JP3426743B2 - Halftone area determination device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention
The original image that is optically read belongs to the halftone area.
The present invention relates to a dot area determination device that determines whether an image is an image. [0002] 2. Description of the Related Art Conventionally, an original image is stored in a CCD (charge coupled).
Optically read with a scanner composed of
To the image data corresponding to
A digital image forming an original image based on data
Copier is used. This type of digital copier
So, characters / line drawings, photos or dots per unit area
Halftone (screen) whose gradation is expressed in the size of
To ensure that high-quality copies of original images can be obtained,
Image is text / line drawing area, photo area or halftone area
It is determined whether the image belongs to each area, and the image processing corresponding to each area is performed.
Is applied. Specifically, in the character / line drawing area,
Image processing such as emphasis or black text
You. In the halftone dot area, smoothing for removing moiré is required.
Which image processing is performed. [0003] The determination as to whether or not the area is a halftone dot area is performed, for example, as follows.
It is done like this. Original image is read optically
When converted to data, multiple lines in the sub-scanning direction
(For example, 11 lines) has a capacity of multiple lines.
Is stored in memory. Then, focus on the pixel of interest
Detection of a continuous fixed range (for example, 3 pixels x 3 lines)
In the output area, the density of the target pixel is higher than that of surrounding pixels.
In contrast, it is determined whether the image is dark or light. As a result, the target pixel
Is determined to be relatively darker than surrounding pixels
Then, the target pixel is detected as a peak pixel. one
On the other hand, if the density of the pixel of interest is relatively lighter than surrounding pixels,
If determined, the pixel of interest is determined to be a dip pixel.
Will be issued. [0004] In this way, the peak pixel in the detection area is obtained.
Or when a dip pixel is detected,
A determination area composed of a certain number of pixels (for example,
(9 pixels x 9 lines)
The appearance pattern of mask pixels represents a halftone area.
Match turn, or peak pixel or
It is determined whether or not the presence density of
You. As a result, there is a matching pattern or presence
If the degree is determined to be equal to or more than a certain
It is determined that it is a point area. [0005] SUMMARY OF THE INVENTION
In the detection of peak pixels or dip pixels,
A memory having a capacity equivalent to a plurality of lines
Therefore, there is a problem that the memory size becomes large.
Was. In the halftone dot area, dots per inch
The number (hereinafter referred to as “line number”) is 2 for fine texture
From about 00 lines to about 65 lines for rough textures
There are even things. Of these, the number of lines less than about 100 lines is small.
The size of the dots that make up the halftone
May run out of the detection pixel. In such a case,
For detecting the above conventional peak pixel or dip pixel
Method accurately detects peak or dip pixels.
There was a defect that the detection was often erroneous. So
Here, an object of the present invention is to solve the above technical problem,
To provide a halftone dot region determination device capable of reducing a memory scale.
That is. Another object of the present invention is to form a halftone dot area.
Regardless of the size of the constituent dots, the peak image
Element or dip pixels can be reliably detected,
A dot area determination device that can accurately determine whether a pixel is a dot area
Is to provide an installation. [0008] [MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The halftone dot determination apparatus according to claim 1 reads a document image
And convert it to image data corresponding to the density
Conversion means, and image data output from the conversion means.
Store image data corresponding to one or more lines from inside
Holding means to hold and images held by the holding means
In the data, the image data corresponding to the pixel of interest and the
Compare with the image data corresponding to the pixels around the pixel of interest
Detecting means for detecting peak pixels and dip pixels
And two pins each alternately detected by the detecting means.
Between the peak pixels using the dark pixels and the dip pixels.
Calculation for finding the distance between pixels and the distance between dip pixels
Between the means and the peak pixel obtained by the distance calculating means.
Difference to find the difference between the distance of the dip and the distance between the dip pixels
Calculating means and the distance difference calculated by the distance difference calculating means
Determining means for determining whether the value is equal to or less than a predetermined value,
In this determination means, the distance difference is equal to or less than a predetermined value.
Is determined by the detection means,
Last detected from peak pixel or dip pixel output
Everything between the dip or peak pixel
Determination means for determining that the pixel is a halftone dot area.See
The detecting means detects image data corresponding to the pixel of interest and
The same line continuing upstream of the pixel of interest in the main scanning direction
Each image data corresponding to the above two pixels and the above attention
1 on the same line continuous on the downstream side of the pixel in the main scanning direction
Compare the image data corresponding to one pixel with the peak image
To detect elementary or dip pixelsFeatures
And [0009] [0010] According to the structure of the first aspect, the detecting means is
The peak pixel and the center of the dots that
And dip pixels in the valley between each dot are detected.
