JPH08149291A - Dot area decision device - Google Patents

Abstract

PURPOSE: To reduce the scale of the memory by deciding a dot area based on the synchronization of appearance of peak picture elements or dip picture elements. CONSTITUTION: When image data are read from a line memory 61 and a noted picture element is detected to be a peak picture element based on the image data, the position of the noted picture element on a line is registered 64. The peak picture element is detected over a decision area corresponding to the number of finite picture elements on the line and a distance between peak picture elements is calculated 65 to judge whether or not the peak picture elements have synchronization and a histogram representing the frequency of incidence of each distance is generated 66. As a result, when a maximum value of the incidence frequency of distance is discriminated to be x (e.g. x=75)% of the total incidence frequency divider or over, the discrimination area is decided 67 to be a dot area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a halftone dot area judging device for judging whether or not a manuscript image optically read by a scanner belongs to a halftone dot area.

[0002]

2. Description of the Related Art Conventionally, an original image is optically read by a scanner composed of a CCD (charge coupled device) or the like to be converted into image data corresponding to a density, and the original image is converted based on the converted image data. A digital copying machine designed to be formed is used. In this type of digital copier, it is possible to obtain a high-quality copy of a character / line drawing, a photograph, or an original image in which halftone dots (screens) whose gradation is expressed by the size of dots per unit area are mixed. It is determined whether the original image belongs to a character / line drawing area, a photograph area, or a halftone dot area, and image processing according to each area is performed. Specifically, in the character / line drawing area, image processing such as edge emphasis or black character emphasis is performed. In the halftone dot area, image processing such as smoothing for removing moire is performed.

The determination as to whether the area is a halftone dot area is made as follows, for example. When the original image is optically read and converted into image data, image data of a plurality of lines (for example, 11 lines) in the sub-scanning direction is held in a memory having a capacity of a plurality of lines. Then, in a continuous detection area (for example, 3 pixels × 3 lines) centering on the target pixel, it is determined whether the density of the target pixel is relatively darker or lighter than surrounding pixels. As a result, if it is determined that the density of the pixel of interest is relatively higher than the surrounding pixels, the pixel of interest is detected as a peak pixel. On the other hand, if it is determined that the density of the pixel of interest is relatively lower than that of surrounding pixels, the pixel of interest is detected as a dip pixel.

When the peak pixel or the dip pixel in the detection area is detected in this way, the peak is detected in the determination area (for example, 9 pixels × 9 lines) formed by a fixed number of pixels among the pixels of interest. It is determined whether the appearance pattern of the pixels or the dip pixels matches the plurality of mask patterns representing the halftone dot area, or whether the existence density of the peak pixels or the dip pixels is equal to or higher than a certain level. As a result, when it is determined that there is a matching pattern or the existence density is equal to or higher than a certain level, the determination area is determined to be a halftone dot area.

[0005]

However, in the conventional detection of the peak pixel or the dip pixel described above, a memory having a capacity corresponding to a plurality of lines in the sub-scanning direction is indispensable, which causes a problem that the memory scale becomes large. there were. Also, in the halftone dot area, the number of dots per inch (hereinafter referred to as “the number of lines”) is 2 if the texture is fine.
There are from about 00 lines to about 65 lines with rough texture.

Among them, in a document having a small number of lines of less than about 100 lines, the size of dots forming halftone dots may exceed the detection pixels of the scanner. In such a case,
The conventional method of detecting the peak pixel or the dip pixel has a problem that the peak pixel or the dip pixel cannot be accurately detected and is often erroneously detected. Therefore, an object of the present invention is to solve the above technical problems,
An object of the present invention is to provide a halftone dot area determination device that can reduce the memory scale.

Another object of the present invention is to reliably detect a peak pixel or a dip pixel regardless of the size of the dots forming the halftone dot area, thereby determining whether or not it is the halftone dot area. An object of the present invention is to provide a halftone dot area determination device that can make an accurate determination.

