JP2004274398A - Image processor, image forming device, image processing method, image processing program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide; an image processor capable of subjecting variably magnified image data after variable magnification processing, to proper image processing which doesn't bring about degradation of image quality and prevents the moire; an image forming device provided with the same; an image processing method; a program for causing the image processing method to be executed on a computer; and a recording medium having the program recorded therein. <P>SOLUTION: The image processor is provided with; a variable magnification part 1 for variably magnifying input image data in accordance with a set variable power rate; a document type automatic discrimination part 2 for calculating a frequency of image data subjected to variable magnification processing in the variable magnification part 1; and a control part 3 for switching filter processing to be applied to the image data after variable magnification, on the basis of the frequency calculation result obtained by the document type automatic discrimination part 2 and output characteristics of an image output device 103 for outputting image data. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is provided with an image processing apparatus that performs appropriate image processing on post-magnification image data that has been subjected to magnification processing based on a frequency (line number) discrimination result and output characteristics of an image output unit, and the image processing apparatus. The present invention relates to an image forming apparatus, an image processing method, a program for causing a computer to execute the image processing method, and a recording medium storing the program.
[0002]
[Prior art]
2. Description of the Related Art As an image forming apparatus such as a copying machine using an electrophotographic process or an ink jet method, a digital type is widely used in addition to a conventional analog type. With the progress of digital image processing technology, image forming apparatuses such as full-color digital copying machines and multifunction peripherals that reproduce color images with high image quality have been commercialized.
[0003]
While digitalization has made it possible to achieve higher image quality and higher functionality, digitalization has also caused problems. One of the problems is moire (interference fringes) generated by a halftone processing method when a printed photographic document (hereinafter, referred to as a halftone image) formed of halftone dots is read. Various countermeasures have been proposed for this moiré.
[0004]
In general, when reproducing and outputting a halftone image after performing scaling processing such as enlargement / reduction, the resolution of input / output devices such as a scanner, a printer, and a display, and the combination of the number of lines of the halftone image, a scaling ratio, etc. Moire occurs in the output image. The screen ruling of the halftone dot image refers to the frequency characteristic of the input image in a broad sense, and is represented by a portion having a periodic characteristic in an image subjected to error diffusion processing in addition to the halftone dot, or a line. This also applies to the image area.
[0005]
Filter processing is performed as means for suppressing the moiré. However, applying a smoothing filter uniformly to any of the combinations will inadvertently blur the entire image, resulting in considerable image quality degradation. Become. In such a case, it is possible to improve the image quality by performing an optimal filter process that does not cause image quality deterioration and prevents the occurrence of moiré in accordance with the number of lines (dot number) or the magnification of the halftone image. It is an important factor.
[0006]
As a specific countermeasure for suppressing moiré, for example, in Japanese Patent Application Laid-Open No. 61-80971 (Patent Document 1), a digital image signal is Fourier-transformed and compared with pattern data corresponding to the number of halftone dots. Thus, an image signal processing apparatus has been proposed which determines the halftone frequency of a document, selects a filter coefficient according to the halftone frequency, and performs a smoothing process.
[0007]
According to the invention described in the publication, an appropriate smoothing process according to the halftone frequency can be performed. However, according to the invention described in the above publication, 1) it is not possible to select an optimum filter corresponding to the scaling process. 2) It is necessary to change input / output characteristics such as input resolution, dither matrix size and output resolution. There is a problem that it cannot be handled.
[0008]
Also, for example, Japanese Patent No. 2680469 (Patent Document 2) includes a low-pass filter that limits a pass band of an image input from an input device, and a calculation unit that determines a cutoff frequency of the low-pass filter. There has been proposed an image reading apparatus that obtains the cutoff frequency as a value that suppresses moiré generated in an output image based on the resolution of an input device, the resolution of an output device, the size of a dither matrix, and the output magnification of an image.
[0009]
According to the invention described in the publication, when reducing or enlarging an image having a strong periodicity such as a halftone dot image, it is possible to suppress moire caused by changing an image output magnification or a dither matrix.
[0010]
[Patent Document 1]
JP-A-61-80971 (published on April 24, 1986)
[0011]
[Patent Document 2]
Japanese Patent No. 2680469 (published August 1, 1997)
[0012]
[Problems to be solved by the invention]
However, according to the invention described in the above-mentioned Japanese Patent No. 2680469, an appropriate image which can prevent the occurrence of moiré without deteriorating the image quality of the scaled image data subjected to the scaling process. There is a problem that processing cannot be performed.
[0013]
Specifically, 1) optimization of the filter coefficient according to the halftone frequency cannot be realized, and 2) since the scaling factor is regarded as the sampling period at the time of image input, it is not possible to cope with various scaling methods. 3) If the scaling method is different, the appearance of moiré in the output image is also different. Therefore, even if the scaling ratio is the same, it is not best to apply the same filter exactly because it is not the best. Image processing cannot be performed.
[0014]
Examples of commonly used scaling processing methods include, for example, a bicubic method, a bilinear method, and a nearest neighbor method. When the scaling method is different, the appearance of moiré in the output image is also different, so it is necessary to apply a filter according to the scaling method.
[0015]
The present invention has been made to solve the above-mentioned conventional problems. An object of the present invention is to provide an image processing apparatus capable of performing appropriate image processing on reduced-magnification image data that has been subjected to magnification processing without deteriorating image quality and preventing occurrence of moire. An object of the present invention is to provide an image forming apparatus including a processing device, an image processing method, a program for causing a computer to execute the image processing method, and a recording medium on which the program is recorded.
[0016]
[Means for Solving the Problems]
According to another aspect of the present invention, there is provided an image processing apparatus for processing input image data read by an image input unit, the image processing apparatus changing the input image data according to a set scaling factor. Multiplying means for multiplying, a frequency calculating means for calculating the frequency of the image data after scaling processed by the scaling means, a frequency calculation result calculated by the frequency calculating means, and outputting the image data And a control unit for switching a filtering process to be performed on the image data after scaling based on an output characteristic of the image output unit.
[0017]
According to the above configuration, when scaling processing is performed on a periodic image such as an area gradation image or a geometric image, the frequency of the scaled image data is calculated after the scaling processing, and the frequency is calculated. Based on the calculation result and the output characteristics of the image output means, the filter processing performed on the scaled image data is controlled. it can.
[0018]
For example, even when a halftone image is scaled (enlarged / reduced), an optimal filter process can be selected according to the number of lines (frequency) of halftone dots of the scaled image data. It is possible to obtain a high quality output image without any.
