JP3784537B2 - Image processing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus for reproducing an image read from a scanner on transfer paper.
[0002]
[Prior art]
As a conventional example of this type, as shown in, for example, Japanese Patent Laid-Open No. 8-274986, in order to realize high image quality mainly in a 400 dpi system, there are many copying machines in a multifunction machine such as a copying machine and a facsimile (FAX). A method for optimizing the parallel operation and the respective image processing by distinguishing the value processing from the binary processing for FAX has been proposed.
[0003]
[Problems to be solved by the invention]
However, since the conventional example does not consider the binary and multi-level circuit configurations and the RAM control, the high density system cannot reduce the number of gradations per pixel and realize high image quality. There is a point. Further, in the above-described conventional example, the background cannot be made to follow due to the fluctuation of the threshold when the simple binarization and binary / multilevel error diffusion processing is performed, and the texture cannot be reduced.
[0004]
In view of the problems of the conventional example, the present invention Binarization based on the fluctuation threshold, and image processing mode according to the document type The purpose is to provide.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the first means performs MTF correction on input image data and outputs MTF correction data, and smoothes input image data and outputs smooth data. Smoothing means, edge detection means for detecting edge signals based on input image data, and edge signals detected by the edge detection means If indicates an edge The MTF correction data To indicate non-edges Selecting means for selecting the smoothed data as output data; and a predetermined fixed threshold value or one of the smoothed data as an edge signal Depending on whether indicates an edge or non-edge Selected, The selected value Fluctuation threshold As Threshold setting means for setting; A first γ conversion means for performing γ conversion with reference to a first γ correction table with respect to the variation threshold set by the threshold setting means, and a second for the output data selected by the selection means second γ conversion means for performing γ conversion with reference to the γ correction table; Said Converted by the first γ converting means Based on the variation threshold Converted by the second γ conversion means And binarizing means for binarizing the output data.
[0011]
First 2 Means 1's In the means, the threshold setting means comprises level determining means for determining the value of the smoothed data based on the result of comparison between the smoothed data and a predetermined value.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention, FIG. 2 is an explanatory diagram showing a scanner γ correction table and a density correction table of the scanner γ correction unit of FIG. 1, and FIG. 3 is a scanner of FIG. 4 is a block diagram showing in detail the γ correction unit, FIG. 4 is a block diagram showing in detail the spatial filter processing unit of FIG. 1, FIGS. 5 and 6 are block diagrams showing in detail the isolated point detection unit of FIG. 4, and FIG. It is a block diagram which shows a threshold value setting part in detail.
[0013]
8 is a block diagram showing in detail the density correction unit and gradation processing unit in FIG. 1, and FIG. 9 is an explanatory diagram showing data when the dither and error diffusion matrix RAM in FIG. 8 is used as a binary data matrix. 10 is an explanatory diagram showing data when the dither and error diffusion matrix RAM in FIG. 8 is used as a multi-value data matrix, and FIG. 11 is an explanatory diagram showing in detail the binary multi-value error diffusion processing unit of FIG. FIG. 12 is a block diagram showing a fixed threshold value / variable threshold value switching circuit.
[0014]
In FIG. 1, image data is sequentially read from a reading unit (scanner) 1, a shading correction unit 2, a scanner γ correction unit 3, a main scanning electric scaling unit 4, which will be described in detail in FIGS. The data is transferred to the writing unit 9 via the spatial filter processing unit 5 described in detail, the density correction unit 6 (6a, 6b), the gradation processing unit 7, and the PWM modulation unit 8 described in detail in FIGS. In addition, a CPU 11, a RAM 12, a ROM 13, and an operation unit 14 are connected to the system bus 10.
[0015]
The reading unit 1 converts the document density into an electric signal by an image pickup device such as a CCD as reflected light of the light source, and then converts the analog signal into a digital image signal. The subsequent shading correction unit 2 corrects the density unevenness in the main scanning direction by the optical system including the light source and CCD of the reading unit 1 for the digital image signal. At this time, the shading correction unit 2 reads a white plate serving as a density reference in advance and stores it in the memory, and corrects the read data of the document in dot units in the main scanning direction based on the reference data. The data characteristics after the shading correction are linear with respect to the reflectance.
