JP2003338935A - Image processing equipment and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide image processing equipment wherein image is compressed in such a manner that high picture quality is maintained in a target size, and to provide its method. <P>SOLUTION: In image compression processing, region dividing is performed to a color document image, a binary MMR compression code is used for a latter region part, and a JPEG compression code is used for a substratum part extracting letters. Data are obtained wherein information regarding both of the latter region and the substratum, region position information and latter color information are synthesized, so that high compression ratio is obtained while picture quality is maintained to be high. In the processing, resolution is determined while resolution conversion is performed repeatedly in such a manner that the whole compression code size is accommodated in a previously designated size. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method.

[0002]

2. Description of the Related Art In recent years, the spread of scanners has promoted the digitization of documents. If you try to store a digitized document in full color bitmap format, for example: In the case of A4 size, 300 dpi requires about 24 Mbytes, which requires a huge amount of memory. Such a large amount of data cannot be said to have a size suitable for being attached to a mail and transmitted. Therefore, compression of a full-color image is usually performed, and JPEG is known as a compression method thereof. JPEG is very effective in compressing a natural image such as a photograph, and has good image quality. On the other hand, however, when a high frequency portion such as a character portion is JPEG-compressed, image deterioration called mosquito noise occurs and the compression rate is poor. Therefore, the JP of the background part is extracted by dividing the area and removing the character area.
There is a method in which EG compression and MMR compression of a character area portion with color information are created, and when decompressing, a white portion transmits a JPEG image and a black portion is represented by a representative character color.

[0003]

In the compression for transmitting a document image, two contradictory matters, high image quality and low data amount, are required. In particular, when the user specifies the amount of data in advance, it is required to perform compression by the compression method that gives the highest image quality, with the data size as the upper limit.

As described above, the present invention is an image processing apparatus which compresses a document image by compressing it within a predetermined size by a compression method so as to obtain higher image quality, and an image processing apparatus therefor. The purpose is to provide a method.

[0005]

In order to achieve the above object, an apparatus according to the present invention comprises an extracting means for extracting a character area from multi-valued image data and generating position data of the character area, and the character area. Binarizing means for binarizing the multivalued image data to generate character area binary image data, color calculating means for calculating a representative color of the character area and generating character color data, Using the multi-valued image data of the area
Conversion means for converting the multi-valued image data of the character area to generate multi-valued image data without characters, and resolution conversion means for reducing the resolution of the multi-valued image data without characters to generate reduced multi-valued image data without characters. And a first compression unit for compressing the reduced character-less multivalued image data and a second compression unit for compressing the character region binary image data, and a predetermined required total compressed data size and a character It is characterized in that the resolution conversion means for characterless multi-valued image data is controlled based on the difference between the area binary image data.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the constituent elements described in this embodiment are merely examples, and the scope of the present invention is not intended to be limited thereto.

FIG. 1 shows a block diagram of a first embodiment of the present invention.

Reference numeral 101 denotes a character area detection unit which detects a character area from an input original image and creates coordinates 109 of a plurality of character areas. Reference numeral 102 denotes a binarizing unit that inputs the above-mentioned character area coordinates and creates a binary image 107 of the character area portion of the original image. Reference numeral 103 denotes a color calculation unit that calculates the representative color 110 of the black portion with reference to the black portion of the binary image and the original image. Reference numeral 104 denotes a character portion filling portion that creates the background image 108 by removing the area of the binary image (black) from the original image and filling the background image 108 with the surrounding color. Reference numeral 105 denotes a binary image compression unit that compresses the plurality of binary images to create a plurality of compression codes D (112). 106 is the base image 10
8 is a base image compression unit that inputs 8 and creates a compression code C (112). Reference numeral 106 denotes a 161 resolution conversion unit that performs reduction, 162 that performs JPEG compression, and 161, 16
2 is composed of a compression controller for controlling the operation. Finally, the data from 109 to 112 surrounded by the broken line are combined to form the compressed data.

FIG. 3 is a flow chart for explaining the processing in the character area detecting section.

In step S301, a color image is input, luminance conversion is performed while thinning to reduce the resolution, and a luminance image J is created. For example, the original image is RGB 24-bit 3
If it is 00 dpi, Y = 0.299R + 0.587G + 0.114B is calculated every four pixels in the vertical and horizontal directions, and when a new image J is created, the image J becomes Y8.
It becomes an image of bit 75 dpi. In step S302, the histogram of the brightness data is taken and the binarization threshold value T is calculated. Next, in step S303, the luminance image J is binarized by T to create a binary image K. Further step S304
The contour lines of black pixels are traced and all black areas are labeled. Next, in step S305, a character-like area in the black area is determined. In step S306, shapes and positions to be combined are combined.