[0008]

To achieve the above object, a halftone dot area determining device according to claim 1 reads a document image, converts it into image data corresponding to its density, and outputs it. Holding means for holding image data corresponding to one or a plurality of lines in the image data output from the converting means, and finite of one or a plurality of lines corresponding to the image data held by the holding means In the determination area corresponding to the number of pixels, a detection unit that compares the image data corresponding to the target pixel with the image data corresponding to the pixels around the target pixel to detect a peak pixel or a dip pixel, and the detection unit. The distance between the registration means for registering the peak pixel or the dip pixel detected in step 1 and each peak pixel or the distance between the dip pixels registered in this registration means. And a periodicity for determining whether or not the periodicity of the distance between each peak pixel or the distance between each dip pixel obtained by this distance calculating means satisfies a certain statistical criterion. When the determination means and the periodicity determination means determine that the periodicity of the distance between the peak pixels or the distance between the dip pixels satisfies the statistical criterion, the determination area is a halftone dot area. And a determination means for determining that

The periodicity determining means may determine the distance between the peak pixels or the frequency of appearance of the distance between the dip pixels, which is obtained by the distance calculating means, as in the configuration described in claim 2, for example. The recognition frequency recognition unit and the maximum value of the appearance frequency of the distance between the peak pixels or the distance between the dip pixels recognized by the frequency recognition unit is equal to or higher than a predetermined ratio for all the appearance frequencies. A frequency discriminating unit for discriminating whether or not there is, and when the frequency discriminating unit discriminates that the maximum value of the appearance frequencies is equal to or more than a predetermined ratio with respect to all the appearance frequencies, The distance between them or the periodicity of the distance between each dip pixel may be characterized by determining that the above statistical criteria are satisfied.

Further, in the halftone dot area judging device according to a third aspect of the invention, the detecting means comprises the image data corresponding to the pixel of interest and two image data corresponding to the pixel of interest on the same line which are continuous on the upstream side in the main scanning direction. The peak pixel or the dip pixel is detected by comparing each image data corresponding to the pixel and the image data corresponding to one pixel on the same line that is continuous on the downstream side of the pixel of interest in the main scanning direction. It is characterized by

Further, in the halftone dot area judging device according to the present invention, the judging area is repeatedly set by shifting an arbitrary number of pixels along the same line, and in the detecting means, a peak pixel or When a dip pixel is detected, it is characterized by further including a judgment area setting means for newly setting the next judgment area starting from the peak pixel or the dip pixel detected first.

[0012]

According to the structure of the first aspect, the peak pixel or the dip pixel is detected in the determination area corresponding to the finite number of pixels in one or a plurality of lines corresponding to the image data held in the holding means. Then, based on whether the detected distance between the peak pixels or the periodicity of the distance between the dip pixels satisfies a certain statistical criterion, the determination area is a halftone dot area. It is determined whether or not there is.

Since the above-mentioned halftone dot area is an area formed by arranging dots periodically, the appearance of a peak pixel corresponding to the center of a dot or a dip pixel corresponding to a valley of each dot does not occur. There is a one-dimensional periodicity. Therefore, according to the above configuration, it is possible to reliably determine whether or not the determination area is the halftone dot area. As described above, according to the above configuration, since the determination of whether the determination region is the halftone dot region is based on the periodicity of the appearance of the peak pixel or the dip pixel, the image data for a plurality of lines is not necessarily required. Instead, for example, image data for one line may be enough to determine whether or not there is periodicity in the appearance of peak pixels or dip pixels. Therefore, it is possible to reduce the memory scale as compared with the related art in which a memory capable of holding image data of at least a plurality of lines (for example, 9 lines) is indispensable for determining whether it is a halftone dot region.

