JPH1117966A - Image processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing unit in which image quality is enhanced by discriminating a dot area with high precision. SOLUTION: An area processing section 23 is provided with a dot area discrimination section 31 and an area dependent adaptive processing section 32. The dot area discrimination section 31 reads color image data C, M, Y of 2-line stored in FIFO memories 22C, 22M, 22Y, stores the read data to a line memory and discriminates to which of 1st to 4th dot areas noted color image data belong by using the 3-line color image data stored in the line memory and the FIFO memories. The area dependent adaptive processing section 32 applies adaptive processing corresponding to the belonging dot area to a certain color image data and gives the result to a black generating processing section 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for performing data processing on image data obtained by reading a document.

[0002]

2. Description of the Related Art A digital copying machine generally determines whether image data obtained by reading an original belongs to a character area, a photograph area, or a halftone area, and performs data processing in accordance with the area. It has a function to apply to image data.

Conventionally, means for determining whether image data belongs to a halftone dot area includes means for detecting two types of screen lines (for example, 85 lines and 133 lines) of screen lines (dots per inch). When any of the screen rulings is detected, the determination is made by determining that the image data belongs to a dot area.

[0004]

However, according to the above-mentioned conventional determination, when the original has a halftone dot area having a screen ruling intermediate between the two types of coarse and dense screen rulings, the image data in this halftone dot area is May be determined as a halftone area or a non-halftone area, and there is a risk that both determinations may be mixed.

Generally, in an image processing apparatus that performs data processing on image data obtained by reading a document image, if it is determined that the image data belongs to a halftone dot area, an adaptive process such as an integration process is performed on the image data. It is applied to
If the determination of the halftone area and the determination of the non-halftone area coexist, the presence or absence of the adaptive processing is switched, and a step occurs in the image at the boundary where the switching is performed.

On the other hand, in the case of a color halftone image composed of cyan, magenta, and yellow, the screen angle of each color is different in order to prevent the occurrence of moire.
That is, for example, with respect to the yellow halftone image, the magenta halftone image is tilted by 15 °, the black halftone image is tilted by 45 °, and the cyan halftone image is tilted by 75 °.

For this reason, there is a possibility that the determination of the halftone dot region may differ depending on the color. In this case, the presence or absence of the adaptive processing differs depending on the color, which changes the color of the image and degrades the image quality. I will.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide an image processing apparatus capable of accurately determining a halftone dot region and improving image quality.

[0009]

According to the present invention, there is provided an image processing apparatus for performing data processing on image data corresponding to each pixel of an input image, wherein the image data corresponds to the screen ruling of a halftone image in advance. A halftone area determining means for determining to which of the plurality of halftone areas belongs, and a halftone area corresponding to each of the halftone areas determined in the adaptive processing set in advance corresponding to each of the halftone areas And an area adaptation processing means for applying the adaptation processing to the image data.

According to this configuration, it is determined to which of a plurality of halftone areas preset in accordance with the screen ruling of the halftone image the image data corresponding to each pixel of the input image belongs. The adaptive processing corresponding to the halftone area determined in the preset adaptive processing corresponding to the halftone area is performed on the image data, so that the optimal adaptive processing according to the screen ruling is performed. As a result, the image quality is improved.

In the image processing apparatus according to the first aspect, the plurality of halftone areas are set such that adjacent halftone areas partially overlap each other (claim 2).

According to this configuration, the plurality of halftone areas set in advance corresponding to the screen ruling of the halftone image are set so that adjacent halftone areas overlap with each other. Even if the screen ruling is appropriate, the screen line is surely determined to belong to any halftone dot region without being erroneously determined to be a non-dot region.

In the image processing apparatus according to the second aspect, the area adaptation processing means adapts the image data determined to belong to both of the mutually overlapping halftone areas to the image data corresponding to both halftone areas. The result of each of the processes is combined (claim 3).

According to this configuration, the image data determined to belong to both of the halftone dot regions overlapping each other are subjected to the adaptive processing corresponding to both of the halftone dot regions, and the result is synthesized. Even when the halftone dot area to which the data belongs is switched, the processing result changes smoothly, and no step occurs in the image.

Further, in the image processing apparatus according to any one of claims 1 to 3, the image data comprises image data of a plurality of colors, and the halftone dot area determination means individually determines each color. The region adaptive processing means individually performs adaptive processing for each color.

According to this configuration, it is determined for each color whether the image data corresponding to each pixel of the input image belongs to a plurality of halftone areas set in advance corresponding to the screen ruling of the halftone image. The adaptive processing corresponding to the halftone area determined in the adaptive processing set in advance corresponding to each halftone area is individually performed on the image data for each color. Optimal adaptive processing according to the number of lines is performed, and the image quality is improved.

