JPH07212578A - Method and device for processing picture - Google Patents

Abstract

PURPOSE:To simplify the method and constitution of a picture processing by using the square value of a density change value as a first judgement value and using a value obtained by adding the first judgement value as a second judgement value. CONSTITUTION:Data of a present line from a shading correction circuit and data of a line B, a line C, a line D from SRAM 21 are inputted to an area separation circuit 5. The picture element of the line C is set to be a notice picture element, and it is judged to which area among a character area, a dot area and a half tone area the notice picture element belongs. An area judgement data generation part 31 calculates a secondary differential value S, the square value SS of the secondary differential value S and the sum SIGMASS of the square value for five nearby picture elements. The respective values of S, SS and SIGMASS value generated in a data generation part 31 and the thresholds held in an area judgement register group 32 are inputted to a first area judgement part 41. The judgement part 41 compares the SS value and the SIGMASS value with the thresholds, and generates a flag SSF where the notice picture element shows the picture element of the character area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a facsimile apparatus, an image scanner apparatus or the like, and can appropriately reproduce a character image, a halftone image and a halftone image to reproduce the image well. The present invention relates to an image processing method and an image processing apparatus which can be performed.

[0002]

2. Description of the Related Art In a device for expressing an optically read image by a binary image such as a facsimile device, a binary image such as a character image and a halftone image such as a photograph are the same. An image cannot be properly reproduced by performing such a process. That is, it is appropriate to perform processing for emphasizing edges of white pixels and black pixels for a character image composed of characters and line drawings, and omit the above-described emphasis processing for a halftone image. Appropriate.

However, a facsimile apparatus may read an image in which a character image and a halftone image are mixed. In this case, a good result cannot be obtained even if the image processing corresponding to only the character image or the halftone image is performed. Therefore, when the pixels forming the image are sequentially processed as the target pixel, it is determined whether the target pixel belongs to the character area or the halftone area, and the target pixel is subjected to the processing corresponding to the determination result. It has been proposed to perform appropriate image processing on each part of the image.

A conventional technique for determining whether a pixel of interest belongs to a character area or a halftone area is described below.
This will be described with reference to FIG. The image processing circuit of the fax machine performs the process by setting each pixel as the pixel of interest X in order in the order of reading the document. In determining whether the target pixel X belongs to the character area or the halftone area, the values of the pixels A, B, C, and D located at the four corners of the matrix of 3 × 3 pixels centered on the target pixel X are referred to. To be done. That is, assuming that the multi-value density of each pixel is represented by the code of each pixel, the secondary differential value S shown in the following equation (1) is calculated. However, α is an arbitrary constant.

S = α × {(XA) + (XD) + (XB) + (XC)} (1) This secondary differential value is compared with a predetermined threshold value, and attention is paid according to the comparison result. The area determination of the pixel X is performed. That is, the density of the image changes rapidly in the character image, whereas the density of each part of the image changes gently in the halftone image. Therefore, the absolute value of the secondary differential value S is large in the character area but small in the halftone area. Therefore, if the magnitude of the secondary differential value S is determined, the character area and the halftone area can be determined.

[0006]

In the above-mentioned prior art,
The character area and the halftone area are separated only by the second derivative S. Therefore, the state of peripheral pixels is neglected, and there is a problem that the image area is not always properly discriminated. More specifically, the image read by the facsimile device includes not only a character image and a halftone image, but also a halftone dot image applied to photo printing and the like. What is a halftone dot image?
It is an image in which light and shade are expressed by the size and density of regularly arranged dots. Pixels that are determined to be a halftone region by the above-described conventional technique include pixels that form an original halftone image such as a photographic image, and pixels that form a halftone image applied to photographic printing and the like. include.

In the facsimile machine, a halftone image is subjected to a halftone process for expressing the density which changes smoothly by the density of dots. However, if this processing is applied to a halftone image in which the density is originally expressed by the density of dots, moire may occur. Therefore, in the above-described conventional technique in which the pixels forming the halftone image cannot be detected separately from the pixels forming the halftone image, appropriate image processing cannot always be performed.

Therefore, an object of the present invention is to solve the above-mentioned technical problem and to detect the constituent pixels of a character image, the constituent pixels of a halftone image, and the constituent pixels of a halftone image in good distinction, Therefore, it is an object of the present invention to provide an image processing method capable of performing appropriate processing on any type of image. Another object of the present invention is to be able to satisfactorily distinguish and detect the constituent pixels of a character image, the constituent pixels of a halftone image, and the constituent pixels of a halftone image, and thus, for any type of image An object of the present invention is to provide an image processing device capable of performing appropriate processing.

[0009]

The invention according to claim 1 for achieving the above object is an image processing method for processing an image composed of a plurality of pixels each having density data, and is an object to be processed. Of a density change value in the vicinity of the pixel to be processed based on the difference between the density data of the pixel and the density data of the surrounding pixels, and the square value of the density change value is calculated as the first determination value. The step of calculating the second judgment value by adding the first judgment value of the pixel having a predetermined positional relationship in the vicinity of the pixel to be processed, and the first judgment value and the second judgment value. A comparison step of comparing with a predetermined threshold and a determination of whether the pixel to be processed is a pixel forming a character image, a halftone image, or a halftone image based on the comparison result in this comparison step With steps The image processing method which comprises a process step for performing a predetermined processing corresponding to the determination result in the determination step to the pixel to be processed.

According to a second aspect of the present invention, in the processing step, the determination result in the determination step for the pixel to be processed and the determination result in the determination step for the pixel having a predetermined positional relationship in the vicinity of the pixel to be processed. And determining the type of processing to be performed on the pixel to be processed based on According to a third aspect of the present invention, there is provided an image processing device for processing an image composed of a plurality of pixels each having density data, and based on a difference in density data between a pixel to be processed and its peripheral pixels, Means for obtaining a density change value in the vicinity of the pixel to be processed, means for calculating the squared value of the density change value as a first determination value, and pixels having a predetermined positional relationship in the vicinity of the pixel to be processed Means for calculating the second determination value by adding the first determination value, comparison means for comparing the first determination value and the second determination value with a predetermined threshold value, and a comparison result by the comparison means. Based on the processing, a determination unit that determines whether the pixel to be processed is a pixel forming a character image, a halftone image, or a halftone image, and a predetermined process corresponding to the determination result by the determination unit is processed. And a processing means to be applied to the target pixel An image processing apparatus which comprises.

According to a fourth aspect of the invention, the processing means comprises:
Based on the determination result by the determination unit for the pixel to be processed, and the determination result by the determination unit for the pixel having a predetermined positional relationship in the vicinity of the pixel to be processed,
It is characterized by including means for determining the type of processing to be performed on the pixel to be processed.

[0012]

According to the invention of claim 1 or 3,
The density change value in the vicinity of the pixel to be processed is obtained based on the difference between the density data of the pixel to be processed and the pixels around it. Then, the squared value of this density change value is calculated and used as the first determination value when determining which of the character image, the halftone image and the halftone image the pixel to be processed belongs to. . Since the density change value is calculated based on the difference in density between the pixel to be processed and its surrounding pixels, it may take positive and negative values, whereas the first determination value is the density change value. Since it is a squared value, only positive values are taken. Therefore, it is not necessary to prepare threshold values for both positive and negative polarities, so that the processing method and configuration of image processing can be simplified.

On the other hand, the second determination value for the determination process is obtained by adding the first determination values of the pixels having a predetermined positional relationship in the vicinity of the pixel to be processed.
Therefore, the second determination value is a value that reflects the state of the pixel to be processed. With this, it is possible to favorably determine which of the character image, the halftone image, and the halftone image the pixel to be processed takes into consideration the states of the peripheral pixels.

According to the second or fourth aspect of the present invention, the type of processing to be performed on the pixel to be processed is determined by referring to the determination processing result regarding the pixel having a predetermined positional relationship in the vicinity of the pixel to be processed. It is determined. Therefore, the process for the pixel to be processed can be more appropriately performed according to the states of the surrounding pixels.

