JP4464261B2 - Image processing apparatus, image processing method, and program - Google Patents

Description

The present invention relates to an image processing apparatus , an image processing method, and a program , and more particularly, to an image processing apparatus , an image processing method, and a program for performing image processing based on a result of separation of an input image signal.

  2. Description of the Related Art Conventionally, there is known a digital color copying machine that reads a document with a scanner unit, performs various image processing on the obtained image data, and outputs the image data with a printer unit. When copying a document in which characters and halftone images are mixed, this copying machine performs various processing on the image data input from the scanner unit, for example, a filter that sharpens the image data in order to output the character portion sharply. Process. However, when this filter processing is applied to the halftone image portion, moire fringes are generated.

  Therefore, many color copiers are configured such that a character area and a halftone dot area are separated into image areas in units of pixels, and a filter process corresponding to a document image can be selected (see, for example, Patent Document 1).

  FIG. 9 is a diagram schematically illustrating a configuration of an image area separation unit of a conventional image forming apparatus.

  In FIG. 9, the image area separation unit of the conventional image forming apparatus receives the image signal 1 and has spatial filters 901, 902, and 903 having different characteristics, and a character determination unit 904 connected to the spatial filter 901. A halftone dot determination unit 905 connected to the spatial filter 902, a halftone dot character determination unit 906 connected to the spatial filter 903, a character determination unit 904, a halftone dot determination unit 905, and a halftone dot character determination unit 906. And a look-up table unit 907 connected to each.

  The spatial filter 901 emphasizes a desired spatial frequency component to perform character determination, and outputs the edge-enhanced image signal 2 to the character determination unit 904. The character determination unit 904 performs character determination processing on the image signal 2 and outputs the character determination signal 5 to the lookup table 907.

  The spatial filter 902 emphasizes a desired spatial frequency component in order to perform halftone dot determination, and outputs the edge-enhanced image signal 3 to the halftone dot determination unit 905. A halftone dot determination unit 905 performs a halftone dot determination process on the image signal 3 and outputs a halftone dot determination signal 6 to the lookup table 907.

  Similarly, the spatial filter 903 emphasizes a desired spatial frequency component in order to perform halftone dot character determination, and outputs the edge-enhanced image signal 4 to the halftone character determination unit 906. A halftone dot character determination unit 906 performs a halftone dot character determination process on the image signal 4 and outputs a halftone dot character determination signal 7 to the lookup table 907.

  The lookup table 907 converts each output signal from the character determination unit 904, the halftone dot determination unit 905, and the halftone dot character determination unit 906 using the lookup table, and outputs the converted image area determination signal 8 To do. This image area determination signal 8 has the same resolution as the input image signal 1.

In recent years, the demand for increasing the resolution of the printer engine is particularly high for the above-mentioned copying machines in order to improve the image quality. The higher the image quality of the copying machine, the higher the resolution of the scanner and the resolution of the scanner. This is done by increasing the resolution of the printer.
JP-A-8-65514

  However, in such a case, particularly when the image signal 1 of the high-resolution image from the scanner or the image whose resolution has been converted to high resolution is input to the spatial filters 901, 902, and 903 by the image area separation unit, Regarding the determination unit 905, since a halftone dot having a certain size is a target, a dedicated determination circuit corresponding to the resolution of the input image signal 1 is necessary, and the versatility is poor, resulting in an increase in development cost. .

An object of the present invention is to provide an image processing apparatus , an image processing method, and a program capable of improving the versatility of a halftone dot determination unit when increasing the resolution of an image signal.

In order to achieve the above object, an image processing apparatus according to the present invention uses one pixel of an input image as a first pixel of interest, and adds a predetermined number of pixels included in a first region of interest including the first pixel of interest. The calculation unit that divides the plurality of first calculation pixel groups and calculates a first partial calculation value for each of the first calculation pixel groups , and the first calculation unit based on the plurality of first partial calculation values calculated by the calculation unit. has a determining halftone determining section 1 pixel of interest or the pixel der Luke not constituting a dot, and the calculation means, among the pixels of the input image, pixels other than the first target pixel of if one is defined as a second target pixel, and sets the second target region including the second target pixel in the same size as the first region of interest, the first pixel included in the second region of interest calculating a second partial calculating values related to the second calculation pixel group which are not included in the target region The halftone determining means, based on a first portion calculating value calculated from the first calculation pixel group included in the first region of interest in the pixel of the second portion calculated value and the second target region, wherein It is characterized by determining whether the 2nd attention pixel is a pixel which comprises a halftone dot.