In the configuration according to any one of claims 1 to 4, pattern data storage means for storing pattern data set in advance at predetermined angles with respect to the number of screen lines belonging to each halftone dot area. Wherein the input image is composed of image data corresponding to pixels of a plurality of lines, the pattern data is composed of image data corresponding to pixels of three lines, If the image data corresponding to the three lines of pixels centered on the pattern data matches the pattern data, the image data may be determined to belong to the halftone dot area corresponding to the pattern data.

According to this structure, the pattern data storage means stores the pattern data consisting of the image data corresponding to the pixels of three lines and set in advance at a predetermined angle for a predetermined number of screen lines. If the image data corresponding to the three lines of pixels centered on the image data to be determined matches the pattern data, the image data is determined to belong to the halftone dot region corresponding to the pattern data. Only by using the image data corresponding to the pixels of the line, the halftone dot area to which the image data to be determined belongs can be accurately determined.

[0019]

FIG. 1 is a block diagram showing an electric configuration of an embodiment of a color digital copying machine to which an image processing apparatus according to the present invention is applied. As shown in FIG. 1, the color digital copying machine includes an image reading unit 1, an image processing unit 2, a laser beam output unit 3, an image forming unit 4, an operation unit 5, and a CPU 6.

The image reading section 1 includes an unillustrated illuminating means for illuminating a color original to be copied, a photoelectric conversion section 11, and a density conversion section 12, and reads a color original to read color image data C, M, and C. Y is obtained.

The image processing unit 2 includes an input processing unit 21 and an FI
FO (First In First Out) memory 22C, 22M, 22
Y, an area processing unit 23, a black generation processing unit 24, an output color selection unit 25, a scaling processing unit 26, and a spatial filter unit 27
And a tone correction unit 28 and an output control unit 29, which perform predetermined processing described later on the color image data C, M, and Y obtained by the image reading unit 1.

The laser beam output unit 3 irradiates a laser beam on the photosensitive member of the image forming unit 4 which has been charged in advance in accordance with the color image data processed by the image processing unit 2, and electrostatically charges the surface of the photosensitive member. This is to form a latent image.

The image forming section 4 includes a photoreceptor (not shown), a developing device,
Equipped with a transfer paper transport device and a fixing device, etc., the electrostatic latent images formed for each color on the photoreceptor surface are sequentially cyan (C),
Transfer toner formed by developing using magenta (M) and yellow (Y) color toners and black (K) toner and transferring it to transfer paper conveyed to the photoreceptor and transferring four color toners The image is fixed on the transfer paper.

The photoelectric conversion units 11 of the image reading unit 1 are arranged in a line, and receive a large number of photoelectric conversion elements (hereinafter, referred to as “pixels”) from a minute area (hereinafter, referred to as “pixel”) of an illuminated color document. R, G, B, which are disposed on the optical path of the reflected light and separate into three primary colors of additive color mixture, red (R), green (G), and blue (B). It has a filter and an A / D converter, and has a red (R) component and a green (G) component.
Component and an analog color image signal of three primary colors proportional to the light intensity of the blue (B) component, and converts this analog color image signal into a predetermined number of bits (8 in this embodiment).
(Bit) digital color image data R, G, B.

The density conversion section 12 outputs color image data R,
G and B are complementary colors of cyan (C) and magenta, respectively.
(M), yellow (Y), that is, color image data C, M, and Y proportional to the density of the three primary colors in the subtractive color mixture.

The input processing unit 21 of the image processing unit 2 performs a frequency conversion process of a reference clock frequency when transmitting each of the color image data C, M, and Y, so that the image reading unit 1
In addition to absorbing the difference between the reference clock frequency in the image processing unit 2 and the reference clock frequency in the image processing unit 2, the image data is subjected to noise removal processing and the like.

The input processing section 21 stores the color image data C, M, and Y in the FIFO memories 22C, 22M, and 22Y after performing the respective processes.

The area processing section 23 includes a halftone area determination section 31 and an area-specific adaptive processing section 32.
The color image data C, M, and Y of a plurality of lines stored in C, 22M, and 22Y are read and stored in a line memory described later, and the color image data of a plurality of lines stored in the line memory are used. This is to determine whether the color image data of interest belongs to any of the character area, the photograph area, and the halftone area.

The area processing unit 23 determines a halftone dot area by the procedure described below, and determines a character area or a photographic area by using a known method described in Japanese Patent Application Laid-Open No. 8-149298. As shown in FIG. 1, the determined region data, that is, the data relating to the distinction between the character region, the photograph region, and the halftone dot region is transmitted to the black generation processing unit 24, the scaling unit 26, the spatial filter unit 27, the gradation The output is sent to the correction unit 28 and the output control unit 29.

If the color image data of interest is a halftone area, the area processing section 23
C, 22M and 22Y stored in the color image data C,
An adaptive process described below is performed on M and Y, and is sent to the black generation processing unit 24 as color image data C ′, M ′ and Y ′.