Further, since the peak pixel or the dip pixel is detected by comparing the image data corresponding to the target pixel with the image data corresponding to the pixels around the target pixel, the size of the dot and the detection pixel of the conversion means is large or small. Regardless of the relationship, the peak pixel or the dip pixel can be surely detected. Further, according to the configuration of claim 3, since the image data corresponding to the pixels on the same line which are not adjacent to the target pixel is used for the detection of the peak pixel or the dip pixel, the dot is detected by the conversion unit. Even if is large, the peak pixel or the dip pixel can be reliably detected.

By the way, for example, when a halftone dot region having a relatively narrow width in the main scanning direction occupies only a part of the determination region, the number of peak pixels required for the periodicity determination of the inter-pixel distance is determined. Alternatively, since the dip pixel may not be detected, the halftone dot area may be missed. Therefore, when some peak pixels or dip pixels are detected in the determination region as in the configuration according to claim 4, when the next determination region is set, it is first detected in the previous determination region. If the next judgment area is newly set with the peak pixel or dip pixel at the top, it is more likely that the number of peak pixels or dip pixels necessary for judging the periodicity of the inter-pixel distance can be detected. Don't miss it!

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 2 is a block diagram showing the electrical construction of the essential parts of a digital color copying machine to which the halftone dot area judging device of the present invention is applied. In this digital color copying machine, the color original image to be copied is optically read and added with the red (R), green (G) and blue (B) color addition method.
Photoelectric conversion to primary color image data and each R, G, B
The three primary color image data of
(Y), magenta (M) and cyan (C) subtraction method 3
The scanner 1 includes a CCD (charge-coupled device) that converts primary color image data and outputs the converted primary color image data. The resolution of the scanner 1 is, for example, about 400 pixels per inch.

Y generated and output by the scanner 1,
Each of the M and C image data corresponds to the density of the original image α
It is digital data represented by bits (for example, α = 8; 256 gradations). The digital color copying machine also forms an electrostatic latent image corresponding to a document image and an image processing circuit 2 for performing various processes on the Y, M, and C image data output from the scanner 1. An output unit 3 for irradiating the photoconductor to be irradiated with light is provided.

More specifically, the image processing circuit 2
Is provided with an input processing circuit 4, and the above Y, M, C
The respective image data of (1) are given to the input processing circuit 4. In the input processing circuit 4, in order to eliminate the clock difference between the scanner 1 and the image processing circuit 2, the Y, M, and C image data are subjected to processing such as clock conversion. After that, the Y, M, and C image data are stored in the FIFO (Firs
t In First Out) Given to memory 5.

Y, M, C provided to the FIFO memory 5
The image data corresponding to any one line of each image data of 1 is given to the character / photo / halftone dot determination circuit 6, and the image for one line provided in the character / photo / halftone dot determination circuit 6 It is held in the line memory 61 capable of holding data. In the character / photograph / halftone dot determination circuit 6, based on the image data held in the line memory 61, the image data is image data belonging to any one of the character / line drawing area, the photograph area, and the halftone dot area. Is determined. The halftone dot area is an area in which gradation is expressed by the size of dots per unit area. The determination result is given to a black generation circuit, a zoom / movement circuit, a filter circuit, a gradation processing circuit, and an output control circuit, which will be described later.

The image data stored in the FIFO memory 5 is also supplied to the black generation circuit 7 via the character / photo / halftone dot judgment circuit 6. The black generation circuit 7 generates black (BK) data for compensating for the insufficient density in the high density portion. Specifically, for example, a value obtained by multiplying the minimum value of each of Y, M, and C image data by a correction coefficient β (for example, β = 0.5 to 1) is removed from each image data, and the removed value is referred to as BK data. Will be generated. The Y, M, and C image data and BK data are supplied to the output color selection circuit 8.

In the output color selection circuit 8, the above Y, M,
Image data corresponding to any one of the C and BK image data is selected. The selected image data is given to the zoom / movement circuit 9 and is subjected to processing such as enlargement or reduction according to the set magnification. After that, the filter circuit 10 is subjected to smoothing processing or edge enhancement processing according to the determination result provided from the character / photo / halftone dot determination circuit 6. Then, it is applied to the gradation processing circuit 11 and is subjected to halftone processing such as so-called dither processing or multi-value dither processing.

