006
• Est. Priority Date: 03/23/2000
• Status: Active Grant

• Current Assignee: RISO Kagaku Corporation
• Original Assignee: RISO Kagaku Corporation
• Inventors: Kashioka, Atsushi
• Granted Patent: US 7,095,889 B2
• Time in Patent Office: Days
• US Class Current: 382/162
• CPC Class Codes: H04N 1/40012 Conversion of colour to monochrome

Abstract

A monochromatic image signal is made from a color image signal. Values of brightness of pixels in a color border region of a type where two color regions which are small in brightness difference and large in chromaticity difference are positioned side by side are changed to new values different from those represented by the image signal component for the pixel of the color image signal, and a monochromatic image signal is generated with values of brightness of pixels in the color border region set to the new values and values of brightness of pixels in regions other than the color border region set to those as represented by the image signal components for the pixels of the color image signal.

Claims

1. An image processing method of making a monochromatic image signal made up of image signal components representing image data on respective pixels from a color image signal made up of image signal components representing image data on respective pixels, the method comprising,

the steps of dividing the color image signal into a plurality of blocks of a predetermined size, and determining the values of brightness and chromaticity of each block on the basis of the values of brightness and chromaticity of each pixel in the block represented by image signal components for the pixel of the color image signal,

the step of determining whether a designated block is a block in a color border region of a type where two color regions which are small in brightness difference and large in chromaticity difference are positioned side by side on the basis of the difference in value of brightness between the designated block and neighbor blocks near the designated block and the difference in value of chromaticity between the designated block and the neighbor blocks,

the steps of, when the designated block is determined to be a block in a color border region of said type, obtaining the values of brightness and chromaticity of at least two colors representative of colors forming the color border on the basis of the values of brightness and chromaticity of the neighbor blocks, and changing the value of brightness of each pixel in the designated block to a new value different from that represented by the image signal component for the pixel of the color image signal on the basis of the values of brightness and chromaticity of the pixel, the values of brightness and chromaticity of the respective representative colors and a preset order of priority of colors, and

the step of making a monochromatic image by setting values of brightness of pixels in the block in the color border region to said new values and setting values of brightness of pixels in the blocks in regions other than the color border region to those as represented by the image signal components for the pixels of the color image signal.

2. An image processing apparatus for making a monochromatic image signal made up of image signal components representing image data on respective pixels from a color image signal made up of image signal components representing image data on respective pixels comprising

a block brightness/chromaticity calculating means which divides the color image signal into a plurality of blocks of a predetermined size and determines the values of brightness and chromaticity of each block on the basis of the values of brightness and chromaticity of each pixel in the block represented by image signal components for the pixel of the color image signal,

a color border determining means which determines whether a designated block is a block in a color border region of a type where two color regions which are small in brightness difference and large in chromaticity difference are positioned side by side on the basis of the difference in value of brightness between the designated block and neighbor blocks near the designated block and the difference in value of chromaticity between the designated block and the neighbor blocks,

a representative color determining means which obtains the values of brightness and chromaticity of at least two colors representative of colors forming the color border concerning the designated block determined to be a block in the color border region on the basis of the values of brightness and chromaticity of the neighbor blocks,

a color border enhancing brightness calculating means which changes the value of brightness of each of the pixels in the block determined to be a block in the color border region to a new value different from that represented by the image signal component for the pixel of the color image signal on the basis of the values of brightness and chromaticity of the pixel as represented by the image signal component for the pixel of the color image signal, the values of brightness and chromaticity of the respective representative colors and a preset order of priority of colors, and

a monochromatic image signal generating means which generates a monochromatic image signal by setting values of brightness of pixels in the color border region to said new values and setting values of brightness of pixels in regions other than the color border region to those as represented by the image signal components for the pixels of the color image signal.

3. An image processing apparatus as defined in claim 2, in which the color border determining means determines that the designated block is a block in a color border region of said type when there is at least one block in the neighbor blocks whose difference in brightness from that of the designated block is smaller than a first threshold value and whose difference in chromaticity from that of the designated block is larger than a second threshold value.

4. An image processing apparatus as defined in claim 2, in which the representative color determining means calculates the differences in chromaticity between a block in the neighbor blocks whose difference in brightness from that of the designated block is smaller than a first threshold value and whose difference in chromaticity from that of the designated pixel is larger than a second threshold value and the other blocks in the neighbor blocks, and takes as the values of chromaticity of the representative colors the values of chromaticity of a pair of blocks which give a maximum difference in chromaticity.

5. An image processing apparatus as defined in claim 2, in which the color border enhancing brightness calculating means determines which of the representative colors the color of each pixel in the block determined to be a block in a color border region belongs to on the basis of the values of brightness and chromaticity of the pixel and the values of brightness and chromaticity of each of the representative colors, changes the value of brightness of the pixel to a new value by adding a predetermined constant to that represented by the image signal component for the pixel of the color image signal when the representative color to which the color of the pixel belongs is higher in the order of priority of colors than the other representative color and changes the value of brightness of the pixel to a new value by subtracting a predetermined constant from that represented by the image signal component for the pixel of the color image signal when the representative color to which the color of the pixel belongs is lower in the order of priority of colors than the other representative color.

6. An image processing apparatus as defined in claim 2, in which the order of priority of colors is in the order of white, yellow, cyan, magenta, red, green, blue, black or in the order of the values of brightness of the representative colors.