The black generation processing section 24 performs under color removal (Under Color Removal) for generating black image data K using the color image data C ′, M ′, and Y ′, and generates the generated image data K. , Each image data C ′, M ′,
The output color selecting section 25 corrects Y ′ and K and outputs image data C ″, M ″, Y ″ and K ′. Is selected and output. The scaling unit 26 performs processing such as enlargement or reduction on the selected image data according to a set magnification or the like.

The spatial filter unit 27 performs a known filter process such as an edge enhancement process or a smoothing process in accordance with the result of the discrimination by the region processing unit 23, or allows the data to pass through without any process. In the case of a region, an edge enhancement process is performed, and in the case of a photograph region and a halftone dot region, a smoothing process is performed.

The tone correcting section 28 performs a tone data correcting process using the range of the effective image data obtained by the CPU 6, and will be described later in detail. The output control unit 29 controls emission of laser light from the laser light output unit 3 according to the image data sent from the gradation processing unit 28.

An operation unit 5 includes a magnification setting key 51 for setting a copy magnification and a print key 52 for instructing start of a copy operation.
Etc. are provided. The CPU 6 has a ROM 61 and a RAM 6
2 to control the operation of each of the above sections according to the operation of the operation section 5 to copy the original. ROM61
Is for storing pattern data described later stored in advance, and the RAM 62 is for temporarily storing data.

FIG. 2 is a block diagram showing an electrical configuration of the halftone dot area determination section 31 in the area processing section 23.

The halftone dot judging section 31 includes a cyan judging section 31.
C, a magenta determination unit 31M, and a yellow determination unit 31Y
And a cyan determination unit 31C includes a first region determination unit 71, a second region determination unit 72, and a third region determination unit 73.
A fourth area determination unit 74, a first line memory 75,
A second line memory 76 and a determination processing unit 77 are provided. The magenta determination unit 31M and the yellow determination unit 3
1Y has the same configuration as the cyan determination unit 31C, and a description thereof will be omitted.

The first line memory 75 and the second line memory 76 are FIFOs each capable of holding one line of color image data C by the CCD line sensor of the photoelectric conversion unit 11 (FIG. 1) stored in the FIFO memory 22C. In the memory, the color image data C stored in the first line memory 75 is sequentially sent to the second line memory 76.

From the FIFO memory 22C, the first line memory 75, and the second line memory 76, color image data C for three lines by the same pixel of the CCD line sensor are synchronously synchronized with the first area determination units 71 to fourth. It is configured to be sent to the area determination unit 74.

First area determination section 71 to fourth area determination section 74
Uses three lines of image data sent from the FIFO memory 22C, the first line memory 75, and the second line memory 76, uses the image data sent from the first line memory 75 as a line of interest, and follows the operation procedure described later. ,
The image data of interest (pixel of interest) is from the first halftone dot region to the fourth halftone dot region.
This is to determine whether or not the pixel belongs to a dot area.

The screen ruling of the halftone image is 200
Lines, 175 lines, 150 lines, 133 lines, 120 lines, 100 lines, 85 lines, 65 lines and the like are generally used.

The first area determination unit 71 determines that the screen ruling is
It is determined that the line belongs to the first halftone dot area when the line is 200 to 150 lines,
The second area determination unit 72 determines that the screen belongs to the second halftone area when the screen ruling is 150 to 100 lines, and the third area determining unit 73 determines that the screen ruling is 100 to 85 lines. Third
The fourth area determination unit 74 determines that the image belongs to the halftone dot area, and determines that the image belongs to the fourth halftone area when the screen ruling is 85 to 65 lines.

As described above, the first halftone area to the fourth halftone area are set so that adjacent halftone areas partially overlap each other. When the screen ruling is 150 lines, the first halftone area is the first halftone area.
When the screen ruling is 100 lines, it is determined to belong to the halftone dot area and the second halftone area, and when the screen ruling is 100 lines, it is determined to belong to the second halftone area and the third halftone area. When the number is 85 lines, it is determined that the line belongs to the third halftone dot region and the fourth halftone dot region.

The determination processing section 77 includes first area determination sections 71 to 71
The halftone area to which the image data of interest belongs is determined based on the determination result of the fourth area determination unit 74, and the determination result is sent to the area-specific adaptive processing unit 32.

The determination processing section 77 includes first area determination sections 71 to 71
If one of the fourth area determination units 74 determines that the pixel belongs to the halftone dot area, the area determination unit 74 determines that the pixel belongs to the halftone dot area. If there is no region determination unit that belongs to the halftone region in the first region determination unit 71 to the fourth region determination unit 74, it is determined that the image data of interest is a non-halftone image.