[0016]
The subsequent scanner γ correction unit 3 converts linear data regarding the reflectance into linear data regarding the document density. At this time, as shown in FIG. 2 (1), the reading characteristic (1) of reading by the scanner 1 is measured in advance, and the conversion table (2) which is the reverse characteristic is downloaded to the RAM 3-1 (FIG. 3). The scanner γ correction unit 3 converts the linear data regarding the reflectance into the linear data regarding the document density by using the conversion table (2).
[0017]
Here, the density characteristic {circle around (1)} shown in FIG. 2A indicates image data after shading correction with respect to the original density, and is not a linear characteristic. That is, it rises sharply in the low concentration region and saturates on the electric signal in the high concentration region, and generally has an Exp (γ) characteristic. A characteristic {circle around (2)} shown in FIG. 2A is a characteristic for converting the characteristic {circle around (1)} to density linear, and the characteristic {circle around (1)} is multiplied by Exp (1 / γ). This increases the dynamic range of the density signal.
[0018]
In addition to this conversion, the scanner γ correction unit 3 also performs density correction by emphasizing the low density part by using the density correction table shown in FIG. FIG. 2B is a table in which the conversion table for correcting the γ characteristic with respect to the process reaction of the writing system 10 and further changing the density is downloaded to the RAM 3-1 (FIG. 3) and multiplied by the characteristic value. Specifically, the data is replaced as a lookup table. In FIG. 2B, the upwardly convex curve is a characteristic that reproduces the low density region more, and the downward convex curve is a characteristic that skips the low density region (not reproduced more). These characteristics can be arbitrarily set by a combination of a mode and a density notch.
[0019]
As shown in FIG. 3, the scanner γ correction unit 3 is configured to download conversion parameters to the RAM 3-1 in order to obtain degrees of freedom of density reproducibility and gradation reproducibility. The RAM 3-1 is for performing scanner γ correction, image data density correction, density correction for fluctuation threshold, dithering, and quantization threshold setting for error diffusion processing. Data download from the CPU 11 and lookup table The switching means is common. FIG. 3 is a diagram for explaining access from the CPU 11 to the RAM 3-1 and switching of table reference. The size of the RAM 3-1 can be arbitrarily set, and the address space only needs to be the number of gradations per pixel of the input image. For example, in the case of a system in which CCD data is A / D converted with 8 bits, the address space may be 8 bits.
[0020]
In the mode in which the CPU 11 accesses for data download, the address bus from the CPU 11 is connected to the address terminal ADDR of the RAM 3-1 via the multiplexer (MUX) 3-2, and the download data from the CPU 11 is transferred to the data of the RAM 3-1. Write through the input terminal DATI. At this time, the RAM 3-1 is set to the write mode via the multiplexer (MUX) 3-3. Note that the RAM 3-1 shown in FIG. 3 is a synchronous RAM synchronized with the clock CLK, but the switching method between the CPU mode and the data reference mode is the same even in the asynchronous RAM.
[0021]
In the normal image processing mode, the converted image is input to the address terminal ADDR of the RAM 3-1 via the multiplexer 3-2, and the RAM 3-1 is set to the read mode via the multiplexer 3-3. Thus, when the value of the converted image is input as an address, the converted value is output via the data output terminal DATO of the RAM 3-1. Therefore, with such a RAM configuration, the circuit configuration and the arithmetic processing can be reduced, and the arbitraryness of data can be ensured.
[0022]
Returning to FIG. 1, the subsequent main scanning electric zooming unit 4 performs enlargement / reduction in the main scanning direction at the time of zooming. At this time, the resolution of the image data can be maintained by performing the scaling process while maintaining the optical system MTF of the reading unit 1 by the convolution method. Note that scaling in the sub-scanning direction is performed by mechanically controlling the reading unit 1.
