JP2000069281A - Image reduction device, its method and computer-readable recording medium recorded with program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce image data while keeping image quality. SOLUTION: This device for reducing digital image data is provided with summing means 19, 20, that obtain a total number of black or white pixels in each division area obtd. by dividing the digital image data into plural divisions respectively, a discrimination means, that discriminates whether a thinning reduction processing or an overlapping reduction processing is executed in each division area, based on a relation between the total pixel number in each division area and the total number of black or white pixels in each division area, and a reduction means that reduces each division area by the reduction processing decided by the discrimination means to obtain reduced image data of the digital image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for reducing digital image data and a computer-readable recording medium on which a program is recorded.

[0002]

2. Description of the Related Art For example, when digital two-dimensional monochrome image data read by a sophisticated image reading device is stored and managed by a computer such as a personal computer or a workstation, the image data is temporarily stored in a hard disk or the like. It is stored in a device, read out from the storage device when necessary, and displayed on a display device such as a display or printed out.

In such a case, in order to display the image data as it is, the image data may be too large to fit on the display device. Therefore, generally, image data is displayed after being reduced in size according to the size of the display device.

[0004] When the original image data is large, it is common to create reduced image data for reference and print it out. FIG. 6 is a block diagram illustrating a configuration of a conventional image processing apparatus that performs the above-described process from reading image data to displaying image data.

The image processing apparatus mainly comprises an image reading device 1, a compressed image file 2, and an image display device 3. A two-dimensional image such as a monochrome photograph or a map drawn on the paper 4 is read by a scanner 5 in the image reading device 1 and temporarily stored in an image memory 6 as image data.

The digital image data stored in the image memory 6 is image-compressed by an image compression processing unit 7 to increase the storage efficiency, and is written and stored as compressed image data in a compressed image file 2.

Various image compression methods have already been implemented in the image compression processing section 7. For example, G4 in facsimile communication for transmitting monochrome image data
In the CCITT (International Telegraph and Telephone Consultative Committee) recommendation T4 or T6 adopted in the system, image compression is performed by coding the number of black pixels and white pixels arranged continuously in the horizontal direction. A method has been defined.

Therefore, if this compression method is adopted in the image compression processing section 7, the compressed image file 2 stores compressed image data composed of a large number of compression codes.

The compressed image data stored in the compressed image file 2 is read by the image display device 3 as needed, and is temporarily stored in the image data memory 8. The compressed image data stored in the image data memory 8 is further processed by an image decompression processing unit 9 into a two-dimensional array (lattice form).
Are decompressed and restored to the state where the pixels are aligned.

[0010] The decompressed and restored image data is temporarily expanded in the bitmap memory 10. The image data expanded in the bitmap memory 10 is reduced by the next image reduction processing unit 11 and then written into the display buffer 12, and the contents of the display buffer 12 are stored in the display device 13.
Displayed by

The image data reduction method adopted by the image reduction processing unit 11 mainly includes a simple thinning method,
There are two methods: a superimposition thinning method. FIG. 7 is a diagram showing a difference between the simple thinning method and the superimposed thinning method.

FIG. 7A shows the relationship between original image data and image data after simple thinning. The simple thinning method is a method of reducing the original image data 14 by removing extra image data in accordance with the reduction ratio when reducing the original image data 14. For example, when reducing to 1/3, the original image data 1 is reduced.
The reduced image data 15 is obtained by randomly excluding two pixel arrays among the three pixel arrays in the horizontal and vertical directions in FIG.

This simple thinning method is effective mainly for reducing photographic image data. FIG. 7B shows the relationship between the original image data and the image data after superimposed thinning.

The superimposition thinning method uses the original image data 1
4 is a method of reducing by overlapping pixels in a predetermined range adjacent to each other. For example, in the case of reducing to 1/3, all nine pixels in an area consisting of three pixels in the horizontal direction × three pixels in the vertical direction are used. The reduced image data 16 is obtained by calculating the logical sum. This superimposition thinning method is effective mainly when reducing drawing or document image data.

[0015]

However, when the image data in which the photograph and the drawing or the photograph and the document are mixed are reduced by using the above-mentioned conventional reduction method, the reduced image data is blurred or crushed. There are cases.

That is, when the simple thinning method is used, blurring occurs due to partial deletion of drawings and sentences in image data. In addition, when the superimposition thinning method is used, since the logical sum in the area is obtained, the photograph portion is crushed black.

Therefore, when it is desired to reduce image data including a photograph and a drawing or a mixture of a photograph and a document to a high image quality by using a conventional reducing method, the drawing / document image data and the photographic image data are separately reduced. It needs to be synthesized.

