JP3434374B2 - Image forming device - Google Patents

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]

By the way, in the halftone dot area, the number of dots per inch (hereinafter referred to as "the number of lines") is about 200 lines for a fine texture and 65 for a rough texture. There are even lines. 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 for detecting the peak pixel or the dip pixel is
There is a problem in that the peak pixel or the dip pixel cannot be accurately detected and is often erroneously detected.

This problem is particularly remarkable in newspaper manuscripts and the like. Therefore, an object of the present invention is to solve the above-mentioned technical problem and to accurately determine whether or not a halftone dot area is irrespective of the size relation between the size of the dots forming the halftone dot area and the detection pixel of the conversion means. An image forming apparatus is provided.

[0007]

According to a first aspect of the present invention, there is provided an image forming apparatus for converting an image of a document, converting the image into image data corresponding to the density, and outputting the image data. A two-dimensional image formed by a holding unit that holds image data corresponding to a plurality of lines in the image data output from the unit, and a predetermined number of pixels among the pixels corresponding to the image data held by the holding unit. An isolated area determining means for determining whether or not there is an isolated area whose density is relatively darker or thinner than the surrounding density in the determination area ;
The judgment area does not include the boundary pixels of the judgment area.
Average density to find the average density of the pixels that make up the region of interest
The frequency value calculation unit and the density of areas other than the attention area
The recognition unit that recognizes the maximum or minimum value of the degree, and the above average
The average density value calculated by the density value calculation unit is confirmed by the recognition unit.
Whether it is larger than the recognized maximum density value, or
The average density value calculated by the average density value calculation unit is
Judgment to determine whether it is smaller than the recognized minimum density value
In the discrimination unit, the average density value is
Greater than the maximum density value above, or the average density value above
If it is determined that it is smaller than the minimum density value, the above determination
It is to determine that there is an isolated area in the area , and when the isolated area determination means determines that there is an isolated area, the determination area is determined to be a halftone dot area. Characterize.

[0008]

[0009] The image forming apparatus according to claim 2, wherein the original
Read the manuscript image and convert it to image data corresponding to its density
Output from the conversion means, and the output from this conversion means
Save the image data corresponding to multiple lines of the image data.
Holding means to hold and images held in this holding means
Composed of a certain number of pixels corresponding to the data
In the two-dimensional judgment area, the density is higher than the surrounding density.
Whether or not there are isolated regions that are relatively darker or thinner
And an isolated area discriminating means which discriminates between the image data corresponding to the pixels constituting the discriminant area in the discriminant area, thereby performing binarization processing to generate binarized data. Based on the binarization processing unit and the binarized data generated by this binarization processing unit,
Whether or not the binarized data changes in the order of low level, high level and low level, or in the order of high level, low level and high level in the judgment area is determined line by line and in a direction orthogonal to the line. And an identification unit for identifying each pixel column, and the identification unit identifies that the binarized data changes in the order of low level, high level and low level, or in the order of high level, low level and high level. Then, the logical product of the holding unit that holds the intermediate-level high-level or low-level binarized data for each pixel and the binarized data held by this holding unit is obtained for each pixel. and a logical product unit, a result of logical product is obtained in the logical unit, if there are pixels that are high or low level, to the determination area All SANYO to determine that the isolated region is present in the isolated region discriminating means, is isolated areas
If it is determined that there exists, the above-mentioned determination area is a halftone dot area.
And a determination means for determining that

An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the first or second aspect , and when the determination area is determined to be a halftone dot area, the determination is made. It is characterized by further including smoothing means for performing a smoothing process on the region.

[0011]

[Action] In this invention, in the two-dimensional determination area composed of a predetermined number of pixels, whether there is a concentration to isolated areas or not. Specifically, as in the configuration of the 請 Motomeko 1, wherein the average density value of the region of interest does not include the boundary pixels of the determination area is higher than the maximum density value of the region other than the target area of the determination region, Alternatively, when it is determined that the density is lower than the minimum density value, it is determined that an isolated area exists in the determination area.

