JP2000022939A - Image reducing device and recording medium recorded with image reducing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sharply reduce characters and a line drawing of an image such as a cartoon wherein characters, a line drawing and dots coexist while suppressing moire. SOLUTION: This image reducing device is provided with an image input means 2 which inputs an image, a character and line drawing area extracting means 3 which extracts a character and line drawing area from the image, a dummy light-shade area extracting means 4 which extracts a dummy light- shade area from the image, an image reducing means 5 which performs reducing processes of the dummy light-shade area, character and line drawing area, and other areas by using different methods, and an image output means 6 which outputs a reduced image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reduction apparatus and a recording medium on which an image reduction program is recorded, and more particularly to an image for reducing an image in which characters, line drawings and halftone dots are combined, such as comics, with high precision while avoiding moire. A recording medium on which a reduction device and an image reduction program are recorded.

[0002]

2. Description of the Related Art Recently, with the development of hardware and software, the publication of electronic books as a form of a new book that replaces existing paper media has been activated, and comics and novels have been displayed on personal computers or portable terminals. You can read. These e-books,
Although it can deal with so-called multimedia data such as audio, images, moving images, animations, etc., it takes a lot of time and labor to produce e-books from the beginning, so existing books can be scanned directly. There are many titles that are read and digitized.

Originally, printed materials such as comics and novels are printed at a very high resolution, and a scanner for reading the printed materials is also 400 dpi (dot per inch) or 6 dpi.
It has a high resolution such as 00 dpi or more. However, the resolution of personal computers and mobile terminals is at most 10
Since it is about 0 dpi, image reduction processing is required to convert an existing book into an image that can be displayed on a personal computer or a mobile terminal.

[0004] In many comics, shading or gradation is artificially applied using a screen tone. Since screen tones are composed of fine halftone dots, lines, and patterns, it is known that when they are reduced, stripes or lattice patterns usually called moiré are generated. In the present invention, an area in which shading or gradation is artificially applied using a screen tone is referred to as a pseudo shading area.

Conventionally, there are two main methods of reducing an image. One is a method of processing the entire image uniformly, and the other is a method of dividing an area and performing a reduction process on each area in an optimal manner. As a method of uniformly processing an image, a thinning process of simply thinning out pixels to reduce the size or an averaging method of determining a pixel value of a reduced image by averaging the pixel values of an original image are generally used. (Kishi Hitoshi, "Digital Image Resolution Conversion", CQ Publishing Company, Interface, June 1998, p. 72).

As a method for dividing an image into regions, there is an image processing apparatus described in Japanese Patent Application Laid-Open No. 4-365182. According to the image processing apparatus described in Japanese Patent Application Laid-Open No. 4-365182, a binarized image is divided into two regions, a line drawing region and a picture region, and the line drawing region is reduced so as to save a thin line. Discloses a method of converting pixel density into multi-valued data, then performing reduction / binarization processing, suppressing moiré generated at the time of reduction, and precisely reducing a character and a line drawing portion.

[0007]

However, in the case of reducing the size of an image such as a comic in which characters, line drawings and halftone dots are mixed,
In the thinning process, moire occurs in a halftone dot portion, and characters and line drawings are blurred or crushed. On the other hand, in the averaging method, moire is suppressed, and characters and fine lines are rarely blurred or crushed, but there is a problem that sharpness is lost as a whole. Therefore, in order to obtain sharpness, edge enhancement processing can be performed after reduction, but there is a problem that even moire that has been suppressed is emphasized and appears. In addition, moiré can be completely eliminated by increasing the average range of pixels,
On the other hand, there is a problem that characters and line drawings fall in love.

As described above, it is impossible to sharpen a character and a line image while suppressing moiré in the uniform processing of the prior art by the thinning processing and the averaging processing. The processing according to the area is required.