The present invention has been made in view of the above situation, and has a case where original image data has a plurality of image properties, such as a case where drawing / document image data and photographic image data are mixed. It is an object of the present invention to provide an image reduction apparatus and method capable of reducing image quality to a high image quality, and a computer-readable recording medium on which a program is recorded.

[0019]

In order to achieve the above object, the present invention takes the following measures. An image reducing device according to a first aspect of the present invention is a device for reducing digital image data, wherein a totaling means for calculating a total number of black pixels or white pixels for each divided region obtained by dividing the digital image data into a plurality. Based on the relationship between the total number of pixels in each divided area and the total number of black or white pixels in each divided area, either the thinning reduction processing or the overlap reduction processing is executed for each divided area. The image reducing apparatus includes: a determining unit that determines whether the digital image data is reduced by the reducing process determined by the determining unit; and a reducing unit that obtains reduced image data of digital image data.

An image reduction apparatus according to a second aspect is the image reduction apparatus according to the first aspect, wherein the divided area is a row or a column of digital image data. An image reduction apparatus according to a third aspect is the image reduction apparatus according to the first or second aspect, wherein the digital image data is obtained by expanding compressed image data. is there.

An image reduction method according to a fourth aspect of the present invention is a method for reducing digital image data, wherein the total number of black pixels or white pixels is determined for each divided area obtained by dividing the digital image data into a plurality. Then, based on the relationship between the total number of pixels in each divided area and the total number of black or white pixels in each divided area, either the thinning reduction processing or the overlap reduction processing is executed for each divided area. This is an image reduction method in which each divided area is reduced by the reduction processing determined by this determination, and reduced image data of digital image data is obtained.

As described above, in each of the above inventions, the reduction processing is switched for each divided area of digital image data according to the relationship between the total number of pixels and the total number of black pixels or white pixels. As a result, the original image data can be reduced by an appropriate reduction method for each of the divided areas. For example, when the drawing / document image data and the photographic image data are mixed, the properties of the original image data are reduced. Even if it changes, high-quality reduced image data can be obtained.

According to a fifth aspect of the present invention, there is provided a computer having a total function of calculating a total number of black pixels or white pixels for each divided area obtained by dividing digital image data into a plurality of divided areas.
Based on the relationship between the total number of pixels in each divided region and the total number of black or white pixels in each divided region, it is determined whether to perform the thinning reduction process or the overlap reduction process for each divided region. A computer-readable recording medium storing a program for realizing a determination function and a reduction function for reducing each divided area by the reduction processing determined by the determination function and obtaining reduced image data of digital image data. is there.

By using a recording medium on which such a program is recorded, even in the case of an apparatus not having the above-mentioned functions, the above-mentioned functions can be easily added.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the present embodiment, an image reduction apparatus to which an image reduction method for switching a reduction process is applied for each pixel array in a horizontal direction or a vertical direction, which is a divided area obtained by dividing image data, will be described.

FIG. 1 is a block diagram showing the configuration of an image reducing apparatus according to the present embodiment. The same parts as those in FIG. 6 are denoted by the same reference numerals, and the description thereof will be omitted or simply described. Here, only different portions will be described in detail.

The image reducing device 17 inputs compressed image data via the image reading device 1 and the compressed image file 2. . Here, the image reading device 1 and the compressed image file 2 have the same functions as those described above.

The image reducing device 17 is used to store the compressed image file 2
The compressed image data read from the memory is temporarily stored in the image data memory 8. For example, image data compression is CCITT
In this case, a compression code is stored in the image data memory as compressed image data.

The image expansion processing section 18 expands the compressed image data. For example, image data compression is CCIT
In the case of conforming to the T standard, the compressed code, which is compressed image data, is converted to a length code representing the length of a black pixel or a white pixel using a code table conforming to the CCITT standard. After the conversion, the image data after expansion is obtained from the length code and output to the bitmap memory 10.

The length code includes a portion for specifying black or white and a portion for indicating a length in which a state similar to the specified black or white continues. The image decompression processing unit 18 outputs the length code to the horizontal pixel counter 19.

The bitmap memory 10 stores the input decompressed image data. The horizontal image counter 19 inputs data relating to the image from the image expansion processing unit 18, and outputs the total number of black pixels for each horizontal pixel array after expansion, that is, for each row of image data (hereinafter referred to as “the number of black pixels in the horizontal direction”). "
) And hold it. Here, a length code is input from the image decompression processing unit 18 as data relating to the image, and the number of horizontal black pixels is obtained for each row.