[0019]
Further, since the number of lines (frequency) is determined after the scaling process, the optimum filter coefficient can always be selected even for devices having different input resolutions and output resolutions. By discriminating the number of lines (frequency) after the scaling process, a table for the scaling ratio is not required, so that the number of filter coefficients set in advance can be reduced. Further, since the method does not depend on the method of the scaling process, even when the frequency characteristic of the halftone frequency of the image data after the scaling is changed by changing the method of the scaling process, occurrence of moire can be prevented.
[0020]
That is, it is possible to provide an image processing apparatus that can perform appropriate image processing on the scaled image data that has been subjected to the scaling processing without deteriorating the image quality and preventing the occurrence of moire.
[0021]
In the image processing apparatus of the present invention, in the above configuration, the control means selects an adaptive mixing filter when the frequency calculation result is larger than a predetermined threshold, and performs smoothing when the frequency calculation result is equal to or smaller than the threshold. It is more preferable to select an activation filter.
[0022]
According to the above configuration, when the number of lines is high, the high frequency component is smoothed, and the low frequency component is generated by the dot period by selecting an adaptive mixing filter having a frequency characteristic of sharpening. It is possible to keep the sharpness of the edge in the image while preventing moiré. Therefore, the entire image is not carelessly blurred and the image quality does not deteriorate.
[0023]
In addition, when the number of lines is low, by selecting a smoothing filter having a characteristic of performing smoothing over all frequency components, it is possible to prevent the moire of low frequency components generated by the halftone dot period, Since the noise of the high-frequency component existing in the image can be blurred, the output image quality can be improved.
[0024]
According to another aspect of the invention, an image forming apparatus includes the image processing apparatus according to any one of the aspects of the invention.
[0025]
According to the above configuration, even when an image having a periodicity such as a halftone image is subjected to scaling processing, optimal filtering is performed in accordance with the number of lines of the halftone dot (frequency of the scaled image data). Therefore, a high-quality output image without moire can be formed.
[0026]
In other words, it is possible to provide an image forming apparatus capable of performing appropriate image processing on the scaled image data that has been subjected to the scaling process without deteriorating the image quality and preventing the occurrence of moire.
[0027]
In order to solve the above-mentioned problem, an image processing method according to the present invention, in an image processing method for processing input image data read by an image input unit, converts the input image data in accordance with a set scaling factor. A magnification step of multiplying, a frequency calculation step of calculating a frequency of an image area having periodicity of the image data after the magnification processing that has been scaled by the magnification step, and a frequency calculation result calculated by the frequency calculation step And a filter processing selecting step of selecting a filter processing to be performed on the scaled image data based on output characteristics of an image output unit that outputs image data; and a filter processing determined by the filter processing selecting step. And an image processing step performed on the image data after scaling.
[0028]
According to the above-described method, when a periodic image such as an area gradation image or a geometric image is scaled, an optimal filter process that does not cause moire in an output image can be performed. For example, even when a halftone image is scaled (enlarged / reduced), an optimum filter process can be selected according to the number of lines (frequency) of the halftone dot, so that a high-quality output image without moire can be obtained. be able to.
[0029]
Further, the optimum filter coefficient can always be selected for devices having different input resolutions and output resolutions. By discriminating the number of lines (frequency) after the scaling process, a table for the scaling ratio is not required, so that the number of filter coefficients set in advance can be reduced. Further, since the method does not depend on the method of the scaling process, even if the method of the scaling process changes and the frequency characteristics change, it is possible to prevent the occurrence of moire.
[0030]
In other words, it is possible to provide an image processing method capable of performing appropriate image processing on the scaled image data that has been subjected to the scaling process without deteriorating the image quality and preventing the occurrence of moire.
[0031]
In the image processing method of the present invention, in the above method, the filter processing selecting step selects an adaptive mixing filter when the frequency calculation result is larger than a predetermined threshold, and when the frequency calculation result is equal to or smaller than the threshold, It is more preferable to select a smoothing filter.
[0032]
According to the above method, when the number of lines is high, the high frequency component is smoothed, and the low frequency component is generated by the dot period by selecting an adaptive mixing filter having a frequency characteristic of sharpening. It is possible to keep the sharpness of the edge in the image while preventing moiré. Therefore, the entire image is not carelessly blurred and the image quality does not deteriorate.
[0033]
In addition, when the number of lines is low, by selecting a smoothing filter having a characteristic of performing smoothing over all frequency components, it is possible to prevent the moire of low frequency components generated by the halftone dot period, Since the noise of the high-frequency component existing in the image can be blurred, the output image quality can be improved.
[0034]
In order to solve the above-mentioned problems, an image processing program according to the present invention causes a computer to function as each unit included in the image processing apparatus according to any one of the above-mentioned inventions.
[0035]
An image processing program according to the present invention causes a computer to execute the image processing method according to any one of the above-mentioned inventions in order to solve the above-mentioned problems.
[0036]
A recording medium according to the present invention is a computer-readable recording medium that stores a program for causing a computer to execute the image processing method according to the present invention in order to solve the above-described problems.
[0037]
Accordingly, the image processing method is implemented using the computer by installing the image processing program in a general computer via the recording medium or the network. In other words, the computer is connected to the image processing apparatus. Can function as
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to this.
[0039]
(A) Image processing device
As shown in FIG. 1, the image processing apparatus 101 according to the present invention applies a cycle of the input image data to a periodic image area of the input image data read by the image input A magnification unit (magnification means) 1 for judging the frequency of an image region having a characteristic and performing processing in accordance with the result of the judgment, in accordance with a set magnification ratio An automatic document type discriminating section (frequency calculating means) 2 for calculating the frequency of the image data after the scaling process performed by the scaling section 1; and a frequency calculation result calculated by the automatic document type discriminating section 2. And a control unit (control unit) 3 for switching a filtering process to be performed on the image data after scaling based on an output characteristic of an image output device (image output unit) 103 that outputs image data.
[0040]
Here, the image area having periodicity includes, in addition to the area gradation image area, for example, an image of a geometric pattern taken by a digital camera. The area gradation image region is, for example, a halftone dot image region composed of halftone dots, a line image region composed of regularly arranged parallel lines, or image data created by error diffusion. This is an image area for expressing a color including a halftone. The area gradation image region also includes an image region expressed by a halftone generation method such as a pixel distribution method / dither method and a density pattern method.
[0041]
FIG. 1 is a configuration diagram of an image processing apparatus 101 used in a digital color image forming apparatus 100 such as a digital copying machine or a multifunction peripheral according to an embodiment of the present invention. The image input device 102 is composed of a CCD (Charge Coupled Device) line sensor, and is a color image signal obtained by separating light reflected from a document into R, G, and B (R: red, G: green, B: blue). (Reflectance signal).