[0015]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electrical configuration of a portion related to image processing of a facsimile apparatus to which an embodiment of the present invention is applied. The original set on the facsimile is read by the scanner 1. The scanner 1 includes an image sensor such as a CCD image sensor or a CIS image sensor for reading an image. The image sensor may be an area image sensor that reads two-dimensional data or a linear image sensor that reads line data. A line image sensor is usually used to inexpensively construct the device.

The image data of the original read by the scanner 1 is given to the input interface section 2, and the interface section 2 performs signal sample and hold processing and the like. The input interface unit 2 is composed of an analog circuit in this embodiment, and the above processing is performed in an analog manner. The image data processed by the input interface unit 2 is given to the AGC circuit 3, and gain control is performed so that the level of the signal (image data) falls within a desired range.

Then, the gain-controlled image data is applied to the shading correction circuit 4 to reduce or remove the shading distortion. Shading distortion is uneven density between pixels due to uneven illumination of the reading light source when the document is read by the scanner 1.
The image data from which the shading distortion has been reduced or removed is then supplied to the area separation circuit 5. In the area separation circuit 5, whether the input image data is image data obtained by reading characters (character data), image data obtained by reading a halftone image such as a photograph (halftone data), or a print photograph For example, it is determined whether or not the image data is halftone dot image data (halftone dot data) obtained by reading a photographic image of newspaper or magazine.

If character data, halftone data and halftone dot data are mixed in the input image data, the area of each data is separated. The reason why the region separation is performed according to the type of data is to perform an appropriate process suitable for the type of data in the subsequent process. On the output side of the area separation circuit 5, a differential filter 6, an integration filter 7 and a pass-through circuit (passing signals without any processing) for performing processing corresponding to character data, halftone dot data and halftone data respectively. Circuit 8) is connected in parallel. The differential filter 6 is for performing appropriate processing on the character data, and has a function of making the boundary between the black pixel and the white pixel clear and enhancing the contour. The integration filter 7 is for performing appropriate processing on the halftone dot data and has a function of smoothing the data. The pass-through circuit 8 corresponds to the halftone data and performs a process of not performing the process.

These data are given to the selector circuit 9. The selection signal from the area separation circuit 5 is input to the selector circuit 9. In response to this selection signal, the selector circuit 9 selects and outputs any one of the data from the differential filter 6, the integration filter 7, and the pass-through circuit 8. The area separation circuit 5 outputs a selection signal for selecting an output of an appropriate circuit among the differential filter 6, the integration filter 7, and the pass-through circuit 8 according to which area the pixel to be processed belongs to, the selector circuit. Give to 9.

The image data processed by the selector circuit 9 is supplied to the γ correction circuit 10, and the sensitivity characteristic of the data is corrected so as to match the characteristic of the human eye. Further, it is given to the error diffusion circuit 11 and processed for good halftone expression. The process executed by the error diffusion circuit 11 is a pseudo halftone process for expressing the density of an image by the density of dots, and the error diffusion circuit 11 binarizes multi-value density data. When the pseudo halftone processing is performed on the halftone dot data after shading correction, there is a possibility that moiré may occur as described above. However, in the present embodiment, the halftone dot data smoothed by the integration filter 7 is Since it is given to the error diffusion circuit 11, moire does not occur. That is, by processing with the integration filter 7, halftone dot data can be treated in the same way as halftone data.

Since the character data has been processed by the differential filter 6, the binary data obtained after the processing by the error diffusion circuit 11 is a good representation of the character image. The data after the above processing is D
Given to the MA (Direct Memory Access) circuit 14,
It is output to a transmission circuit or a printing circuit (not shown).

This embodiment relates to the processing and configuration in the area separation circuit 5, the differentiation filter 6, the integration filter 7, the pass-through circuit 8 and the selector 9 among the above-mentioned configurations. FIG. 2 is a diagram for explaining the processing in the area separation circuit 5. The image data read by the scanner 1 is processed for each pixel according to the reading order. When processing each pixel as the pixel of interest X,
The data of the pixels A, B, C and D at the four corners of the matrix of 3 × 3 pixels centering on the target pixel X (multi-value density data after shading correction) is used. That is, assuming that the data of each pixel is represented by its code, the following (2)
The second derivative S shown in the formula is calculated, and further, the following (3)
The squared value SS (X) of the secondary differential value S (X) shown in the equation is calculated.

S (X) = α × {(XA) + (XD) + (XB) + (XC)} (2) SS (X) = S (X) × S (X) ) Further, five pixels X-2, X-1, aligned in the main scanning direction when the document is read by the scanner 1 with the pixel of interest X as the center,
The sum ΣSS (X) of the squared values of the secondary differential values calculated for X, X + 1, and X + 2 is calculated according to the following expression (4).

ΣSS (X) = SS (X-2) + SS (X-1) + SS (X) + SS (X + 1) + SS (X + 2) (4) In this embodiment, The above-mentioned squared value SS (X) and the sum of squared values ΣSS (X) are used as main judgment values, and the target pixel X
It is determined which of the character area, the halftone area and the halftone area belongs to. FIG. 3 is a flow chart for explaining the processing in the area separation circuit 5. First, the square value SS (X) and the sum ΣSS (X) of the square values are calculated (step n1). Then, the halftone region is extracted by the following judgment formula (5) (step n).
2).

ΣSS (X) <a (5) That is, if the above equation (5) is satisfied, it is determined that the pixel of interest X is a pixel belonging to the halftone region (step n2). In the above equation (5), a is a constant threshold value for extracting the halftone area. In a halftone image like a photograph, the density difference between adjacent pixels is small,
The SS value becomes smaller. Therefore, if the pixel of interest X belongs to the halftone region, the SS value of the neighboring 5 pixels is also small, so that ΣSS (X) should eventually take a small value.
Therefore, it is possible to determine whether or not the pixel of interest X is a pixel belonging to the halftone region by the determination using the expression (5). The larger the threshold value a, the larger the number of pixels determined to belong to the halftone area.

If the above equation (5) does not hold, then
The first halftone dot area determination is performed according to the following determination formula (6) (step n3). However, b is a constant threshold value for extracting the halftone dot region, and b> a. The larger b is, the smaller the number of pixels determined to belong to the halftone dot area is. ΣSS (X)> b (6) If the above expression (6) is satisfied, it is tentatively determined that the pixel of interest X belongs to the halftone dot area. This determination is tentative, and after the process of step n7 described later, it is determined again whether or not the target pixel X is a pixel in the halftone dot area.

Some halftone dot images have 65 to 200 lines. The number of lines is the number of lines per inch in which halftone dots are aligned. Therefore,
The larger the number of lines, the higher the density of halftone dots and the higher the density. Since the halftone dot image is composed of dots, the density suddenly changes microscopically. Therefore, if the target pixel X is a pixel in the halftone dot area, a large value is included in the SS values of the five pixels included in ΣSS (X). Therefore, ΣSS regarding the target pixel X
Since (X) has a large value, it can be determined whether or not the pixel of interest X belongs to the halftone dot area by the determination according to the expression (6).

Note that, for example, the resolution of the scanner 1 is 1
When 6 dots / mm, SS for 5 consecutive pixels
Since the determination is performed using the value, it is possible to distinguish and extract the pixels belonging to the halftone dot image in the range of 85 to 200 lines. Specifically, the scanner 1
The dot spacing of 0.0625 (1/16) mm is 85 lines /
The halftone dot image spacing is 0.300 (= 25.4 / 85) mm, and the 200 line / inch halftone image dot spacing is
It is 0.127 (= 25.4 / 200) mm. Therefore, four dots of the scanner 1 can exist between the halftone dots of the halftone dot image of 85 lines / inch (∵0.300 / 0.0625 = 4.8), 2
Scanner 1 between the halftone dots of the 00 line / inch halftone image
There can be two dots (∵0.127 / 0.0625 = 2.03). Therefore, at least one pixel corresponding to the halftone dot exists in the continuous five pixels. Therefore, by performing the determination based on the SS value of 5 pixels, it is possible to extract the pixels belonging to the halftone dot image in the range of 85 to 200 lines.