In order to achieve the above object, according to an image processing method of the present invention, one pixel of an input image is used as a first pixel of interest, and pixels included in a first region of interest including the first pixel of interest are provided every predetermined number. A first calculation step of dividing the plurality of first calculation pixel groups and calculating a first partial calculation value for each of the first calculation pixel groups , and a plurality of first partial calculation values calculated in the first calculation step. a first dot determination step of determining whether the pixel der Luke not the first target pixel constitutes a halftone dot based, among the pixels of the input image, one of the pixels other than the first target pixel Is set as the second target pixel, the second target region including the second target pixel is set in the same size as the first target region, and the pixel included in the second target region is set as the first target region. second calculation for calculating a second partial calculating values related to the second calculation pixel group not included And degree, based on a first portion calculating value calculated from the first calculation pixel group included in the first region of interest in the pixel of the second portion calculated value and the second region of interest, the second target pixel And a second halftone dot determining step for determining whether or not the pixel constitutes a halftone dot.

In order to achieve the above object, a program of the present invention causes a computer to set one pixel of an input image as a first pixel of interest, and add a predetermined number of pixels included in the first region of interest including the first pixel of interest. Divided into a plurality of first calculation pixel groups and calculating a first partial calculation value for each of the first calculation pixel groups, and a plurality of first partial calculation values calculated in the first calculation step A first halftone dot determining step for determining whether or not the first target pixel is a pixel constituting a halftone dot, and one of the pixels of the input image other than the first target pixel. Is set as the second target pixel, the second target region including the second target pixel is set in the same size as the first target region, and the pixel included in the second target region is set as the first target region. Calculate the second partial calculated value for the second calculated pixel group not included On the basis of the second calculation step, the second partial calculation value and the first partial calculation value calculated from the first calculation pixel group included in the first target region with the pixels of the second target region. And a second halftone dot determining step for determining whether or not the two target pixel is a pixel constituting a halftone dot .

According to this image processing apparatus or the like, it is configured to perform determination using a predetermined halftone dot determination pattern for a pixel signal that has been subjected to thinning processing based on the resolution of the input image signal with respect to the coordinate position of the target pixel . In this case, the versatility of the halftone dot determination unit can be improved when the resolution of the image signal is increased.

Further, according to this image processing apparatus or the like , determination is performed using a predetermined halftone dot determination pattern for each pixel signal binarized with respect to the pixel of interest, and then binarization is performed with respect to a pixel adjacent to the pixel of interest. In the case where the determination is performed on each pixel signal using a predetermined halftone dot determination pattern, the versatility of the halftone dot determination unit can be improved when the resolution of the image signal is increased.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically showing a configuration of a halftone dot determination unit of an image processing apparatus according to an embodiment of the present invention.

  The halftone dot determination unit in FIG. 1 includes a spatial filter 101 to which an image signal is input, a memory controller 102 connected to the spatial filter 101, and a halftone dot determination unit 104 described later with reference to FIG. 2 connected to the memory controller 102. And a memory 103 that is connected to the memory controller 102 and temporarily stores an image processing signal.

  The spatial filter 101 binarizes the image signal to perform halftone dot determination, converts the image signal into a 1-bit signal, enhances and extracts a desired frequency component, and outputs an edge-enhanced image signal.

  The memory controller 102 temporarily stores the edge-enhanced image signal in the memory 103, selects the image signal of the peripheral pixel based on the two-dimensional coordinate position of the target pixel, reads out the image signal from the memory 103, and reads the network signal. Output to the point determination unit 104. Since the memory 103 stores as a line memory, when the image signal has a double resolution, the memory 103 requires twice the memory capacity, and all subsequent memories also require a double memory capacity.

  As will be described in detail with reference to FIG. 2, the halftone dot determination unit 104 outputs a halftone dot determination signal as an output. The halftone dot determination process treats each pixel as a pixel of interest at any resolution, and the output halftone dot determination signal has the same resolution as the input image signal.