[0042]
A color image signal (RGB analog signal) input by the CCD line sensor of the image input device 102 is converted into an RGB digital signal by an A / D (analog / digital) converter 4. This RGB digital signal is a reflectance signal from which various distortions generated in the illumination system, the imaging system, and the imaging system of the image input device 102 have been removed by the shading correction unit 5.
[0043]
The input processing unit 6 converts the reflectance signal into a density signal suitable for image processing. That is, the input processing unit 6 converts the reflectance signal into a CMY (C: cyan, M: magenta, Y: yellow) signal that is a complementary color of the RGB signal.
[0044]
The magnification unit 1 performs magnification processing for enlarging or reducing an image (input image data) based on a signal input from an operation panel (operation means) 104 provided in the image forming apparatus 100.
[0045]
The document type automatic discrimination unit 2 determines whether or not the document (image data after scaling) subjected to the scaling process by the scaling unit 1 includes an area gradation image area. If the image data after scaling includes an area gradation image area, the number of lines (frequency) is calculated. Among the output signals from the document type automatic discrimination unit 2, the CMY signal is output to the area separation processing unit 7, and the information on the calculated number of lines (frequency) is output to the control unit 3.
[0046]
The document type automatic discrimination unit 2 determines whether the input document type is a text document, a text / print photo document, a text / print paper photo document, a print photo document, or a photographic paper photo document. May be provided.
[0047]
The calculation of the number of lines performed by the document type automatic discrimination unit 2 will be described in detail later in “(F) Document Type Automatic Discrimination Unit”.
[0048]
The control unit 3 determines a filtering process to be performed on the scaled image data based on the frequency calculation result calculated by the document type automatic determination unit 2 and the output characteristics of the image output device 103 that outputs the image data. I do. A filter coefficient, which is an output signal of the control unit 3, is output to the spatial filter unit 10.
[0049]
Next, in order to improve the reproducibility of black characters, color characters, and halftone dots in a document in which various types of regions such as characters, photographs, and halftone dots are mixed, the region separation processing unit 7 Is determined. The region separation processing unit 7 outputs a region identification signal as an output signal to each of the black generation / under color removal unit 9, the spatial filter unit 10, and the halftone generation unit 11, and each unit performs processing suitable for various regions. Is applied. Further, the area separation processing section 7 outputs a CMY signal to the color correction section 8 as another output signal.
[0050]
The color correction unit 8 performs a process for improving color reproducibility on the CMY signals. The color correction unit 8 outputs, to the black generation / under color removal unit 9, a CMY signal that has been subjected to processing for improving color reproducibility as an output signal.
[0051]
The black generation / under color removal unit 9 converts the CMY signal into a four-color signal obtained by adding black (K) to cyan, magenta, and yellow, that is, a CMYK signal. The black generation / under color removal unit 9 performs processing suitable for various regions such as characters, photographs, and halftone dots on the CMYK signals in accordance with the region identification signal from the region separation processing unit 7. The black generation / under color removal unit 9 outputs a CMYK signal to the spatial filter unit 10 as an output signal.
[0052]
The spatial filter unit 10 enhances the edge of the CMYK signal from the black generation / under color removal unit 9 based on the region identification signal from the region separation processing unit 7 and the filter coefficient output from the control unit 3. Perform processing and smoothing processing. The spatial filter unit 10 outputs a CMYK signal to the halftone generation unit 11 as an output signal.
[0053]
The halftone generation unit 11 performs a tone reproduction process for outputting an image (magnified image data) with respect to the CMYK signal from the spatial filter unit 10 in accordance with the region identification signal from the region separation processing unit 7. Perform The halftone generator 11 outputs a CMYK signal to the image output device 103 as an output signal.
[0054]
The image output device 103 forms an output image according to the CMYK signal from the halftone generation unit 11. As the image output device 103, for example, an image output device such as an electrophotographic or inkjet printer or an image display device such as a liquid crystal display may be used.
[0055]
When the image output device 103 is implemented by an image display device, the processes performed by the black generation / under color removal unit 9 and the halftone generation unit 11 are unnecessary, so that the processes in the region separation processing unit 7 may be omitted. . In this case, the color correction unit 8 converts the CMY signals into RGB signals for the image display device, and performs a γ correction process according to the γ characteristics of the image display device. The color correction unit 8 outputs the RGB signals to the spatial filter unit 10 as output signals. The spatial filter unit 10 performs the above-described edge enhancement processing and smoothing processing on the RGB signals. Next, the spatial filter unit 10 outputs the image output data to an image display device as the image output device 103.
[0056]
Each of the above-described processes performed in the image processing apparatus 101 is controlled by a CPU (Central Processing Unit) not shown.
[0057]
(B) Processing content
FIG. 2 shows a basic operation flowchart of the image processing apparatus 101 according to the present invention.
[0058]
The scaling unit 1 performs a scaling process on an input image (input image data) based on a signal input from the operation panel 104 (step 1, hereinafter step is abbreviated as S).
[0059]
The document type automatic discrimination unit 2 determines whether or not the scaled image data subjected to the scaling process in S1 includes an area gradation image area (S2). In S2, if it is determined that the full-scale image region is included, the process proceeds to S3, and if it is determined that the full-scale image region is not included, the process proceeds to S5. The document type automatic discrimination unit 2 automatically proceeds to S3 when the character / print photo mode or print photo mode is selected as the image mode on the operation panel 104.
[0060]
The document type automatic discrimination unit 2 calculates the number of lines (frequency) (S3). The control unit 3 selects an appropriate filter coefficient based on the number of lines of the document (image data after scaling) and output characteristics (the size of the dither matrix and the resolution of the image output device) (S4).
[0061]
In order to enhance the reproducibility of black characters, color characters, and halftone dots in a document mixed with various areas (characters, photographs, halftone dots, etc.), the area separation processing unit 7 determines which area each pixel belongs to. Is performed (S5). Based on the determination result in S5, the area identification signal is distributed as an output signal from the area separation processing section 7 to the black generation / under color removal section 9, the spatial filter section 10, and the halftone generation section 11. In each part, processing suitable for various regions is performed.
[0062]
The spatial filter unit 10 performs a process using the filter coefficient selected by the control unit 3 on the area gradation image area (S6).