The pixels of the halftone dot image with the number of lines in the range of 65 to 85 lines are determined to be the pixels of the character area in this embodiment and are processed by the differential filter 6. This is because when a halftone dot image having a low density of halftone dots is to be determined as a halftone dot area, the pixels forming the character image may be mistakenly determined to be pixels in the halftone dot area.
This is because it has been confirmed by an experiment that moire does not occur even if differential filter processing is performed on a halftone dot image of 5 to 85 lines / inch.

When the above expression (6) is not satisfied, the first character area determination is performed by checking whether the condition of the following expression (7) is satisfied (step n4). However, c is a fixed threshold for determining the character area. The larger the threshold value c is set, the smaller the number of pixels determined to belong to the character area becomes. SS (X-2)> c and SS (X-1)> c and SS (X)> c and SS (X + 1)> c and SS (X + 2)> c (7) Characters and line drawings In a character image including, the density difference between adjacent pixels is large. Therefore, the SS value also becomes large. Further, since characters and lines are formed by a series of dots, a large SS value will be continuous. Therefore, when the SS values of all five pixels continuous in the main scanning direction are large,
It is determined that the pixel of interest X is a pixel belonging to the character area.

When the condition of the above expression (7) is not satisfied, the second halftone dot area determination is executed by further checking whether the following expression (8) is satisfied (step n5). However, in the following expression (8), d is a constant threshold value for extracting the halftone dot area, and is a value smaller than the threshold value b in the above-mentioned first halftone dot area determination. That is, b>d> a is established. The larger the threshold value d, the smaller the number of pixels determined to belong to the halftone dot area.

ΣSS (X)> d (8) If the above expression (8) is satisfied, the pixel of interest X is provisionally determined to belong to the halftone dot area. The principle of this second halftone dot area determination is the same as that of the above first halftone dot area determination. However, when the number of lines in the halftone dot area is large, the density of halftone dots is high, and due to the relationship with the MTF (Modulation Transfer Function) of the sensor applied to the scanner 1, there is a difference in the density data between pixels. It becomes a little smaller. Therefore, the ΣSS value also becomes small, and in the above-described first halftone dot area determination, pixels in a halftone dot area having a large number of lines may not be extracted. Therefore, by using the threshold value d smaller than the threshold value b in the first halftone dot area determination, pixels in the halftone dot area having a large number of lines can be reliably extracted.

If the above equation (8) does not hold, then by checking whether the following equation (9) holds,
The second character area determination is executed (step n6). However, e is a fixed threshold value for character area determination. This threshold value e is preferably set so that c ≧ e. The larger the threshold value e, the larger the number of pixels determined to be a character area.

SS (X)> e (9) If the expression (9) is satisfied, the pixel of interest X is determined to be a pixel belonging to the character area. Step n4 above
In the first character area determination in (1), continuous character area pixels (pixels forming a line or the like) can be extracted, but isolated character area pixels such as dots cannot be extracted. Therefore, among the pixels that are not determined to be pixels in the halftone dot area,
Pixels having a large SS value are determined to belong to the character area.

When it is tentatively determined that the target pixel X is a pixel in the halftone dot area by the first or second halftone dot area determination in step n3 or step n5, the redetermination in step n7 is executed. It That is, all the nine pixels that are continuous along the main scanning direction centering on the pixel of interest X are pixels that are provisionally determined to belong to the halftone dot area in the first or second halftone dot area determination. You can check whether or not. If this condition is satisfied, the target pixel X is determined as a pixel in the halftone dot area. Otherwise, it is not determined to be a pixel in the halftone dot area.

When the above equation (9) is not satisfied in step n6, and when it is not determined in step n7 that the pixel is in the halftone dot area,
The processing in step n8 is received. That is, it is checked whether all three pixels arranged in the vertical direction, the horizontal direction, the right diagonal direction, or the left diagonal direction around the pixel of interest X are larger than a certain threshold value f. That is, it is determined whether any one of the following expressions (10) to (13) is satisfied (see FIG. 2). The threshold f is preferably set to a value similar to the threshold e.

SS (E)> f and SS (X)> f and SS (H)> f (10) SS (X-1)> f and SS (X)> f and SS (X + 1) > f ‥‥ (11) SS (B)> f and SS (X)> f and SS (C)> f ‥‥ (12) SS (A)> f and SS (X)> f and SS (D) > f (13) If at least one of the expressions (10) to (13) is satisfied, the pixel of interest X is determined to be a pixel in the character area. Otherwise, the pixel of interest will be determined to be a pixel in the halftone region.

FIG. 4 is a diagram conceptually showing the relationship between the threshold value for the ΣSS value and the determination result. Pixels whose ΣSS value is smaller than the threshold value a are classified into the halftone region RM. ΣS
Pixels whose S value is larger than the threshold value b are tentatively determined to be the pixels of the halftone dot in the first halftone dot area determination, and the ΣSS value is the threshold values d to b.
Pixels in the range are tentatively determined to be halftone dot pixels by the second halftone dot region determination, and when nine halftone dot region pixels are consecutive, they are classified into halftone dot regions RD. Region RC1 is first
The region RC2 corresponds to the pixel determined to belong to the character region by the character region determination, and the region RC2 corresponds to the pixel determined to belong to the character region in the second character region determination. Also, the region R
C3 corresponds to the pixel determined to belong to the character area by the processing in step n8 of FIG. Other areas are undetermined pixels that are not determined as pixels in any area, but such pixels are subjected to the same processing as the pixels in the halftone area (processing by the pass-through circuit 8). become.

The area separating circuit 5 outputs the output of the differential filter 6 to the pixels determined to belong to the character area and the output of the integration filter 7 to the pixels determined to belong to the halftone area to the halftone area. With respect to the pixels determined to belong, a selection signal is generated so that the output of the pass-through circuit 8 is selected, and the selection signal is given to the selector 9. However, the area separation circuit 5 generates a selection signal for selecting the output of the pass-through circuit 8 even if the pixel is determined to belong to the character area when the following condition is satisfied.

When at least one pixel determined to belong to the halftone dot area exists in the matrix of 3 × 3 pixels centered on the target pixel X. That is, pixel A,
When any of E, B, X-1, X + 1, C, H, and D (see FIG. 2) is a pixel in the halftone dot area. Pixels X-1, X + 1, C, H, around the target pixel X
When it is determined that all of D belong to the halftone area. Instead of this condition, it is determined that all the pixels A, E, B, X-1, X + 1, C, H, D around the target pixel X are determined to belong to the halftone region. Good.

By carrying out such a processing, it is possible to prevent the pixels belonging to the halftone dot area or the halftone area from being erroneously subjected to the differential filter processing corresponding to the pixels of the character area. The area separation circuit 5 further includes two or more halftone dot areas including a pixel to be processed in a matrix of 2 × 2 pixels for integral filter processing even if the pixel is determined to belong to the halftone dot area. When the pixel does not exist, a selection signal for selecting the output of the pass-through circuit 8 is generated. That is, the integral filtering process is prohibited. As a result, when the pixels forming the character image are erroneously determined to be halftone dot pixels, it is possible to prevent a problem such as blurring of the outline of the image.

Next, the processing in the differentiation filter 6, integration filter 7 and pass-through circuit 8 will be described. The differential filter 6 is a so-called Laplacian filter. Specifically, the differential filter 6 obtains a secondary differential value S similar to that calculated by the area separation circuit 5 according to the following equation (14), and creates post-processing data FOUT shown in Table 1 below. And input to the selector 9.