You. In the distance calculating means, the two values detected by the detecting means are used.
The distance between the peak pixels of and the two dip pixels
The distance between them is obtained, and the distance
The difference between the peak pixel distance and the dip pixel distance
Can be Then, this distance difference is equal to or less than a predetermined pixel.
The first detected peak or dip pixel
From the last detected dip pixel or peak pixel.
Is determined to be a halftone dot area. In the halftone dot area, dots are periodically arranged.
The peak pixel and data
Dip pixels indicate that the document is extremely bright or extremely dark.
Unless otherwise noted, they appear alternately at the same frequency. Accordingly
The peak pixel distance and the dip image
Ideally, the difference between elementary distances is exactly the same,
Is less than or equal to a predetermined value. Therefore, according to the above configuration,
Then, it can be reliably determined whether or not the area is a dot area. As described above, according to the above configuration, the peak image
Halftone area based on similarity of appearance between element and dip pixel
Since it is determined whether or not it is a halftone dot area,
Does not necessarily require image data for multiple lines,
For example, in one line of image data, the peak pixel or
Can determine if the appearance of dip pixels is periodic
It is sufficient if there is some image data. Therefore, the dot area
At least a plurality of lines (for example, 9 lines)
Memory that can hold the image data of
The memory scale can be reduced as compared with the related art. [0013]MaWas,Detection of dark pixels or dip pixels
Corresponding to pixels on the same line that are not adjacent to the pixel of interest
Dot and conversion means
Regardless of the magnitude relationship with the detected pixel, the peak pixel or
Can reliably detect a dip pixel. [0014] BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described in detail with reference to FIG. FIG. 2 shows a halftone dot area according to the present invention.
Of the main part of a digital color copier to which
FIG. 3 is a block diagram illustrating an electrical configuration. This digital camera
Color copiers optically copy color original images to be copied.
Read 3 colors by red (R), green (G) and blue (B)
In addition to photoelectric conversion into primary color image data, each R, G, B
Of the three primary color image data, which are complementary colors of yellow
(Y), magenta (M) and cyan (C) color reduction methods 3
CCD (Charge Coupled Device) that converts to primary color image data and outputs it
The scanner 1 is a conversion means composed of
Have been. The resolution of the scanner 1 is, for example, 1 inch.
Per pixel. Y, which is generated and output by the scanner 1,
Each of the M and C image data is represented by α corresponding to the density of the original image.
Bits expressed in bits (for example, α = 8; 256 gradations)
Digital data. Digital color copiers
Each image of Y, M and C output from the scanner 1
An image processing circuit 2 for performing various processes on the data, and
Light on the photoreceptor on which an electrostatic latent image corresponding to
An output unit 3 for irradiating the light is provided. More specifically, the image processing circuit 2
Is provided with an input processing circuit 4, and the above Y, M, C
Are supplied to the input processing circuit 4. Entering
In the power processing circuit 4, each of the Y, M, and C image data is processed.
To solve the clock difference between the scanner 1 and the image processing circuit 2.
In order to erase the data, processing such as clock conversion is performed. That
Thereafter, each of the Y, M, and C image data is stored in a FIFO (Firs
t In First Out) is given to the memory 5. Y, M, C given to FIFO memory 5
Image data corresponding to any one line of each image data
Are given to the character / photo / halftone determination circuit 6 respectively.
1 line provided in the character / photo / half-tone dot decision circuit 6.
A line that is a holding means that can hold image data for IN
It is held in the memory 61. Character / photo / halftone dot judgment circuit 6
Now, the image data stored in the line memory 61
Based on the image data, the text / line drawing area and photo area
Or image data belonging to any of the halftone dot areas.
Is determined. The dot area is the dot per unit area.
It is the area where the gradation is expressed in the size of the dot. Size
The fixed result is a black generation circuit, zoom / movement circuit,
Filter circuit, gradation processing circuit, and output control circuit.