[0063]
(C) Changes in frequency characteristics due to scaling processing
The change in the frequency characteristic due to the scaling process will be described below with reference to FIG. FIG. 3 is a graph showing a change in the peak position of the frequency characteristic when a scaling process is performed on a halftone image having a certain number of lines by the nearest neighbor method. The vertical axis indicates MTF (modulation transfer function), and the horizontal axis indicates frequency. The peak position of the frequency characteristic when the magnification is 100% indicates the state before the magnification processing, and the peak position of the frequency characteristic when the magnification is 200% and the magnification is 50% indicates the state after the magnification processing.
[0064]
According to FIG. 3, the peak position of the frequency characteristic at the magnification of 200% is shifted to the lower frequency side as compared with the peak position of the frequency characteristic at the magnification of 100%. Further, the peak position of the frequency characteristic at the magnification of 50% is shifted to a higher frequency side than the peak position of the frequency characteristic at the magnification of 100%.
[0065]
As described above, since the frequency characteristic of the halftone dot image changes according to the magnification, the occurrence of moiré in the output image also changes by performing the magnification process. Further, even if the scaling ratio is the same, if the method of the scaling process is different, the appearance of moire in the output image is different.
[0066]
Therefore, in order to suppress the occurrence of moiré, when the scaling process is performed, or when the scaling ratio is the same but the scaling process method is changed, the filtering is performed according to the change in the frequency characteristic of the halftone image. The coefficients need to be selected each time. Thereby, optimal filter processing according to the scaling processing is performed, and occurrence of moire can be suppressed.
[0067]
Here, an example in which the nearest neighbor method is used as the method of the scaling process has been described, but the scaling process performed in the scaling unit 3 of the image processing apparatus 101 according to the present invention is not limited to the nearest neighbor method. Instead, a commonly used scaling process such as a bicubic method or a bilinear method can be applied.
[0068]
The nearest neighbor method is a method of performing a process of thinning out the pixels of the input image every other pixel when the magnification is 50%, and performing a process of overlapping the pixels of the input image one by one at a magnification of 200%.
[0069]
(D) Difference in number of lines and frequency characteristics
The difference in the number of lines and the frequency characteristics will be described with reference to FIG. FIG. 4 is a graph showing frequency characteristics of a halftone image having eight different numbers of lines at a certain magnification, for example, 100%. The vertical axis indicates MTF, and the horizontal axis indicates frequency. According to FIG. 4, the peak position of the frequency characteristic regarding the halftone dot image having eight types of lines differs for each line number.
[0070]
Thus, the difference in the number of lines of the halftone image appears as a difference in the peak position in the frequency characteristic. Therefore, by selecting a filter coefficient according to the peak position of the frequency characteristic, it is possible to perform an optimal filter process according to the halftone frequency of the image data after scaling.
[0071]
(E) Filter setting
A filter coefficient and a filter coefficient table of the control unit 3 of the image processing apparatus 101 according to the present invention will be described below with reference to FIGS.
[0072]
As described above, if the frequency characteristics in the image after the scaling process for the input image are obtained and the control is performed so as to select the filter coefficient according to the peak frequency, the scaling ratio, the scaling method, and the number of halftone dots are obtained. Optimal filter processing according to (frequency of the input image) can be performed.
[0073]
The control unit 3 has a filter coefficient table corresponding to various output characteristics in order to perform optimal filtering even when output characteristics such as the size and resolution of the dither matrix of the image output device 103 change. Is preferred.
[0074]
The control unit 3 determines a filter coefficient table for the peak frequency of the input image after the scaling process and the output characteristic of the image output device 103, that is, the number of halftone dots after the scaling process, It is more preferable to have a filter coefficient table for the resolution and the size of the dither matrix. FIG. 5 is a diagram schematically showing the configuration of the filter coefficient table.
[0075]
The number of lines corresponding to the peak frequencies Fa to Fh after the scaling process in FIG. 5, that is, 65 lines / inch ("lines / inch" is abbreviated as "lines" in the drawings and hereinafter), and 85 lines. , 100 lines, 120 lines, 133 lines, 150 lines, 175 lines, and 200 lines indicate the number of lines at an input resolution of 600 × 600 dpi (dot per inch) and a magnification of 100%. For example, when the input resolution is 300 × 300 dpi, the cycle viewed in pixel units becomes shorter, and the peak frequency appears on the higher frequency side even with the same number of lines. This will be described with reference to FIG.
[0076]
FIG. 6 is a diagram schematically showing an enlarged state of a pixel when a line pattern of 120 lines is read at input resolutions of 600 × 600 dpi and 300 × 300 dpi. Black dots represent the black density portion of the line, and white dots represent the white density portion between the lines in pixel units. When a line pattern of 120 lines is read at 600 × 600 dpi, black pixels appear every 4 to 5 pixels, whereas when read at 300 × 300 dpi, black pixels appear almost every 3 pixels.
[0077]
That is, when viewed in pixel units, the latter has a shorter cycle than the former, and the peak frequency shifts to the higher frequency side. That is, even if the number of lines is the same, the position of the peak changes when the input resolution is different. Therefore, the peak positions Fa to Fh shown in FIG. Absent.
[0078]
The control unit 3 of the image processing apparatus 101 stores a filter coefficient table as shown in FIG. The control unit 3 reads out a filter coefficient corresponding to a frame referred to by a line frequency (frequency) calculation result, which is an output signal of the document type automatic discrimination unit 2, and an output characteristic of the image output device 103, and outputs a spatial filter unit 10. Is controlled by a CPU (not shown).
[0079]
In the graph shown in FIG. 4, when the peak position of the frequency characteristic of the image data is in the range of Fa, the filter coefficient is selected from the table a in FIG. , Filter coefficient A is selected. Since the peak position of the frequency characteristic appears differently depending on the input resolution as described above, the scaled image data after the scaling processing includes information on the input resolution of the image input device 102.
[0080]
As shown in FIG. 5, when the resolution of the image output device 103 is represented by “OutN” and the size of the dither matrix is represented by “Dsize”, the output characteristics of the image output device 103 can be represented by “OutN / Dsize”. . The output image is represented as a dither matrix pattern (period). Therefore, the output characteristic “OutN / Dsize” indicates the substantial resolution of the output image.
[0081]
The filter coefficient table shown in FIG. 5 includes 65 lines (Fa), 85 lines (Fb), 100 lines (Fc), 120 lines (Fd), 133 lines (Fe), 150 lines (Ff), and 175 lines (Fg). ) And 200 lines (Fh) for eight types of line numbers, and corresponding filter coefficient tables a to h are stored, and filter coefficients A to E are set in each of the filter coefficient tables a to h. This is a diagram schematically showing the state in which it is performed.