S (X) = 2 × {X− (A + B + C + D) / 4} = (1/2) {(X-A) + (X-B) + (X-C) + (X-D)} ... (14)

[0044]

[Table 1]

When the target pixel X belongs to the character area as described above, the image data whose contour is emphasized by the differential filter 6 is selected. In Table 1, SLB
Is a threshold for black pixel enhancement processing, and SWB is a threshold for white pixel enhancement processing. In the process in the integration filter 7, multi-value density data (density data after shading correction) of pixels in a matrix of 2 × 2 pixels including the target pixel X is used. That is, referring to FIG. 2, the data after shading correction of the pixels X, X + 1, D and H is used. If the data after shading correction is represented by the sign of each pixel, the integration filter 7
The processing in is represented by the following expression (15). That is, the integration filter 7 outputs the value FOUT (X) of the following expression (15) for the pixel of interest X.

FOUT (X) = {X + (X + 1) + H + D} / 4 (15) By this processing, the density difference between the pixel of interest X and the adjacent pixel is reduced, and the image is smoothed. . As described above, when the target pixel X belongs to the halftone dot area, the data smoothed by the integration filter 7 is selected. As a result, the halftone image is subjected to the γ correction processing and the error diffusion processing after being smoothed and brought close to the halftone image.

The process in the pass-through circuit 8 is a process in which nothing is done as described above. For the pixel determined to belong to the halftone area, the pass-through circuit 8
Output data is selected by the selector 9. In addition,
When the reading resolution of the scanner 1 is 16 dots / mm and the MTF after shading correction is a value shown in Table 2 below, the above threshold values a, b, c, d, e, f are as follows. A value such as 3 is preferable.

[0048]

[Table 2]

[0049]

[Table 3]

The value of MTF in Table 2 is MTF.
As the measurement chart, a rectangular wave chart of white / black 5 line pairs (specifically, the white / black line pair of the facsimile test chart No. 1 of the Institute of Image Electrophotography) is used.
It is calculated based on the following formula based on the maximum density difference ΔA between the adjacent line pair parts of 1 dot / mm white / black.

[0051]

[Equation 1]

FIG. 5 is a block diagram for explaining a hardware configuration related to the area separation circuit 5. In the processing in the area separation circuit 5, data for 4 lines is used. In the following description, the current line to which the data input from the shading correction circuit 4 belongs is called the “A line”, the line before the A line is called the “B line”, and the B line
The line before the line is called "C line", and the line before the C line is called "D line".

SRAM provided in the facsimile machine
In the storage area in the (static random access memory) 21, line data storage memories LD, LC and LB capable of storing data for three lines are secured. The A line data sequentially input from the shading correction circuit 4 is stored in the storage position of the D line data after the processing. As a result, the processing using the data of four lines can be executed using the line buffer of three lines secured in the SRAM 21.

The data in the line data storage memories LD, LC and LB are processed by the differential filter 6, the integral filter 7 and the pass-through circuit 8. Then, after receiving the processing in which the data in the C line is the target pixel, any one of the data is selected by the selector 9.
The selected data is input to the γ correction circuit 10 (see FIG. 1).

The current line data from the shading correction circuit 4 and the B line, C line and D line data from the SRAM 21 are input to the area separation circuit 5. Then, the pixel on the C line is set as the target pixel, and it is determined which of the character region, the halftone dot region, and the halftone region the target pixel belongs to. The area separation circuit 5 includes an area determination data generation unit 31. The area determination data generation unit 31 calculates the sum ΣSS of the above-described secondary differential value S, the square value SS of the secondary differential value S, and the square values SS of the five adjacent pixels. As will be described later, the area determination data generation unit 31 has a built-in shift register that holds necessary data of A line, B line, C line, and D line. A part of the data held in the shift register built in the area determination data generation unit 31 is used for processing by the differential filter 6 and the integral filter 7.

The area separation circuit 5 is further provided with a threshold value SSA for area determination (corresponding to the threshold value b in the above equation (5)),
Threshold SSAM (corresponding to the threshold d in the above equation (8)),
The threshold value SSC (corresponding to the threshold value a of the above expression (6)), the threshold value BEDGE (corresponding to the threshold values e and f of the above expression (9) and the expression (10)), the threshold value BEDGEH (the above description).
This corresponds to the threshold value c in the equation (7). ), A register group 32 including a plurality of registers respectively holding The data held in the registers in the register group 32 is set by a control circuit (not shown). The data held in each register can be variably set from an input device (not shown) connected to the control circuit. As the input device, a key input device provided in the facsimile device may be used, or an input device externally attached to the facsimile device may be used as necessary. By changing the data held in each register, the number of pixels determined to belong to each of the character area, the halftone area, and the halftone dot area can be changed, so that the image quality can be adjusted.

The respective values of S, SS and ΣSS generated by the area determination data generation section 31 and the threshold value held in the area determination register group 32 are the first area determination section 4
Input to 1. In the first area determination unit 41, the SS value and the ΣSS value and the above-mentioned threshold values SSA, SSAM, SSC,
A comparison with BEDGE and BEDGEH is made. As a result, a 2-bit flag SSF that tentatively indicates that the pixel of interest is an image of a character area, a halftone area, or a halftone dot area is generated for each pixel.

The value of the flag SSF has the following significance, for example. SSF = 11 ... It was provisionally determined to be a pixel in the halftone dot area. SSF = 01 ... It was determined to be a pixel in the halftone region. SSF = 10 ... It was determined to be a pixel in the character area. SSF = 00 ... Not determined This flag SSF is input to the second area determination unit 42. The second area determination unit 42, based on the SSF flag,
A flag AMCF is created by determining whether or not all of the nine pixels aligned in the main scanning direction centering on the pixel of interest are pixels in the halftone dot area. The flag AMCF is a 2-bit flag and has the following meanings.

AMCF = 11 ... It was determined to be a pixel in the halftone dot area. AMCF = 01 ... It was determined to be a pixel in the halftone region. AMCF = 10 ... It was determined to be a pixel in the character area. AMCF = 00 ... Undetermined This flag AMCF is input to the filter processing determination unit 35 and the third region determination unit 43. Third area determination unit 43
Determines whether or not the SS value of three pixels aligned vertically, horizontally, and diagonally around the target pixel is larger than the threshold value BEDGE in order to make a determination about the pixel of the flag AMCF = 00 (( That is, step n8 in FIG.
Processing), a 1-bit flag B corresponding to the determination result
Generate F. That is, if a positive determination is made,
The flag BF is set to "1" to indicate that the pixel is in the character area, and the flag BF is set to "0" to indicate that the pixel is in the halftone area if a negative determination is made. This flag BF is also input to the filtering process determination unit 35.

The filtering process determining section 35 determines the flag AMC.
Based on F and BF, it is determined which of the character area, the halftone area and the halftone area the pixel of interest belongs to, and a 3-bit selection signal corresponding to the determination result is input to the selector 9. Specifically, each flag and selector 9
The selection signal is created so that the relationship with the circuit selected by is as follows.

AMCF = 11 ... Integral filter 7 AMCF = 01 ... Pass-through circuit 8 AMCF = 10 ... Differential filter 6 AMCF = 00 and BF = 1 ... Differential filter 6 AMCF = 00 And BF = 0 ... Pass-through circuit 8 However, even when the differential filter 6 should be selected,
When at least one halftone dot region pixel exists in a matrix of 3 × 3 pixels centered on the pixel of interest, and pixels around the pixel of interest (pixels X-1, C, H, D and X + 1 in FIG. 2). , Or all eight surrounding pixels) are all pixels in the halftone area, a selection signal for selecting the output of the pass-through circuit 8 is generated.

Even when the integration filter 7 is to be selected, two or more pixels are included in the matrix of 2 × 2 pixels including the target pixel (the matrix including the pixels X, X + 1, H and D in FIG. 2). When there are no halftone dot pixels (that is, when only the pixel of interest is a halftone dot pixel), a selection signal for selecting the output of the pass-through circuit 8 is generated. This is due to the fact that halftone dot pixels cannot exist alone. That is, when the pixel determined to belong to the halftone dot region exists alone, the determination is likely to be incorrect, so the integration filter process is omitted.

