JPH09233323A - Digital image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the degradation of a reproduced image by imparting a decision circuit selecting the binarization processing data due to a dither processing or an error diffusion to a sub-scanning direction intermediate density edge area in an image area separation processing. SOLUTION: This device has an image area separation means 2 deciding whether the picture element under consideration in an inputted image is a character area or a pattern area and a means 5 selecting either one of means of a pressing means 3 taking preference of resolution and a processing means 4 taking preference of gradation, based on the detection result of the image area separation means 2. The image separation means 2 is provided with an edge area detection means changing from the white ground background of a sub-scanning direction to intermediate density, is provided with a processing means deciding that the edge area is the pattern area and prevents the degradation of a reproduced image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital image reading device, and more particularly to an image area separating device for separating a character area and a picture area with high accuracy.

[0002]

2. Description of the Related Art Generally, when an image is divided into areas by a small amount of hardware and adaptively binarized, the method is generally disclosed in Japanese Patent Laid-Open No.
-176167, JP-A-5-308516, JP-A-6-150059, etc., the character area and the picture area are separated and, for example, after MTF correction is performed on the character area. Binarization is performed with a fixed threshold value, and dithering processing or binarization processing by error diffusion is performed on the picture area to achieve both character resolution and picture gradation.

The switching of the reading density in the digital image reading apparatus is performed by a combination of density conversion by digital calculation with interpolation correction in the main scanning direction and density conversion by changing the conveying speed of the traveling body or the original in the sub scanning direction. There is.

In the above-mentioned image area separation processing, in order to perform good image area separation for the data read at these various densities, it is mainly performed by switching the sag threshold value for judging the connectivity of the areas. It was

In recent years, the quality of printer output devices has improved, and the number of output devices with high resolution has increased. When the binarized data information scanned at a low reading density is output from these high-resolution output devices, it is enlarged and output to match the reproduction size. For example, A4 size: 2
The bitmap data read at 00 dpi is
When outputting in A4 size from a dpi output printer, the length and width are doubled and the area is enlarged to four times.

[0006]

In this case, since the presence of the erroneous separation area is emphasized by the enlargement processing, a more accurate image area separation processing is desired. However, according to the experiment by the applicant, in the above-described image area separation device, the edge portion of the picture in the sub-scanning direction is erroneously determined to be a character area in the above case, and therefore fixed threshold binarized data is set in the same area. However, the reproduction quality of the image was deteriorated. Further, when the pattern portion has a high density, the writing edge portion does not cause a visual discomfort even when black data based on the fixed threshold binarized data appears, but when the pattern portion is not high density, Since the difference is abrupt, an uncomfortable feeling is caused, and the reproduction quality of the image is significantly deteriorated.

The present invention has been made in order to solve the above-mentioned drawbacks of the conventional technique, and in the adaptive judgment (image area separation) processing, an edge area changing from a low density area in the sub-scanning direction to an intermediate density area. By adding a determination circuit for selecting binarized data by dither processing or error diffusion to the intermediate density edge area in the sub-scanning direction,
This is to prevent deterioration of the reproduced image.

[0008]

According to a first aspect of the present invention, there is provided an image area separating means for determining whether a target pixel in an input image is a character area or a picture area, and a detection result of the image area separating means. On the basis of the above, in the digital image reading apparatus provided with a means for selecting one of the processing means for giving priority to resolution and the processing means for giving priority to gradation, the image area separating means has a white background in the sub-scanning direction. An edge area detecting unit that changes from a background to an intermediate density is provided, and a processing unit that determines the edge area as a pattern area is provided. Therefore, from the low density area in the sub-scanning direction to the intermediate density area. Deterioration of the reproduced image is prevented by detecting a changing edge area and providing a determination circuit for selecting binarized data by dither processing or error diffusion to the intermediate density edge area in the sub-scanning direction. It is obtained by way.

According to a second aspect of the present invention, in the first aspect of the present invention, the edge region detecting means for changing from the white background in the sub-scanning direction to the intermediate density has a neighborhood (m × n pixels) with respect to the target pixel.
A means for determining whether or not the pixel of interest is the edge area based on the determination result of the area, and means for changing the size of the neighboring (m × n pixel) area according to the reading density. Accordingly, the intermediate density edge region determination processing in the sub-scanning direction according to claim 1 comprises a filter circuit for m × n pixel regions and a circuit for determining connectivity of the regions, and the read density or the document By changing the threshold value for determining the connectivity according to the above, deterioration of the reproduced image can be prevented more accurately according to the reading density or the document.