The data applicable to the image is not limited to the length code. Simply, the line of the image data after expansion and contraction is input as the image data.
The number of black pixels in the horizontal direction may be obtained.

The vertical counter 20 receives image data from the image reduction processing section 21. In addition, in the input image data, the total number of black pixels (hereinafter, referred to as “the number of black pixels in the vertical direction”) is obtained and held for each pixel array in the vertical direction, that is, for each column of the image data.

The image reduction processing section 21 mainly has a function of determining a reduction method and a reduction function of reducing image data according to the determined reduction method. That is, this image reduction processing unit 21
, The number of black pixels in the horizontal direction for each row is input, and the expanded image data is input from the bitmap memory 10.

Further, a ratio of the number of black pixels in the horizontal direction to the total number of pixels in the row (hereinafter referred to as "horizontal black pixel ratio") is determined for each row based on the input number of black pixels in the horizontal direction for each row. .

Further, the horizontal black pixel ratio and the reduction ratio for each row are compared, and if the horizontal black pixel ratio is equal to or greater than the reduction ratio, this row is reduced by simple thinning and the horizontal black pixel ratio is reduced. Is smaller than the reduction ratio, this line is reduced by overlapping thinning. This allows
Image data reduced in the horizontal direction is obtained.

Next, the image reduction processing section 21 outputs the image data reduced in the horizontal direction to the vertical pixel counter, and receives the number of black pixels in the vertical direction for each column as a response.

On the basis of the input number of vertical black pixels in each column, the ratio of the number of vertical black pixels to the total number of pixels in each column (hereinafter, referred to as "vertical black pixel ratio") for each column. Ask for.

Further, the vertical black pixel ratio and the reduction ratio of each column are compared, and if the vertical black pixel ratio is equal to or greater than the reduction ratio, this column is reduced by simple thinning and the vertical black pixel ratio is reduced. If the ratio is smaller than the reduction ratio, this column is reduced by superimposing and thinning. This allows
Image data reduced in both the horizontal and vertical directions is obtained.

The image reduction processing section 21 stores the reduced image data in the display buffer 12. FIG. 2 is a diagram showing a change state of the image data handled by the image reduction processing device 21. One third in the horizontal direction and one third in the vertical direction.
3 shows a case where the area is reduced to 3 and the area is reduced to 1/9.

The compression code 22 in the image data memory 8
Is converted into a length code 23 in the image decompression processing unit 18. Also, the length code 23 obtained by this conversion
Is the image data 2 after expansion in the image expansion processing unit 18.
4 and stored in the bitmap memory 10.

Further, from the length code 23, the horizontal pixel counter 19 obtains the number of black pixels in each row in the horizontal direction. For example, when the reduction ratio is 1/3, since the total number of pixels in the row of this image data is 12, reduction is performed by simple thinning out in rows where the number of black pixels in the horizontal direction is 4 or more. For rows with a number smaller than 4, reduction is performed by superimposition thinning.

In the decompressed image data 24, the upper six lines are thinned out for superposition, and the lower six lines are simply thinned out. Thereby, the image data 25 reduced in the horizontal direction is obtained in the image reduction processing unit 21.

Further, from the image data 25 reduced in the horizontal direction, the vertical pixel counter 20 obtains the number of vertical black pixels in each column. Here, since the total number of pixels in the column of the image data 25 is 12, reduction is performed by simple thinning in a row in which the number of black pixels in the vertical direction is 4 or more, and overlapping is performed in a row in which the number of black pixels in the vertical direction is smaller than 4. Reduction is performed by thinning.

In the image data 25 after reduction in the horizontal direction, all four columns are simply thinned out. Thereby, reduced image data 26 is obtained in the image reduction processing unit 21.

Hereinafter, the image reducing apparatus 1 according to the present embodiment will be described.
7 is described. In this image reduction apparatus, first processing is performed until the expanded image data and the number of black pixels in the horizontal direction are obtained from the compressed image data. Next, a second process is performed until image data reduced in the horizontal direction is obtained from the compressed image data and the number of pixels in the horizontal direction. Then, a third process is performed until the final reduced image data is obtained from the image data reduced in the horizontal direction.

Hereinafter, each process will be described separately. FIG.
5 is a flowchart illustrating a first process of the image reduction device according to the present embodiment.

In the first process, after the compressed image data is stored in the image data memory 8, the bit map memory 10
The expanded image data is stored in the horizontal pixel counter 19 and the horizontal pixel counter 19 calculates the number of black pixels in the horizontal direction.

First, 1 is assigned to the horizontal line number loop variable A in the horizontal pixel counter 19 (s1).
Next, in the horizontal pixel counter 19, zero is substituted for a black pixel count variable X (s2).