The filtering processing determination unit 35 further creates a flag AMCF corresponding to the final determination result based on the flag AMC and the flag BF, and writes the created flag AMCF in the flag memory 37.
The flag memory 37 is formed in the storage area of the SRAM 21. The newly created flag AMCF has the following values.

When AMCF = 11: AMCF = 11 When AMCF = 01: AMCF = 01 When AMCF = 11: AMCF = 10 When AMCF = 00 and BF = 1: AMCF = 10 AMCF = 00 and BF = 0 ... AMCF = 00 FIG. 6 is a diagram for explaining the processing in the area determination data generation unit 31. In FIG. 6 and FIG. 7, which will be described next, the data of the A line is shown with double diagonal lines, the data of the B line is shown with horizontal lines, and the data of the C line is shown with upward-sloping diagonal lines. The vertical line is added to the data of the D line.

Line data storage memories LB, LC, LD for three lines secured in the storage area of the SRAM 21.
The storage data of is read into the shift register 40 built in the area determination data generation unit 31. The shift register 40 holds necessary data of the A line, B line, C line and D line, and can shift the held data in the direction opposite to the main scanning direction. The shift register 40 has a configuration of one stage for each of the A line and the B line, a configuration of nine stages for the C line, and a configuration of three stages for the D line. The data after shading correction for one pixel can be held. W1 represents a window for calculating the secondary differential value S, W2 represents a window in which differential filtering is performed, and window W3, which is an overlapping portion of windows W1 and W2, represents a window in which integral filtering is performed.

It is assumed that the pixel for which the processing by the shading correction circuit 4 has been completed is the 11th pixel A11 on the A line. In this case, the area separation processing up to the pixel C3 has been completed. The data after the shading correction processing of the pixel A11 is stored in the shift register 40 and the line data storage memory LD. The data storage position of the pixel A11 is the storage position where the data of the pixel D11 was stored. Therefore, although the data of the pixel D11 is lost from the SRAM 21, if the data of the pixel D11 is read into the shift register 40 before the writing of the data of the pixel A11, no problem will occur.
That is, before the data of the pixel A11 is written in the shift register 40 and the line data storage memory LD, the pixels D10, D11;
C3 to C10 are written.

Following the writing of the data after the shading correction processing of the pixel A11, the pixels D12, C11, B1
The data after each shading correction process of 0 is SRAM2.
It is read from 1 to the shift register 40. As a result, the shift register 40 has pixels D10 to D12; C.
3 to C11; the data after the shading correction processing of B10 and A11 is held.

On the other hand, the area determination data generating section 31 has
Another shift register 39 is built in. The shift register 39 has a two-stage shift register for holding the addition result of the data after the shading correction processing of the B line and the D line, and holds the addition result of the data after the shading correction processing of the B line and the C line. And a shift register of two stages for holding the addition result of the data after the shading correction processing of the A line and the C line. This shift register 3
9 is capable of shifting the held data along the direction opposite to the main scanning direction.

A value obtained by adding the data of the pixels B8 and D8 and a value obtained by adding the data of the pixels B9 and D9 to the shift register 39 before the data after the shading correction processing of the pixel A11 is input. Pixel B9 and pixel C9
The value obtained by adding the data of A, the data obtained by adding the data of pixel A9 and the pixel C9, and the value obtained by adding the data of pixel A10 and C10 are previously calculated and stored.

Based on the data held in the shift registers 39 and 40, the secondary differential value S is calculated with the pixel B10 as the pixel of interest. That is, according to the following formula (16),
The secondary differential value S (B10) of the pixel B10 is obtained. S (B10) = α × {(B10-C9) + (B10-C11) + (B10-A9) + (B10-A11)} = 4α × [B10-{(A9 + C9) + A11 + C11} / 4] (16) Further, the data held in the shift registers 39 and 40 is given to the differential filter 6 and the integral filter 8, and the processing in these filters is executed.

That is, in the differential filter 6, with the pixel C9 as the pixel of interest, the secondary differential value S (C
9) is calculated. In this operation, the shift register 3
By using the value [B8 + D8] held in 9, the number of addition operations can be reduced, so that the hardware configuration of the differential filter 6 can be simplified. S (C9) = 2 [C9-{(B8 + D8) + B10 + D10} / 4] ... (17) Processing shown in Table 1 above based on the calculated second derivative S (C9) Thus, the data FOUT (C9) after the filtering process regarding the pixel C9 is obtained.

Further, in the integration filter 7, the pixel C9 is used as the pixel of interest to calculate the data IOUT (C9) after the filtering process shown in the following expression (18). At this time, since the number of addition operations can be reduced by using the data [B9 + C9] held in the shift register 39,
The hardware configuration of the integration filter 7 can be simplified. IOUT (C9) = {(B9 + C9) + B10 + C10} / 4 (18) The data [B9 + D9] in the shift register 39 is the pixel C.
The data [A10 + C10] is used in the differential filtering process for 10 and the second differential value S is calculated for the pixel B11.

At the time when the data after the shading correction processing regarding the pixel A11 is input, the pixel for which the region determination processing has been completed is the pixel C3. This is due to the delay of the pipeline processing in the area separation circuit 5.
Due to such a delay, the data corresponding to each processing result of the differential filter processing, the integral filter processing, and the pass-through processing regarding the pixels C3 to C9 is stored in the differential filter 6, the integral filter 7, and the pass-through circuit 8 at the timing. Shift register for adjustment (not shown)
Held in. Then, at the time when the data after the shading correction processing regarding the pixel A11 is input to the shift register 40 and the SRAM 21, the data corresponding to the pixel C3 is input to the selector 9 from the differential filter 6, the integration filter 7 and the pass-through circuit 8.

FIG. 7 is a diagram for explaining the area separation determination processing. This FIG. 7 shows the processing when the secondary differential value S (B10) for the pixel B10 is input. First, an outline of the configuration will be described. A built-in shift register 51 capable of holding SS values for the latest 5 pixels of the B line, a comparison result of the SS values for the latest 5 pixels of the B line and the threshold value BEDGEH are shown. A built-in shift register 52 that can hold a flag BHF that represents it, a built-in shift register 53 that can hold a flag SSF for 9 pixels of pixels B0 to B8 on the B line, and 3 × 3 pixels centered on pixel C3 Built-in shift register 54 capable of holding flags BF (corresponding to the comparison result of the SS value and the threshold value BEDGE) for the pixels in the matrix of B and the pixels B5 to B10 of the B line,
In addition, a built-in shift register 55 that can hold the flag AMCF of the pixels in the matrix of 3 × 3 pixels centered on the pixel C3 is provided. Furthermore, SR
The flag AMC for two lines is stored in the storage area of the AM21.
The above-mentioned flag memory 37 capable of holding F and the flag BF is secured. Flag memory 37
Has line memories LFC and LFD. The flag memory 37 has a flag AMCF for each pixel.
And the 3-bit data corresponding to the flag BF may be held, or 2-bit data created by combining the flag AMCF and the flag BF for each pixel may be held.

The second derivative S (B10) of the pixel B10 is
The square value SS (B10) is input to the square processing unit 57 and calculated. The squared value SS (B10) is input to the shift register 51 and also to the comparators 61 and 62. Pixel B6 held in shift register 51
The SS values of the five pixels of B10 to B10 are added by the addition processing unit 59, and the sum ΣSS (B8) of the squared values of the pixel B8 is calculated. This ΣSS (B8)
Is an SSF determination processing unit 7 for creating a flag SSF.
Input to 0.

In the comparators 61 and 62, the squared value SS (B10) of the second derivative of the pixel B10 and the threshold value BED.
GE and BEDGEH are compared respectively. The comparison result of the comparator 61 is stored in the shift register 54 as a 1-bit flag BF. This flag BF
Is set to "1" when the squared value SS (B10) is larger than the threshold value BEDGE, and is set to "0" otherwise. On the other hand, the comparison result in the comparator 62 is stored in the shift register 52 as a 1-bit flag BHF.
For this flag BHF, the square value SS (B10) is the threshold value BE.
When it is larger than DGEH, it is set to "1", and otherwise it is set to "0".