Further, it may have a structure as described in claim 2 . Specifically, in the identification unit, low level, high level, and low level in this order, or high level,
When it is identified that there is a line and a pixel column in which the binarized data changes in the order of low level and high level, the intermediate level high level or low level binarized data is held for each pixel, and the logical sum is obtained. Is required. As a result, if there is a high-level or low-level pixel, it can be determined that the region corresponding to the intermediate high-level or low-level binarized data is a region isolated in terms of density. It is determined that there is an isolated area in the area.

As a result of the discrimination, if it is discriminated that an isolated region exists in the discrimination region, the discrimination region is judged to be a halftone dot region. By the way, since the halftone dot area is an area in which dots are arranged periodically, an area where the density is relatively darker or lighter than the surrounding density exists independently.
On the other hand, in the character / line drawing area or the photographic area, areas where the density is relatively darker or lighter than the surrounding density are almost continuous.

Therefore, according to the above configuration, the character / line drawing area or the photograph area is not erroneously determined as the halftone dot area. Moreover, since the two-dimensional area constituted by a predetermined number of pixels is used as the judgment area, even if the dot size is so small that the number of lines is so small as to exceed the detection pixels of the conversion means, it is surely judged as the halftone area. it can.

By the way, in the structure according to claim 1 or 2 , it is judged whether or not the judgment area is a halftone dot area based on whether or not an isolated area exists in the judgment area. There is a possibility that a judgment area including noise may be erroneously judged as a halftone dot area. Therefore, in such a case, if the smoothing process is performed on the halftone dot area as in the configuration according to the third aspect , the noise is erased, and there is not much problem.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. <First Embodiment> FIG. 1 is a block diagram showing the electrical construction of the essential parts of a digital color copying machine to which the image forming apparatus of the present invention is applied.

In this digital color copying machine, a color original image to be copied is optically read and red (R) and green (G) are read.
In addition to photoelectrically converting the three primary color image data by the additive method of blue and blue (B), the image data of the three primary colors of R, G and B are complementary colors of yellow (Y), magenta (M) and cyan (C ) The scanner 1 is provided which is a conversion unit composed of a CCD (charge coupled device) or the like for converting into three primary color image data by the subtractive color method and outputting. 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. Thereafter, the Y, M, and C image data are given to the character / photo / halftone dot decision circuit 5.

In this embodiment, the above characters, photographs,
The halftone dot decision circuit 5 corresponds to the isolated area decision means and the decision means. Of the image data given to the character / photograph / halftone dot decision circuit 5, it is held in a line memory 51 which is a holding means for holding image data of an arbitrary s (for example, s = 5) line.

In the character / photograph / halftone dot decision circuit 5, based on the image data held in the line memory 51, the image data belongs to any of the character / line image area, the photograph area or the halftone dot area. It is determined whether it is data. The halftone dot area is an area in which dots are arranged periodically and 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 output from the input processing circuit 4 is also supplied to the black generation circuit 6 via the character / photo / halftone dot determination circuit 5. The black generation circuit 6 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 7.

In the output color selection circuit 7, 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 8 and is subjected to processing such as enlargement or reduction according to the set magnification. After that, it is applied to the filter circuit 9 functioning as a smoothing means and the like, and is processed according to the determination result supplied from the character / photo / halftone dot determination circuit 5. Specifically, the area determined to be the halftone dot area is subjected to smoothing processing for removing moire. Then, it is applied to the gradation processing circuit 10 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 required for output by the output control circuit 11 and then provided to the output section 3. The feature of this embodiment is that the characters
This is a halftone dot area judging function in the photograph / halftone dot judging circuit 5. FIG. 2 is a flow chart for explaining the halftone dot area determination processing in the character / photo / halftone dot area determination circuit 5.

In this halftone dot area determination process, first, a plurality of pixels forming a two-dimensional determination area HE are respectively corresponded from the image data represented by α bits representing the density stored in the line memory 51. Read the image data. Next, in the read image data, based on the image data respectively corresponding to the plurality of pixels forming the attention area TE set in the determination area HE, An average value D _{av of the} density is obtained (step S1).