It is. The image data stored in the FIFO memory 5
The data also passes through the character / photo / halftone dot determination circuit 6
It is provided to the forming circuit 7. In the black generation circuit 7,
(BK) data is generated to compensate for the density
You. Specifically, for example, for each of the image data of Y, M, and C,
The minimum value is multiplied by a correction coefficient β (for example, β = 0.5 to 1)
Values are removed from each image data, and the removed values are
Data. Each image of Y, M, C
Data and BK data are supplied to the output color selection circuit 8.
Can be In the output color selection circuit 8, the above Y, M,
Corresponds to one of the colors of C and BK image data
Image data is selected. The selected image data is
Provided to the camera / moving circuit 9 and expanded according to the set magnification.
Processing such as large or reduced is performed. Then filter
Provided to the circuit 10 and from the character / photo / halftone dot judging circuit 6
Smoothing processing or edge strength according to given judgment result
Toning processing and the like are performed. Then, the gradation processing circuit 11
Given, so-called dithering or multi-valued dithering
Which halftone processing is performed. The image data subjected to the halftone processing is output
Processing necessary for output is performed by the control circuit 12, and the output unit
3 given. The feature of this embodiment is that
A dot area determination function in the dot determination circuit 6; Figure
1 is a halftone dot area in the character / photograph / halftone dot determination circuit 6.
It is a block diagram which shows the flow of area determination processing. The character / photo / halftone dot judging circuit 6
Thus, the image data of any color of the Y, M, and C image data
Holds image data corresponding to any one line of data
A line memory 61 is provided. Also, characters
The photo / dot determination circuit 6 includes a peak detection unit 62 and a data
A dip detector 63 is provided. In this example,
The peak detecting section 62 and the dip detecting section 63
Is equivalent to In the peak detector 62, first, the line memo
Continuous 4 out of the image data held in the
Pixel P₁, P_Two, P_Three, P_Four(See Fig. 3)
Α-bit image data D representing the corresponding density₁, D_Two, D
_Three, D_FourIs read. At this time, the pixel of interest is pixel P_Three
It is said. Then, the target pixel P_ThreeConstitutes a dot area
Whether the pixel is the peak pixel at the center of the dot or not
Data D₁~ D_FourIs detected based on In particular,   D_Three-D₁> D_TH1  Or D_Three-D_Two> D_TH2              ‥‥ (1)   D_Three≧ D_Four                                                  ‥‥ (2)   D_Three> D_TH3                                                ‥‥ (3) It is determined whether or not the logical product of the judgments of each expression holds
(However, d_TH2<D_TH1<D_TH3, For example, d_TH1= 1
0, d_TH2= 5, d_TH3= 35). In the peak detecting section 62, the left end 2
Pixel P₁, P_Two(See FIG. 3) and one pixel P at the right end
_n(See FIG. 3), peak pixel detection processing is performed.
It is not noticeable near the edge of the original image
There is no particular problem if you ignore it. As a result of the above determination,
It is determined that the logical product of the judgments in equations (1) to (3) does not hold.
And the target pixel P_ThreeIs detected as not a peak pixel
You. If it is detected that the pixel is not the peak pixel, then the above read
Pixel P₁~ P_FourImage in the main scanning direction M
Pixel P shifted by element_Two~ P_Five(See Fig. 3)
Corresponding image data D_Two~ D_FiveIs read (the pixel of interest is
Pixel P_Four), Peak pixel detection processing similar to the above is performed.
It is. Such peak pixel detection processing is based on the peak pixel
Is repeated until is detected. By the way, in the above equation (1), the pixel of interest is
Pixel P_ThreePixel P adjacent to _Two, P_FourOne other than
Pixel P away₁Image data D₁Is used for the net
The size of the dots constituting the dot area is
This is because consideration is given to the case of protruding elements. More specific
More specifically, for example, if the dot size is
Over four pixels (that is, the number of lines in the halftone dot region is approximately
Pixel P which is 50 pixels) and is the pixel of interest_ThreeTo
When there is a center of the object, for example, as shown in FIG.
Pixel P _ThreeImage data D_ThreeAnd this pixel P_ThreePicture adjacent to
Element P_TwoImage data D_TwoIs a relatively small difference Δ
There is only d1 and pixel P_ThreeImage data D_ThreeAnd pixel P₁of
Image data D₁Has a relatively large difference Δd2 between
You. Therefore, if pixel P_ThreePicture adjacent to
Element P_Two, P_FourEach image data D_Two, D_FourOnly use
If not, the logical sum in the above equation (1) does not hold,
Pixel P_ThreeCannot be detected as a peak pixel
There is a risk. Therefore, the pixel P_ThreePixel P away from
₁Image data D corresponding to₁I use. like this
In this embodiment, the dot size is detected by the scanner 1.