The flag BHF for five pixels held in the shift register 52 and the flag BF corresponding to the pixel B8 held in the shift register 54 are the SSF determination processing unit 7
Given to 0. The SSF determination processing unit 70 includes comparators 63, 64 and 65 for comparing the input ΣSS value with the threshold values SSA, SSAM and SSC, respectively. The processing in the SSF determination processing unit 70 is the same as in FIG.
Follow the processing of. Specifically, the flag SSF is generated by the following processing, and the generated flag SSF is stored in the shift register 53.

When ΣSS <SSC, SSF =
10 (corresponding to the character area). This process corresponds to the process of step n2 in FIG. When ΣSS> SSA, SSF = 11 (corresponding to the halftone dot area). This processing corresponds to the first halftone dot area determination processing in step n3 of FIG. When SSA ≧ ΣSS ≧ SSC and all the flags BHF for five pixels given from the shift register 52 are “1 (representing SS> BEDGEH)”, S
SF = 10 (corresponding to the character area). This process corresponds to the process of step n4 in FIG.

5 given from the shift register 52
When at least one of the pixel flags BHF is “0” and SSA ≧ ΣSS> SSAM, SSF = 11 (corresponding to the halftone dot area). This processing corresponds to the second halftone dot area determination processing in step n5 of FIG. SSAM ≧ ΣSS ≧ SSC and the flag BF regarding the pixel B8 given from the shift register 54
Is “1 (indicating that SS ≦ BEDGE)”, SSF = 10 (corresponding to the character area). This processing corresponds to the processing in the case of branching to YES in step n6 of FIG.

When SSAM ≧ ΣSS ≧ SSC and the flag BF related to the pixel B8 given from the shift register 54 is “0 (indicating that SS ≦ BEDGE)”, SSF = 00 (undetermined). (Corresponding to the process when branching to NO in step n6 of FIG. 3). Pixels B0 to B8 held in the shift register 53
The flag SSF for 9 consecutive pixels of the AMC determination processing unit 7
Input to 3. The AMC determination processing unit 73 determines the pixel B
A flag AMCF corresponding to 4 is created, and a flag SSF for 9 pixels held in the shift register 53 is created.
Is checked to see if they all have the value "11" corresponding to the halftone dot area. Then, the following processing is executed.

(A) When the SSFs of 9 pixels are all "11", AMCF = 11 is set and the pixel B4 is determined as a pixel in the halftone dot area (corresponding to the process of step n7 in FIG. 3). (b) When at least one value other than “11” is included in the SSF of 9 pixels, the following processing is performed according to the value of SSF. When SSF = 10 (corresponding to the character area), AM
With CF = 10, the pixel B4 is determined as a pixel in the character area.

When SSF = 01 (corresponding to the halftone area), AMCF = 01, and the pixel B4 is determined as the pixel of the halftone area. When SSF = 11 (corresponding to halftone dot area), AM
CF = 00 is set, and the determination result for the pixel B4 is undetermined. When SSF = 00 (corresponding to undetermined), AMC
With F = 00, the determination result for the pixel B4 is undetermined.

The flag AMCF thus obtained for the pixel B4 is input to the shift register 55.
The flag AMCF for the pixels D2 to D4, C2 to C4 and B2 and B3 is read out from the flag memory 37 and stored in the shift register 55. Based on the flag AMCF in the matrix of 3 × 3 pixels held in the shift register 55, it is checked whether or not there are pixels in the halftone dot area (pixels with AMCF = 11) around the pixel C3. Then, there is at least one halftone dot area pixel around the pixel C3, and the flag AMC of the pixel C3 is present.
When F has the value "10" corresponding to the character area pixel, the selector 9 is supplied with a selection signal for selecting the output of the pass-through circuit 8 for the pixel C3.

Further, based on the flag AMCF for 3 × 3 pixels in the shift register 55, all the pixels C2, C4, B2, B3 and B4 around the pixel C3 are halftone region pixels (pixels with AMCF = 01). ) Is determined. Then, when all of the pixels C2, C4, B2, B3, B4 are halftone region pixels, and the flag AMCF of the pixel C3 has the value "10" corresponding to the character region pixel, the pixel C3 is concerned. A selection signal for selecting the output of the pass-through circuit 8 is given to the selector 9. Note that instead of the above condition, the fact that all of the pixels D2 to D4, C2, C4, and B2 to B4 around the pixel C3 are halftone region pixels means that the flag flag A of the pixel C3.
It may be a condition for selecting the output of the pass-through circuit 8 when the MCF is “10”.

When the above condition is not satisfied for the flag AMCF of the matrix of 3 × 3 pixels held in the shift register 55, the selection signal corresponding to the flag AMCF of the pixel C3 is generated. That is, AMCF = 1
If it is 1, the output of the integration filter 7 is selected and the AMCF
= 10, the output of the differential filter 6 is selected and AM
If CF = 01, the output of the pass-through circuit 8 is selected.

However, when the flag AMCF is "00", the following processing is executed using the data held in the shift register 54. That is, first, in the shift register 54, the pixels D2 to D2 are read from the flag memory 37.
The flags AMC of D4 and C2 to C4 are read and held. For the B line, a 1-bit flag BF is held. Then, in a matrix of 3 × 3 pixels centered on the pixel C3, three vertical pixels (D3, C3, B3) including the pixel C3 and three horizontal pixels (C2, C3, C) are included.
4), all the 3 pixels of any set of the diagonally right 3 pixels (B2, C3, D4) and the diagonally left 3 pixels (B4, C3, D2) are flag AMCF corresponding to the character area pixel.
Alternatively, it is checked whether or not the flag BF corresponding to SS> BEDGE is included. If this condition is met,
The flag AMCF corresponding to the pixel C3 is set to the value “10” corresponding to the character area, and the selection signal for selecting the output of the differential filter 6 is input to the selector 9. When the above conditions are not satisfied, the flag AMCF corresponding to the pixel C3 remains "00". In this case, the output of the pass-through circuit 8 is selected as in the case of the halftone area pixel. After this processing, a new flag AMCF corresponding to the pixel C3 is written in the flag memory 37.

On the other hand, in the shift register 55, the pixel B
3 based on the flag AMCF stored corresponding to 3 and the flag BF stored in the shift register 54 corresponding to the pixel B3, a 2-bit flag AMCF corresponding to the pixel B3 is newly created, It is stored in the line data storage memory LFD of the dedicated memory 37. Specifically, a new flag AMCF is created as follows.

When AMCF ≠ 00, the AMCF held in the shift register 55 is used as it is as a new AM.
CF. AMCF = 00 and BF = 1 (SS> BEDGE)
In the case of, AMC = 10 (corresponding to the character area). AMCF = 00 and BF = 0 (SS ≦ BEDGE)
In case of, AMC = 00.

Since the line data storage memory LFD stores the flag AMCF of the pixel of the D line in addition to the flag AMCF of the pixel of the B line,
The writing of the flag AMCF of No. 3 needs to be executed after the AMC flag of the pixel D3 is read to the shift registers 54 and 55. By doing so, it is possible to execute the process using the pixel data of 3 lines by using the flag storing memory 37 for 2 lines.

As described above, according to the present embodiment, since the sum ΣSS value of the SS values of 5 pixels continuous in the main scanning direction is used, the pixel of interest is the character area, the halftone area and the halftone dot area. In determining which one of them belongs, it is possible to make a determination in consideration of the situation of surrounding pixels. Therefore, it is possible to accurately determine in which area the pixel of interest is a pixel. As a result, it is possible to perform appropriate processing on the pixels in each area, and it is possible to reliably avoid a situation in which moire occurs particularly when a halftone image is reproduced.