3 and 4 are diagrams for explaining a method of setting the judgment area HE and the attention area TE.
The halftone dot area to be determined in the flowchart of FIG. 2 is an area in which dots are periodically arranged, as shown in FIG. Therefore, in the halftone dot area, there are isolated areas in which the density is relatively higher than the surrounding density. On the other hand, in the character / line drawing area or the photographic area, areas having relatively high density exist substantially continuously.

Therefore, for example, as shown in FIG. 3, the area E1 and the area E2 not including the boundary pixels of the area E1.
By setting, it is possible to extract the area including the pixels corresponding to the dots DP forming the halftone dot area as a density-isolated area. Therefore, in this embodiment, since only the halftone dot area is recognized, areas such as the area E1 and the area E2 are set as the determination area HE and the attention area TE, respectively.

Next, the judgment area HE and the attention area T are set.
The determination of the size of E will be described. In the character / line-drawing area or the photograph area, as described above, there are almost no isolated areas, but in the case of the character / line-drawing area, there are some isolated areas such as “,”. On the other hand, the isolated area of the character / line drawing area is large enough to be visually recognized by human eyes. Therefore, in this embodiment, in order to prevent the isolated area of the character / line drawing area from being recognized as the isolated area of the halftone dot area, the determination area HE is set to a size equal to or smaller than the limit visually recognizable by human eyes. .

Specifically, for example, as shown in FIG.
The size of the determination area HE is set to 10 dots and 5 lines in the main scanning direction M and the sub scanning direction S, respectively. The size of the attention area TE is set to 4 dots and 3 lines in the main scanning direction M and the sub scanning direction S, respectively. This means that if the scanner 1 has a detection pixel of 400 pixels / inch, the determination area HE is 0.635 (mm) x
Corresponding to the size of 0.3175 (mm), the attention area TE is 0.254 (m
It corresponds to a size of m) × 0.1905 (mm).

Returning to FIG. 2, when the average density value D _av of the attention area TE is obtained in step S1, the attention area TE of the determination area HE in the read image data is obtained.
The maximum value D _max in the densities of the respective pixels forming the outer frame area RE is recognized based on the image data corresponding to the plurality of pixels forming the outer frame area RE other than the above (step S2).

Next, in order to determine whether the attention area TE is an isolated area or not, the average density value D _av of the attention area TE is the maximum density value D of the outer frame area RE as shown in the following equation (1). _{ma x} to a predetermined value D ₀ (when a gradation is 256, for example, D ₀ = 20) to determine greater or not than the sum (step S3). D _av > D _max + D ₀ (1) As a result, if it is determined that the formula (1) is satisfied, the attention area TE is an isolated area having a relatively higher density than the outer frame area RE. It is determined that the determination area HE is a halftone dot area (step S4).

When the halftone dot area determination process described above is completed, the determination area HE is moved to a position shifted by one pixel in the main scanning direction M.
Is newly set and the same processing as above is repeated. Then, the processing is performed until the right edge boundary pixel row of the set determination area HE matches the right edge pixel row of the document, and when the processing ends, the left edge boundary pixel row matches the left edge pixel row of the document, and The next determination area HE is set at a position shifted by one pixel in the sub-scanning direction S.

In this way, the determination area HE is repeatedly set, and the determination area HE in which the lower right edge pixel matches the lower right edge pixel of the original is set and the above-mentioned processing is performed.
The halftone dot area determination processing for the image data of any color among the M, C, and Y image data ends. Then, by performing the above-described halftone dot area determination processing on the image data of the remaining colors, the halftone dot area determination processing on all the image data ends.

As described above, according to the digital color copying machine of this embodiment, since it is determined whether or not there is an isolated area in a certain determination area HE, it is determined whether or not it is a halftone dot area. The character / line drawing area or the photograph area where there is almost no will not be mistakenly determined as a halftone dot area. Moreover, since the two-dimensional determination area HE composed of a plurality of pixels is used, even a halftone dot area with a small number of lines that the size of the dot exceeds the detection pixel of the scanner 1 can be reliably determined as the halftone dot area. it can.