The image processing apparatus described in Japanese Patent Application Laid-Open No. 4-365182 performs area separation and performs reduction processing according to the area. However, comics and the like have a line drawing written in halftone dots. However, characters and line drawings cannot be separated by simple pattern matching. In addition, since characters are written as balloons in an image, it is difficult to separate them with a simple rectangle. Character / line drawing area and area other than character / line drawing 2
In the method of performing smoothing in a region other than the character / line drawing region, a character / line drawing region extraction error easily occurs. For example, thin lines and intricate characters in intricate characters may not be extracted as character / line drawing areas because they have few edge components. There is a problem.

An object of the present invention is to solve the above-mentioned problems by recording an image reduction apparatus and an image reduction method for sharply reducing an image in which a character / line image and a halftone dot are combined, such as a comic, without any moiré. The purpose of the present invention is to provide a recording medium.

[0011]

In order to solve the above problems, an image reducing apparatus according to the present invention comprises: an image input unit for inputting an image; a character / line drawing region extracting unit for extracting a character / line drawing region from the image; A pseudo-shading area extracting means for extracting a pseudo-shading area from an image; an image reducing means for performing reduction processing using a different method in a pseudo-shading area or a character / line drawing area or a region other than a pseudo-shading / character / line drawing; Image output means for outputting the processed image.

Further, the image reducing means performs a smoothing process on a pseudo shade region of the input image, performs an averaging process on a character / line drawing region, and then performs an edge emphasizing process to perform pseudo emphasis. It is characterized in that only the averaging process is performed on the area other than the shading / character / line drawing.

Further, the character / line drawing area extracting means includes:
A character / image line drawing area is extracted before a pseudo shade area is extracted from an input image.

Further, the character / line drawing area extracting means includes:
It is characterized in that a character / image line drawing area is extracted by performing edge extraction after performing a smoothing process on an input image.

Further, the pseudo-shading area extracting means obtains the variance of the peripheral pixels for each pixel of the input image, and the character / image line drawing extracting means extracts the pixels having a large variance as a character / line drawing area. It is characterized in that an area that has not been extracted is extracted as a pseudo shade area.

Further, the pseudo-shading area extracting means obtains a correlation of peripheral pixels for each pixel of the input image, and among the pixels having a low correlation, the character / image line drawing extracting means extracts the pixel as a character / line drawing area. It is characterized in that an area that has not been extracted is extracted as a pseudo shade area.

Further, the pseudo-shading area extracting means detects edges of the input image, and, among the detected edges, those which are not extracted as character / line drawing areas by the character / image line drawing extracting means. Is extracted as a pseudo shade area.

Further, the image reduction means detects an edge of the extracted pseudo shade area and stops the reduction processing when the edge value is equal to or more than a predetermined value.

Further, the image reduction means detects an edge of the extracted pseudo shade area, and performs a smoothing process again on an area whose edge value is equal to or more than a predetermined value.

Further, the recording medium on which the image reduction program of the present invention is recorded has a function of inputting an image, a function of extracting a character / line drawing area from an image, a function of extracting a pseudo-shading area from an image, and a function of pseudo-shading. It is characterized in that a computer realizes a function of performing reduction processing using different methods in an area, a character / line drawing area, or an area other than pseudo shade / character / line drawing, and a function of outputting a reduced image.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[Embodiment 1] FIG. 1 is a block diagram showing a processing flow of an image reducing apparatus 1 according to an embodiment of the present invention. An image is input by the image input means 2 and characters and
The character / line drawing area is extracted by the line drawing area extracting means 3. The pseudo-shade area extracting means 4 includes the input image and the character / line drawing extracting means 3.
The pseudo shade is extracted from the result of. The image reduction means 5 performs reduction processing on the input image in different ways in a character / line drawing area, a pseudo-shading area, and an area other than the character / line drawing / pseudo-shading, and the image output means 6 outputs the processed image.

The image input means 2 is realized by an image reading device such as a scanner, a copying machine, a camera and the like. Also, a device for reading a medium such as a CD-ROM, a hard disk, a floppy disk, and a magneto-optical disk in which an image obtained by reading an original in advance is stored,
It may be a semiconductor memory or the like.

