JPH04341068A - Picture data compressor, picture data expander and picture data compression/expansion system - Google Patents

Abstract

PURPOSE:To compress/expand a picture data at a high picture compression rate even to an original picture data having a multi-value picture and a binary picture in mixture. CONSTITUTION:A picture separation means 1 separates an original picture data into a binary picture portion and a multilevel picture portion and the separated binary picture portion and multilevel picture portion are subjected to compression respectively by picture compression means 2, 3 employing different compression method and they are stored in a memory 4. At decoding, the compressed binary picture portion and multilevel picture portion are read respectively from the memory 4 and decoding means 5, 6 apply inverse conversion to that at compression to decode a picture. The decoded picture data is synthesized by a picture synthesizes means 7 and the original picture is reproduced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an image data compression device that compresses image data with high efficiency during image data transmission, storage on a storage medium, printing, etc., and an image data decompression device that expands compressed image data. , and an image data compression/expansion system including these.

0002

2. Description of the Related Art When recording or transmitting image data onto a recording medium, the image data is compressed and encoded in order to efficiently record or transmit the image data. 2. Description of the Related Art Conventionally, methods for performing orthogonal transformation such as two-dimensional discrete cosine transformation and apparatuses using the same have been known as methods for compressing image data with high efficiency and image data compression apparatuses using this compression method. (For example, JP-A-63-3
08474, Japanese Patent Application Laid-open No. 1-173974)

[0003] These methods of compressing image data reduce the amount of information in the image data by dividing the original image into a plurality of blocks and applying orthogonal transformation such as two-dimensional discrete cosine transformation to the image data of each divided block. It performs compression. According to such compression encoding of image data, image data is encoded according to its frequency components.

0004

[Problems to be Solved by the Invention] Conventional image compression methods have been devised mainly for compressing images for facsimile communications and television images, that is, multivalued images composed of dot images. , CDA(C
It is not suitable for compressing binary images such as line drawings such as computer aided design). Therefore, when compressing graphic image data that is a mixture of multivalued natural images and binary line diagrams that are composed of area areas such as television images and illustrations, the compression rate is not necessarily high. There was a problem that there was no limit.

[0005] Especially in recent years, DTP (Desk Top Pu
blishing) makes it easy to paste an image read by an image sensor (multilevel image) onto a text screen, and also paste a line drawing (binary image) drawn with drawing software onto the same text screen. Therefore, when image data created in this way that includes a mixture of multivalued images and binary images is compressed and encoded and transmitted, stored, or printed, a reduction in the compression ratio has become a particular problem.

An object of the present invention is to provide an image data compression device that has a high image compression rate even for image data in which an original image contains a mixture of multivalued images and binary images, and an image data compressed by this compression device. An object of the present invention is to provide an image data decompression device and an image data compression/decompression system including the same.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the image data compression/expansion system of the present invention includes an image separation means 1 for separating original image data into a binary image part and a multivalued image part; a first image compression means 2 that compresses the binary image portion separated by the separation means 1 using a first image compression method and outputs first compressed image data; a second image compression means 3 which compresses the multivalued image portion by a second image compression method different from the first image compression method and outputs second compressed image data; Storage means 4 connected to the image compression means 2 and 3 and storing first and second compressed image data;
a first decoding means 5 for decoding the compressed image data of by a first image decompression method;
a second decoding means 6 for decoding compressed image data using a second image decompression method; and an image synthesizing means 7 for synthesizing the decoded first and second image data to reproduce one image. Established.

[0008]

[Operation] According to the present invention, original image data is separated into a binary image part and a multivalued image part by the image separation means 1, and the image data of the separated binary image part and the image data of the multivalued image part are separated. The first and second image compression means 2 and 3 each use different compression methods to compress the image and store it in the storage means 4.

When decoding, the compressed binary image part and the multivalued image part are each read out from the storage means 4, and the first and second decoding means 5 and 6 respectively apply the inverse transformation to that during compression. to decode the image. The decoded signals are combined by the image combining means 7, and the original original image is reproduced.