In the above embodiment, a certain judgment area HE
Since it is determined whether or not it is a halftone dot region on the basis of whether or not there is an isolated region, the determination region HE including noise is
May be determined as a halftone dot area. However, since the filter circuit 9 (see FIG. 1) performs the smoothing process for removing moire in the halftone dot area as described above, the noise is erased and there is not much problem.

Further, in the above embodiment, it is determined whether or not the average density value D _av of the target area TE is larger than the maximum density value D _max of the outer frame area RE plus the predetermined value D ₀ . It is determined whether or not there is an isolated area in the determination area HE. In parallel with this, the average density value D _av of the attention area TE is determined to be the outer frame area R as shown in the following equation (2), for example.
The determination area HE is determined by determining whether it is smaller than a value obtained by subtracting the predetermined value D ₀ from the minimum density value D _{min of} E.
It is preferable to determine whether or not there is an isolated area.

D _av <D _min −D ₀ (2) <Second Embodiment> FIGS. 5 and 6 show halftone dot area determination processing in a digital color copying machine to which the image forming apparatus of the present invention is applied. It is a flow chart for explaining.
Similar to the halftone dot area determination processing of the first embodiment, the halftone dot area determination processing of the second embodiment determines whether or not the halftone dot area is based on whether or not an isolated area exists in a certain judgment area. It is a judgment.

In the halftone dot area determination processing of the second embodiment,
The buffers A, B and C and the flag F (see FIG. 1, shown by broken lines in the figure) provided in the character / photo / halftone dot decision circuit 5 are used. In the halftone dot area determination processing of the second embodiment, first, m dots × n lines (for example, m = 8, n = 8 in the example shown in FIG. 7) from the image data held in the line memory 51. The image data corresponding to each of the plurality of pixels forming the two-dimensional determination area IE is read (step P1). Next, binarization processing is performed on the read image data, and the binarized data is stored in the buffer A.
(Step P2).

The threshold value in this binarization processing is set to 100 when the gradation is 256, for example. Therefore, the image data of the pixel corresponding to the dot is converted into high level binarized data, and the image data corresponding to the background portion is converted into the low level. For example, Figure 7 (a)
As shown in FIG. 7, when the dot DP is present in the determination area IE, as a result of the binarization process, as shown in FIG. Appears near the center of the determination area IE, and low-level binarized data appears near the boundary of the determination area IE.

In the following, the description will proceed with the determination area IE shown in FIG. 7 as an example. Returning to FIG. 5, after the binarized data is held in the buffer A in step P2, the buffers B and C, which will be described later, are cleared (step P2).
3) Then, the flag F is reset (step P4), and the preprocessing for the determination area IE ends. Here, in order to determine whether the flag F has an isolated region in a line of the determination region IE and a pixel column in the direction orthogonal to this line, the logic of the binarized data is inverted in the line and the pixel column. This is for indicating that it is set when the binarized data changes from the low level to the high level and reset when the binary data changes from the high level to the low level.

When the preprocessing is completed, the left end pixel P ₂₁ of the second line in the judgment area IE is set as the target pixel (step P5). Here, the reason why the leading line in the determination area IE is ignored is as follows. In this embodiment, since it is attempted to determine whether it is a halftone dot region or not based on whether or not there is an isolated region in the determination region IE, whether or not there is high-level binary data at the boundary of the determination region IE. This is because it is only necessary to know whether or not there is an isolated area in the determination area IE, regardless of whether or not it is present. Therefore, as will be described later, in this embodiment, the final line, the leftmost pixel column, and the rightmost pixel column in the determination area IE are also ignored.

Next, the target pixel P ₂₁ and the pixel P ₂₂ adjacent to the target pixel P ₂₁ in the main scanning direction M on the same line.
In order to determine whether or not there is an isolated area on the line based on the binarized data corresponding to, whether the binarized data has changed from the low level to the high level in the main scanning direction M. For confirmation, it is determined whether or not the flag F is reset (step P6). In the case of FIG. 7 described above, since the binarized data remains at the low level, the process proceeds to step P8.