According to a third aspect of the present invention, in the first aspect of the present invention, the edge area detecting means that changes from a white background in the sub-scanning direction to an intermediate density has a pixel of interest with respect to a threshold value and a neighborhood (m ×).
(n pixels), the connectivity is determined based on the magnitude relationship, and based on the result, it is determined whether the pixel of interest is the edge region or not, and the threshold size is determined according to the read density. Is provided, the intermediate density edge area determination processing in the sub-scanning direction according to claim 1 comprises a filter circuit for m × n pixel areas and a circuit for determining connectivity of areas. By changing the threshold value for determining the connectivity according to the reading density or the original, deterioration of the reproduced image can be prevented more accurately according to the reading density or the original.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the edge area detecting means that changes from a white background in the sub-scanning direction to an intermediate density has a pixel of interest with respect to a threshold value and a vicinity (m ×).
(n pixels), and means for determining connectivity based on the magnitude relationship with the pixel, and as a result, correction is performed to determine that the pixel of interest is the edge region when there are a predetermined number or more of pixels with connectivity in the vicinity of the pixel of interest. It is characterized by including a means, therefore, for the intermediate density edge region determination result in the sub-scanning direction,
By expanding the m × n pixels, the deterioration of the reproduced image can be prevented more accurately according to the reading density or the original.

[0012]

FIG. 1 is a block diagram for explaining an embodiment of an image reading apparatus of the present invention. A scanner 1 has a photoelectric conversion element such as a CCD camera and scans an original. A black and white grayscale signal is output, and the grayscale signal is converted into, for example, a 6-bit digital signal and output. As shown in FIG. 2, the image area separation processing unit 2 is composed of an edge area detection circuit 21, a white background detection circuit 22, a sub-scanning intermediate density edge detection circuit 23, and a determination circuit 24. The judgment result is output to. The image reading apparatus further includes a resolution priority processing unit 3 including an MTF correction circuit 31 and a fixed threshold binarization circuit 32, and a smoothing circuit 41.
The gradation priority processing unit 4 including the dither processing unit 42 is provided. The selection circuit 5 for selecting an image signal selects either the image subjected to the resolution priority processing or the image subjected to the gradation priority processing according to the determination signal from the image area separation processing unit 2, and causes the host or the printer 6 to perform the selection. Output.

FIG. 2 is a diagram showing the configuration of the image area separation processing unit 2 shown in FIG. 1. In the image area separation processing unit, as described above, the edge area detection circuit 21, the white background detection circuit 22, Intermediate density edge detection circuit 23 in the sub-scanning direction and determination circuit 2
4. The determination process in the image area separation processing unit 2 is as follows. The determination result is output for each pixel. That is, (1) the pixel of interest is determined to be an edge region, there is a white background region within a predetermined range in both horizontal directions sandwiching the pixel of interest, and the pixel of interest is not an intermediate density edge region in the sub-scanning direction. When the output signal is determined to be the resolution priority area
1) is output. (2) When the pixel of interest is not the above (1), it is determined to be the gradation priority area, and the output signal “0” is output.

Specific examples of the edge area detecting circuit 21 and the white background detecting circuit 22 are disclosed in Japanese Patent Application Laid-Open No. H5-1993 filed by the present applicant.
Since it is described in detail in Japanese Patent Publication No. 176167, a description thereof will be omitted.

FIG. 3 is a detailed block diagram of the intermediate density edge detection circuit 23 in the sub-scanning direction. This detection circuit 23 is composed of a filter forming circuit 23A and an intermediate density edge detection circuit 23B, and is an area of 3 pixels × 2 lines. In the above, it is detected whether or not the pixel of interest is an intermediate density edge portion in the sub-scanning direction. That is, the detection result is as follows. (1) When the pixel of interest is the intermediate density edge in the sub-scanning direction, the output signal "1" is output. (2) If the pixel of interest is not the above (1), "0" is output.

FIG. 4A is a schematic configuration diagram of the filter forming circuit 23A, and the filter forming circuit 23A uses the 1-line buffer 23 ₁ to perform "A to F" as shown in FIG. 4B.
3 pixels × 2 lines spatial filter is formed. The pixel of interest at this time is "E". The intermediate density edge detection circuit 23B in the sub-scanning direction determines whether or not the pixel of interest "E" is an intermediate density edge based on the values of the data "A to F" from the filter formation circuit 23A. Table 1 shows the judgment conditions.