The image data that has been subjected to the halftone processing is subjected to processing necessary for output by the output control circuit 12, and is provided to the output section 3. The feature of this embodiment resides in the halftone dot area judging function in the character / photo / halftone dot judging circuit 6. FIG. 1 is a block diagram for explaining the flow of the halftone dot area determination processing in the character / photo / halftone dot determination circuit 6.

As described above, the character / photo / halftone dot decision circuit 6 stores the image data corresponding to one or a plurality of lines in the image data of any color of the Y, M, and C image data. A line memory 61 for holding is provided. Also,
The character / photo / halftone dot determination circuit 6 is provided with a peak detection unit 62.

In the peak detection section 62, first, four consecutive image data stored in the line memory 61 are selected.
The α-bit image data D ₁ , D ₂ , D ₃ and D ₄ representing the densities of the pixels P ₁ , P ₂ , P ₃ and P ₄ (see FIG. 3) are read. At this time, the pixel of interest is the pixel P ₃ . Then, it is detected based on the image data D _{1 to} D ₄ whether or not the pixel P _{3 which} is the target pixel is a peak pixel. Specifically, D ₃ -D _1> d _TH1 or D ₃ -D _2> d _TH2 each formula _{‥‥ (1) D 3 ≧ D} 4 ‥‥ (2) D 3> d TH3 ‥‥ (3) It is determined whether or not the logical product of the determinations is satisfied (provided that d _TH2 <d _TH1 <d _TH3 , for example d _TH1 = 1.
0, d _TH2 = 5, d _TH3 = 35).

As a result, when it is determined that the logical product of the determinations of the above expressions (1) to (3) is established, the pixel P of interest is selected.
The density of ₃ is considered to be relatively darker than the surrounding pixels P ₁ , P ₂ , and P ₄ , and the pixel P ₃ is detected as the peak pixel which is the center of the dots forming the halftone dot area. In the peak detection unit 62, the leftmost two pixels P ₁ and P _{2 of the} original image are
(See FIG. 3) and one pixel P _{z at the} right end (see FIG. 3) are not detected as to whether they are peak pixels or not. There is no.

When the detection of the peak pixel in the case where the pixel of interest is the pixel P ₃ is completed, the image data D _{2 to} D ₅ corresponding to the pixels P _{2 to} P ₅ are subsequently read from the line memory 61. At this time, the pixel of interest is the pixel P ₄ . Then, the same processing as described above is performed. The above-described peak pixel detection processing is performed by the pixel which is the target pixel and is determined in advance by n.
The process is repeated until the number of pixels reaches (for example, n = 50), and the process ends.

In the following, the n pixels which are the target pixels are
The area including all pixels is the “judgment area” of the line.
Say. By the way, in equation (1) above,
Pixel P₃Pixel adjacent to ₂, P_FourOne apart from
Pixel P₁Image data D₁Is the halftone dot area
The size of the dots that make up the area depends on the detection pixels of the scanner 1.
This is because the case where it protrudes is considered.

More specifically, for example, dots
The size of 4 pixels of the scanner 1 (that is,
The number of lines in the halftone dot area is about 50) and the pixel of interest
Pixel P₃If there is a dot center in
For example, as shown in FIG. ₃Image data D₃Toko
Pixel P₃Pixel adjacent to₂Image data D₂Between
Has a relatively small difference Δd1, and the pixel P₃Image of
Data D₃And pixel P₁Image data D₁Relative to
There is a large difference Δd2.

Therefore, if the pixel P₃Image adjacent to
Elementary P₂, P_FourEach image data D₂, D_FourOnly used
If not, the logical sum in equation (1) above will not hold and
Pixel P that is a pixel₃Cannot be detected as a peak pixel
There is a risk. Therefore, the pixel P₃Image corresponding to
Data D₃Pixel away from₁Image data D corresponding to ₁
Are using.