In step P8, contrary to step P6, the binarized data is changed from high level to low in the main scanning direction M based on the binarized data corresponding to the target pixel P ₂₁ and the pixel P ₂₂ , respectively. It is determined whether or not the level has changed and whether or not the flag F is set. In the case of FIG. 7 described above, since the binarized data remains at the low level, the process directly goes to step P10.

In step P10, the pixel to be the pixel of interest is shifted by one pixel in the main scanning direction M on the same line. Then, it is determined whether or not the pixel P ₂₂ newly set as the pixel of interest is the right end pixel of the determination area IE held in the buffer A (step P11). As a result, if it is not the right end pixel, the above step is performed. The process from P6 is repeated.

As a result of repeating the processing from step P6, in the case of FIG. 7, when the pixel of interest is the pixel P ₂₄ ,
Since the binarized data has changed from the low level to the high level and the flag F has been reset, the above step P6
The condition of will be satisfied. Therefore, when the pixel of interest is the pixel P ₂₄ , the process proceeds to step P7. In step P7, since the binarized data has changed from low level to high level, the flag F is set and the position of the target pixel P ₂₄ is held.

After that, the pixel to be the target pixel is subjected to the main scanning method.
Pixel P shifted by one pixel in the direction M _{twenty five}And then binary
Data changes from high level to high level
Therefore, both conditions of steps P6 and P8 are satisfied.
do not do. Furthermore, the pixel of interest is shifted by one pixel
P₂₆, The binarized data will be high level → low level.
Change according to step P7.
Since lug F has been set, the conditions in step P8 above
Will meet the requirements. Therefore, the target pixel is set to the pixel P.₂₆
If so, the process proceeds to step P9.

At step P9, since the binary data has changed from high level to low level, the flag F is reset. Further, the binarized data corresponding to the target pixels P ₂₄ and P ₂₅ held as a result of the processing in step P7 are held in the buffer B while maintaining their positional relationship. In this way, the high-level binarized data of the intermediate rank is held in the buffer B only when the binarized data changes from low level to high level to low level on the same line. Therefore, when the high-level binarized data is simply continuous on the line from the right and left pixels of the determination area IE, the binarized data corresponding to the pixels on the line is not held in the buffer B. However, even if there is continuous high-level binarized data on a line, if there are isolated high-level binarized data on the same line, the binarized data is buffered in the same manner as above. Hold on.

When it is determined in step P11 that the pixel of interest is the right end pixel P _{28 of} the determination area, the processing of the second line of the determination area IE ends, and the pixel of interest is moved to the next third line. Is set to the leftmost pixel P ₃₁ (step P
12). Then, it is determined whether or not the line set as the pixel of interest is the final line (step P13). As a result, if it is determined that the line is not the final line, the processes from step P4 are repeated.

Then, the above processing is performed in the judgment area IE.
Repeat for all but the last line in. FIG. 8 (a) shows the buffer B in the case of the example of FIG.
Shows the memory state of. If it is determined in step P13 that the line of interest is the last line, then in the determination area IE, processing for determining an isolated area in the pixel row in the sub-scanning direction S is performed.

The process for determining an isolated region in a pixel row in the sub-scanning direction S is basically the same as the process for determining an isolated region in a line in the main scanning direction M described above. Specifically, steps P14 to P, which are processes for determining an isolated region in a pixel row in the sub-scanning direction S.
The process up to 23 is basically the same as the process up to steps P4 to P13 described above, except that the direction to be scanned is not the main scanning direction M but the sub-scanning direction S, and the pixel at step P19. The buffer is only buffer C, not buffer B. Therefore, a detailed description of the processes of steps P14 to P23 will be omitted.

FIG. 8B shows the storage state of the buffer C in the case of FIG. Here, for example, as shown in FIG.
In the case where there is a relatively dense area that is in contact with only one side of the determination area IE, only the change from the high level to the low level in the line (main scanning direction M), the buffer B
Does not hold the isolated region determination result. On the other hand, in the pixel row (sub-scanning direction S), since there is a change from low level → high level → low level, only the buffer C holds the isolated region determination result. Therefore, if only the isolated area determination result held in either one of the buffers B and C is adopted, there is a possibility that it may be erroneously determined that an isolated area exists.