An example will be shown. For example, the color original shown in FIG. 4 is input, and the histogram of the thinned and converted luminance is obtained as shown in FIG. Average from this histogram,
A threshold value T = 150 is calculated using data such as variance, and the binarized image is as shown in FIG. If the contour lines of the black pixels in FIG. 6 are traced and all are labeled and, for example, only the collection of black pixels whose width is less than or equal to the threshold value or height is less than the threshold value is allowed as characters, the collection of black pixels shown in FIG. It becomes a character area (it is an image, not such an image is actually created).

When these groups of black pixels are grouped according to the closeness of position, width and height, 17 character areas as shown in FIG. 8 can be detected. These coordinate data are stored in 109 of FIG.

In the above process, the color image is not binarized, but a differential filter is applied to calculate edge amounts of all pixels with neighboring pixels, and the edge amounts are binarized. The obtained binary image may be similarly contour-tracked to detect the character region.

The binarizing unit 102 creates a binary image of 17 character areas obtained by the above method. This binary image may be binarized by, for example, T calculated by the character area detection unit, or a histogram may be taken for each area to calculate an optimum binarization threshold for the character area. . As compared with the histogram of the entire surface shown in FIG. 5, the luminance histogram of a part of the character area can be expected to have a simple shape as shown in FIG. 9, so that the threshold value can be easily determined. 90
Reference numeral 1 is a set of base colors, and 902 is a set of character colors.

An example of the processing of the character portion filling portion 104 utilizing the binarization result will be described with reference to FIGS. 10 and 11.

An image as shown in FIG. 10A, in which a blue character ABC is drawn near the center with a gradation image as a background, is an original image. It is assumed that a binary image of one character area as shown in (b) is obtained from this original image. In the present embodiment, the entire image is a 32 × 32 area (hereinafter, parts)
Divide into and process each part. Figure 10 (c)
Shows how the parts are divided. For the sake of simplicity, this figure shows a state of being divided into 5 × 4 parts. The number on the upper left of each area shows the part number. When divided in this way, parts 00-04,10,14,2
Nos. 0, 24, 30 to 35 are determined to have no character area in step S1103, and thus no processing is performed,
Go to the next part. Step S for parts 11
Proceeding to 1104, the corresponding binary image is referenced, and the RGB value (or YU) of the color image corresponding to the white part of the binary image (or YU
The average value ave_color of V) may be calculated. Next, in step S1105, the corresponding binary image is referred to, and the density data of the pixel corresponding to the black pixel is set as the ave_color.

The above processing is performed for the part 1 having a character area.
Repeat steps 2, 13, 21, 22, 23.

In this manner, the pixel having the character can be filled with the average value of the pixels around the portion having the character, and the background image 108 in which only the character is apparently removed naturally is generated. It

On the other hand, FIG. 12 shows an example of a character color calculation unit utilizing the above binarization result. In the present embodiment, the result of the partial binarization result 107 is used, but the present invention is not limited to this. For example, only the coordinates of the character area and the color image are input, and the color calculation process is performed using the result of binarizing the color image again. You may go. Since processing is performed for all the extracted character areas, it is checked in step S1201 whether or not there is an unprocessed character coordinate, and if there is, it proceeds to step S1202, and if there is none, it proceeds to end. Step S1202
The thinning process of the binary image referred to by the character coordinates is performed to reduce the black corresponding to the changing portion from the background to the character portion at the time of reading by the scanner, and a new binary image newbi is created. Next, in step S1203, a histogram of each value of RGB of the original image corresponding to the black pixel of newbi is obtained (of course, another color space such as YUV may be used). In step S1204, representative values of RGB are calculated. For example, it may be the largest value. Alternatively, the number of steps in the histogram may be reduced to obtain the largest value in the rough histogram, and then the largest value in the fine histogram existing in this histogram may be obtained. By repeating the above process for all the character coordinates, one representative color is calculated for all the character coordinates.

At 105, each of the partial binary images 107 is MMR compressed to generate a compression code D.

At 106, resolution conversion and JPEG compression are performed on the base image to create a compression code C.

The details of the processing of the background image compression section 106 will be described with reference to the flowchart of FIG.

In step S1301, the target size P of the base compression code is calculated from the difference between the total compression code size S given in advance and the code size B of the compression code D obtained by compressing the partial binary image.

In step S1302, the background multi-valued image is subjected to JPEG compression to create a temporary compression code X.

In step S1303, the size of X ≦ P
At that time, X is output as the final compressed code C, and the process ends. Otherwise, the process proceeds to step S1304.

In step S1304, 1/2 resolution conversion is applied to the background multi-valued image. After that, the process returns to S1302 and the processes from S1302 to S1304 are repeated.