As described above, in this embodiment, since the case where the dot size extends beyond the detection pixel of the scanner 1 is taken into consideration, the peak pixel can be surely detected even if the dot size is large. In the detection of the peak pixel, not only the pixel 1 pixel away from the pixel of interest but also γ
Image data corresponding to pixels separated by (for example, γ = 2, 3) pixels may be used.

When the peak detection unit 62 detects that the pixel of interest is the peak pixel, the detection signal is given to the peak number counter 63. In the peak number counter 63, the count value is incremented each time a detection signal is given. When the peak detection unit 62 detects that the pixel of interest is a peak pixel, the position of the pixel of interest on the line is given to the peak position storage unit 64. The peak position storage unit 64 stores the position of the pixel of interest.

Further, in the peak detection section 62, when the peak pixel detection processing for n pixels is completed, an end signal is given to the peak position storage section 64. When the end signal is given to the peak position storage unit 64, the peak number is read from the peak number counter 63 in response to the end signal,
It is determined whether or not the number of peaks is equal to or more than a predetermined number k (for example, k = 10). As a result, when it is determined that the number of peaks is k or more, it is determined whether or not the appearance of the peak pixel has periodicity. Given to 65. On the other hand, if it is determined that the number of peaks is less than k, it is considered that the determination area is unlikely to be a halftone dot area, and after the positions of all the saved target pixels are erased, The process shifts to the halftone dot area determination processing in the determination area. At this time, the count value of the peak number counter 63 is cleared.

In the peak-to-peak distance calculation unit 65, the distance between adjacent pixels of interest is calculated. For example, in FIG.
As shown in, the distance between the pixel P ₂ detected as the peak pixel and the pixel P ₄ detected next as the peak pixel is calculated to be “2”. The calculated peak-to-peak distance is provided to the histogram creation unit 66. The histogram creation unit 66 creates a histogram representing the frequency of appearance of the peak-to-peak distance. For example, as shown in FIG. 6, a histogram representing the appearance frequency of the peak-to-peak distance is created such that the peak-to-peak distance “2” is 7 times and the peak-to-peak distance “3” is 3 times. The created result is given to the halftone dot judging section 67.

In the halftone dot judging section 67, whether or not the maximum value of the histogram (the frequency of appearance of the peak-to-peak distance having the highest frequency of appearance) is x% or more (for example, x = 75) of the total frequency of appearance in the above histogram. Is determined. As a result, when it is determined that the maximum value is x% or more of all appearance frequencies, the determination area is determined to be a halftone dot area. When the peak position storage unit 64 determines that the count value of the peak number counter 63 is less than k, or when the determination process by the halftone dot determination unit 67 ends, Similar halftone dot area determination processing is performed.

Here, the next determination area is set in two ways depending on whether or not there is a pixel detected as a peak pixel in the previous determination area. More specifically, if there is no pixel detected as a peak pixel in the previous determination area, the next determination area HE2 is the same as the previous determination area HE1 as shown in FIG. 7 (a). It is set as the range from the next pixel Q ₁ to n pixels _n shifted in the main scanning direction S.

On the other hand, if there is only one pixel detected as a peak pixel in the previous determination area, regardless of whether the number of peak pixels detected is k or more, the figure As shown in 7 (c), the next judgment area HE2
It is set as the range of the previous determination area HE1 until the first pixel Q _{P + n} shifted from the detected pixel Q _P as peak pixel into n main scanning direction S.

Next, the reason for this will be described. For example, when the halftone dot area M slightly overlaps the previous determination area HE1 and the next determination area HE2 as shown in FIG. 7B,
There is a possibility that the number of target pixels detected as peak pixels in each of the determination areas HE1 and HE2 may be less than k. In this case, although the partial regions M1 and M2 of the determination regions HE1 and HE2 are the halftone dot regions M respectively, they are erroneously determined not to be the halftone dot regions M.