[0082]
As the filter coefficients A to E, for example, filter coefficients of 7 × 7 pixel size shown in FIGS. 7A to 7C and FIGS. 8A and 8B are used. Note that the size of the filter coefficient is not limited to 7 × 7. FIGS. 7 (d) to 7 (f) and FIGS. 8 (c) and 8 (d) show graphs representing the frequency characteristics of the respective filter coefficients. The vertical axis is MTF, and the horizontal axis is frequency. is there.
[0083]
The filter coefficients A to E are set to an optimum value set in advance by actually outputting various images by several kinds of general image output devices having various output characteristics and confirming the degree of moiré and the degree of image blurring. Value. It is preferable that the filter coefficients A to E are set to have such a characteristic that the MTF of the frequency is reduced in order to remove the moire generated at the peak frequency of the image data after scaling.
[0084]
As a method of obtaining the optimum value of the filter coefficient, for example, an output image is created while empirically changing the filter coefficient based on the analysis of the frequency characteristics of the input image in the image forming apparatus, and the optimum image quality is obtained. It is possible to use a method of determining the optimum value of the filter coefficient by trying several patterns of the operation of visually confirming whether the filter coefficient has been set.
[0085]
Note that these filter coefficients A to E are designed so as to prevent moiré even when the nearest neighbor method, which is liable to generate moiré, is used as a method of scaling processing. As described above, if the filter coefficient is set in consideration of the scaling method and the peak frequency at which moiré occurs, the optimum output image quality free from moiré even when the scaling method is changed. Can be realized.
[0086]
The control unit 3 compares the frequency calculation result with a predetermined threshold, selects an adaptive mixing filter if the frequency calculation result is larger than the threshold, and smoothes if the frequency calculation result is equal to or less than the threshold. It is more preferable to select an activation filter.
[0087]
FIGS. 7A to 7C show filter coefficients A to C as setting examples of a smoothing filter to be applied to a halftone image having a low screen ruling (low frequency). FIGS. 8A and 8B show filter coefficients D and E as setting examples of an adaptive mixing filter to be applied to an image.
[0088]
The degree of smoothing is set so that filter coefficient A> filter coefficient B> filter coefficient C, and the degree of sharpening is set so that filter coefficient D <filter coefficient E.
[0089]
In the present embodiment, each filter coefficient is set as described above, but the present invention is not limited to this, and the coefficient is mainly determined according to which frequency range the MTF is to be reduced. A to E may be changed. Therefore, for example, the degree of sharpening of the coefficients D and E in the low-frequency range may be reversed.
[0090]
In the filter coefficient table of FIG. 5, when the input resolution is 600 × 600 dpi, the magnification is 100%, and the output characteristic is characteristic A, the peak frequency position is equal to or less than Ff, that is, the line number of the halftone dot is equal to or less than 150 lines. The number of lines is determined to be higher than Fg, ie, 175 lines or higher. When the input resolution is 600 × 600 dpi, the magnification is 100%, and the output characteristic is the characteristic B, the peak frequency position is equal to or less than Fc, that is, the number of halftone dots is equal to or less than 100 lines, and the low number of lines is used. The above is determined as a high screen ruling.
[0091]
The thresholds for determining the number of low lines and the number of high lines are determined by outputting various images by several types of general image output devices having various output characteristics and forming the images in accordance with the output characteristics. Is a value set in advance based on the quality of the image. This threshold value may be set together with the above-described optimum value of the filter coefficient.
[0092]
The threshold value may be set while confirming the image quality visually output by an adjustment operation using an actual image forming apparatus. That is, for example, using many images, a combination as shown in FIG. 5 is created, and it is determined in advance which line number is appropriate to be considered as a high line number according to the quality of the output image, The corresponding number of lines may be set as the threshold.
[0093]
In the case of a halftone dot image with a low screen ruling, by applying a smoothing filter which is a filter having a characteristic of smoothing over all frequency components, it is possible to prevent the moire of low frequency components generated by the halftone dot period, and Since the noise of the high-frequency component existing therein can also be blurred, the output image quality can be improved.
[0094]
In the case of a halftone dot image with a high screen ruling, by applying an adaptive mixing filter having a frequency characteristic of smoothing high frequency components and sharpening low frequency components, moire of high frequency components generated by the dot period is reduced. This prevents the sharpness of the edge of the low-frequency component existing in the image. Therefore, a good output image quality can be realized without causing image quality deterioration such as inadvertently blurring the entire image.
[0095]
As described above, by selecting a filter based on the frequency characteristics of the scaled image data after the scaling process and the output characteristics of the image output device 103, a halftone dot image with various numbers of lines (a periodic image) ), The magnification of the scaling process, and the optimum filter process corresponding to the input / output resolution.
[0096]
(F) Document type automatic discrimination unit
The document type automatic discrimination unit 2 of the image processing apparatus 101 according to the present invention will be described in more detail with reference to FIG.
[0097]
The document type automatic discrimination unit 2 includes an area gradation judgment unit 13 and a line number calculation unit 19. The area gradation determining section 13 determines whether or not the scaled image data indicated by C, M, and Y in the drawing includes an area gradation image area. The number of lines (frequency) in the image area is calculated.
[0098]
The area gradation determining unit 13 includes an area gradation area determining unit 14, an area gradation area pixel counter 15, a total pixel number counter 16, a divider 17, and a determining unit 18. The area gradation determining unit 13 determines whether or not the scaled image data indicated by C, M, and Y in the drawing includes an area gradation image area such as a halftone dot area, an area subjected to error diffusion processing, and a line. The determination as to whether or not to do so is made, for example, as in the following (1) to (6). First, (1) to (3) are performed by the area gradation region determination unit 14.
[0099]
(1) The pixels in the mask of m × n (for example, 50 × 50 pixels) including the target pixel are extracted, and the pixels in the mask are binarized using a value such as an average value calculated from each pixel value as a threshold value. .
[0100]
(2) From the binarized image, the number of inversions, that is, the number of transition points from “0” to “1” and “1” to “0” is calculated in the main scanning direction and the sub-scanning direction.
[0101]
(3) The maximum value of the calculated number of inversions is selected. If the maximum value is larger than a predetermined threshold value, it is determined that the target pixel is an area gradation image area pixel. It is determined that the pixel is an area gradation image area pixel.
[0102]
(4) The area gradation area pixel counter 15 counts pixels in the area gradation area in the image data after scaling.
[0103]
(5) The divider 17 divides the count value of the pixels in the area gradation area by the total number of pixels obtained by the total pixel number counter 16.