In extracting the character area, the halftone area, and the halftone dot area, the threshold values corresponding to the SS value and the ΣSS value are individually set for each area, so that the pixel area can be accurately determined. be able to. Further, since the squared value SS and the sum ΣSS of the SS values of five pixels are used as the judgment value, not the second derivative value S, the judgment value does not take a negative value. That is, since the secondary differential value S can take both positive and negative values, it is necessary to prepare two types of threshold values, positive and negative, for determining the magnitude.
If the SS value and the ΣSS value are used as the determination values, it is sufficient to prepare only the positive threshold value. Therefore, the hardware configuration can be simplified.

Further, in the above-described hardware configuration, the filtering process such as differentiation / integration and the region determination process regarding the target pixel are performed in parallel. Therefore, when the area determination regarding the pixel of interest is completed, the data after the differential filter processing, the integration filter processing, and the pass-through processing are already prepared, so if any data is selected based on the area determination processing result, Appropriate processing can be performed on each pixel in the character area, the halftone area, and the halftone area. Thereby, the processing can be performed at extremely high speed.

Further, in the above hardware configuration, the processing for each pixel in the area separation circuit 5 is performed by pipeline processing. Therefore, it is possible to perform the region determination processing on a plurality of pixels in parallel.
This speeds up the area determination processing, which can contribute to speeding up the image processing. Further, as described above, the processing using the data after the shading correction processing for 4 lines is realized by the line data storage memory for 3 lines secured in the SRAM 21. Further, the processing using the flag AMCF for three lines is realized by using the flag memory 37 for two lines secured in the SRAM 21. Therefore, appropriate processing can be performed on a character image, a halftone image, and a halftone image without requiring a large storage capacity.

Next, another embodiment of the present invention will be described with reference to FIGS. In the description of this embodiment, FIG. 1 to FIG. 5 described above will be referred to again. In the following description, a process for generating the flag AMCF indicating which of the character area, the halftone area, and the halftone dot area the seventh pixel C7 of the C line belongs to will be described. At the timing of performing the area determination processing on the pixel C7, the data after the shading correction processing of the pixel A15 on the A line is input from the shading correction circuit 4 to the area determination data generation unit 31. At this time, using the data after the shading correction processing of the pixels in the window W22 including the matrix of 3 × 3 pixels centering on the pixel B14, the second derivative value S (B14) for the pixel B14 is the following (19) It is calculated based on the formula.

S (B14) = 2 (B14-AV) + R1 + R2-1 ... (19) However, AV = (A13 + A15 + C13 + C15) / 4 ... (20). Further, R1 and R2 are respectively set to the following values according to the remainder of the division on the left side of the expression (20).

Remainder = 0 ... R1 = 1, R2 = 1 Remainder = 1 ... R1 = 0, R2 = 1 Remainder = 2 ... R1 = 1, R2 = 0 Remainder = 3 ... R1 = 0, R2 = 0 The secondary differential value S obtained according to the equation (19) is as understood from the following modification. , Which is equivalent to the second derivative S of the equation (2).

S (B14) = 2 (B14-AV) + R1 + R2-1 = (2/4) {4B14- (A13 + A15 + C13 + C15)} = (2/4) {(B14-A13) + ( B14-A15) + (B14-C13) + (B14-C15)} The data after the shading correction processing of the pixels A13, C13 and C15 is the area determination data generation unit 31 (see FIG. 5).
It is held in the built-in shift register (not shown) of the above) as it is or in the form of adding two pixels.

On the other hand, pixels C10-C14 and pixels B10-
The pixel C1 with the symbol "*" added using the second derivative S of each pixel in the window W22 for 10 pixels including B14.
The squared value SS (C12) of the secondary differential value is calculated for 2, and ΣSS (B12) is calculated for the pixel B12. That is, the area determination data generation unit 31 is provided with a built-in shift register (not shown) for holding the secondary differential value S calculated for each pixel in the window W21.

Second-order differential value S (B1 for pixel B12
The square value SS (B12) of 2) and the sum ΣSS (B12) of the square values of five consecutive pixels are given by the following equations (21) and (22).
It is calculated according to the formula. The same applies to the pixel C12. SS (B12) = S (B12) × S (B12) ・ ・ ・ ・ (21) ΣSS (B12) ＝ SS (B10) + SS (B11) + SS (B12) + SS (B13) + SS (B14) (22) Using the above SS value and ΣSS value, the first area determination unit 41 generates the flag SSF according to the following rules.

When ΣSS (B12) <SSC, SSF = 01 (corresponding to the halftone region) is set (corresponding to step n3 in FIG. 3). When ΣSS (B12)> SSA, SSF = 1
1 (corresponding to the halftone dot area) (corresponding to step n2 in FIG. 3). SSC ≤ ΣSS (B12) ≤ SSA and SS (B10)> BEDGEH and
SS (B11)> BEDGEH and SS (B12)> BEDGEH and SS (B13)> BE
When DGEH and SS (B14)> BEDGEH, SSF = 10
(Corresponding to the character area) (corresponding to step n4 in FIG. 3).

Other than, ΣSS (B12)> S
In the case of SAM, SSF = 11 (corresponding to step n5 in FIG. 3). When SS (B12)> BEDGE other than the above, SSF = 10 (YE at step n6 in FIG. 3).
It corresponds to the case of branching to S). When other than ~, SSF = 00 (Fig. 3)
It corresponds to the case of branching to NO at step n6. ) The pixel C12 is similarly processed.

FIG. 9 is a diagram for explaining the process in the second area determining unit 42, and is a diagram for explaining the process for generating the flag AMCF using the flag SS. A flag AMCF is generated for pixels C8 and B8 marked with a "*". In order to generate the flag AMCF corresponding to the pixels B8 and C8, the flag SSF of each pixel in the window W23 including 9 consecutive pixels in each line centered on each of the pixels B8 and C8 is referred to. That is, the pixels B4 to B12 and C4 to
A built-in shift register (not shown) for holding the flag SSF of C12 is provided in the second area determination unit 42. The area determination process for the pixel B12 is as follows.

All of SSF (B4) to SSF (B12) are “11”
, The flag AMCF is set to the value "1" corresponding to the halftone dot area.
1 ”(corresponding to the case of branching to YES in step n7 of FIG. 3). When SSF (B8) = 01, the flag AMCF is
The value "01" corresponding to the halftone area is set.

When SSF (B8) = 10, the flag AMCF is set to the value “10” corresponding to the character area. Otherwise, the flag AMCF is set to the value "00" corresponding to the undetermined area (step n in FIG. 3).
It corresponds to the case of branching to NO in 7.) FIG. 10 is a diagram for explaining the process performed by the third region determination unit 43 to generate the flag AMCF using the threshold value BEDGE. Pixel C with symbol "*"
A flag AMCF is generated for 7. At this time, the SS value of each pixel in the window W24 including the matrix of 3 × 3 pixels centered on the pixel C7 is referred to. The third area determination unit 43 includes an SS value of 3 × 3 pixels and a threshold value BEDG.
A shift register (not shown) capable of holding the result of comparison with E is incorporated.

The flag AMCF for the pixel C7 is generated by the following processing. This process is performed by the second area determination unit 4
It is executed for the pixel for which AMCF = 00 by the processing in 2. SS (D6)> BEDGE and SS (C7)> BEDGE and SS
(B8)> BEDGE or SS (C6)> BEDGE and SS (C7)> BEDGE and SS (C8)> BEDGE or SS (B6)> BEDGE and SS (C7)> BED
GE and SS (D8)> BEDGE or SS (D7)> BEDGE and SS (C
When 7)> BEDGE and SS (B7)> BEDGE, AMCF = 1
It is set to 0 (corresponding to the character area) (corresponding to the case of branching to YES in step n8 of FIG. 3).