[0023]
The subsequent spatial filter processing unit 5 has various functions such as MTF correction, smoothing processing, edge line segment detection, and variation threshold setting in order to perform preprocessing and feature amount extraction for the gradation processing unit 7. The spatial filter processing unit 5 will be described in detail with reference to FIGS. 4 to 7. First, a two-dimensional image matrix 5-1 is configured using a plurality of line memories 5-2 as shown in FIG. Within these two dimensions, correction of the frequency characteristics of the input image and feature quantity extraction based on the density characteristics are performed. More specifically, the MTF correction unit 5-3 is configured so that the MTF correction coefficient and the correction intensity can be arbitrarily set independently in the main scanning direction and the sub-scanning direction in order to correct the MTF deterioration in the optical system of the reading unit 1. Therefore, it can be widely applied to the processing mode, the read original, and the type of the optical system of the reading unit 1.
[0024]
The isolated point detection unit 5-4 detects background noise and document noise that are expected to deteriorate due to generation copying. At this time, the regularity of the pixel arrangement is detected to determine whether the pixel is a complete isolated point or a part of a low-density halftone original, and the target pixel is narrowed down. The isolated point detector 5-4 will be described in detail with reference to FIGS. 5 and 6. Each matrix 5 of 5 × 5 pixels, 7 × 7 pixels, and 9 × 9 pixels is used to detect an isolated state from the surroundings. -4-1, 5-4-2, 5-4-3 is selected (5-4-4 in the figure), and the target pixel (center pixel of the matrix) and the outermost pixel are completely separated. In this case, the target pixel is regarded as an isolated point.
[0025]
In this case, isolated points can be detected up to a maximum size of 4 × 4 pixels by using a 7 × 7 pixel matrix 5-4-2 at the same magnification. Further, since the interval between the isolated point pixel and the surrounding pixels is also reduced at the time of reduction, a 5 × 5 pixel matrix 5-4-1 is used to detect 4 × 4 isolated point pixels at the time of 50% reduction. What is necessary is just to detect a block having a size of 2 × 2 pixels. On the other hand, when the enlargement is 200% or more, the 4 × 4 isolated point pixels are also enlarged, and cannot be detected unless the 9 × 9 pixel matrix 5-4-3 is used. Therefore, one of the matrices 5-4-1, 5-4-2, and 5-4-3 is selected by changing the matrix selection signal kmx in accordance with the scaling factor.
[0026]
Here, the low-density dither pattern, which is useful information in the document, is removed only by removing the isolated points by the 5 × 5 pixel and 7 × 7 pixel matrices 5-4-1 and 5-4-2. . In order to solve this problem, first, a determination signal T1 indicating whether or not the pixel of interest is a white background or an isolated point (T1 = 1 in the case of a white background or an isolated point, T1 = 0 in other cases). Is used. Further, the comparator 5-4-6 compares the image data with the threshold kbth to determine whether or not the pixel is a white pixel (T2 = 1 for a white pixel, T2 = for a non-white background). 0) is generated.
[0027]
Further, the state transition determination unit 5-4-7 counts the determination signals T1 and T2, the number of consecutive white pixels 5-4-8, and the isolated point size 5-4-9. Here, the state state of the pixel determined by the state transition determination unit 5-4-7 includes a paper state in which white pixels are widely continuous, a dot state that is an isolated point, a pattern, a character, or a low density halftone dot. Transition between image states in which part or white pixels are not widely continuous. The state state starts from the paper state.
[0028]
The determination unit 5-4-5 outputs the isolated point detection signal result to the intensity calculation unit 5-4-10 shown in FIG. 6 based on the determination signals T1 and T2 and the state state. Further, the image data mtfo and the correction data ktj after the MTF correction are applied to the intensity calculator 5-4-10. Here, since the image data mtfo after the MTF correction is enhanced, the isolated points are emphasized, and if this process is repeated a plurality of times by grandchild copy, the generation deteriorates and the low-quality black is noticeable. It becomes an image.