The image output means 6 is, for example, a CRT (Cath
mode Ray Tube) or LCD (Liquid)
This is realized by an image display device such as a Crystal Display. The image output means 6 may be an image output device such as a printer, a device for writing an image on a medium such as a CD-R, a hard disk, a floppy disk, a magneto-optical disk, or a semiconductor memory.

Next, the character / line drawing area extracting means 3 will be described. The character / line image area extraction means 3 performs an edge extraction after performing a smoothing process on the input image. By performing the smoothing process, even if a line image is drawn in the pseudo shade, the pseudo shade portion can be accurately removed and only the edge components of the character and the line image can be extracted. In the smoothing process, for example,

[0026]

(Equation 1)

Using a filter as described above, the surrounding pixels are simply averaged. Although the size of the filter is 5 × 5, the size may be changed according to the resolution of the original image. Also, a filter such as a Gaussian filter in which weights are changed between the center and the periphery may be used. In edge extraction, for example,

[0028]

(Equation 2)

And

[0030]

(Equation 3)

Using the two edge extraction filters as described above, the sum of the absolute values of the outputs of the filters is used as the edge extraction result.

Using the result of the edge extraction, a pixel having a value larger than a predetermined threshold value is determined as a character or line drawing area. Among pixels having a value larger than a predetermined threshold value, an isolated point or the like may be excluded from the character or line drawing area as noise. Also, a small area surrounded by edges can be determined to be a complicated part of a character, and may be included in a character area.

Next, the pseudo shaded area extracting means 4 will be described. The pseudo shade area extracting means 4 obtains the variance of the peripheral pixels, and among the pixels having a large variance, those excluding the character / line drawing area extracted by the character / line drawing area extracting means 3 are extracted as pseudo shade areas. This is because the variance value increases both at the pseudo shade and at the edge part of the character / line drawing, etc.Therefore, it is possible to extract only the pseudo shade part by removing the character / line drawing area part from the pixel having the large variance value. it can.

FIG. 2 is an explanatory diagram of a range for obtaining a variance in a target pixel. The hatched portion in FIG. 2 is the pixel of interest, and the range surrounded by the thick line is the range for which dispersion is to be obtained. In FIG. 2, the variance is calculated for each pixel in a 5 × 5 region, but the size of the region may be changed according to the resolution of the original image. The variance value for each pixel is

[0035]

(Equation 4)

Is obtained by Here, pi is the pixel value, m is the average value of the pixels in the area to be examined for variance, and n is the number of pixels included in the area to be examined for variance.

Next, the image reducing means 5 will be described. The image reduction means 5 performs reduction by smoothing in the pseudo-shading area, performs reduction by averaging in the character / line drawing area, and then performs edge emphasis, and performs reduction by averaging only in the area other than the pseudo-shading / character / line drawing. As a result, moire is prevented in the pseudo shade area, and sharpness is maintained by performing edge emphasis while preventing blurring and crushing by averaging processing in the character / line image area. By performing only the averaging process in areas other than pseudo shades, characters, and line drawings, even if area separation has failed, it is possible to prevent noise from unnecessary smoothing and increase in noise due to unnecessary edge enhancement. . If the text / line drawing area and the pseudo shade area are adjacent to each other, the smoothing processing and the edge enhancement processing are adjacent to each other, and the image quality changes extremely. By doing so, the image quality may be smoothly changed.

FIG. 3 is a diagram for explaining the reduction processing by averaging. The small grid indicated by the broken line in the image is the grid of the original image, and the large grid indicated by the thick line is the grid of the reduced image. For the sake of simplicity, the reduced image is １ ／ of the original image.
Although it is assumed to be a multiple, it is not necessarily required to be a multiple of an integral number. If it is not a multiple of an integer, the grids of the original image and the reduced image do not match, but the coordinate values may be rounded to an integer, or pixels may be weighted and averaged according to the area ratio of the common part of the grid. The pixel value of the target pixel Pm shown in FIG. 3 is obtained by averaging the pixels indicated by oblique lines.