If two or more of the first to fourth region determination units 71 to 74 determine that the pixel belongs to the halftone dot region, the determination processing unit 77
The determination is made as follows.

When it is determined that the pixel belongs to the first halftone dot area and the second halftone dot area, it is determined that the pixel belongs to an intermediate area between the first and second halftone dot areas. When it is determined that the pixel belongs to the second dot area and the third dot area, it is determined that the pixel belongs to an intermediate area between the second and third dot areas. When it is determined that the pixel belongs to the third dot area and the fourth dot area, it is determined that the pixel belongs to an intermediate area between the third and fourth dot areas.

When it is determined that the pixel belongs to the first halftone area, the second halftone area and the third halftone area, it is determined that the pixel belongs to an intermediate area between the first halftone area and the second halftone area. When it is determined that the pixel belongs to the first halftone area, the second halftone area, and the fourth halftone area,
It is determined that the pixel belongs to an intermediate area between the first and second halftone dot areas. When it is determined that it belongs to the first halftone area, the third halftone area, and the fourth halftone area, it is determined that it belongs to the intermediate area between the third halftone area and the fourth halftone area. The second halftone area, the third halftone area, and the fourth halftone area
When it is determined that the pixel belongs to the dot area, it is determined that the pixel belongs to an intermediate area between the second and third dot areas. If it is determined that it belongs to all the halftone areas from the first halftone area to the fourth halftone area, it is determined that it belongs to the intermediate area between the first and second halftone areas.

FIG. 3 is a block diagram showing an electrical configuration of the area-specific adaptive processing section 32 in the area processing section 23. FIGS. 4 to 7 show image data in the first adaptive processing section 81 to the fourth adaptive processing section 84, respectively. FIG. 6 is a diagram for explaining an adaptive process performed on the image data.
In FIGS. 4 to 7, pixels surrounded by thick solid lines indicate target pixels.

As shown in FIG. 3, the area-specific adaptive processing section 32
Represents a cyan processing unit 32C, a magenta processing unit 32M,
A yellow processing section 32Y, and a cyan processing section 32C.
Includes a first adaptive processing unit 81, a second adaptive processing unit 82, a third adaptive processing unit 83, a fourth adaptive processing unit 84, a first synthesis processing unit 85, a second synthesis processing unit 86, A third combination processing unit 87 and a processing result selection unit 88 are provided. Since the magenta processing unit 32M and the yellow processing unit 32Y have the same configuration as the cyan processing unit 32C, the description will be omitted.

First to fourth adaptive processing units 81 to 84
Performs predetermined adaptive processing on each color image data C stored in the FIFO memory 22C. The first adaptive processing unit 81 performs a 2 × 2 integration processing shown in FIG. And multiplies by 1, and sends the result to the processing result selection unit 88.

The second adaptive processing section 82 performs the 3 × 3 integration processing shown in FIG.
/ 5 and sends the result to the processing result selection unit 88.

Further, the third adaptive processing section 83 performs the 3 × 3 integration processing shown in FIG.
/ 9 and sends the result to the processing result selection unit 88.

Further, the fourth adaptive processing section 84 performs the 4 × 4 integration processing shown in FIG.
/ 16 and sends the result to the processing result selection unit 88.

The first synthesis processing unit 85 averages the results of the first and second adaptive processing units 81 and 82 and forms a second synthesis processing unit 86
Averages the results of the second and third adaptive processing units 82 and 83,
The third synthesis processing unit 87 includes third and fourth adaptive processing units 83 and 8.
4 are averaged, and the processing result selection units 8
The average value obtained in step 8 is sent.

The processing result selecting unit 88 determines whether each of the processing units 81 to 87 and the FIFO
The data is selected from the data sent from the memory 22C and output to the black generation processing unit 24 as color image data C '.

That is, the processing result selecting section 88 outputs the data from the first adaptive processing section 81 when the determination result of the determination processing section 77 is the first halftone area, and the second adaptive processing when the determination result is the second halftone area. The data from the unit 82, the data from the third adaptive processing unit 83 for the third halftone area, and the fourth data for the fourth halftone area.
The data from the adaptive processing unit 84, the data from the first combining processing unit 85 in the case of the intermediate area between the first and second halftone dot areas, and the second combining processing in the case of the intermediate area between the second and third halftone dot areas. Part 8
6, the data from the third combination processing section 87 is selected and output in the case of the intermediate area between the third and fourth halftone areas, and the data from the FIFO memory 22C is output in the case of the non-halftone area.

Next, an example of the halftone dot area judging operation will be described with reference to FIGS. 8 to 13 are diagrams showing examples of halftone dot image patterns. In the drawings, three columns of black frames indicated by bold solid lines indicate pixels of three lines of the CCD line sensor, and pixels indicated by arrows are: A black pixel whose density is equal to or higher than a certain value is shown.