[0029]
Therefore, the intensity calculation unit 5-4-10 and the selection unit 5-4-11 do not perform MTF emphasis on the isolated points, and smooth the surroundings or replace them with white levels. At this time, the isolated point removal processing is switched on and off by the signal kmod, and is switched by the correction data ktj in the case of processing. The correction data ktj is set to the maximum (= 0) when it is converted to a forced white level, and the image data mtfo after MTF correction is weakened to 1/32, 1/8, 1/2.
[0030]
The isolated point removal unit 5-7 shown in FIG. 4 selects whether to remove the detected isolated point completely or replace it with the average value of the surrounding pixels to remove the noise component. Next, the thinning / thickening processing unit 5-8 performs the processing independently in the main scanning direction and the sub-scanning direction, and also reproduces the line density in conjunction with the MTF correction coefficient in order to reproduce the line density. Adjust the direction balance.
[0031]
The smoothing processing unit 5-5 removes the moiré component generated by the halftone original and the aliasing distortion at the time of A / D conversion, and sets the variation threshold value in the density correction units 6a and 6b and the gradation processing unit 7 in the subsequent stage. Therefore, the surrounding information is extracted. The edge detection unit 5-6 detects edge line segments of horizontal, vertical, and left and right diagonal components and outputs them as selection signals to the selector 5-9. Further, the edge detection unit 5-6 and gradation correction units 6a and 6b and gradations The processing unit 7 extracts surrounding information in order to set a variation threshold. The selector 5-9 selects the output of the thinning / thickening processing unit 5-8 when the edge detection signal is input from the edge detection unit 5-6, and the smoothing processing unit when the non-edge detection signal is input. The output 5-5 is selected and output to the subsequent density correction unit 6a.
[0032]
FIG. 7 shows the threshold setting unit 5-10 in detail. First, for use in a noise and density stable region, the image signal smoothed by the level determination unit 5-10-1 is compared with an upper limit value and a lower limit value set in a register (not shown). To define the smoothed signal. At this time, when the smoothed signal is equal to or lower than the lower limit value, the lower limit value is replaced. When the smoothed signal is equal to or higher than the upper limit value, the upper limit value is replaced. When the smoothed signal is between the lower limit value and the upper limit value, the smoothed signal is used.
[0033]
Next, the selector 5-10-2 uses a fixed threshold value set in a register (not shown) based on the edge detection signal, or a smoothed signal between the lower limit value and the upper limit value from the level determination unit 5-10-1. Select. In this case, in the case of a complete variation threshold value that follows the background density, the fixed threshold value is selected at the non-edge portion, and the above-described smoothed signal is selected at the edge portion. In addition, when separating the high density edge and the low density edge and reproducing them, a threshold value of two stages is selected. At this time, a fixed threshold value is selected for the edge portion, and the above smoothing signal is selected for the non-edge portion. select. Basically, the fixed threshold value functions as a binarization threshold value for a high density edge, and the lower limit value for the smoothed data functions as a binarization threshold value for a low density edge.
[0034]
The spatial filter processing unit 5 outputs the filtered image data and the fluctuation threshold value for binarization, and the density correction units 6a and 6b shown in detail in FIG. Density correction is performed on the image data from 5 and the variation threshold. At this time, the reproduction density conversion corresponding to the γ correction and density latch of the writing system 9 is performed, and arbitrary conversion data in the RAM 12 is downloaded. Although it is basic to download the same data for the image data and the variation threshold, different data may be used to intentionally change the gradation characteristics.
[0035]
The subsequent gradation processing unit 7 converts density data per pixel into area gradation in order to convert the image data so as to match the characteristics of the writing system 10. The gradation processing unit 7 also has functions such as simple multi-value quantization, binarization, dither processing, error diffusion processing, and phase control, and a quantization threshold value within a certain area when converting to area gradation. To disperse. Further, when distributing this threshold value, an arbitrary threshold value is downloaded to the matrix RAM 6-10 (FIG. 8), and an appropriate quantization is selected by switching the RAM access means according to the processing mode.