  FIG. 2 is a diagram schematically showing the configuration of the halftone dot determination unit 104 in FIG.

  In FIG. 2, the halftone dot determination unit 104 includes a thinning processing unit 201 to which an image signal is input, a low-line halftone dot determination unit 202 connected to the thinning processing unit 201, and a high line connected to the thinning processing unit 201. A line halftone dot determination unit 203; and a memory 204 that is connected to a set of the low line halftone dot determination unit 202 and the high line halftone dot determination unit 203 and temporarily stores an image signal used for halftone dot determination. Prepare.

  The thinning-out processing unit 201 determines the area of the halftone dot determination pattern and the determination when an image signal having a normal integer multiple of resolution is input to the halftone dot determination processing in which the halftone dot determination unit 104 functions at a normal resolution. The determination is made by changing only the position without changing the reference so that halftone dot determination processing can be performed on an image having a plurality of resolutions by one algorithm and determination circuit.

  For example, FIG. 3 shows an image signal that is subjected to thinning processing when the image signal has twice the normal resolution, and FIG. 4 shows an image signal after thinning processing when the target pixel is “126”.

  In FIG. 3, the signal of the pixel of interest and the signal around the pixel of interest in the main scanning direction are represented as 1, such as “4”, “6”, “8”, “10”, “12”. Select every other and read. Also in the sub-scanning direction, the signal of the pixel of interest and the signal around the pixel of interest are represented as 1,..., “82”, “122”, “162”, “202”, “242”. Read every other. Next, when the target pixel moves by one pixel in the main scanning direction or the sub-scanning direction, the signal of the target pixel and every other signal around the target pixel are similarly read out. For example, when the pixel of interest moves from the main scanning direction “126” to “127”, with respect to the main scanning direction,..., “5”, “7”, “9”, “11”, “13”. Read every other. Further, when the target pixel moves from “126” to “146” in the sub-scanning direction, “92”, “132”, “172”, “212”, “252”,. Read every other. In this way, the thinning processing unit 201 selects every other pixel having a resolution twice that of the normal pixel as the target pixel, and selects every other image signal of the surrounding pixels and sends it to the halftone determination unit 105. Although the halftone dot determination unit 104 is a normal resolution determination circuit, it can refer to a wide range with respect to an image having twice the normal resolution.

  The low-line halftone dot determination unit 202 performs low-line halftone dot determination on the image signal thinned out by the thinning-out processing unit 201 using, for example, the determination pattern of FIG. For example, by using an image signal that has been subjected to the thinning process of 1200 dpi as a determination pattern as shown in FIG. 6, the halftone dot determination pattern used in an image having a normal resolution can be used for an image having a double resolution.

  Here, one determination pattern is composed of an inner region and an outer region. If the total number of black pixels inside the extracted image signal is more than a certain amount than that in the outer region, a black dot is present on the white background. If the total number of black pixels in the isolated and outer area is more than a certain amount than that in the inner area, it is determined that the white point is isolated on the black background.

  If either one of the two isolated amount determinations is satisfied, it is determined that it is “isolated”, that is, “halftone dot”, and “1” is output as a determination signal. Is output.

  In addition, a plurality of determination patterns are prepared for a low number of halftone dots. By these pattern matching, a low line number halftone dot determination signal is output.

  The high-line halftone dot determination unit 203 performs high-line halftone dot determination on the image signal thinned out by the thinning-out processing unit 201 using, for example, the determination pattern of FIG. The isolation amount determination similar to that of the unit 202 is performed. A plurality of determination patterns are also prepared for a high number of halftone dots. By these pattern matching, a high dot number halftone dot determination signal is output.

When the low line determination unit 202 and the high line determination unit 203 perform halftone dot determination, the memory 204 temporarily stores the result of the determination once for use again. The function of the memory 204 will be described with reference to FIG. 7, for example. When the target pixel is f, the determination pattern is image signals a to k, and assuming that halftone dot determination is performed with the total, the sum of b, f, and j is first given. Is stored in the memory 20 4 (1), and similarly, the sum of c, g, and k is stored in the memory 20 4 (2). Next, when the target pixel moves from f to g by one pixel in the main scanning direction, halftone dot determination is performed using the contents of the stored memory 20 4 (1) and memory 20 4 (2). Of course, even when a different pattern is used, the determination result can be used in the same manner.