FIGS. 14 to 17 are diagrams for explaining the processing in the first area determination section 71 to the fourth area determination section 74, respectively. FIG. 18 shows 200 lines to 1 stored in the ROM 61.
It is a figure which shows an example of the pattern data for determination of 50 lines, ie, a 1st dot area.

In this embodiment, the photoelectric conversion unit 11
The resolution of the CCD line sensor shown in FIG.
inch). Therefore, CC at each screen ruling
The halftone dot interval (hereinafter referred to as “pitch”) with respect to the pixel interval of the D line sensor is 1.00 pitch for 200 lines and 1.14 for 175 lines.
Pitch, 150 lines 1.33 pitch, 133 lines 1.50 pitch, 120
Lines have 1.67 pitches, 100 lines have 2.00 pitches, 85 lines have 2.35 pitches, and 65 lines have 3.08 pitches.

Further, since the first area determination section 71 to the fourth area determination section 74 are constituted by hardware using a logic circuit, the halftone area determination is performed in the middle as described below. Even if you do, the operation will be performed to the end,
The configuration is such that the result of the determination on the way is retained.

First, the operation of the first area determination section 71 will be described. As described above, the first area determination unit 71 determines that the screen belongs to the first halftone dot area when the screen ruling is 200 lines, 175 lines, and 150 lines. That is, it is determined whether the interval between the black pixels is 1.00 to 1.33 pitches.

(1) First, a black pixel whose density is equal to or higher than a predetermined value is determined. (2) Next, black pixels (halftone dots) on the line of interest, ie, in the image data sent from the first line memory 75
Are regularly present or halftone dots are not regularly present on the line of interest, but are sent from either the line above or below the line of interest, ie, from the FIFO memory 22C or the second line memory 76. It is determined whether black pixels are regularly present in the incoming data.

If black pixels are regularly present, it is determined whether or not the interval is 1.00 to 1.33 pitches.

For example, in the case of FIG. 8, one white pixel exists between the black pixels and has a pitch of 1.00. At this point, the first area determination unit 71 It is determined that the target pixel belongs to the first halftone dot area having a screen ruling of 200 lines.

In the case of FIG. 9, since the intermediate gradation and the white pixel are regularly present between the black pixels in the lines above and below the line of interest,
The first area determination unit 71 determines that the pixel of interest belongs to the first halftone area of 150 lines.

FIGS. 8 and 9 show halftone images in which the screen angle with respect to the CCD line sensor is 0 °.

(3) Next, the density of a pixel at a distance D from the target pixel is determined. That is, in FIG. 14, the density of the pixel of D = 1.00 (in the figure, ,,) from the target pixel X,
From the pixel of interest X, the density of the pixel of D = 1.41 (in the figure,,) is determined.

When the target pixel X is a black (white) pixel and there is no white (black) pixel in the pixels 〜, at this point, the first area determination unit 71 determines that the target pixel is It is determined that the line does not belong to the first halftone dot area of 150 lines.

(4) Subsequently, the distribution pattern of the black pixels in the fixed area for three lines is checked against the pattern data for 200 to 150 lines shown in FIG. Then, it is determined that the target pixel belongs to the first halftone dot area of 200 to 150 lines.

The pattern data stored in the ROM 61 is, for each screen ruling, at a constant angle, for example, at 15 ° intervals of 0 °, 15 °, 30 °, 45 °, 60 °, 75 °, and 90 °. With this arrangement, it is possible to correspond to the screen angle of each color image data C, M, Y. The pattern data stored in the ROM 61 is not limited to 15 ° intervals, and may be, for example, 5 ° intervals.

For example, FIG. 10 shows a pattern in which white pixels and pixels of intermediate gradation alternate between black pixels and black pixels.
It is determined that the line belongs to 200 lines, that is, the first halftone dot area.

FIG. 11 shows a pattern in which a pixel of intermediate gradation and a white pixel exist between black and black pixels.
That is, it is determined that the pixel belongs to the first halftone dot area.

On the other hand, if there is no matching pattern data, the first area determination section 71 determines that the target pixel is 200
It is determined that the line does not belong to the first halftone dot region of the line to 150 lines.

Next, the operation of the second area determination section 72 will be described. As described above, the second area determination unit 72 determines that the screen belongs to the second halftone dot area when the screen ruling is 150 lines, 133 lines, 120 lines, and 100 lines. That is, it is determined whether or not the interval between the black pixels is 1.33 to 2.00 pitch.

(1) Similarly to the first area determination section 71, first,
A black pixel whose density is equal to or higher than a certain value is determined. (2) Next, similarly to the first area determination unit 71, whether or not halftone dots (black pixels) are regularly present on the line of interest, that is, in the image data sent from the first line memory 75, or Although halftone dots do not exist regularly on the line of interest, either one of the lines above or below the line of interest, ie, FI
It is determined whether black pixels are regularly present in the data sent from the FO memory 22C or the second line memory 76.