On the other hand, in FIG. 7C, the judgment area HE1
When the determination area HE2 is started from the pixel Q _p which is first detected as the peak pixel in
At E2, the number of pixels detected as peak pixels is likely to be k or more. Therefore, if there is even one pixel detected as a peak pixel in the previous determination area, the determination area HE2 is set as described above.

In the vicinity of the right end of the original image, the judgment area is forced to be the pixel P _z-1 (see FIG. 3) from the right end of the original image to the second pixel even if it is less than n pixels. Is set automatically. This is because the peak pixel detection process requires pixels adjacent to the pixel of interest in the main scanning direction as described above, but the pixel P _{z at} the right end of the original image (see FIG. 3) is a peak pixel. It is not detected whether or not there is.

As described above, the halftone dot area determination process is repeated while updating the determination area. Then, when the halftone dot area determination processing in the determination area set near the right end of the original image is completed, the halftone dot area determination is performed on the image data of any one line of any color held in the line memory 61. The process ends. Then, the halftone dot area determination processing as described above is performed for other lines, and further, for all color image data, all the halftone dot area determination processing ends.

As described above, according to the digital color copying machine of this embodiment, the periodicity of the appearance of the peak pixel is used to determine whether it is a halftone dot area, so it is possible to determine whether it is a halftone dot area. Line memory 61 that should hold image data required for
Does not require a capacity for a plurality of lines. Therefore, the memory scale can be reduced as compared with the related art in which a memory having a capacity of a plurality of lines is required at least in the sub-scanning direction (direction perpendicular to the main scanning direction S).

Further, since it is detected whether or not it is a peak pixel by utilizing the image data corresponding to the pixel one pixel away from the pixel of interest, regardless of the size of the dots forming the halftone dot area. Whether or not it is a peak pixel can be reliably detected. Therefore, the periodicity of the peak pixel can be reliably determined. 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-described embodiment, the periodicity of the appearance of the peak pixels is used to determine whether or not it is a halftone dot region. For example, the periodicity of the appearance of so-called dip pixels between dots forming the halftone dot region is determined. You may make it determine whether it is a halftone dot area or not.

Whether or not the pixel of interest is a dip pixel
Is detected by the logical product of the following equations (4), (5) and (6).
It is performed based on the determination result of whether or not to do. D₁-D₃> D_TH1 Or D₂-D₃> D_TH2 (4) D₃≤D_Four (5) D_Four> D_TH3 (6) As a result, if it is determined that the logical product of each expression is established,
Pixel P that is the eye pixel ₃Is the surrounding pixel P₁, P₂, P_Four
Are considered to be relatively whiter than
It is detected as a dip pixel between dots.

Further, it may be possible to determine whether or not it is a halftone dot area by utilizing the periodicity of appearance of both the peak pixel and the dip pixel. In this case, when either the peak pixel or the dip pixel has periodicity, it may be determined as the halftone dot area. Further, in the above-described embodiment, the peak pixel or the dip pixel is detected by using four pixels which are continuous in the main scanning direction. The peak pixel and the dip pixel may be detected respectively.

However, in the following description, FIG. 8 is also referred to. Further, in the following description, D _{A to} D _L are image data corresponding to the pixels P _{A to} P _L , respectively. Further, the pixel of interest is the pixel P _G. D _F <D _G and D _G > D _H and D _G > d
_TH3 'D _F> D _G and D _G <D _H and D _H> d
_TH3 These 'can prevent erroneous detection more than later'.

D _F <D _G and D _G > D _H ′ D _F > D _G and D _G <D _{H In} these, ′, a halftone dot area has a large number of lines from a peak pixel or a dip pixel. It is possible to detect even a peak pixel or a dip pixel in the dot region.