[0104]
(6) The determination unit 18 compares the result of the division in the above (5) with a predetermined threshold. If the result is larger than the threshold, it is determined that the area gradation image area is included, and the determination is equal to or less than the threshold. If so, it is determined that the area gradation area is not included.
[0105]
The number-of-lines calculating unit 19 calculates the number of lines (frequency) when the area gradation determining unit 13 determines that the area gradation image region is included. If it is determined that the area gradation image area is not included, the processing is through (does nothing).
[0106]
A method of calculating the number of lines (frequency) of a halftone dot in the number of lines calculation unit 19 will be described below. The calculation of the number of lines in the number-of-lines calculating unit 19 only needs to be able to calculate the number of halftone dots of the area gradation image area, and may be performed using a conventionally known method of calculating the number of lines. For example, a method for determining the number of lines disclosed in JP-A-11-155067 may be used.
[0107]
In the frequency characteristics of the image, the halftone dot components are distributed with the peak of the signal intensity in the high frequency region. The angular direction in which the signal intensity distribution of each plate of CMY is located corresponds to the halftone dot angle of each plate, and the diameter of the position where the peak indicating the maximum value of the signal intensity occurs corresponds to the number of printing lines of each plate. . Here, any of the C, M, and Y scaled image data is subjected to a two-dimensional Fourier transform to extract a frequency characteristic distribution, which is converted into a signal intensity distribution expressed in polar coordinates. The signal intensity is calculated for each diameter, and the halftone frequency (frequency) is estimated from the maximum diameter.
[0108]
The image forming apparatus 100 according to the present invention may include the above-described image processing apparatus 101, and may further include another configuration.
[0109]
(G) Image processing method
An image processing method according to the present invention will be described below with reference to FIG. The image processing method according to the present invention determines the frequency of the periodic image area of the input image data for the periodic image area of the input image data read by the image input unit, and determines the determination result. In the image processing method for performing the processing according to the above, a scaling step (Step 11, hereinafter step is abbreviated as S) for scaling the input image data according to the set scaling ratio, and the scaling step (S11) Frequency calculating step (S12) for calculating the frequency of an image area having periodicity of the scaled image data subjected to the scaling processing according to (1), the frequency calculation result calculated in the frequency calculating step (S12), and the image data A filter process selecting step (S13) for selecting a filter process to be applied to the scaled image data based on an output characteristic of an image output unit that outputs the image data; Having an image processing step of performing filtering processing determined by-option step (S13) with respect to the scaled image data (S14), the. It should be noted that the image processing method according to the present invention is not limited to this, and may include other steps.
[0110]
The scaling step of S11 is a step of performing scaling processing for enlarging or reducing the input image data according to the set scaling factor. In the scaling process in the scaling step (S11), it is sufficient that the input image data can be enlarged or reduced in accordance with the set scaling ratio, and a conventionally known scaling method generally used can be used. For example, a bicubic method, a bilinear method, or a nearest neighbor method may be applied as the scaling processing method.
[0111]
The frequency calculating step of S12 is a step of calculating the frequency of a periodic image area of the scaled image data subjected to the scaling process. The frequency calculation step of S12 only needs to be able to calculate the frequency of the periodic image area of the scaled image data, and may be performed using a conventionally known method. The calculation of the frequency of the image area having periodicity of the image data after scaling may be performed by using, for example, a line number determination method disclosed in Japanese Patent Application Laid-Open No. H11-155067.
[0112]
The filtering process selecting step of S13 is based on the frequency calculation result calculated in the frequency calculating step (S12) and the output characteristics of the image output device (image output means) for outputting the image data. This is a step of selecting a filter process to be performed on the image. The selection of the filter processing in the filter processing selection step (S13) may be any method as long as the filter coefficients for the filter processing prepared in advance can be selected based on the above conditions, that is, the frequency calculation result and the output characteristics.
[0113]
The image processing step of S14 is a step of applying the filter processing selected in the filter processing selecting step (S13) to the image data after scaling. The image processing step (S14) is only required to be able to perform the filter processing selected in the filter processing selection step (S13) on the image data after the above-mentioned magnification, and the specific method is not particularly limited. is not.
[0114]
The filter processing selecting step of S13 compares the frequency calculation result with a predetermined threshold, and selects an adaptive mixing filter if the frequency calculation result is greater than the threshold, and determines whether the frequency calculation result is When the value is equal to or less than the threshold value, it is more preferable to select a smoothing filter.
[0115]
When the number of lines is high, high-frequency components are smoothed, and low-frequency components are sharpened. By selecting an adaptive mixing filter having a frequency characteristic that sharpens low-frequency components, moire caused by halftone dot periods can be prevented, and Edge sharpness can be maintained. Therefore, the entire image is not carelessly blurred and the image quality does not deteriorate.
[0116]
In addition, when the number of lines is low, by selecting a smoothing filter having a characteristic of performing smoothing over all frequency components, it is possible to prevent the moire of low frequency components generated by the halftone dot period, Since the noise of the high-frequency component existing in the image can be blurred, the output image quality can be improved.
[0117]
(G) Application examples other than digital copiers / multifunction machines
An application example of the image processing apparatus 101 according to the present invention other than a digital copying machine / multifunction machine will be described below.
[0118]
(1) A form in which an image input device, an image processing device (server), and an image output device are connected via a network
The input resolution may be determined based on the header information of the input image data, and the output characteristics may be controlled based on information about the image output device such as a manufacturer and a model number. The filter coefficient correspondence table shown in FIG. 5 may be controlled so that a table of filter coefficients corresponding to the halftone frequency (frequency) is created for each image output device.
[0119]
(2) Application software
The method (1) is implemented as application software. This implementation method will be described in detail in “(H) Application Software” described later.
[0120]
(3) Processing for images taken with a digital camera
When a subject having a geometrically fine pattern is photographed, moire occurs due to interference between the pattern of the subject and the pattern of the CCD. In order to remove the moiré, the image taken by the digital camera 106 may be taken into the computer 105 for processing, or may be directly input to the printer (image forming apparatus 100) for processing (see FIG. 11). ). Note that in FIG. 11, the decoding processing unit 20 performs decoding, inverse quantization, and inverse orthogonal transform processing on the compressed image data in the JPEG (Joint Photographic Experts Group) format or the like input from the digital camera to perform YCrCb decoding. (Y: luminance, Cr · Cb: color difference) pixel data. In this example, the YCrCb data is further converted to CMY data (data obtained by complementing RGB data with complementary colors).
[0121]
In this case, the input resolution may be the resolution of the digital camera 106, and the number of lines may be the frequency of a geometrically fine pattern.