[0017]

[Table 1]

The judgment of condition 1 in Table 1 uses all the data in the 3 × 2 filter, that is, the matrix size is 3 × 2. The determination of condition 2 uses the data of “B and E”, that is, the matrix size is 1 × 2. The matrix size is switched according to the reading density or the document. In this embodiment, the condition 2 is used at a read density of 200 dpi or less, and the condition 1 is used otherwise.

FIG. 5 is a diagram for explaining the relationship between the threshold data and the density. The threshold data th1, th2 and th3 are
As shown in FIG. 5, the threshold data that can be set by the CPU is used to determine the connectivity of the intermediate density edge areas in the sub-scanning direction, and the relationship of “th1 <th2 <th3” is maintained. These thresholds are switched according to the reading density or the original. The set values in this embodiment are shown in FIG.

FIG. 7 is a diagram showing the structure of the intermediate density edge detection circuit 23 in the sub-scanning direction. This detection circuit 23 is composed of a filter forming circuit 23A, an intermediate density edge detection circuit 23B and an expansion circuit 23C. Is to detect whether or not it is an intermediate density edge portion in the sub-scanning direction. That is, the detection result is as follows. (1) When the pixel of interest is the intermediate density edge in the sub-scanning direction, the output signal "1" is output. (2) If the pixel of interest is not the above (1), "0" is output. The filter forming circuit 23A and the intermediate density edge detecting circuit 23B in the sub-scanning direction are the same as those in the above embodiment.

The expansion circuit 23C performs expansion processing on the output result of the intermediate density edge detection circuit 23B using a mask of 1 pixel × 3 lines as shown in FIG. That is, in the mask of FIG. 8, if even one pixel has a pixel determined to be "1" by the intermediate density edge detection circuit 23B, the target pixel in the mask is set to "1" as an intermediate density edge pixel in the sub-scanning direction. Is output. Such an expansion process is a process performed when the erroneous separation of the intermediate density edge region in the sub-scanning direction is large in the edge separation and the white background background separation.

FIG. 9 is a diagram showing the overall configuration of the image reading apparatus according to the present invention. As is well known, the original platen glass 101 is shown.
The original placed on the table is illuminated by an illumination lamp 103 that is integrally formed with the first mirror 102, and the reflected light is
First mirror 102 and second mirror 10 integrally configured
4, the third mirror 105 scans. After that, the reflected light is focused by the lens 138, irradiated on the CCD 106, and photoelectrically converted. The first mirror 102, the illumination lamp 103, the second mirror 104, and the third mirror 105 are movable in the A direction by using the traveling body motor 107 as a drive source.

The originals stacked on the original tray 108 are picked up by a pickup roller 109 and a pair of registration rollers 11.
0, the conveyance drum 111, and the conveyance roller 112 pass through the reading position B, are fed to the pair of paper ejection rollers 113 and 114, and are ejected onto the paper ejection tray 115. When passing through the reading position B, the document is illuminated by the illumination lamp 103 moving in the vicinity of the reading position B, and the reflected light is the first light.
The mirror 102 and the second mirror 104 integrally formed,
The third mirror 105 scans. After that, the reflected light is converged by the lens 138, irradiated on the CCD 106, and photoelectrically converted. The pickup roller 109 and the registration roller pair 110 in these processes are driven by a paper feed motor (not shown), and the transport drum 111, the transport roller 112, and the paper discharge roller pair 113 and 114 are
It is driven by the transport motor 116.

In the present embodiment, reading density conversion is performed independently for the main and the sub. The reading density conversion in the main scanning direction is performed by electric scaling. Since the diaphragm (focusing rate) of the lens 138 and the number of read pixels on the CCD 106 are fixed,
The reading density in the main scanning direction has a constant value. In this embodiment, the reading density in the main scanning direction is 400 dpi. An electrical circuit (not shown) using a line memory performs interpolation processing on the read data at 400 dpi while performing thinning processing or 2
By writing it repeatedly, it is scaled to an arbitrary dpi. For example,
In order to reduce to 200 dpi, two adjacent pixels of 400 dpi read data are interpolated and converted into one thinned pixel. Also, to expand to 800 dpi, 1
It is converted into two pixels by writing it twice while interpolating the pixel.

The scaling in the sub-scanning direction is performed by mechanical scaling. The traveling body motor 107 and the conveyance motor 116 use stepping motors. By changing the drive speeds of these motors, the scanning speed of the document in the sub-scanning direction is changed, that is, the density of the sub-scanning direction is converted. To do. For example, 40
Scanning speed at 0 dpi: 200 dpi for A
To read with, the motor is driven to scan at a scanning speed of 2 × A, and to read at 800 dpi, the motor is driven to scan at a scanning speed of A / 2.