FIG. 4 is a diagram for explaining a reduction process by smoothing. The small grid indicated by the broken line in the image is the grid of the original image, and the large grid indicated by the thick line is the grid of the reduced image. The pixel value of the target pixel Pb shown in FIG. 4 is obtained by averaging the pixels indicated by oblique lines in a range slightly wider than the grid of the reduced image. The range in which the smoothing is performed may be changed according to the reduction ratio or the resolution of the original image.

Edge enhancement is

[0041]

(Equation 5)

This is performed by the filter shown in FIG. By performing the edge enhancement on the reduced image, it is possible to sharpen the rounding of the image due to the average reduction.

[Embodiment 2] FIG. 5 is a block diagram showing a flow of processing of an image reducing apparatus according to a second embodiment of the present invention. An image is input by the image input means 2 and characters and
The character / line drawing area is extracted by the line drawing area extracting means 3. The pseudo shade area extracting means 7 extracts the pseudo shade from the input image and the result of the character / line image area extracting means 3. The image reduction means 5 performs reduction processing of the input image in a different manner for each of the character / line drawing area and the pseudo shade area, and the area other than the character / line image / pseudo shade, and the image output means 3 outputs the processed image. . The configuration other than the pseudo-shading area extracting means 7 is the same as that of the first embodiment, and thus the description is omitted.

Next, the pseudo shade area extracting means 7 will be described. The pseudo shade area extracting means 7 obtains a correlation around the target pixel, and extracts pixels having low correlation excluding the character / line drawing area extracted by the character / line drawing area extracting means 3 as pseudo shade areas. The pseudo-shade area has a low correlation with surrounding pixels, and the edge part has a high correlation in either the vertical, horizontal, or diagonal direction.Therefore, there is little possibility that a character or a line drawing part is included in the pseudo-shade area. Become.

FIG. 6 is an explanatory diagram of a method for obtaining a correlation between surrounding pixels. First, a certain area including the target pixel is set as a reference area. The reference area A is shifted in the (x, y) direction by (+
1,0), (+ 1, + 1), (0, + 1), (-1,-
A region which is moved in four directions in the vertical, horizontal, and oblique directions in 1) is referred to as a comparison region Bi (i = 1, 2, 3, 4). At this time, the correlation value C at the pixel of interest is

[0046]

(Equation 6)

Obtained as follows.

Where | A−Bi | represents the sum of the absolute values of the differences between the corresponding pixels in the regions A and B, n is the number of pixels in the region, and Min is i = 1,. . , 4 are shown. In the present embodiment, the correlation value is obtained by the difference between the regions, but the correlation may be obtained by another method. It is determined that the larger the correlation value C, the lower the correlation, and the smaller the correlation value C, the higher the correlation.
Since the vertical, horizontal, and oblique lines have a high correlation in any of the four directions, they can be excluded from the pseudo-shade region from the beginning, and the pseudo-shade region can be extracted more accurately.

In the pseudo shade area extraction 7, pixels which are not extracted by the character / line drawing area extracting means 3 are extracted as pseudo shade areas from among the pixels whose correlation value is larger than a predetermined value (pixels having low correlation). As a result, it is possible to reliably extract only the pseudo shade area.

[Embodiment 3] In this embodiment, only the pseudo gray area extracting means of the first or second embodiment is changed, and the means other than the pseudo gray area extraction are the same as those of the first embodiment. Alternatively, the description can be omitted because it can be shared with the second embodiment. The pseudo shade area extracting means in the present embodiment detects an edge of an image, and removes, from among the pixels having a large edge value, those excluding the character / line drawing area extracted by the character / line drawing area extracting means 3, the pseudo shading. Extract as a region. This is because the output of the edge detection filter increases in both the pseudo shades and the edge portions of characters and line drawings, etc.
This is because by removing the line drawing area portion, only the pseudo shade portion can be extracted.

FIG. 7 is a diagram showing a schematic flow of processing of the image reducing apparatus according to the first to seventh aspects. S1
A processing module for inputting an image is a processing module for reading an image from an image input device such as a scanner or a storage medium into a memory of an image reduction device. S
2 is a processing module for extracting a character / image area,
After performing a smoothing process on the input image, a character / image region is extracted by performing edge extraction. S3 is a processing module for extracting a pseudo-shade area, and extracts a pseudo-shade area in accordance with the method described in the first, second, or third embodiment. S4 is S
This is a processing module that executes the image reduction processing described in the first, second, or third embodiment on the character / image area or the pseudo shade area extracted by the processing module 2 or S3. S5 is a processing module for outputting the image reduced in S4 to the image output means.