[0122]
(H) Application software
A case where the image processing method according to the present invention is implemented as application software will be described below with reference to FIG.
[0123]
When the image processing method according to the present invention is implemented as application software, for example, the input image data captured by the image input device 102 such as a scanner is compared with the entire image data or the selected image area on the computer 108 on the computer 108. The image processing method according to the present invention is implemented as application software together with image processing such as color tone correction processing such as color adjustment. The image processed by the image processing method according to the present invention is displayed on an image display device 107 such as a display or output from an image output device 103 such as a printer. When outputting with a printer, color correction processing (RGB → CMYK) and halftone processing are performed by a printer driver.
[0124]
A computer system 120 shown in FIG. 12 includes an image input device 102 such as a flatbed scanner, a film scanner, and a digital camera, a computer 108 that performs various processes such as the image processing method by loading a predetermined program, and a mouse. And a user interface 109 such as a keyboard, an image display device 107 such as a CRT display or a liquid crystal display for displaying the processing results of the computer 108, and an image output device 103 such as a printer for outputting the processing results of the computer 108 to paper or the like. You.
[0125]
The computer system 120 may further include an external recording device 110 for storing data, and a communication unit 111 such as a modem or a network card for connecting to a server or the like via a network.
[0126]
(I) Program / recording medium
An image processing program according to the present invention is a program for causing a computer to function as each unit included in the image processing apparatus 101. An image processing program according to the present invention is a program for causing a computer to execute the image processing method according to the present invention.
[0127]
A recording medium according to the present invention is a computer-readable recording medium storing the image processing program. That is, the recording medium according to the present invention is a computer-readable recording medium capable of recording a program to be executed by a computer, in which the image processing method according to the present invention is recorded.
[0128]
As a recording medium in the present embodiment, a memory (not shown) for processing by a microcomputer, for example, a ROM itself may be a program medium. It may be a program medium provided with a device and readable by inserting a recording medium into the device.
[0129]
The program stored in the recording medium may be configured to be accessed and executed by a microprocessor.
[0130]
Further, the program stored in the recording medium may read the program, the read program may be downloaded to a program recording area (not shown) of the microcomputer, and the program may be executed. . In this case, it is assumed that the download program is stored in the main device in advance.
[0131]
Here, the program medium is a recording medium configured to be separable from the main body, such as a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a floppy (registered trademark) disk or a hard disk, a CD-ROM / MO / Disc system of optical disc such as MD / DVD, card system such as IC card (including memory card) / optical card, or mask ROM, EPROM (Erasable Programmable Read Only Memory), EEROM (Electrically Erasable Programmable Read Only) Flash, It may be a medium that carries a fixed program including a semiconductor memory such as a ROM.
[0132]
Further, in the present embodiment, since the system configuration is such that a communication network including the Internet can be connected, a medium that carries the program in a fluid manner such that the program is downloaded from the communication network may be used. When the program is downloaded from the communication network, the download program may be stored in the main device in advance, or may be installed from another recording medium.
[0133]
The recording medium is read by a program reading device provided in a digital color image forming apparatus or a computer system to execute the above-described image processing method.
[0134]
According to the above program, the computer reads and executes an image processing method capable of performing an appropriate filtering process on the scaled image data that has been scaled based on the frequency (line number) determination result and the output characteristics. This image processing method can be made general-purpose.
[0135]
According to the recording medium described above, it is possible to easily provide a program of an image processing method capable of performing appropriate filter processing on image data after scaling, which has been subjected to scaling based on the frequency (number of lines) determination result and output characteristics. Can be supplied to the computer.
[0136]
【The invention's effect】
As described above, the image processing apparatus according to the present invention, in the image processing apparatus that processes the input image data read by the image input unit, includes a scaling unit that scales the input image data according to a set scaling factor. Means, a frequency calculating means for calculating the frequency of the image data after scaling processed by the scaling means, a frequency calculation result calculated by the frequency calculating means, and an image output means for outputting image data. And control means for switching a filtering process to be performed on the image data after scaling based on the output characteristics.
[0137]
Therefore, when performing scaling processing on an image having periodicity such as an area gradation image or a geometric image, the frequency of the image data after scaling is calculated after the scaling processing, and the frequency calculation result and the image are calculated. Since the filtering process to be performed on the image data after scaling is controlled based on the output characteristics of the output means, it is possible to perform the optimal filtering process on the image data after scaling without generating moiré in the output image.
[0138]
For example, even when a halftone image is scaled (enlarged / reduced), an optimal filter process can be selected according to the number of lines (frequency) of halftone dots of the scaled image data. It is possible to obtain a high quality output image without any.
[0139]
Further, since the number of lines (frequency) is determined after the scaling process, the optimum filter coefficient can always be selected even for devices having different input resolutions and output resolutions. By discriminating the number of lines (frequency) after the scaling process, a table for the scaling ratio is not required, so that the number of filter coefficients set in advance can be reduced. Further, since the method does not depend on the method of the scaling process, even when the frequency characteristic of the halftone frequency of the image data after the scaling is changed by changing the method of the scaling process, occurrence of moire can be prevented.
[0140]
In other words, it is possible to provide an image processing apparatus that can perform appropriate image processing on the scaled image data that has been subjected to the scaling processing without deteriorating the image quality and preventing the occurrence of moire. It works.
[0141]
In the image processing apparatus of the present invention, in the above configuration, the control means selects an adaptive mixing filter when the frequency calculation result is larger than a predetermined threshold, and performs smoothing when the frequency calculation result is equal to or smaller than the threshold. It is more preferable to select an activation filter.
[0142]
Therefore, when the number of lines is high, the high-frequency component is smoothed, and the low-frequency component is sharpened. The sharpness of the edge in the image can be maintained. For this reason, there is an effect that the entire image is not carelessly blurred and the image quality is not deteriorated.
[0143]
In addition, when the number of lines is low, by selecting a smoothing filter having a characteristic of performing smoothing over all frequency components, it is possible to prevent the moire of low frequency components generated by the halftone dot period, Since the noise of the high frequency component existing in the image can be blurred, the effect of improving the output image quality can be realized.
[0144]
As described above, an image forming apparatus according to the present invention includes the image processing apparatus according to any one of the above-described aspects.
[0145]
Therefore, even when an image having a periodicity such as a halftone dot image is subjected to scaling processing, an optimal filter process is performed in accordance with the number of lines of the halftone dot (frequency of the image data after scaling). It is possible to form a high-quality output image without any defect.