According to the present invention, when an original image contains a multivalued image and a binary image, each of these is compressed and decoded, so that image data can be compressed and expanded at a high image compression rate. can.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a block diagram of an image compression/expansion system including an image data compression device and an image data expansion device according to the present invention.

The image compression/expansion system of this embodiment has an image separation circuit 1 to which original image data is input. The image separation circuit 1 separates input original image data into binary image data and multivalued image data. The output from the image separation circuit 1 is binary image data that is sent to the first image compression circuit 2.
The multivalued image data is sent to the second image compression circuit 3. The first image compression circuit 2 is an encoding circuit that compresses and encodes binary image data, and performs MMR encoding (Modified
Signal compression is performed using Modified Reading). The second image compression circuit 3 is an encoding circuit that compresses and encodes multivalued image data, and performs signal compression by DCT (discrete cosine transform). The image data compressed by the first image compression circuit 2 and the second image compression circuit 3 is sent to the memory 4 and stored at predetermined addresses, respectively. The above circuit constitutes an image data compression device.

The compressed image data sequentially read out from the memory 4 is sent to a first decoding circuit 5 and a second decoding circuit 6, respectively. The first decoding circuit 5 performs inverse transformation of the first image compression circuit 2, that is, inverse M
Perform MR conversion. The second decoding circuit 6 performs inverse transformation of the second image compression circuit 3, that is, inverse DCT, on the multivalued image data.
Perform the conversion.

First decoding circuit 5 and second decoding circuit 6
The decoded image data is sent to the image synthesis circuit. The image synthesis circuit 7 synthesizes the decoded binary image data and multi-value image data sent from the first decoding circuit 5 and the second decoding circuit 6, respectively, and reproduces the original image.

The operation of this embodiment will be explained using FIGS. 2 to 4. The original image shown in Figure 2 is “BBB...FF
It consists of a text area indicated as "FF" and an image area of a map of Japan. Furthermore, the image area of the Japanese map consists of a multivalued area shown by hatching in the figure, and a binary area made up only of prefectural boundaries. That is, although Hokkaido, Tohoku prefectures, Niigata, Nagano, and Gifu prefectures are simply shown as hatching on the diagram, they are actually displayed as multivalued images with gradations.

As shown in FIG. 2, the original image signal input to the image separation circuit 1 is separated into a multilevel image and a binary image according to the principle described later. The image signal of the binary image is sent to the first image compression circuit 2, and the image data is compressed by the MMR method. On the other hand, the image signal of the multivalued image is sent to the second image compression circuit 3, and the image data is compressed by the DCT method. The compressed image data of the binary image and the multivalued image are stored in the memory 4, respectively. When decoding, the data of the compressed binary image part and the data of the multivalued image part are read from the memory 4, and the data of the binary image part undergoes inverse MMR conversion in the first decoding circuit 5, which is the reverse of the compression process. The second decoding circuit 6 decodes the data of the multivalued image portion by subjecting it to inverse DCT transformation, which is the reverse of the compression process. The decoded image signals are synthesized by an image synthesis circuit 7, and the original original image is reproduced.

Next, a method of image separation in the image separation circuit 1 will be explained. 3 and 4 show examples of data of the original image signal input to the image separation circuit 1, which is 8×8
The image is divided into blocks, with each pixel as one block, and image data for each block is sequentially input to the image separation circuit 1.

FIG. 3 shows two adjacent blocks of a binary image part, in which the hatched part indicates a binary logic "1", and the unhatched part indicates a logic "0". show. Figure 4 shows two adjacent blocks of a multilevel image part, where the blacked out part is the part with the highest gradation, followed by the large cross hatched part, the small cross hatched part, and the diagonal line with wide intervals. The applied part,
The gradation level decreases in the order of narrow diagonal lines and white areas.

The image separation circuit 1 examines the gradation of each dot in one block of image data that has been taken in.
It is determined whether there are two or more gradations within the block. If there are only dots of two different gradation levels, the block is determined to be composed of binary image data. On the other hand, if there are dots of three or more gradation levels, the block is determined to be composed of multivalued image data. In the case of the original image shown in Figure 2, the binary area consisting only of the text area and prefecture boundaries is based on the logic "1
Since the image consists of only "" and "0", it is determined to be a binary image area, and the hatched areas in the image area of the map of Japan have 3 or more gradations as shown in Figure 4. It is determined that it is a multivalued image area.