Since the case where the pixel is protruding is considered,
The size of the bit is larger than the detection pixel of the scanner 1
Also, the peak pixel can be reliably detected. Returning to FIG. 1, the above-mentioned peak pixel detection processing will be described.
Is performed, for example, the pixel P_{a- Two}, P_a-1, P_a,
P_{a + 1}Is read (see FIG. 3, the pixel of interest is the pixel P
_a), The logical product of the judgments in the above equations (1) to (3) is
When separated, the target pixel P_aThe density of the three surrounding pixels P
_a-2, P_a-1, P_{a + 1}Is considered relatively darker than
The above noted pixel P_aAre detected as peak pixels. In the peak detector 62, the target pixel P_aBut
If the pixel of interest P is detected as_aRank
Is stored in the PEAK1 storage unit 64 as PEAK1.
You. PEAK1 is stored in the PEAK1 storage unit 64
Then, in the dip detection unit 63, the peak pixel is
Four pixels P read when detected_a-2,
P_{a- 1}, P_a, P_{a + 1}For each pixel in the main scanning direction
Four pixels P shifted to M_{a- 1}, P_a, P_{a + 1}, P_{a + 2}
(See FIG. 3)_a-1, D
_a, D_{a + 1}, D_{a + 2}Is read (the pixel of interest is pixel P
_{a + 1}). Then, the target pixel P_{a + 1}Constitutes a dot area
Whether the pixel is a dip pixel in the valley of dots
It is detected based on the image data. In particular,   D_a-1-D_{a + 1}> D_TH1  Or D_a-D_{a + 1}> D_TH2        ‥‥(Four)   D_{a + 1}≤D_{a + 2}                                              ‥‥(Five)   D_{a + 2}> D_TH3                                              ‥‥ (6) It is determined whether or not the logical product of the judgments of each expression holds
(However, d_TH2<D_TH1<D_TH3, For example, d_TH1= 1
0, d_TH2= 5, d_TH3= 35). In the dip detecting section 63, the left end of the original image
2 pixels P₁, P_TwoAnd one pixel P at the right end_nAgainst
No detection processing is performed for the pixel, but as described above,
The edges of the original image are almost inconspicuous, so ignore them.
There is no particular problem. As a result of the above discrimination, the above equations (4) to (6)
If it is determined that the logical product of the determinations does not hold,
Pixel P_{a + 1}Is not detected as a dip pixel. Day
If it is detected that the pixel is not a
Element P_a-1, P_a, P_{a + 1}, P_{a + 2}In the main scanning direction M
Pixel P shifted by one pixel each_a, P_{a + 1},
P_{a + 2}, P _{a + 3}(See FIG. 3)
Data D_a, D_{a + 1}, D_{a + 2}, D_{a + 3}Is read
The element is pixel P_{a + 2}), The same dip pixel detection processing as above.
Is performed. Such a dip pixel detection process is as follows.
This is repeated until a dip pixel is detected. As a result of the dip pixel detection processing,
For example, pixel P_b-2, P_b-1, P_b, P_{b + 1}(See Figure 3
Image data D respectively corresponding to_b-2, D_b-1, D
_b, D _{b + 1}Is read (the pixel of interest is pixel P_b),
It is determined that the logical product of the judgments of the above equations (4) to (6) is satisfied.
Then, the target pixel P_bThe density of the three surrounding pixels P_b-2,
P_b-1, P_{b + 1}Is considered relatively thinner than
Eye pixel P_bAre detected as dip pixels. In the dip detecting section 63, the target pixel P_bBut
If it is detected as a dip pixel, the target pixel P_b
Is stored in the DIP1 storage unit 65 as DIP1.
You. When DIP1 is stored in the DIP1 storage unit 64,
In the peak detector 62, the pixel P_b-2, P
_b-1, P_b, P_{b + 1}One pixel in the main scanning direction M from
Pixel P shifted_b-1, P_b, P_{b + 1}, P_{b + 2}(See Figure 3
Image data D respectively corresponding to_b-1, D_b, D
_{b + 1}, D_{b + 2}Is read (the pixel of interest is pixel P_{b + 1}),Up
As described above, peak pixel detection processing detects peak pixels.