D _F <D _G and D _G ≧ D _H ′ D _F > D _G and D _G ≦ D _{H In} these, ′, the peak pixel or the dip pixel in the halftone dot area having a smaller number of lines than the above ′ Can be detected. D _G > D _B , D _C , D _D , D _H , D _L , D _K , D
_J, D _F (logical _{product) 'D G <D B,} D C, D D, D H, D L, D K, D
_J , _DF (logical product) These and ′ can relatively prevent false detection. However, it is difficult to detect the peak pixel or the dip pixel in the halftone dot area where the number of lines is smaller than that of the following.
Also, a line memory for three lines is required.

D _G > D _C , D _H , D _K , D _F (logical product) ′ D _G <D _C , D _H , D _K , D _F (logical product) It is possible to detect a peak pixel or a dip pixel in a halftone dot area having a small number of lines. However, the number of false detections is increased compared to the above '. Also, a line memory for three lines is required.

D _G ≧ D _B , D _D , D _L , D _J (logical product) and D _G > D _C , D _H , D _K , D _F (logical product)
AND of and. ′ D _G ≦ D _B , D _D , D _L , D _J (logical product) and D
_{G <D C, D H,} D L, D F and (logical AND), logical product of.

In these ', the erroneous detection is
It is an intermediate point between'and ', and the number of lines in the detectable dot area is also an intermediate point between'and'. Also,
Line memory for 3 lines is also required. Furthermore, in the above-described embodiment, the peak pixel is detected in the determination area of n pixels and it is determined whether or not it is a halftone dot area, and this process is shifted by a certain number of pixels over one line, and then in the next determination area. The peak pixels are detected again and the same process is repeated thereafter. For example, the peak pixels are detected for one line first, and then the judgment area is set to determine whether or not each judgment area is a halftone dot area. May be determined.

Further, in the above embodiment, on the same line
Only a fixed decision area containing n pixels is used
However, if the pixel detected as a peak pixel is
When it reaches k, it is regarded as the pixel of interest at that time.
It is also possible to use a variable judgment area with the selected pixel as the final pixel.
Yes. More specifically, for example, as shown in FIG.
K peak pixels before reaching n pixels
(P_p1~ P_Pk) When detected, the k-th peak pixel P _Pk
Is determined as the final pixel when the pixel of interest is detected
After ending E1, the next determination area HE2 is set to the previous determination area H.
The first detected peak pixel P at E1_P1The first picture
Set as plain.

Furthermore, in the above embodiment, the digital color copying machine has been described as an example, but the present invention can be applied to, for example, a digital monochrome copying machine, a color / monochrome facsimile machine or a color / monochrome printer.
The present invention can be applied to other image forming apparatuses that require processing for determining whether or not a document image is a document image in a halftone dot area. Other various design changes are possible within the scope of the present invention.

[0053]

As described above, according to the halftone dot area judging device of the present invention, since it is judged whether or not it is a halftone dot area on the basis of the periodicity of the appearance of the peak pixel or the dip pixel, a plurality of pixels are judged. Image data for lines is not always necessary,
For example, it is sufficient if there is image data for one line. Therefore, the memory scale can be reduced as compared with the conventional technique in which a memory capable of holding image data of at least a plurality of lines is indispensable for determining whether it is a halftone dot region.

Further, since the peak pixel or the dip pixel is detected by comparing the image data corresponding to the target pixel and the image data corresponding to the pixels around the target pixel, the size of the dot and the detection pixel of the conversion means is large or small. It is possible to reliably detect the peak pixel or the dip pixel regardless of the relationship. In particular, according to the configuration of claim 3, since the image data corresponding to the pixels on the same line that are not adjacent to the pixel of interest is used for detecting the peak pixel or the dip pixel, the dot is detected by the conversion unit. Even if is large, the peak pixel or the dip pixel can be detected more reliably.