Next, one compressed code, which is compressed image data, is read from the image data memory 8 to the image decompression processing unit 18 (s3). Next, the read compression code is converted by the image decompression processing unit 18 to obtain a length code (s4). This length code is output from the image expansion processing section 18 to the horizontal pixel counter 19.

Here, in the horizontal pixel counter 19,
When the length code indicates the length of the black pixel (s5), the number X of black pixel count variables is added by the number of times indicated by the length code (s6).

On the other hand, in the image decompression processing section 18, the length code is converted into the pixel of the image data, and drawn in the bit map memory 10 (s7). Next, it is determined whether or not the compression code of the compressed image data read from the image data memory 8 is the last code in the A-th row (s8).

If the result of this determination is not the last code on line A, the same processing as described above is performed. On the other hand, as a result of the determination, in the case of the last code in the A-th row, the value of the black pixel count variable X is held in the horizontal pixel counter 19 as the number of black pixels in the A-th row in the horizontal direction (s9).

Then, it is determined by the image decompression processing section 18 whether or not all the compressed codes of the compressed image data have been read from the image data memory 8 (s10). 1 is added to the variable A (s11).

When all the codes of the compressed image data have been read, the processing of the image expansion processing section 18 and the horizontal pixel counter 19 is terminated. Subsequently, FIG. 4 is a flowchart illustrating a second process of the image reduction device according to the present embodiment.

In the second process, the bit map memory 1
Decompressed image data stored in 0 and horizontal pixel counter 1
Processing until the horizontal reduction image data is obtained by the image reduction processing unit 21 based on the number of horizontal black pixels calculated in 9 is performed.

First, an initial value 1 is substituted for a loop variable H (t1). Next, the H-th row of the decompressed image data is read from the bitmap memory 10 by the image reduction processing unit 21 (t2).

Next, the number of horizontal black pixels in the H-th row is read from the horizontal counter 19 by the image reduction processing section 21 (t3). Next, based on the total number of pixels in the H-th row and the number of black pixels in the horizontal direction, the horizontal-direction black pixel ratio in the H-th row is obtained by the image reduction processing unit 21 (t
4).

Next, the image reduction processing section 21 determines the magnitude relationship between the horizontal black pixel ratio of the H-th row and the reduction ratio (t5). As a result of the magnitude relationship investigation, if the black pixel ratio in the horizontal direction is equal to or greater than the reduction ratio, the H-th row of this image is reduced by simple thinning (t6).

On the other hand, if the black pixel ratio in the horizontal direction is smaller than the reduction ratio, the H-th row of this image data is reduced by superimposition thinning (t7). Here, if H is less than the total number N of rows of the decompressed image data, H is set to 1
Are added, and the same processing is repeated (t8).

FIG. 5 is a flowchart showing a third process of the image reducing apparatus according to the present embodiment. In the third processing, processing until final reduced image data is obtained based on the horizontal reduced image data obtained by the image reduction processing unit 21 is performed.

First, an initial value 1 is substituted for a loop variable V (u1). Next, the number of black pixels in the vertical direction in the V-th row of the image data after the horizontal reduction is obtained by the vertical pixel counter 20 (u2).

Next, based on the total number of pixels in the V-th row and the number of black pixels in the vertical-direction, the ratio of the vertical black pixels in the V-th row is obtained by the image reduction processing section 21 (u3). Next, the image reduction processing unit 21 determines the magnitude relationship between the vertical black pixel ratio on the V-th row and the reduction ratio (u4).

As a result of the magnitude relationship investigation, if the ratio of black pixels in the vertical direction is equal to or greater than the reduction ratio, the V
The line is reduced by simple thinning (u5). On the other hand, if the black pixel ratio in the vertical direction is smaller than the reduction ratio,
The V-th row of this image data is reduced by superimposition thinning (u6).

Then, it is determined whether or not V is equal to or greater than the total number M of columns of the reduced image data in the horizontal direction (u7). Where V
Is greater than or equal to the total number M of columns of horizontal reduced image data,
The reduced image data is output to the display buffer 12 (u
8) If V is smaller than the total number M of rows of the reduced image data in the horizontal direction, 1 is added to V and the same processing as described above is repeated (u9).

As described above, in the image reducing apparatus 17 according to the present embodiment, the ratio of black pixels occupied for each row or column of image data is obtained, and the reduction method is switched based on this ratio. That is, simple thinning is applied to the reduction of a row or column determined to be dark, and overlap thinning is applied to the reduction of a row or column determined to be dark.