Repeated until As a result, for example, the pixel P_c-2, P_c-1,
P_c, P_{c + 1}(See FIG. 3)
TA D_c-2, D_c-1, D_c, D_{c + 1}Is read (Note
Eye pixel is pixel P_c), The noted pixel P_cIs the peak pixel
If it is detected that there is, the target pixel P_cIs PEAK2
And stored in the PEAK2 storage unit 66. PEAK2 insurance
When PEAK2 is stored in the storage section 66, the dip
In the detection unit 63, the pixel P_c-2, P_c-1, P_c,
P_{c + 1}Pixels shifted by one pixel in the main scanning direction M from
P_c-1, P_c, P_{c + 1}, P_{c + 2}(See Fig. 3)
Corresponding image data D_c-1, D_c, D_{c + 1}, D_{c + 2}Read
(The pixel of interest is pixel P _{c + 1}), As above,
The detection process of the dip pixel is repeated until the dip pixel is detected.
Will be returned. As a result, for example, the pixel P_d-2, P_d-1,
P_d, P_{d + 1}(See FIG. 3)
TA D_d-2, D_d-1, D_d, D_{d + 1}Is read (Note
Eye pixel is pixel P_d), The noted pixel P_dIs the dip pixel
Is detected, the target pixel P_dIs DIP2
And stored in the DIP2 storage unit 67. As above
PEAK1 storage unit 64, PEAK2 storage unit 66, DI
P1 storage unit 65 and DIP2 storage unit 67
EAK1, PEAK2, DIP1 and DIP2 stored
The distance between PEAK1 and PEAK2, and
And the distance between DIP1 and DIP2 is PEAK
Calculated by the difference calculator 68 and the DIP difference calculator 69
It is. PEAK difference calculator 68 and DIP difference calculator
Each output of 69 is given to the comparison unit 70. In this embodiment, the PEAK difference
The calculating unit 68 and the DIP difference calculating unit 69 are distance calculating means.
And the comparing unit 70 includes a distance difference calculating unit and a discriminating unit.
And determination means. By the way, the dot area is
Since the dots are periodically arranged, the center of the dot
The corresponding peak pixel and the dit corresponding to the valley between each dot.
The pixels appear at the same period as each other. Therefore, the comparing section 70 uses a PEAK difference meter.
PEAK distance PL and DIP difference given from the arithmetic unit 68
The difference from the DIP distance DL given from the minute calculation unit 69 is
It is determined whether or not the pixel is equal to or less than a predetermined pixel A.
You. In particular,   | PL-DL | ≦ A ‥‥ (7) Is determined whether or not is satisfied. Here, the above “A” is, for example, “1”.
Can be considered. Next, the reason will be described. Normal,
The peak pixel distance and dip pixel distance are
For example, if the resolution of the scanner 1 is 400
In the case where the halftone dot area of the original or original image is 200 lines. )
Thus, they are completely identical to each other. However, for example
As shown in FIG.
In case of reaching outgoing pixels (for example, if the resolution of the scanner 1 is 40
0 pixels, when the halftone area of the original image is 100 lines. )
Indicates that pixel “1” or pixel “2” is detected as the peak pixel.
Will be issued. The same applies to dip pixels. This
In such a case, the error between the peak pixels is 1 pixel or less.
Appears and the distance between dip pixels is less than 1 pixel.
Appears. Therefore, the distance between the peak pixels and the dip image
There is a high possibility that the distance difference from the elementary distance is one pixel or less.
Therefore, it is preferable to set “1” as “A”.
No. As a result of the above determination, the above equation (7) was satisfied.
Is determined, the pixel P detected as PEAK1_a
P detected as DIP2 from_dEverything in between
All the pixels are determined to be a halftone area. In particular,
For example, as shown in FIG._aFrom pixel P_dUntil
It is determined that the area Q including all the pixels between
Is determined. When the determination as to whether or not the area is a dot area is completed,
It is stored in the PEAK2 storage unit 66 and the DIP2 storage unit 67.
The stored PEAK2 and DIP2, respectively,
The PEAK1 storage unit 64 and the DIP1 storage unit 65, respectively.
To the next halftone area determination process.