Then, when the black pixels are regularly present, the second area determination section 72 determines whether or not the interval is 1.33 to 2.00 pitches.

For example, in the case of FIG. 9 described above, in the lines above and below the line of interest, intermediate gradations and white pixels are regularly present between black pixels. , The second area determination unit 72 determines that the pixel of interest belongs to the second halftone area of 150 lines.

In the case of FIG. 12, since the black pixel, the white pixel, and the white pixel are regularly present between the black pixel and the black pixel, the second area determination unit 72 at this time. Determines that the pixel of interest belongs to the second halftone dot area of 100 lines.

FIG. 12 shows a halftone image in which the screen angle with respect to the CCD line sensor is 0 °.

(3) Next, the density of a pixel at a distance D from the target pixel is determined. That is, in FIG. 15, the density of the pixel (=, in the figure) of D = 1.41 from the target pixel X, the density of the pixel (=, in the figure) of D = 2.00 from the target pixel X, and D = 2.24 from the target pixel X. And the density of the pixel (, in the figure). This is because the halftone dot size of 150 to 100 lines is larger than the read pixel.

When the target pixel X is a black (white) pixel, if there is no white (black) pixel in the pixels で, at this point, the second area determination unit 72 determines that the target pixel is It is determined that the line does not belong to the second halftone dot area of 100 lines.

(4) Subsequently, the distribution pattern of the black pixels in the fixed area for three lines is compared with the pattern data for 150 to 100 lines stored in the ROM 61, and the pattern data to be matched is obtained. Exists, the pixel of interest is
It is determined that the pixel belongs to the second halftone dot area of 150 to 100 lines.

For example, FIG. 11 shows a pattern in which a pixel of intermediate gradation and a white pixel exist between black pixels, thereby providing a screen angle of 15 °.
It is determined that the line belongs to 150 lines, that is, the second halftone dot area.

In FIG. 13, a pixel having an intermediate gradation and a white pixel are present between black pixels, and a similar pattern is present in an adjacent portion. At 15 °, it is determined that the line belongs to 100 lines, that is, the second halftone dot area.

On the other hand, if there is no matching pattern data, the second area determination section 72 determines that the target pixel is
It is determined that the line does not belong to the second halftone dot region of the line to the 100th line.

Next, the operation of the third area determination section 73 will be described. As described above, the third area determination unit 73 determines that the screen belongs to the third halftone dot area when the screen ruling is 100 lines or 85 lines. That is, it is determined whether the interval between the black pixels is 2.00 to 2.35 pitch.

(1) Similarly to the first area determination section 71, first,
A black pixel whose density is equal to or higher than a certain value is determined. (2) Next, similarly to the first area determination unit 71, whether or not halftone dots (black pixels) are regularly present on the line of interest, that is, in the image data sent from the first line memory 75, or Although halftone dots do not exist regularly on the line of interest, either one of the lines above or below the line of interest, ie, FI
It is determined whether black pixels are regularly present in the data sent from the FO memory 22C or the second line memory 76.

Then, when the black pixels are regularly present, the third area determination section 73 determines whether or not the interval is 2.00 to 2.35 pitch.

For example, in the case of FIG. 12, since the black pixel, the white pixel, and the white pixel regularly exist between the black pixel and the black pixel on the target line and the upper line, At this point, the third area determination unit 73 determines that the pixel of interest belongs to the third halftone area of 100 lines.

(3) Next, the density of a pixel at a distance D from the target pixel is determined. That is, in FIG. 16, the density of the pixel of interest D = 2.24 from the target pixel X (in the figure), the density of the pixel of interest D = 3.00 (in the figure), and the density of the target pixel X to D = 3.16 And the density of the pixel (, in the figure). This is because the halftone dot size of 100 to 85 lines is larger than the read pixel.

When the target pixel X is a black (white) pixel and there is no white (black) pixel in the pixel 〜, at this point, the third area determination unit 73 determines that the target pixel X It is determined that the pixel does not belong to the third halftone dot area of line 85.

(4) Subsequently, the distribution pattern of the black pixels in the fixed area for three lines is compared with the pattern data for 100 lines and 85 lines stored in the ROM 61,
If there is pattern data to be matched, it is determined that the pixel of interest belongs to the third halftone dot area of 100 to 85 lines.

For example, in FIG. 13 described above, a pixel of intermediate gradation and a white pixel exist between black pixels, and a similar pattern exists in an adjacent portion. 100 lines at 15 °, third
It is determined that the pixel belongs to a dot area.

On the other hand, if there is no matching pattern data, the third area determination section 73 determines that the target pixel is 100
It is determined that the line does not belong to the third halftone dot area of the line to the 85th line.