  In this way, by selecting the target pixel and its surrounding pixels according to the resolution of the input image and performing halftone dot determination, even if the input image has a resolution n times that of the normal image, a normal circuit with a small circuit scale The resolution halftone dot determination unit is used for general purposes by changing only the position without changing the area of the halftone dot determination pattern and the determination reference, and sequentially outputs image signals of n times resolution for output. The halftone dot determination can be performed without reducing the resolution of the halftone dot determination signal.

  In the above description, an example is described in which halftone dot determination is performed using a normal resolution halftone determination circuit when the input image has a normal resolution and a double resolution. If the edge extraction signal is selected in the direction of decreasing the resolution, such as from the quadruple resolution to the normal resolution, halftone dot determination can be performed in the same manner.

  FIG. 8 is a diagram schematically showing a configuration of a modified example of the halftone dot determination unit of FIG.

  The halftone dot determination unit of FIG. 8 includes the halftone dot determination unit of FIG. 2, and the same components as those of the halftone dot determination unit of FIG.

  In addition to the halftone dot determination unit of FIG. 2, the halftone dot determination unit of FIG. 8 further receives an image signal directly, and has a low-line halftone dot determination unit 402 similar to the low-line halftone dot determination unit 202. An image signal is directly input and connected to a set of a high-line halftone dot determination unit 403 similar to the high-line halftone dot determination unit 203, a low-line halftone dot determination unit 402, and a high-line halftone dot determination unit 403. And a memory 404 for temporarily storing an image signal used for halftone dot determination.

  The low line halftone dot determination unit 201 outputs a halftone dot determination signal A, the high line halftone dot determination unit 202 outputs a halftone dot determination signal B, and the low line halftone dot determination unit 402 outputs a halftone dot. The determination signal C is output, and the high-line halftone dot determination unit 403 outputs a halftone dot determination signal D.

  In this modification, a halftone dot determination method that does not perform thinning processing is added to the halftone dot determination method that performs thinning processing in the above embodiment. As a result, in the above embodiment, the two types of determinations, the high line halftone signal and the low line halftone signal, are the halftone determination signal A, the halftone determination signal B, and the halftone determination signal C. And halftone dot determination signal D can be determined, and finer classification can be performed.

  The low-line halftone dot determination unit 402 has the same configuration as that of the low-line halftone dot determination unit 202, and by performing no thinning process on the image signal, for example, in the above embodiment, the high-line halftone dot There are only two types of determination results with the number of lines of 150 to 200 in the determination signal and the number of lines of 80 to 150 with the low-line halftone dot determination signal, but in this modification, the number of lines of 300 to 400 and 160 to A determination with a doubled number of lines such as 300 is possible, and four types of determination results can be obtained. Although an example in which the number of lines in a wide area can be determined is used, of course, for example, each halftone dot determination signal is obtained by changing parameters so that the number of lines in the range of 80 to 400 is determined in the range of 80 to 200, for example. You can narrow the range of the number of lines that have.

  Another object of the present invention is to supply a storage medium (or recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or apparatus, and to perform computer (or CPU or MPU) of the system or apparatus. Needless to say, this is also achieved by reading and executing the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

  The above-described program only needs to be able to realize the functions of the above-described embodiments by a computer, and the form includes forms such as object code, a program executed by an interpreter, and script data supplied to the OS. But you can.

  As a recording medium for supplying the program, for example, RAM, NV-RAM, floppy (registered trademark) disk, optical disk, magneto-optical disk, CD-ROM, MO, CD-R, CD-RW, DVD (DVD-ROM, DVD-RAM, DVD-RW, DVD + RW), magnetic tape, non-volatile memory card, other ROM, etc. may be used as long as they can store the above programs. Alternatively, the program is supplied by downloading from another computer or database (not shown) connected to the Internet, a commercial network, a local area network, or the like.

  Even if the present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), it is also applied to an apparatus (for example, a copying machine, a facsimile device, etc.) composed of a single device. can do.