[0026]

According to the first aspect of the present invention, an edge area changing from a low density area to an intermediate density area in the sub-scanning direction is detected, and a dithering process or an error diffusion is performed on the intermediate density edge area in the sub-scanning direction. The deterioration of the reproduced image could be prevented by adding the determination circuit for selecting the binarized data.

Effect corresponding to claim 2: The intermediate density edge area determination processing in the sub-scanning direction according to claim 1 is composed of a filter circuit for m × n pixel areas and a circuit for determining connectivity of areas, and the read density Alternatively, by changing the filter size according to the original, it is possible to prevent deterioration of the reproduced image with higher accuracy according to the reading density or the original.

Effect corresponding to claim 3: The intermediate density edge area determination process in the sub-scanning direction according to claim 1 comprises a filter circuit for m × n pixel areas and a circuit for determining connectivity of the areas, and the read density Alternatively, it is possible to prevent deterioration of the reproduced image with higher accuracy according to the reading density or the original by switching the threshold value for determining the connectivity according to the original.

Effect corresponding to claim 4: With respect to the intermediate density edge region determination result in the sub-scanning direction according to claims 2 and 3, m ×
By performing the expansion processing of n pixels, it was possible to prevent deterioration of the reproduced image more accurately according to the reading density or the original.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an image reading apparatus of the present invention.

FIG. 2 is a diagram showing a configuration of an image area separation processing unit 2 shown in FIG.

3 is a configuration diagram of an intermediate density edge detection circuit 23 in the sub-scanning direction shown in FIG.

FIG. 4 is a schematic configuration diagram of a filter forming circuit 23A shown in FIG.

FIG. 5 is a diagram for explaining the relationship between threshold data and density.

FIG. 6 is a relationship diagram between threshold data and a set value of density.

FIG. 7 is a diagram showing another configuration of the intermediate density edge detection circuit 23 in the sub-scanning direction.

FIG. 8 is a diagram showing a mask of 1 pixel × 3 lines.

FIG. 9 is an overall configuration diagram of an image reading apparatus according to the present invention.

[Explanation of symbols]

1 ... Scanner, 2 ... Image area separation processing unit, 3 ... Resolution priority processing unit, 4 ... Gradation priority processing unit, 5 ... Selection circuit, 6 ... Host printer, 21 ... Edge area detection circuit, 22 ... White background Detection circuit 23, sub-scanning intermediate density edge detection circuit,
23A ... filter forming circuit, 23B ... intermediate density edge detection circuit, 23C ... expansion circuit, 23 ₁ ... 1 line buffer, 24 ... judgment circuit, 31 ... MTF correction circuit, 32 ... fixed threshold binarization circuit, 41 ... smoothing Circuit, 42 ... Dither processing section.

Claims (4)

[Claims] 1. An image area separation means for determining whether a pixel of interest in an input image is a character area or a picture area, and processing means and a floor for giving priority to resolution based on the detection result of the image area separation means. In a digital image reading apparatus provided with a means for selecting any one of processing means giving priority to tonality, the image area separating means is an edge area detecting means for changing from a white background in the sub-scanning direction to an intermediate density. A digital image reading apparatus comprising: a processing unit that determines that the edge area is a pattern area. 2. The digital image reading apparatus according to claim 1, wherein the edge area detection unit that changes from a white background in the sub-scanning direction to an intermediate density is based on a determination result of a neighborhood (m × n pixels) area with respect to the pixel of interest. It is provided with means for determining whether or not the pixel of interest is the edge area, and means for changing the size of the neighborhood (m × n pixels) area according to the reading density. Digital image reading device. 3. The digital image reading apparatus according to claim 1, wherein the edge area detecting unit that changes from a white background in the sub-scanning direction to an intermediate density is based on a magnitude relation between a target pixel and a neighborhood (m × n pixels) with respect to a threshold value. The device further comprises means for determining connectivity and determining whether or not the pixel of interest is in the edge region based on the result, and means for changing the magnitude of the threshold value according to the reading density. A digital image reading device. 4. The digital image reading apparatus according to claim 1, wherein the edge area detection unit that changes from a white background in the sub-scanning direction to an intermediate density is based on a magnitude relation between a target pixel and a neighborhood (m × n pixels) with respect to a threshold value. And a correction unit that determines that the pixel of interest is the edge region when a predetermined number or more of the pixels of connectivity are present in the vicinity of the pixel of interest. Digital image reading device.