Next, the operation of the fourth area determination section 74 will be described. As described above, the fourth area determination unit 74 determines that the screen ruling belongs to the fourth halftone dot area when the screen ruling is 85 lines or 65 lines. That is, the interval between black pixels is
It is determined whether the pitch is between 2.35 and 3.08.

(1) Similarly to the first area determination section 71, first,
A black pixel whose density is equal to or higher than a certain value is determined. (2) Next, similarly to the first area determination unit 71, whether or not halftone dots (black pixels) are regularly present on the line of interest, that is, in the image data sent from the first line memory 75, or Although halftone dots do not exist regularly on the line of interest, either one of the lines above or below the line of interest, ie, FI
It is determined whether black pixels are regularly present in the data sent from the FO memory 22C or the second line memory 76.

Further, when the black pixels are regularly present, the fourth area determination section 74 determines whether or not the interval is 2.35 to 3.08 pitches.

Then, black pixels regularly exist, and
If the interval is between 2.35 and 3.08 pitches, at this time, the fourth area determination unit 74 determines that the pixel of interest belongs to the fourth halftone dot area.

(3) Next, the density of a pixel at a distance D from the target pixel is determined. That is, in FIG. 17, the density of the pixel (D in the figure) of D = 3.16 from the target pixel X, the density of the pixel (D in the figure) of D = 4.00 from the target pixel X, and the density of D = 4.12 from the target pixel X And the density of the pixel (, in the figure). This is because the halftone dot size of the 85th to 65th lines is larger than the read pixel.

When the target pixel X is a black (white) pixel and there is no white (black) pixel in the pixels 〜, at this point, the fourth area determination unit 74 determines that the target pixel It is determined that the pixel does not belong to the fourth halftone dot area of the 65th line.

(4) Subsequently, the distribution pattern of black pixels in a certain area of three lines is checked against the pattern data for the 85th to 65th lines stored in the ROM 61, and the pattern data to be matched is obtained. Exists, the target pixel is 85
It is determined that the line belongs to the fourth halftone dot area of the line to the 65th line.

On the other hand, if there is no matching pattern data, the fourth area determination section 74 determines that the target pixel does not belong to the fourth halftone area of the 85th to 65th lines.

As described above, according to the present embodiment, it is individually determined whether the pixel of interest belongs to the first halftone area to the fourth halftone area set in advance according to the screen ruling of the halftone image. And the first adaptive processing section 81 to the fourth adaptive processing section 84 perform adaptive processing corresponding to the halftone dot region to which the target pixel belongs, on the target pixel. Adaptive processing can be performed.

Further, the screen ruling of the halftone dot image is divided into four areas of a first halftone area to a fourth halftone area, and the first area determination units 71 to 74 respectively determine the first halftone area. By determining whether it belongs to the dot area to the fourth dot area,
The range of the screen ruling belonging to one halftone dot area is reduced, thereby making it possible to easily determine whether or not the screen belongs to the halftone dot area.

Therefore, it is possible to determine whether or not a pixel belongs to a halftone dot region based on only three lines of image data including a pixel of interest. Is unnecessary, and the configuration of the apparatus can be simplified.

When the screen ruling is 150 lines,
If it belongs to the first halftone area and the second halftone area, it is determined that it belongs to the second halftone area. If it is 100 lines, it is determined that it belongs to the second halftone area and the third halftone area. Are redundantly determined to belong to the third halftone area and the fourth halftone area, and in these cases, the first synthesis processing unit 85 to the third synthesis processing unit 87 correspond to each halftone area. Since the processing result obtained by synthesizing the adaptive processing to be used is used, even when the determination of the halftone dot area is switched, it can be smoothly changed without a step at the boundary, thereby improving the image quality. be able to.

The present invention is not limited to the above embodiment, but can adopt the following modifications (1) to (3). (1) In the above embodiment, the area processing unit 23 is configured by a logic circuit and data processing is performed by hardware. However, instead of this, a high-speed microcomputer is configured and data processing is performed by software. It may be.

(2) As shown by a dashed line in FIG. 1, an external device 7 may be provided. For example, when an external scanner is provided as the external device 7, data read by the external scanner is input to the input processing unit 21. If a facsimile device is provided as the external device 7, the data from the tone correction unit 28 is sent to the facsimile device.

(3) In the above embodiment, a description has been given of a form applied to a color digital copying machine provided with the image reading section 1, but the image is read by a single image reading apparatus (image scanner) and is read by a personal computer or the like. A form in which data processing is performed on the image data of the captured original may be used.

[0110]

As described above, according to the present invention,
It is determined whether the image data corresponding to each pixel of the input image belongs to a plurality of predetermined halftone areas corresponding to the screen ruling of the halftone image, and is set in advance corresponding to each halftone area. Since the adaptive processing corresponding to the halftone dot area determined in the adaptive processing is performed on the image data, it is possible to perform the optimal adaptive processing according to the screen ruling,
Thereby, image quality can be improved.