If the condition of is not satisfied, AMC
= 00 (undetermined area) (corresponding to the case of branching to NO in step n8 of FIG. 3). FIG. 11 is a diagram for explaining the process executed by the filter process determination unit 35 to determine whether to perform the differential filter process. The Laplacian filter process executed by the differential filter 6 is executed using the data after the shading correction process in the window W25 including the matrix of 3 × 3 pixels centered on the pixel C7.

The flag AMCF of the pixel in the window W25 is referred to in order to determine whether or not the Laplacian filter process is performed. The flags AMCF for 8 pixels (in the window W26) of the pixels D1 to D8 are read from the flag memory 37, and the filtering process determination unit 35 is performed.
It is held in a built-in shift register (not shown). In this built-in shift register, the flags AMCF for eight pixels C1 to C8 (in the window W27) and the pixel B
6, the flag AMCF of B7 and B8 is held. Based on this, the following processing is performed.

When there is at least one halftone dot pixel (AMCF = 11) in the window W25, the Laplacian filter process is not performed. That is, the pixel C7
When the flag AMCF corresponding to is "10 (corresponding to a character area)", the filtering process determination unit 35 generates a selection signal for causing the selector 9 to select the output of the pass-through circuit 8.

Pixels C6, C8, B6, B7 and B
8 (or D6, D7, D8, C6, C8, B6, B
7 and B8) are all halftone region pixels (AMCF = 0
When 1), the filtering process is not performed. That is, as in the case of, the flag AM corresponding to the pixel C7
When CF is "10", a selection signal for selecting the output of pass-through circuit 8 is generated.

Otherwise, if the flag AMCF = 10 corresponding to the pixel C7, then the differential filter 6
A selection signal is generated to select the output of the. That is, the Laplacian filter process is enabled. 12
FIG. 6 is a diagram for explaining a process for determining whether or not to perform an integration filter process. The integral filtering process on the pixel C7 is executed based on the flag AMCF of each pixel in the window W28 including the matrix of 2 × 2 pixels including the pixels C7, C8, B7 and B8. Specifically, it is processed as follows.

When there are two or more halftone dot area pixels including the determination pixel C7 in the window W28, the filtering process is performed. That is, the flag A corresponding to the pixel C7
If the MCF is “11 (corresponding to the halftone dot area)”, the filter processing determination circuit 35 generates a selection signal for causing the selector 9 to select the output of the integration filter 7. In other cases, the filtering process is not performed. That is, when the flag AMCF corresponding to the pixel C7 is “11”, a selection signal for selecting the output of the pass-through circuit 8 is generated.

After the similar processing on the pixel C9 is completed, the flag AMCF of each pixel in the window W27 (see FIG. 11) is stored in the flag memory 37 together for eight pixels. As described above, the same operation and effect as in the case of the above-described first embodiment can be achieved by this embodiment as well.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above embodiment, the facsimile apparatus is taken as an example, but the present invention is applicable to an apparatus such as an image scanner apparatus or a digital copying machine, which processes image data obtained by optically reading an image. It can be widely applied. In addition, various design changes can be made within the scope of the technical matters described in the claims.

[0114]

According to the invention of claim 1 or 3, the square value of the density change value is used as the first judgment value, and the value obtained by adding the first judgment value is used as the second judgment value. Therefore, all judgment values take only positive values. Therefore, it suffices to prepare only positive values for the threshold values corresponding to the respective judgment values, so that the image processing method and configuration can be simplified.

Since the second judgment value reflects the state of the pixels in the vicinity of the processing target, in addition to the local judgment by the first judgment value, the second judgment value is used to detect the surrounding pixels. Judgment that reflects the status can be performed. As a result, it is possible to favorably detect the constituent pixels of the halftone dot image, which could not be conventionally detected. As a result, it can be satisfactorily discriminated whether the pixel to be processed constitutes a character image, a halftone image, or a halftone dot image. Therefore, by performing appropriate processing corresponding to this discrimination result, Images can also be processed appropriately.

According to the invention of claim 2 or claim 4, since the determination processing result regarding the pixel having a predetermined positional relationship in the vicinity of the pixel to be processed is referred to, it is appropriate according to the states of the peripheral pixels. It is possible to perform various image processing on the pixel to be processed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration related to image processing of a facsimile apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a diagram for explaining a region determination process for determining which one of a character region, a halftone region and a halftone region a pixel belongs to.

FIG. 3 is a flowchart illustrating an area determination process.

FIG. 4 is a diagram conceptually showing a relationship between a threshold value related to a ΣSS value and a determination result.

FIG. 5 is a diagram illustrating a hardware configuration for area determination processing.

FIG. 6 is a diagram illustrating a process of generating a determination value for a region determination process.

FIG. 7 is a diagram for explaining a process for generating an area determination flag using a determination value.

FIG. 8 is a diagram for explaining a process in a first area determination unit according to another embodiment of the present invention.

FIG. 9 is a diagram for explaining processing in a second area determination unit.

FIG. 10 is a diagram for explaining processing in a third area determination unit.

FIG. 11 is a diagram for explaining a determination process of whether or not to perform a differential filter process.

FIG. 12 is a diagram for explaining a determination process of whether or not to perform an integration filter process.

[Explanation of symbols]

 1 Scanner 5 Region Separation Circuit 6 Differential Filter 7 Integral Filter 8 Pass Through Circuit 9 Selector 21 SRAM 31 Region Judgment Data Generator 32 Region Judgment Register Group 35 Filtering Judgment Unit 37 Flag Memory 39 Shift Register 40 Shift Register 41 1st Area determination section 42 Second area determination section 43 Third area determination section 51 Shift register 52 Shift register 53 Shift register 54 Shift register 55 Shift register 57 Square processing section 59 Addition processing section 61 Comparator 62 Comparator 63 Comparator 64 Comparison Vessel 65 comparator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Higashii Hideo Higashi 3-3-1, Kochoji-minami, Toyonaka City, Osaka Prefecture No. 302-1 Veli (72) Inventor Satoshi Iwatsubo 9-2 Yada, Higashi-Sumiyoshi-ku, Osaka City, Osaka Prefecture No. 28 Terrace FLORA No.

Claims (4)

[Claims] 1. An image processing method for processing an image composed of a plurality of pixels each having density data, wherein the processing target image is processed based on a difference in density data between a processing target pixel and its surrounding pixels. A step of obtaining a density change value in the vicinity of a pixel; a step of calculating a squared value of the density change value to obtain a first judgment value; 1 step of adding a judgment value to calculate a second judgment value; a comparison step of comparing the first judgment value and the second judgment value with a predetermined threshold; A determination step of determining whether the pixel to be processed is a pixel forming a character image, a halftone image, or a halftone image, and a predetermined process corresponding to the determination result in this determination step is performed. An image processing method characterized by comprising the processing steps to be performed on elephant pixel. 2. The processing step is based on the determination result of the determination step for the pixel to be processed, and the determination result of the determination step for the pixel having a predetermined positional relationship in the vicinity of the pixel of the processing target. The image processing method according to claim 1, further comprising the step of determining the type of processing to be performed on the target pixel. 3. An image processing apparatus for processing an image composed of a plurality of pixels each having density data, wherein the processing target image is processed based on a difference in density data between a processing target pixel and its surrounding pixels. Means for obtaining a density change value in the vicinity of a pixel, means for calculating a squared value of the density change value as a first determination value, and Based on the comparison result by the comparing means, means for calculating the second determination value by adding 1 determination value, comparison means for comparing the first determination value and the second determination value with a predetermined threshold value, A determination unit that determines whether the pixel to be processed is a pixel forming a character image, a halftone image, or a halftone image, and a pixel to be processed by performing a predetermined process corresponding to the determination result by the determination unit. And processing means to apply to The image processing apparatus according to claim and. 4. The processing means performs processing based on a determination result of the determination means for a pixel to be processed and a determination result of the determination means for a pixel having a predetermined positional relationship in the vicinity of the pixel to be processed. The image processing apparatus according to claim 3, further comprising means for determining a type of processing to be performed on the target pixel.