Further, according to the structure of claim 4, when the peak pixel or the dip pixel is detected in the conventional determination area, the first detected peak pixel or the dip pixel is set to the head and the next pixel is detected. Since the determination area is newly set, there is a high possibility that the number of peak pixels or dip pixels necessary for determining the periodicity of the inter-pixel distance can be detected. Therefore, the halftone dot area is never missed.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining a flow of a halftone dot area determination process in a digital color copying machine of an embodiment to which a halftone dot area determination device of 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 for explaining a peak pixel detection process.

FIG. 4 is a diagram for explaining a peak pixel detection process.

FIG. 5 is a diagram for explaining how to determine a peak-to-peak distance.

FIG. 6 is a diagram showing an example of a histogram of peak-to-peak distance.

FIG. 7 is a diagram for explaining a determination area.

FIG. 8 is a diagram for explaining a peak pixel or dip pixel detection method according to another embodiment of the present invention.

FIG. 9 is a diagram for explaining a variable determination area setting method according to another embodiment of the present invention.

[Explanation of symbols]

 1 Scanner 2 Image Processing Circuit 6 Character / Photograph / Halftone Discrimination Circuit 61 Line Memory 62 Peak Detection Unit 63 Peak Number Counter 64 Peak Position Saving Unit 65 Peak Distance Calculation Unit 66 Histogram Creation Unit 67 Halftone Region Determination Unit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication H04N 1/40 104 (72) Inventor Haruo Yamamoto 1-2-2 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Within Mita Industry Co., Ltd.

Claims (4)

[Claims] 1. A conversion means for reading an original image, converting it into image data corresponding to its density and outputting the image data, and image data corresponding to one or a plurality of lines from the image data output from this conversion means. Holding means for holding and 1 corresponding to the image data held in the holding means
Or, in the determination area corresponding to the finite number of pixels in the plurality of lines, the image data corresponding to the pixel of interest is compared with the image data corresponding to the pixels around the pixel of interest,
Detecting means for detecting the peak pixel or dip pixel, registering means for registering the peak pixel or dip pixel detected by this detecting means, distance between each peak pixel registered in this registering means, or each dip pixel Distance calculation means for calculating the distance between the two, and whether the distance between the peak pixels or the distance between the dip pixels calculated by the distance calculation means satisfies a certain statistical criterion. A periodicity determining means for determining, and in the periodicity determining means, when it is determined that the periodicity of the distance between the peak pixels or the distance between the dip pixels satisfies the statistical criterion, the determination area Is a halftone dot area, and a halftone dot area judging device is included. 2. A frequency recognition unit for recognizing the frequency of appearance of the distance between each peak pixel or the distance between each dip pixel obtained by the distance calculation unit, and the frequency recognition unit. And a frequency discriminating unit for discriminating whether or not the maximum value of the appearance frequencies of the distances between the peak pixels or the distances between the dip pixels recognized in is equal to or higher than a predetermined ratio with respect to all the appearance frequencies. When the maximum value of the appearance frequency is determined to be equal to or higher than a predetermined ratio with respect to all the appearance frequencies by the frequency determination unit, the distance between the peak pixels or the distance between the dip pixels is included. 2. The halftone dot area determining apparatus according to claim 1, wherein the periodicity of is determined to satisfy the statistical criteria. 3. The image data corresponding to the pixel of interest, the image data corresponding to two pixels on the same line that are continuous on the upstream side of the pixel of interest in the main scanning direction, and the pixel of interest. 3. A peak pixel or a dip pixel is detected by comparing with image data corresponding to one pixel on the same line that is continuous on the downstream side in the main scanning direction. Halftone dot area determination device. 4. The determination area is repeatedly set by shifting an arbitrary number of pixels along the same line, and when a peak pixel or a dip pixel is detected by the detection means, first, 4. The halftone dot area determination device according to claim 1, further comprising a determination area setting unit that newly sets a next determination area with the detected peak pixel or dip pixel as a head.