By setting a plurality of halftone areas set in advance corresponding to the screen ruling of the halftone image so that adjacent halftone areas partially overlap each other, Therefore, it is possible to reliably determine that a pixel belongs to any of the halftone dot regions without erroneously determining that the pixel region is a non-dot region.

Further, the image data determined to belong to both of the halftone dot regions overlapping each other are subjected to the adaptive processing corresponding to both of the halftone dot regions, and the results are combined, whereby the halftone dot to which the image data belongs is synthesized. Even when the area is switched, the processing result changes smoothly, so that no step is generated in the image, and thereby the image quality can be improved.

It is determined individually for each color whether the image data corresponding to each pixel of the input image belongs to a plurality of predetermined halftone areas corresponding to the screen ruling of the halftone image. The adaptive processing corresponding to the halftone area determined in the preset adaptive processing corresponding to each halftone area is individually applied to the image data for each color, so that the optimal processing according to the screen ruling is performed. Adaptive processing,
Thereby, image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of a color digital copying machine to which an image processing apparatus according to the present invention is applied.

FIG. 2 is a block diagram showing an electric configuration of a halftone dot area determination unit 31 of the area processing unit 23.

FIG. 3 is a block diagram illustrating an electrical configuration of a region-specific adaptive processing unit in the region processing unit.

FIG. 4 is a diagram illustrating an adaptive process performed on image data in a first adaptive processing unit.

FIG. 5 is a diagram illustrating an adaptive process performed on image data in a second adaptive processing unit.

FIG. 6 is a diagram illustrating an adaptive process performed on image data in a third adaptive processing unit 83.

FIG. 7 is a diagram illustrating an adaptive process performed on image data in a fourth adaptive processing unit.

FIG. 8 is a diagram showing an example of a dot image pattern.

FIG. 9 is a diagram showing an example of a dot image pattern.

FIG. 10 is a diagram illustrating an example of a dot image pattern.

FIG. 11 is a diagram illustrating an example of a dot image pattern.

FIG. 12 is a diagram illustrating an example of a dot image pattern.

FIG. 13 is a diagram illustrating an example of a dot image pattern.

FIG. 14 is a diagram illustrating processing in a first area determination unit 71.

FIG. 15 is a diagram illustrating a process in a second area determination unit 72.

FIG. 16 is a diagram illustrating a process in a third area determination unit 73.

FIG. 17 is a diagram illustrating processing in a fourth area determination unit 74.

18 is a diagram showing an example of pattern data for determining a first halftone dot area stored in a ROM 61. FIG.

[Explanation of symbols]

 Reference Signs List 1 image reading unit 2 image processing unit 3 laser light output unit 4 image forming unit 5 operation unit 6 CPU 11 photoelectric conversion unit 12 density conversion unit 21 input processing unit 22C, 22M, 22Y FIFO memory 23 area processing unit 24 black generation processing unit Reference Signs List 31 halftone area determination section 31C cyan determination section 31M magenta determination section 31Y yellow determination section 32 adaptive processing section 32C cyan processing section 32M magenta processing section 32Y yellow processing section 61 ROM 62 RAM 71 first area determination section 72 second area Judgment unit 73 Third area judgment unit 74 Fourth area judgment unit 75 First line memory 76 Second line memory 77 Judgment processing unit 81 First adaptive processing unit 82 Second adaptive processing unit 83 Third adaptive processing unit 84 Fourth adaptive Processing unit 85 First synthesis processing unit 86 Second synthesis processing unit 87 Third synthesis processing unit 88 Processing result selection unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 9/67 H04N 1/40 B 9/73 1/46 Z

Claims (4)

[Claims] 1. An image processing apparatus for performing data processing on image data corresponding to each pixel of an input image, wherein the image data includes a plurality of halftone dot areas set in advance corresponding to the screen ruling of a halftone image. And an area for applying adaptive processing to the image data corresponding to the halftone area determined in the adaptive processing set in advance corresponding to each of the halftone areas. An image processing apparatus comprising: an adaptive processing unit. 2. The image processing apparatus according to claim 1, wherein
An image processing apparatus, wherein the plurality of halftone areas are set such that adjacent halftone areas partially overlap with each other. 3. The image processing apparatus according to claim 2, wherein
The area adaptation processing means synthesizes a result of performing adaptive processing corresponding to both halftone areas on image data determined to belong to both of the mutually overlapping halftone areas. Image processing apparatus. 4. The image processing apparatus according to claim 1, wherein said image data comprises image data of a plurality of colors, and said halftone dot area determination means individually determines each color. The image processing apparatus according to claim 1, wherein the area adaptation processing means performs an adaptation process individually for each color.