For this reason, even if the image data includes a mixture of photographs, documents, and drawings, it is possible to suppress blurring and crushing and to provide high-quality reduced image data. In the present embodiment, whether the image is dark or whitish is determined from the magnitude relationship between the ratio of the black pixels occupying the row or column and the reduction ratio, but may be determined based on other factors. For example, the determination may be made based on parameters that can be freely set by the user.

In this embodiment, the reduction method is switched according to the ratio of black pixels. However, the same effect can be obtained by switching the reduction method according to the ratio of white pixels.

Furthermore, in the present embodiment, the reduction in the vertical direction is performed after the reduction in the horizontal direction. Conversely, the reduction in the horizontal direction may be performed after the reduction in the vertical direction. Further, when handling image data having a large data capacity in the present embodiment, the image data may be divided and handled one by one.

Further, in the present embodiment, the unit of the area for switching the image data reduction method is a row or a column. However, this area is not limited to a row or a column. It can be freely defined as in

Further, each function of the image reduction apparatus according to the present embodiment is implemented as a program that can be executed by a computer, for example, a magnetic disk (floppy disk, hard disk, etc.), an optical disk (CD-RO).
M, DVD, etc.), a semiconductor memory or the like, and can be applied to the recording medium, or transmitted by a communication medium and applied to various devices. A computer that implements the present apparatus reads the program recorded on the recording medium, and executes the above-described processing by controlling the operation of the program.

[0072]

As described above in detail, in the computer-readable recording medium on which the image reducing apparatus and method and the program according to the present invention are recorded, black pixels or white pixels are provided for each divided area of digital image data. The total number is obtained, and the type of reduction processing executed for each divided area is switched based on the total number.

Therefore, an appropriate reduction process is determined and executed based on the ratio of black pixels or white pixels in each region.
For example, high-quality reduced image data can be obtained even when the characteristics of the original image data change, such as when the drawing / document image data and the photographic image data are mixed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image reduction device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a change state of image data handled by the image reduction processing device 21 according to the embodiment.

FIG. 3 is a flowchart showing first processing of the image reduction device according to the embodiment;

FIG. 4 is a flowchart showing a second process of the image reduction device according to the embodiment;

FIG. 5 is a flowchart showing a third process of the image reduction device according to the embodiment;

FIG. 6 is a block diagram showing a configuration of a conventional image processing apparatus that performs from reading image data to displaying image data.

FIG. 7 is a view showing a difference between a simple thinning method and a superimposed thinning method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Image reading device 2 ... Compressed image file 3 ... Image display device 4 ... Paper 5 ... Scanner 6 ... Image memory 7 ... Image compression processing unit 8 ... Image data memory 9, 18 ... Image decompression processing unit 10 ... Bitmap memory 11 , 21 image reduction processing unit 12 display buffer 13 display device 14 original image data 15, 16, 26 reduced image data 17 image reduction device 19 horizontal pixel counter 20 vertical pixel counter 22 compression code 23 Length code 24: expanded image data 25: horizontal reduced image data

Claims (5)

[Claims] 1. An apparatus for reducing digital image data, comprising: summing means for calculating a total number of black pixels or white pixels for each of divided areas obtained by dividing the digital image data into a plurality of pieces; Based on the relationship between the total number of pixels for each divided area and the total number of black or white pixels for each divided area, which of the thinning reduction processing or the overlap reduction processing is executed for each of the divided areas And a reduction unit that reduces each of the divided areas by the reduction processing determined by the determination unit and obtains reduced image data of the digital image data. 2. The image reduction device according to claim 1, wherein the divided area is a row or a column of the digital image data. 3. The image reduction device according to claim 1, wherein the digital image data is obtained by expanding compressed image data. apparatus. 4. A method for reducing digital image data, comprising: obtaining a total number of black pixels or white pixels for each divided region obtained by dividing the digital image data into a plurality of divided regions; Based on the relationship between the total number of pixels and the total number of black pixels or white pixels for each of the divided areas, it is determined whether to perform the thinning reduction processing or the superimposition reduction processing for each of the divided areas. An image reduction method, wherein each of the divided areas is reduced by a reduction process determined by the determination to obtain reduced image data of the digital image data. 5. A computer, comprising: a total function for calculating a total number of black pixels or white pixels for each divided region obtained by dividing digital image data into a plurality of divided regions; a total number of pixels for each divided region; A determining function of determining whether to perform a thinning-out reduction process or an overlay reduction process for each of the divided regions based on a relationship with the total number of black pixels or white pixels for each of the divided regions; A computer-readable recording medium storing a program for realizing a reduction function for reducing each of the divided areas by a reduction process determined by a function and obtaining reduced image data of the digital image data.