Therefore, in order to surely determine whether or not an isolated area exists, when the isolated area determination processing in the sub-scanning direction S is completed, a logical product is obtained between the buffer B and the buffer C (step P24). ). As a result, FIG.
As shown in the areas surrounded by thick lines in (a) and (b), the buffer B,
When the high-level binarized data is held in any of C, only the binarized data remains as the high-level data. Then, the remaining high level data is held in the buffer B.

Next, it is judged whether or not there is high level data held in the buffer B (step P2).
5) As a result, when it is determined that the high-level data is held in the buffer B, it is determined that an isolated area exists in the determination area IE, and the determination area IE is determined to be a halftone dot area. (Step P26). When the halftone dot area determination process described above is completed, the subsequent steps are the same as in the case of the first embodiment, so a detailed description thereof will be omitted.

As described above, the digital color copying machine of the second embodiment also determines whether or not a halftone dot area is present based on whether or not an isolated area exists in the determination area IE. There is no erroneous determination of a character / line-drawing area or a photograph area in which half-tone dot exists as a halftone dot area. Moreover, since the two-dimensional determination area IE composed of a plurality of pixels is used, even in a halftone dot area where the number of lines is so small that the dot size extends beyond the detection pixels of the scanner 1,
It can be reliably determined as a halftone dot area.

In the second embodiment, the image data of the pixels corresponding to the dots and the background portion are converted into high level and low level binarized data, respectively.
For example, the logic may be reversed, and the image data of the pixels corresponding to the dots and the background portion may be converted into low-level and high-level binarized data, respectively. In this case, the binarized data may be held in the buffer B or the buffer C when the binarized data changes in the order of high level, low level, and high level in the line or the pixel column.

In the second embodiment, whether or not the binarized data corresponding to the dots is isolated is used. For example, the binarized data corresponding to the dip area where the density between the dots is the lowest is used. It may be possible to use whether or not the encoded data is isolated. More specifically, in the halftone dot area, the background portion does not have the same density, and the dip area in the valley between the dots is the lowest. Therefore, if a density value slightly higher than the minimum density value is used as the threshold value in the binarization process, only the binarized data corresponding to the dip area becomes low level, and the binarization data corresponding to other background areas and dots is set. The digitized data becomes high level. That is, the dip area can be a density-isolated area. Therefore, when the binarized data changes in the order of high level → low level → high level, the buffer B
Alternatively, if the buffer C holds the binarized data, it is possible to determine whether or not the isolated region exists in the determination region. <Other Embodiments> This embodiment has been described above, but the present invention is not limited to the above embodiments. For example, although the digital color copying machine has been described as an example in the above embodiment, the present invention is a digital monochrome copying machine, a color / monochrome facsimile apparatus or a color / monochrome printer, and the original image is an original image in a halftone dot area. It is also applicable to other image forming apparatuses that require a process for determining whether or not it is.

Other various design changes are possible within the scope of the invention.

[0058]

As described above, according to the image forming apparatus of the first or second aspect, it is determined whether the dot area is the dot area based on whether the isolated area exists in the judgment area. A character / line drawing area or a photograph area in which there are almost no isolated areas is not erroneously determined as a halftone dot area. Moreover, since the two-dimensional determination area composed of a predetermined number of pixels is used, even if the dot area has a small number of lines such that the dot size exceeds the detection pixel of the conversion means, the dot area is reliably determined. it can. Therefore, for example, when the image forming apparatus of the present invention is applied to a digital copying machine, an appropriate processing can be performed on a halftone dot area, so that a high quality copy can be obtained.

According to the image forming apparatus of the third aspect , since the halftone dot area is subjected to the smoothing process, noise is erroneously recognized as a dot, and it is erroneously determined that an isolated area exists in the determination area. However, since the above noise is eliminated, there is not much problem.

[Brief description of drawings]

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

FIG. 2 is a flowchart for explaining halftone dot area determination processing in the digital color copying machine.

FIG. 3 is a diagram for explaining a method of setting a determination area and an attention area.

FIG. 4 is a diagram showing an example of a determination region and a region of interest.