[0146]
In other words, it is possible to provide an image forming apparatus that can perform appropriate image processing on the scaled image data that has been subjected to the scaling processing without deteriorating the image quality and preventing the occurrence of moire. It works.
[0147]
As described above, the image processing method according to the present invention is the image processing method for performing processing on input image data read by an image input unit, wherein the scaling is performed by scaling the input image data according to a set scaling factor. A frequency calculation step of calculating a frequency of an image area having periodicity of the scaled image data subjected to the scaling processing in the scaling step, a frequency calculation result calculated in the frequency calculation step, and an image A filter process selecting step of selecting a filter process to be performed on the scaled image data based on an output characteristic of an image output unit that outputs data; and a filtering process determined by the filter process selecting step. And an image processing step performed on the data.
[0148]
According to the above-described method, when a periodic image such as an area gradation image or a geometric image is scaled, an optimal filter process that does not cause moire in an output image can be performed. For example, even when a halftone image is scaled (enlarged / reduced), an optimum filter process can be selected according to the number of lines (frequency) of the halftone dot, so that a high-quality output image without moire can be obtained. be able to.
[0149]
Further, the optimum filter coefficient can always be selected for devices having different input resolutions and output resolutions. By discriminating the number of lines (frequency) after the scaling process, a table for the scaling ratio is not required, so that the number of filter coefficients set in advance can be reduced. Further, since the method does not depend on the method of the scaling process, even if the method of the scaling process changes and the frequency characteristics change, it is possible to prevent the occurrence of moire.
[0150]
In other words, it is possible to provide an image processing method that can perform appropriate image processing on the scaled image data that has been subjected to the scaling process without deteriorating the image quality and preventing the occurrence of moire. It works.
[0151]
In the image processing method of the present invention, in the above method, the filter processing selecting step selects an adaptive mixing filter when the frequency calculation result is larger than a predetermined threshold, and when the frequency calculation result is equal to or smaller than the threshold, It is more preferable to select a smoothing filter.
[0152]
According to the above method, when the number of lines is high, the high frequency component is smoothed, and the low frequency component is generated by the dot period by selecting an adaptive mixing filter having a frequency characteristic of sharpening. It is possible to keep the sharpness of the edge in the image while preventing moiré. For this reason, there is an effect that the entire image is not carelessly blurred and the image quality is not deteriorated.
[0153]
In addition, when the number of lines is low, by selecting a smoothing filter having a characteristic of performing smoothing over all frequency components, it is possible to prevent the moire of low frequency components generated by the halftone dot period, Since the noise of the high frequency component existing in the image can be blurred, the effect of improving the output image quality can be realized.
[0154]
As described above, an image processing program according to the present invention is characterized by causing a computer to function as each unit included in the image processing apparatus according to any one of the above-described inventions.
[0155]
An image processing program according to the present invention causes a computer to execute the image processing method according to any one of the above-mentioned inventions in order to solve the above-mentioned problems.
[0156]
A recording medium according to the present invention is a computer-readable recording medium that stores a program for causing a computer to execute the image processing method according to the present invention in order to solve the above-described problems.
[0157]
Accordingly, the image processing method is implemented using the computer by installing the image processing program in a general computer via the recording medium or the network. In other words, the computer is connected to the image processing apparatus. The effect that it can be made to function as is produced.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of an image processing apparatus according to the present invention.
FIG. 2 is a flowchart showing a schematic processing content of the image processing apparatus according to the present invention.
FIG. 3 is a graph showing a change in a frequency characteristic due to a scaling process.
FIG. 4 is a graph showing a relationship between a difference in the number of lines and a frequency characteristic.
FIG. 5 is a schematic diagram illustrating a configuration of a filter coefficient table of the image processing apparatus according to the present invention.
FIG. 6 is an explanatory diagram showing that frequency characteristics change when images having the same number of lines are captured at different input resolutions.
7A to 7C are tables showing examples of coefficients A to C in the filter coefficient table of FIG. 5, and FIGS. 7D to 7F are frequencies of coefficients A to C in the filter coefficient table of FIG. It is a graph which shows a characteristic.
8 (a) and (b) are tables showing examples of coefficients D and E in the filter coefficient table of FIG. 5, and FIGS. 8 (c) and (d) are frequencies of coefficients D and E in the filter coefficient table of FIG. It is a graph which shows a characteristic.
FIG. 9 is a block diagram illustrating a configuration example of a document type automatic discrimination unit of the image processing apparatus according to the present invention.
FIG. 10 is a flowchart showing a schematic processing procedure of an image processing method according to the present invention.
FIG. 11 is a block diagram illustrating a configuration example of an image processing apparatus according to the present invention.
FIG. 12 is a block diagram illustrating a configuration example in a case where the image processing method according to the present invention is implemented as application software.
[Explanation of symbols]
1 Magnification unit (magnification means)
2 Document type automatic discrimination unit (frequency calculation means)
3 control part (control means)
101 Image processing device
102 Image input device (image input means)
103 Image output device (image output means)

Claims (8)

In an image processing apparatus that processes input image data read by an image input unit,
Scaling means for scaling the input image data according to the set scaling ratio,
Frequency calculating means for calculating the frequency of the scaled image data subjected to scaling processing by the scaling means,
Control means for switching filter processing to be performed on the scaled image data based on the frequency calculation result calculated by the frequency calculation means and an output characteristic of the image output means for outputting image data. Image processing device. The control means selects an adaptive mixing filter when the frequency calculation result is larger than a predetermined threshold value, and selects a smoothing filter when the frequency calculation result is equal to or less than the threshold value. An image processing apparatus according to claim 1. An image forming apparatus comprising the image processing apparatus according to claim 1. In an image processing method for processing input image data read by an image input unit,
A scaling step of scaling the input image data according to the set scaling factor;
A frequency calculating step of calculating a frequency of an image area having periodicity of the image data after the scaling process, which has been scaled by the scaling process,
A frequency calculation result calculated by the frequency calculation step, and an output characteristic of an image output unit that outputs image data, a filter processing selection step of selecting a filter processing to be performed on the scaled image data,
An image processing step of performing the filtering process determined in the filtering process selecting step on the scaled image data. The filter processing selecting step selects an adaptive mixing filter when the frequency calculation result is larger than a predetermined threshold, and selects a smoothing filter when the frequency calculation result is equal to or smaller than the threshold. Item 5. The image processing method according to Item 4. An image processing program for causing a computer to function as each unit included in the image processing apparatus according to claim 1. An image processing program for causing a computer to execute the image processing method according to claim 4. A computer-readable recording medium recording the image processing program according to claim 6.

Images