FIG. 8 is a diagram showing a schematic flow of processing of the image reducing apparatus according to the eighth aspect. S10 to S13
Is a processing module that performs the same processing as S1 to S4 in FIG. In step S14, the edge of the reduced pseudo shade area is detected. Since the pseudo shade area is smoothed, the edge value should not increase, but when moire occurs, the edge is detected.

Step S15 is a processing module for smoothing only pixels (for example, 60) whose edge value detected in step S14 is equal to or greater than a predetermined value. As described above, the feature is that the smoothing is applied to the reduced image. S16 is a processing module that outputs an image, and performs the same processing as S5.

FIG. 9 is a diagram showing a schematic flow of processing of the image reducing apparatus according to the ninth aspect. Steps S20 to S23 are processing modules that perform the same processing as steps 1 to 4 in FIG. 7 or steps S10 to S13 in FIG. In step S24, the edge of the reduced pseudo shade area is detected. Since the pseudo shade area is smoothed, the edge value should not increase, but when moire occurs, the edge is detected.

In step S25, if there is a pixel (for example, 60) whose edge value detected in step S24 is equal to or greater than a predetermined value, it is determined that moire has occurred and the reduction process is interrupted (S27). At this time, a warning may be issued only. If there is no pixel whose edge value is equal to or greater than the predetermined value, an image is output and the process ends (S2).
6).

[0056]

According to the first or second aspect of the present invention, an image is divided into three regions, ie, a pseudo-shade region, a character / line drawing region, and a region other than the pseudo-shade / character / line drawing. , Characters and line drawings can be sharpened and reduced while suppressing moire in pseudo shaded portions. For example, even when moire occurs when an image is read at a target resolution, the image is read at a high resolution that does not cause moire, and the image is reduced by the image reduction method of the present invention. A sharp image can be obtained without moiré.

Further, claim 3 or claim 4 of the present invention.
According to, by performing edge extraction after performing a smoothing process on an image, even if a character or a line drawing is written in pseudo shades, characters and line drawings can be accurately extracted without being affected by pseudo shades.
Only the line drawing part can be extracted.

Further, according to the fifth aspect of the present invention, the variance of the peripheral pixels is obtained, and the pixels having a large variance that are not extracted as the character / line image area are extracted as the pseudo shade area, thereby obtaining the character / line image. Excluding the area, only the pseudo shade area can be accurately extracted.

According to the sixth aspect of the present invention, the correlation between the peripheral pixels is obtained, and among the pixels having a low correlation, those which are not extracted as the character / line drawing area are extracted as the pseudo-shading area. It is possible to accurately extract only the pseudo shade area, excluding the character / line drawing area.

According to the seventh aspect of the present invention, the edge of the input image is detected, and among the detected edges,
By extracting, as a pseudo-gray area, an area that is not extracted as a character / line drawing area by the above-described character / image line drawing extracting means, the edge detection filter is simple, so that the pseudo-gray part can be detected more quickly. it can.

According to the eighth aspect of the present invention, the edge detection of the extracted pseudo shade area is performed, and the smoothing process is performed again on the area where the edge value is equal to or more than the predetermined value. When moiré due to the edge of the pseudo shade area that should disappear by smoothing appears, the moiré can be eliminated, and the image of a manga or the like can be reduced more accurately.

According to the ninth aspect of the present invention, the edge of the extracted pseudo shade area is detected, and when the edge value is equal to or more than a predetermined value, the reduction processing is stopped to interrupt the unnecessary processing. And normal processing can be continued.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of a range for obtaining a variance in a target pixel.

FIG. 3 is a diagram illustrating a reduction process using averaging.

FIG. 4 is a diagram illustrating a reduction process by smoothing.