And DIP1. And the above dot area
The area determination process is repeatedly performed, and the pixel P_n-1(See Fig. 3)
Is completed as the target pixel.
This means that any information held in the line memory 61
Halftone dot area for any one line of image data
The fixed processing is forcibly terminated. Here, the termination condition of the above-mentioned halftone dot area determination processing
Is the pixel P_n-1Is the pixel of interest.
The process of detecting a peak pixel or a dip pixel is as described above.
Thus, a pixel adjacent to the pixel of interest in the main scanning direction is required.
That's because. Therefore, the rightmost pixel P of the original image_n
(See Fig. 3)
No element detection processing is performed. Then, the above-described halftone dot area determination processing is performed.
This is done for other lines, and for all color images
Is performed on the data, and
finish. As described above, the digital color
According to the copier, the appearance of peak pixels and dip pixels
Is performed based on the similarity of
Image data necessary to determine whether or not a dot area should be retained
The line memory 61 does not need a capacity for a plurality of lines.
Therefore, at least a plurality of lines are used to determine
Compared to the conventional technology that required image data for
The size of the moly can be reduced. Also, a pixel one pixel away from the target pixel is
Peak pixels and dips using corresponding image data
Because pixels are detected, the dots that make up the halftone dot area
Regardless of the size relationship with the detection pixels of the scanner 1, the peak
The black pixel and the dip pixel can be reliably detected. This departure
Although the description of the embodiment has been given above, the present invention
The present invention is not limited to the above embodiment. For example above
In the embodiment, the PEAK2 storage unit 66 and the DIP2 storage
PEAK2 and DI respectively stored in section 67
P2 is the PE in the next halftone dot area determination process.
Explanation about the case of using as AK1 and DIP1
However, for example, in the next halftone dot area determination process,
PEAK2 and PEAK2 detected in the halftone dot area determination process
PEAK1 and DAK2 without DIP2 and DIP2
You may make it detect IP1. In the above embodiment, PEAK1, DI
Peak pixels and PAKs in the order of P1, PEAK2 and DIP2.
And DIP pixels to detect PEAK1 to DIP2.
It is determined whether the pixel at is a halftone area or not.
For example, DIP1, PEAK1, DIP2 and PEAK
The peak pixel and the dip pixel are detected in the order of 2.
Whether the pixels from IP1 to PEAK2 are halftone areas
May be determined. Further, in the above embodiment, in the main scanning direction M,
A peak pixel or a decimation using four pixels which are consecutive to each other.
Is detected, but for example,
By satisfying the conditions of
Detect peak and dip pixels respectively.
You may. However, in the following description, FIG. 7 is also referred to at the same time.
I do. Also, D_A~ D_LIs the pixel P in FIG._A~ P
_LImage data. Further, the pixel of interest is pixel P_Gso
is there. D_F<D_G  And D_G> D_H  Or
Tsu D_G> D_TH3 'D_F> D_G  And D_G<D_H  And D_H> D
_TH3 In these cases, the erroneous detection is more prevented than in the case of
Can be stopped.     D_F<D_G  And D_G> D_H 'D_F> D_G  And D_G<D_H In these and ', the pitch in the halftone dot area with a small number of lines is
From dark pixels or dip pixels to halftone dot areas with a large number of lines
A peak pixel or a dip pixel can be detected. D_F<D_G  And D_G≧ D_H 'D_F> D_G  And D_G≤D_H These 'have a smaller number of lines than the above'.
Detect peak pixel or dip pixel in halftone area
it can.     D_G> D_B, D_C, D_D, D_H, D_L, D_K, D
_J, D_F(Logical AND) 'D_G<D_B, D_C, D_D, D_H, D_L, D_K, D
_J, D_F(Logical AND) In these, ', erroneous detection can be relatively prevented. Was
However, in the dot area with fewer lines than
It is difficult to detect a peak pixel or a dip pixel.
Also, three line memories are required. [0046]     D_G> D_C, D_H, D_K, D_F(Logical AND) 'D_G<D_C, D_H, D_K, D_F(Logical AND) These 'have a smaller number of lines than the above'.