FIG. 5 is a flow chart for explaining halftone dot area determination processing in the digital color copying machine of the second embodiment to which the image forming apparatus of the present invention is applied.

FIG. 6 is a flowchart for explaining the halftone dot area determination processing in the digital color copying machine of the second embodiment to which the image forming apparatus of the present invention is applied.

FIG. 7 is a diagram for explaining an example in which the binarized data is at a high level in the determination area.

FIG. 8 is a diagram for explaining an appearance state of binarized data to be held in buffers B and C.

FIG. 9 is a diagram showing a case where high-level binarized data is in contact with only one side of a determination area.

[Explanation of symbols]

2 Image processing circuit 5 character / photo / halftone judgment circuit 51 line memory HE, IE judgment area TE attention area RE outer frame area

Front page continuation (72) Inventor Haruo Yamamoto 1-2-2 Tamatsukuri, Chuo-ku, Osaka City, Osaka Prefecture Mita Industry Co., Ltd. (56) Reference JP-A-3-276966 (JP, A) JP-A-2- 186876 (JP, A) JP 4-207575 (JP, A) JP 6-30266 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/40-1 / 409 H04N 1/46 H04N 1/60

Claims (3)

(57) [Claims] 1. A conversion unit for reading an original image, converting it into image data corresponding to its density, and outputting it, and a holding unit for holding image data corresponding to a plurality of lines of the image data output from this conversion unit. In the two-dimensional determination area composed of a predetermined number of pixels among the pixels corresponding to the image data held in the holding means, the isolated area whose density is relatively darker or lighter than the surrounding density there comprises an isolated area determining means for determining whether or not present, the isolated area discriminating means, in the determination region, including the boundary pixels of the determination region
The average value of the densities of the pixels that make up the region of interest
The uniform density value calculation unit and the maximum density value of the areas other than the attention area of the determination area or
Is the recognition unit that recognizes the minimum value and the average density value obtained by the average density value calculation unit
Whether it is larger than the maximum density value recognized by the intelligence department,
Is the average density value obtained by the average density value calculation unit
Determine whether it is smaller than the minimum density value recognized by the recognition unit
And a discriminating unit that separates the average density value and the maximum density value.
Greater than or the above average density value is the above minimum density value
If it is determined that it is smaller than
The image is characterized by determining that there is an area , and when the isolated area determination means determines that an isolated area exists, the determination area is determined to be a halftone dot area. Forming equipment. 2. An image corresponding to the density of an original image read.
A conversion unit that converts the image data to output the image data, and a plurality of lines of the image data output from the conversion unit.
Holding means for holding the image data corresponding to the down, image corresponding to the image data held in the holding means
Within a two-dimensional judgment area composed of a predetermined number of pixels
, The density is relatively higher than the surrounding density.
Area that determines whether or not a thin or thin isolated area exists
And a discriminating means, wherein the isolated area discriminating means performs binarization processing on the image data corresponding to pixels forming the discrimination area in the discrimination area to generate binarized data. Section and binarization data generated by the binarization processing section, in the determination region, binarize in the order of low level, high level and low level, or in the order of high level, low level and high level. A discriminating unit that discriminates whether or not the data has changed for each line and for each pixel column in the direction orthogonal to the line, and in the discriminating unit, a low level, a high level, and a low level in this order, or a high level. When it is identified that the binarized data changes in the order of level, low level, and high level, the binarization of the high level or low level of the above intermediate rank is performed. A holding portion for holding the over data for each pixel, and a logical product unit for obtaining the logical product of the binary data held by the holding portion for each pixel, logical product obtained in this logical product unit As a result, if there is a high-level or low-level pixel, it is determined that there is an isolated region in the determination region.
If there is an isolated area in this isolated area discrimination means,
When it is determined, the determination area is determined to be a halftone dot area.
Images forming device you; and a that judging means. If the decision regions in the method according to claim 3 wherein said determining means is determined to be a halftone dot region, according to claim 1 or characterized in that it further comprises a smoothing means for applying smoothing processing to the determination region Is an image forming apparatus described in 2 .