FIG. 5 is a block diagram illustrating a processing flow of an image reduction device according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram of a method for obtaining a correlation between surrounding pixels.

FIG. 7 is a diagram showing a schematic flow of processing of the image reduction device according to claims 1 to 7;

FIG. 8 is a diagram showing a schematic flow of a process of an image reduction device according to claim 8;

FIG. 9 is a diagram showing a schematic flow of a process of an image reduction device according to claim 9;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image reduction device 2 Image input means 3 Character / line drawing area extraction means 4 Pseudo density area extraction means 5 Image reduction means 6 Image output means 7 Pseudo density area extraction means S1 Processing module for inputting images S2 Character / image area extraction Processing module S3 Processing module for extracting pseudo-shading area S4 Processing module for executing image reduction processing S5 Processing module for outputting image to image output means S14 Processing module for detecting edge of reduced pseudo-shading area S15 Edge value S27: A processing module that performs smoothing only on pixels whose value is equal to or greater than a predetermined value.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Katsuhiko Sato 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 5B057 AA11 CA06 CA07 CA12 CA16 CB06 CB07 CB12 CB16 CC03 CC04 CD05 CE03 CE05 5C076 AA02 AA16 AA31 BA09 5C077 LL03 MP06 MP07 NN06 PP03 PP15 PP20 PP27 PP43 PP47 PP51 PP58 PQ12 SS02 TT08

Claims (10)

[Claims] An image input unit for inputting an image; a character / line drawing region extracting unit for extracting a character / line drawing region from the image; a pseudo gray region extracting unit for extracting a pseudo gray region from the image; Image reduction comprising image reduction means for performing reduction processing using a different method in a character / line drawing area or an area other than pseudo-shading / character / line drawing, and image output means for outputting a reduced image. apparatus. 2. The image reduction unit according to claim 1, wherein the image reduction unit performs a smoothing process on a pseudo shade region of the input image, performs an averaging process on a character / line image region, and then performs an edge enhancement process on the input image. 2. The image reducing apparatus according to claim 1, wherein only the averaging process is performed on an area other than the shading / character / line drawing. 3. The image according to claim 1, wherein the character / line drawing area extracting means extracts a character / image line drawing area before extracting a pseudo shade area in the input image. Reduction device. 4. The character / line drawing area extraction unit extracts a character / image line drawing area by performing edge extraction after performing a smoothing process on an input image. Image reduction device. 5. The pseudo-shading area extracting means obtains the variance of peripheral pixels for each pixel of the input image, and extracts the pixels having a large variance as a character / line drawing area by the character / image line drawing extracting means. 5. The image reducing apparatus according to claim 1, wherein an image in a non-existing area is extracted as a pseudo shade area. 6. The pseudo-shading area extracting means obtains a correlation between neighboring pixels for each pixel of the input image, and among the pixels having a low correlation, the character / image line drawing extracting means calculates a character / image line drawing.
5. The image reducing apparatus according to claim 1, wherein an area not extracted as a line drawing area is extracted as a pseudo shade area. 7. The pseudo-shading area extracting means detects an edge of an input image, and detects an edge of the detected image which is not extracted as a character / line drawing area by the character / image line drawing extracting means. 5. The image reduction apparatus according to claim 1, wherein the image is extracted as a pseudo shade area. 8. The image reduction unit according to claim 1, wherein the image reduction unit detects an edge of the extracted pseudo-shade area, and performs a smoothing process again on an area whose edge value is equal to or more than a predetermined value. The image reduction device according to claim 7. 9. The image reduction unit according to claim 1, wherein the image reduction unit detects an edge of the extracted pseudo-shade area and stops the reduction processing when the edge value is equal to or more than a predetermined value. An image reduction device as described in the above. 10. A function of inputting an image, a function of extracting a character / line drawing area from an image, a function of extracting a pseudo-shading area from an image, a function of a pseudo-shading area or a character / line drawing area or a pseudo-shading / character / line drawing. A recording medium on which an image reduction program for realizing, by a computer, a function of performing a reduction process using a different method in a region other than the above and a function of outputting a reduced image are provided.