Finally, for the background image, the compression code C having the highest possible resolution is generated with the target size P as the upper limit.

Finally, if necessary, a format in which the character region coordinates (109), the character portion representative color (110), the compression code C (111), and the compression code D (112) are combined is created.

The format may be PDF or XML.

FIG. 2 shows a configuration diagram at the time of expansion.

A compressed code C is input to 201, and JPEG is input.
This is a JPEG decompression unit that performs decompression processing and creates a multi-valued image E. Reference numeral 202 denotes an MMR decompression unit that inputs a compression code and creates a binary image F. 203 inputs the multi-valued image E,
An enlargement unit that enlarges and creates an image G. Reference numeral 204 is an image for inputting coordinates of a character area and a representative color, selecting the image G for the white portion and the representative color for the black portion while referring to the binary image F, and creating an image H207 as a final image. It is a united part.

FIG. 14 shows an example of the result of the merge processing 204.
First, FIG. 14A shows a JPEG decompression result of the compressed code C. When the quantized lossy method of JPEG compression is used, the pixel values are slightly different from those in FIG. 10C. However, compared to the case where the original image before the character part is removed is compressed by the JPEG lossy compression method, the pixel value changes less when the same quantization table is used. By referring to the binary image (b), representative color (20, 30, 255) data is placed on the image (a) corresponding to the black pixel, and finally an image as shown in (c) is completed. This becomes the expanded image 207.

As described above, according to the present invention, in the case of performing compression with a predetermined compression code size as a target in the electronic transmission of a document, the information amount is always provided to the important character portion in the document by the high resolution. By keeping the value high and reducing the resolution as needed for portions other than the character portion, it is possible to realize an image processing apparatus that efficiently provides a compressed code of a high image quality within a target size.

[Other Embodiments] In the first embodiment, the background image compression section obtains a compression code that asymptotically approaches the target size while repeatedly performing resolution conversion. However, at the same time, compression in JPEG compression is performed. The rate may be changed to obtain a compressed code closer to the target size.

As a second embodiment of the present invention, the operation of the background image compression unit in that case will be described with reference to the flowchart of FIG.

In step S1501, the target size P of the compression code C of the background image is obtained from the target total size S and the size B of the compression code D.

In step S1502, the background multi-valued image is subjected to JPEG compression to obtain a temporary compression code X. Here, a quantization table with a low compression rate is used.

In step S1503, if the size of X ≦ P, X is set as the final compressed code C, and the process ends. Otherwise, the process advances to step S1504.

In step S1504, the background multi-valued image is subjected to JPEG compression to obtain a temporary compression code X '. Here, a quantization table that has a higher compression rate than S1502 is used.

In step S1505, if the size of X'≤P, X'is set as the final compressed code C, and the process ends. Otherwise, the process proceeds to step S1506.

In step S1304, 1/2 resolution conversion is applied to the background multi-valued image. After that, the process returns to S1502 and the processes from S1502 to S1304 are repeated.

In this description, the compression ratio of JPEG is set to two levels, low and high, but it may be divided into more detailed stages.

As described above, also in the second embodiment of the present invention, when the compression is performed with the predetermined compression code size as the target in the electronic transmission of the document, the important character portion in the document For high resolution, the amount of information is always kept high, and for non-text portions, the resolution is reduced as necessary, and the JPEG compression rate is selected, so that high image quality can be achieved efficiently within the target size. An image processing apparatus that provides the compressed code of

(Other Embodiments) Although the embodiments of the present invention have been described in detail above, the present invention may be applied to a system composed of a plurality of devices, or an apparatus composed of a single device. May be applied to.

In the present invention, a software program for realizing the functions of the above-described embodiments is supplied to a system or device directly or remotely, and the computer of the system or device reads the supplied program code. Including cases that can be achieved by executing. In that case, the form need not be a program as long as it has the functions of the program.

Therefore, the program code itself installed in the computer to implement the functional processing of the present invention by the computer also implements the present invention. That is, the claims of the present invention include the computer program itself for realizing the functional processing of the present invention.

In this case, the program may take any form such as an object code, a program executed by an interpreter, or script data supplied to an OS as long as it has the function of the program.

A recording medium for supplying the program is, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, an MO, a CD.
-ROM, CD-R, CD-RW, magnetic tape, non-volatile memory card, ROM, DVD (DVD-ROM,
DVD-R).

In addition, as a method of supplying the program,
It can also be supplied by connecting to a homepage on the Internet using a browser of a client computer, and downloading the computer program itself of the present invention or a compressed file having an automatic installation function from the homepage to a recording medium such as a hard disk. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from different homepages. That is, a WWW server that allows a plurality of users to download a program file for implementing the functional processing of the present invention on a computer is also included in the claims of the present invention.