[0020] Then, for a block determined to be a block of a binary image, it is determined whether the number of dots of two gradation levels is large, and the gradation level with the largest number of dots is the one with the least number of dots in the background of that dot. The gradation level is determined to be a line drawing part. For such blocks of binary images, the first image compression circuit 2 performs MMR conversion on the line drawings to compress and encode the images. On the other hand, the image data determined to be multivalued image data is sent to the second image compression circuit 3, and the image is compressed and encoded using the DCT method.

As described above, according to this embodiment, image data is separated into a binary image area and a multivalued image area, and the optimal image compression method is selected for each area to compress and encode the image data. ing. Therefore, since image data in the binary image area is compressed by MMR conversion with a high compression rate, all image data is
The efficiency of image compression is improved compared to compression encoding using the CT method.

In this embodiment, M is used as an image compression method.
Although the MR method and the DCT method are used, the compression of image data according to the present invention is not limited to these methods, and any other image data compression method may be used as long as it is a compression method suitable for binary image data and multivalued image data. may also be used.

[0023]

Effects of the Invention According to the present invention, the original image contains a multivalued image and two
In the case of an image containing a mixture of value images, the image data can be compressed and encoded and expanded and reproduced at a high image compression rate. Therefore, in the case of such an image, the capacity of the storage medium can be saved and the transmission efficiency of image data can be increased.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an image compression/decompression system according to the present invention.

FIG. 2 is an explanatory diagram showing an example of image separation according to the present invention.

FIG. 3 is a diagram showing an example of a binary image compressed according to the present invention.

FIG. 4 is a diagram showing an example of a multivalued image compressed according to the present invention.

[Explanation of symbols]

1 Image separation circuit 2 Image compression circuit 3 Image compression circuit 4 Memory 5 Decoding circuit 6 Decoding circuit 7 Image synthesis circuit

Claims (7)

[Claims] 1. An image data compression device for compressing image data containing a mixture of a binary image and a multivalued image, the device comprising image separation means for separating the image data into a binary image portion and a multivalued image portion. and a first image compression means that performs image compression using a first image compression method on the image data of the binary image portion separated by the image separation means;
A second image compression method different from the first image compression method is applied to the image data of the multivalued image portion separated by the image separation means.
An image data compression device comprising: a second image compression means for compressing an image using the image compression method described above. 2. The image data compression apparatus according to claim 1, wherein the first image compression means performs MMR encoding. 3. The image data compression apparatus according to claim 1, wherein the second image compression means performs discrete cosine transformation. 4. A first decoding means for decoding first image data compressed by a first image data compression method using a first decompression method; and a second image data different from the first image data compression method. The second image data compressed by the data compression method is decoded by the second decompression method.
and an image synthesizing means for synthesizing the first image data and the second image data decoded by the first decoding means and the second decoding means to reproduce one image. An image data decompression device comprising: 5. The first image data compression method is MM.
5. The image data decompression apparatus according to claim 4, wherein image compression is performed by R encoding. 6. The image data decompression apparatus according to claim 4, wherein the second image data compression method is image compression using discrete cosine transformation. 7. An image data compression/expansion system that compresses and expands original image data in which a binary image and a multivalued image are mixed.
image separation means for separating into a value image part and a multivalue image part;
a first image compression means for compressing the image data of the binary image portion separated by the image separation means using a first image compression method and outputting first compressed image data; and the image separation means. a second image compression means for compressing the image data of the multivalued image portion separated by a second image compression method different from the first image compression method and outputting second compressed image data; , storage means connected to the first and second image compression means and storing the first and second compressed image data; and storage means for storing the first and second compressed image data read from the storage means; a first decoding means for decoding the second compressed image data read from the storage means using a second image decompression method; An image data compression/expansion system comprising: image synthesis means for synthesizing image data decoded by the second decoding means to reproduce one image.