Image compression method and apparatus, and image coding method and apparatus
First Claim
1. An image compression method of compressing a color image, comprising:
- an index conversion step of converting each pixel of the color image into an index assigned in correspondence with a color value and generating color information containing the number of pixels for each indexed color and an index image obtained by converting each of the pixels into an index;
a background determination step of determining a color value corresponding to a predetermined index in the index image as a background color of the color image;
an order determination step of determining, on the basis of the color information and the background color, an order in which the color image is compressed for each index;
a binary image generating step of generating a binary image for each index from the index image;
a compression step of compressing the binary image according to the order; and
a generating step of generating compressed image data by integrating background data containing a size of the color image and a color value of the background color and compressed data of the binary image for each of the indexes.
1 Assignment
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Accused Products
Abstract
There are provided an image coding method and apparatus and image compression method and apparatus which can properly compress a color document image with a high compression efficiency. First of all, a color reduction processing unit (102) converts each pixel of a color document image into an index assigned in correspondence with a color value, and generates color information (103) containing the number of pixels for each indexed color and an index color image (104). A color information sort unit (105) and the like determine, for example, a color value corresponding to an index of the maximum number of pixels as a background color. An order determination unit (113) determines an order. A binary image generation compression unit (109) generates a partial binary image for each index and compresses the binary image according to the order. A data integrating unit (111) generates compressed image (112) by integrating background data (108) and the compressed data of the partial binary image.
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Citations
21 Claims
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1. An image compression method of compressing a color image, comprising:
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an index conversion step of converting each pixel of the color image into an index assigned in correspondence with a color value and generating color information containing the number of pixels for each indexed color and an index image obtained by converting each of the pixels into an index; a background determination step of determining a color value corresponding to a predetermined index in the index image as a background color of the color image; an order determination step of determining, on the basis of the color information and the background color, an order in which the color image is compressed for each index; a binary image generating step of generating a binary image for each index from the index image; a compression step of compressing the binary image according to the order; and a generating step of generating compressed image data by integrating background data containing a size of the color image and a color value of the background color and compressed data of the binary image for each of the indexes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. An image compression method of compressing a color image, comprising:
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an index conversion step of converting each pixel of the color image into an index assigned in correspondence with a color value and generating color information containing the number of pixels for each indexed color and an index image obtained by converting each of the pixels into an index; a background determination step of determining a color value corresponding to a predetermined index in the index image as a background color of the color image; an order determination step of determining an index order on the basis of the color information and the background color; a binary image generating step of generating a binary image for each index from the index image; a compression step of compressing the binary image according to the index order; and a generating step of generating compressed image data by integrating background data containing a size of the color image and a color value of the background color and compressed data of the binary image for each of the indexes.
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19. An image compression method of compressing a color image, comprising:
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a sorting step of storing each pixel constituting the color image to one of a predetermined number of specific colors; a specifying step of specifying a color of the specific colors which corresponds to a background color; a ranking step of ranking the respective specific colors in a relationship in terms of overwriting with reference to a luminance value of the background color in accordance with luminance values of the specific colors except for the background color; a generating step of generating, for each of the specific colors, a concatenated pixel group constituted by a pixel corresponding to the specific color and neighboring pixels of the pixel; a replacing step of, for a concatenated pixel group corresponding to a predetermined specific color, when neighboring pixels contained in the concatenated pixel group include a pixel of a specific color ranked higher than the predetermined specific color in the relationship in terms of overwriting, replacing the neighboring pixel with the predetermined specific color; and a compression step of compressing the concatenated pixel group obtained in the replacing step.
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20. An image compression apparatus for compressing a color image, comprising:
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index conversion means for converting each pixel of the color image into an index assigned in correspondence with a color value and generating color information containing the number of pixels for each indexed color and an index image obtained by converting each of the pixels into an index; background determination means for determining a color value corresponding to a predetermined index in the index image as a background color of the color image; order determination means for determining, on the basis of the color information and the background color, an order in which the color image is compressed for each index; binary image generating means for generating a binary image for each index from the index image; compression means for compressing the binary image according to the order; and generating means for generating compressed image data by integrating background data containing a size of the color image and a color value of the background color and compressed data of the binary image for each of the indexes.
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21. A computer-readable medium storing a computer program for causing a computer to execute
an index conversion procedure of converting each pixel of the color image into an index assigned in correspondence with a color value and generating color information containing the number of pixels for each indexed color and an index image obtained by converting each of the pixels into an index; -
a background determination procedure of determining a color value corresponding to a predetermined index in the index image as a background color of the color image; an order determination procedure of determining, on the basis of the color information and the background color, an order in which the color image is compressed for each index; a binary image generating procedure of generating a binary image for each index from the index image; a compression procedure of compressing the binary image according to the order; and a generating procedure of generating compressed image data by integrating background data containing a size of the color image and a color value of the background color and compressed data of the binary image for each of the indexes.
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Specification