The program of the present invention is encrypted to C
By storing the information in a storage medium such as a D-ROM and distributing it to the user, and having the user who satisfies the predetermined conditions download the key information for decrypting the encryption from the home page via the Internet, and by using the key information It is also possible to execute the encrypted program and install the program in a computer to realize it.

Further, the computer executes the read program to realize the functions of the above-described embodiments, and the OS running on the computer executes the actual processing based on the instructions of the program. The function of the above-described embodiment can be realized also by performing a part or all of the above.

Further, after the program read from the recording medium is written in the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, based on the instruction of the program,
CPU provided on the function expansion board or function expansion unit
Performs a part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0053]

According to the present invention, a color document image is divided into areas, a character area portion is a binary MMR compression code, and a background portion without characters is a JPEG compression code. In image compression processing that obtains a high compression rate while maintaining high image quality by combining area position information and character color information, a higher quality image can be obtained within the limit of the total code size desired by the user. An image processing device can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a compression device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a decompression device according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing processing of a character area detecting unit according to the first embodiment of this invention.

FIG. 4 is a diagram showing an example of an original image for explaining a character area detection process according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a histogram for explaining a character area detection process according to the first embodiment of the present invention.

FIG. 6 is a diagram showing an example of a binary image for explaining a character area detection process according to the first embodiment of the present invention.

FIG. 7 is a diagram showing an example of a character area image for explaining the character area detection processing according to the first embodiment of the present invention.

FIG. 8 is a diagram showing an example of a character area portion for explaining a character area detecting process according to the first embodiment of the present invention.

FIG. 9 is a diagram showing an example of a histogram result of a character area input to the binarizing unit 109 according to the first embodiment of this invention.

FIG. 10 is a diagram illustrating a character part filling process according to the first embodiment of this invention.

FIG. 11 is a flowchart illustrating a character part filling process according to the first embodiment of this invention.

FIG. 12 is a flowchart illustrating a process of a color calculation unit according to the first embodiment of the present invention.

FIG. 13 is a flowchart illustrating a process of a background image compression unit according to the first embodiment of the present invention.

FIG. 14 is a diagram for explaining a united portion 204 of the extension device according to the first embodiment of the present invention.

FIG. 15 is a flowchart illustrating a process of a background image compression unit according to the second embodiment of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/40 H04N 1/40 FF term (reference) 5B057 CA01 CA08 CA16 CB01 CB08 CB16 CD05 CE12 CE16 CG01 CH07 DA08 DB06 DB09 DC23 DC25 5C076 AA21 AA22 BA06 5C077 LL19 MP08 PP27 PP28 PP32 PQ19 PQ23 RR02 RR21 5C078 BA27 BA57 CA02 CA21 CA27 DA01 DA07 5L096 AA02 FA06 FA37 FA44 GA34

Claims (6)

[Claims] 1. A character area is extracted from multi-valued image data,
Extraction means for generating position data of the character area, binarization means for binarizing the multi-valued image data of the character area to generate character area binary image data, and calculation of a representative color of the character area Then, the color calculating means for generating the color data of the character and the converting means for converting the multivalued image data of the character area by using the multivalued image data of the area other than the character to generate the multivalued image data without character. A resolution conversion means for reducing the resolution of the characterless multi-valued image data to generate reduced characterless multi-valued image data; a first compression means for compressing the reduced characterless multi-valued image data; An image processing apparatus comprising: a second compression unit that compresses the value image data. 2. The image processing apparatus according to claim 1, wherein the first compression unit complies with JPEG compression. 3. The image processing apparatus according to claim 1, wherein the second compression unit complies with MMR compression. 4. The image processing apparatus according to claim 1, wherein the resolution conversion unit determines the resolution by repeatedly performing resolution conversion so that the resolution falls within a total compression code size designated in advance. 5. The resolution conversion means and the first compression means determine the resolution and the compression ratio by repeating the resolution conversion and the compression of a plurality of compression degrees so as to be within the total compression code size designated in advance. The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. 6. An image processing apparatus for decompressing an image compressed by the image processing apparatus according to claim 1, wherein the image is compressed by the first compression means. A first decompression unit for decompressing the reduced character-less multivalued image data, a second decompression unit for decompressing the character region binary image data compressed by the second compression unit, and a reduced characterless multivalued image data A resolution conversion unit for increasing the resolution to generate the characterless multi-valued image data, the position data and the color data are input, and the multi-valued image is obtained from the character area binary image data and the characterless multi-valued image data. An image processing device, comprising: an image merging unit that generates data.