It is a figure which shows roughly the structure of the halftone dot determination unit of the image processing apparatus which concerns on embodiment of this invention. It is a figure which shows roughly the structure of the halftone dot determination part in FIG. It is a figure of the image signal by which the thinning-out process part in FIG. 2 performs a thinning process, and shows the case where a resolution is 2 times normal. It is a figure of the image signal by which the thinning-out process part in FIG. 2 was performed, and the case where an attention pixel is "126" is shown. FIG. 3 is a diagram used for explaining a determination pattern of an image signal that has been subjected to thinning processing by the thinning processing unit in FIG. 2, in which FIG. The case of a line number determination pattern is shown. It is a figure of the image signal by which the thinning-out process part in FIG. 2 performed the 1200 dpi thinning-out process. It is a figure used for demonstrating the function of the memory in FIG. It is a figure which shows roughly the structure of the modification of the halftone dot determination unit of FIG. It is a figure which shows schematically the structure of the image area separation part of the conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Spatial filter 102 Memory controller 103 Memory 104 Halftone determination part 201 Thinning process part 202 Low line halftone dot determination part 203 High line halftone dot determination part 204 Memory 402 Low line halftone dot determination part 403 High line halftone dot determination Part 404 memory

Claims (6)

One of the pixels of the input image is set as a first target pixel, and a pixel included in the first target region including the first target pixel is divided into a plurality of first calculation pixel groups for each predetermined number, and the first calculation pixel Calculating means for calculating a first partial calculated value for each of the groups;
Anda dot determination unit that determines whether the pixel der Luke not the first target pixel constitutes a halftone dot based on the calculated plurality of first partial calculating value of said calculating means,
Said calculation means, among the pixels of the input image, when one of the pixels other than the first target pixel and the second target pixel, including the second target pixel in the same size as the first region of interest Setting a second region of interest , calculating a second partial calculated value for a second calculated pixel group that is included in the second region of interest and not included in the first region of interest ;
The halftone dot determining means is configured to determine the first partial calculated value calculated from the second partial calculated value and a first calculated pixel group included in the first focused region among the pixels of the second focused region . 2. An image processing apparatus for determining whether or not a pixel of interest is a pixel constituting a halftone dot.   The image processing apparatus according to claim 1, further comprising storage means for storing each of the first partial calculated values calculated by the calculating means. The second target pixel is an image processing apparatus according to claim 1 or 2, characterized in that a pixel adjacent to the first pixel of interest. 4. The image processing according to claim 1, wherein the first and second partial calculated values are total pixel values of pixels included in the first and second regions of interest. 5. apparatus. One of the pixels of the input image is set as a first target pixel, and a pixel included in the first target region including the first target pixel is divided into a plurality of first calculation pixel groups for each predetermined number, and the first calculation pixel A first calculation step of calculating a first partial calculated value for each of the groups;
A first dot determination step of determining whether the pixel der Luke not the first target pixel constitutes a halftone dot based on the plurality of first partial calculating value calculated by the first calculation step,
When one of the pixels of the input image other than the first pixel of interest is a second pixel of interest, a second region of interest including the second pixel of interest is the same size as the first region of interest. A second calculation step of setting and calculating a second partial calculation value related to a second calculation pixel group that is not included in the first target region with pixels included in the second target region;
Based on the second partial calculated value and the first partial calculated value calculated from the first calculated pixel group included in the first target region with the pixels of the second target region , the second target pixel has a halftone dot . A second halftone dot determining step for determining whether or not the pixel is a constituent pixel ;
An image processing method comprising: On the computer,
One of the pixels of the input image is set as a first target pixel, and a pixel included in the first target region including the first target pixel is divided into a plurality of first calculation pixel groups for each predetermined number, and the first calculation pixel A first calculation step of calculating a first partial calculated value for each of the groups;
A first halftone dot determination step for determining whether or not the first pixel of interest is a pixel constituting a halftone dot based on a plurality of first partial calculation values calculated in the first calculation step;
When one of the pixels of the input image other than the first pixel of interest is a second pixel of interest, a second region of interest including the second pixel of interest is the same size as the first region of interest. A second calculation step of setting and calculating a second partial calculation value related to a second calculation pixel group that is not included in the first target region with pixels included in the second target region;
Based on the second partial calculated value and the first partial calculated value calculated from the first calculated pixel group included in the first target region with the pixels of the second target region, the second target pixel has a halftone dot. And a second halftone dot determination step of determining whether or not the pixel is a constituent pixel .

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