Detect peak pixel or dip pixel in halftone area
it can. However, the number of erroneous detections increases compared to
You. Also, three line memories are required. D_G≧ D_B, D_D, D_L, D_J(Conclusion
Logical) and D_G> D_C, D_H, D_K, D_F(Logical AND)
And the logical product of 'D_G≤D_B, D_D, D_L, D_J(Logical product) and D
_G<D_C, D_H, D_L, D_F(Logical product) and logical product. In these, ', the erroneous detection is
′ And ′, between the detectable halftone dot areas
The number of lines is also halfway between 'and'. Also,
Line memory is also required for three lines. In addition, the above implementation
In the example, a digital color copier has been described as an example.
However, the present invention relates to a digital monochrome copying machine,
Color / monochrome facsimile machine or color / mono
If the original image is a halftone dot original image
Other image forming devices that need to determine whether
Applicable. Others within the scope described in the claims
It is possible to make various design changes. [0050] As described above, the halftone dot determining apparatus of the present invention
The appearance of peak and dip pixels
Since it is determined based on the similarity whether or not it is a dot area,
To determine whether a region is an area, image data for multiple lines is required.
It is not necessary, for example, one line of image data
I just need. Therefore, it is difficult to determine whether the area is a dot area.
At least a memory that can hold multiple lines of image data is required.
Memory size can be reduced compared to the conventional technology
You. The image data corresponding to the pixel of interest and the
Compare the image data corresponding to the pixels around the eye pixel with the image data.
Detected a dark or dip pixel.
Regardless of the magnitude relationship between
A dark pixel or a dip pixel can be reliably detected. Special
To,Target pixel for detection of dark pixels or dip pixels
Image data corresponding to pixels on the same line that are not adjacent to
Is used, so that the dots are
Larger, more reliable peak or dip pixels
Can be detected.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram for explaining a flow of a dot area determining process in a digital color copying machine according to an embodiment to which a dot area determining apparatus according to the present invention is applied. FIG. 2 is a block diagram showing an electrical configuration of a main part of the digital color copying machine. FIG. 3 is a diagram illustrating a process of detecting a peak pixel and a dip pixel in an arbitrary line of a document image; FIG. 4 is a diagram for explaining a peak pixel detection process; FIG. 5 is a diagram for explaining how a peak pixel and a dip pixel appear. FIG. 6 is a diagram for explaining an area to be determined whether or not it is a dot area; FIG. 7 is a diagram for explaining another embodiment of the present invention. [Description of Signs] 1 Scanner 2 Image processing circuit 6 Character / photo / halftone dot determination circuit 61 Line memory 62 Peak detection unit 63 Dip detection unit 64 PEAK1 storage unit 65 DIP1 storage unit 66 PEAK2 storage unit 67 DIP2 storage unit 68 PEAK distance Calculation unit 69 DIP distance calculation unit 70 Comparison unit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Haruo Yamamoto 1-2-2, Tamazo, Chuo-ku, Osaka City, Osaka Prefecture Inside Mita Kogyo Co., Ltd. (56) References JP 5-145759 (JP, A) JP JP-A-62-88478 (JP, A) JP-A-63-69375 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1 / 60

Claims (1)

(57) [Claim 1] A conversion means for reading a document image, converting the read image into image data corresponding to the density, and outputting one or more of the image data output from the conversion means. Holding means for holding image data corresponding to a plurality of lines; and in the image data held in the holding means, comparing the image data corresponding to the pixel of interest with the image data corresponding to pixels around the pixel of interest. Detecting means for detecting a peak pixel and a dip pixel; and calculating a distance between the peak pixels and a distance between the dip pixels by using two peak pixels and the dip pixels alternately detected by the detecting means. Distance calculating means; distance difference calculating means for calculating a difference between the distance between the peak pixels obtained by the distance calculating means and the distance between the dip pixels; Determining means for determining whether or not the distance difference obtained by the distance calculating means is equal to or less than a predetermined value; and detecting, when the determining means determines that the distance difference is equal to or less than a predetermined value, detecting the distance. first look including the the determining means is a halftone dot region all pixels between the detected peak pixels or dip pixel to dip pixel or peak pixels detected last in the means, said detecting means And the image data corresponding to the pixel of interest
The same line continuing upstream of the pixel of interest in the main scanning direction
Each image data corresponding to the above two pixels and the above attention
1 on the same line continuous on the downstream side of the pixel in the main scanning direction
Compare the image data corresponding to one pixel with the peak image
A halftone dot region determination device for detecting elementary or dip pixels .