[0036]
FIG. 8 shows the density correction units 6a and 6b and the gradation processing unit 7 in detail. First, as a lookup table, a RAM 6-1 for a density conversion γ correction table for a variation threshold, a RAM 6-8 for a density conversion γ correction table for image data, and a dither and error diffusion matrix A RAM 6-10 is provided. The threshold value converted by the RAM 6-1 and the γ conversion unit (threshold value) 6-2 (density correction unit 6b) is applied to the fluctuation binarization unit 6-3, and the RAM 6-8 and the γ conversion unit ( (Density) 6-7 (density correction unit 6b) converts the image data into a fluctuation binarization unit 6-3, a binary / error diffusion processing unit 6-11 constituting the gradation processing unit 7, It is applied to the multilevel level converter 6-18 and the binary / multilevel dither processor 6-20.
[0037]
That is, a binary processing path and a multi-value processing path are provided, and the threshold value converted by the RAM 6-1 and the γ conversion unit (threshold value) 6-2 at the time of the simple binarization process is changed to a variable binarization unit. 6-3, each pixel process is performed in the leading edge pixel control unit 6-4 and the binary filter 6-5.
[0038]
The dither processing and error diffusion processing are performed by a common circuit for both binary and multi-value, and the binary and multi-value processing is switched by switching the data contents of RAM 6-10 and address / access. In addition, during the processing of the multi-level conversion unit 6-18 and the multi-level error diffusion unit 6-11, phase information for dot formation according to the density distribution before and after the main scanning direction is combined with the density process. 6-15, 6-19 and selection unit 6-1 6 Add by. For example, in the case of ternarization, 2 bits are assigned to the signal level and “00”, “01”, “10”, and “11” are set.
[0039]
This is usually called quaternarization, but if “00” is set to white, “11” is set to black, and both “01” and “10” have a duty ratio in PWM of 50%, the density level is ternary. It becomes. Even when the ratio is 50%, the laser is turned on in the right half of the dot formation area when the phase is “01”, and the laser is turned on in the left half of the dot formation area when the phase is “10”. At this time, the process is performed by defining the above-mentioned phase in conjunction with the PWM modulation unit 9.
[0040]
The same pulse code is also generated during the ternarization processing by the 2 / multi-value dither processing unit 6-20. This will be described in detail when referring to FIG. In the multi-value processing, the simple edge detection unit 6-21 performs simple edge detection in the main scanning direction, and the selection unit 6-16 selects simple multi-value processing or multi-value error diffusion processing based on the line segment edge information. To do.
[0041]
FIG. 9 shows binary dither matrix download data when the address space of the dither and error diffusion matrix RAM 6-10 is composed of 8 bits. As the binary dither matrix, the main scanning direction can be set to 4, 6, 8, 16 pixels, and the sub-scanning direction can be set to 4, 6, 8, 16 pixels. At this time, a combination and pattern data are selected in accordance with the number of necessary lines and the state of thinning out the lines of the image. Further, the RAM 6-10 access is not a sequential access to simplify processing, control and configuration, but seek processing based on a two-dimensional array.
[0042]
FIG. 10 shows a case where the dither and error diffusion matrix RAM 6-10 is used as a multi-value data matrix. In particular, when the matrix size is 4 × 4 pixels A to P in FIG. 10A, FIG. In the case of 6 × 6 pixels aa to ff, FIG. 10 (3) shows the case of 8 × 8 pixels aa to hh. This matrix access performs a seek process based on a two-dimensional array, but requires twice as many addresses in the main scanning direction. For example, in the case of 4 × 4 pixels shown in FIG. 6A, 2 addresses are assigned to each pixel in the main scanning direction and 8 addresses are referred to.
[0043]
For the pixel A, the thresholds A0 and A1 are referred to internally. As a result, each matrix-corresponding pixel is compared with two threshold values. In the case of the left pulse, thresholds A0 and A1 are set such that the magnitude relationship is A0 <A1, and in the case of the right pulse, thresholds A0 and A1 of A0> A1 are set. When the pixel A is smaller than the threshold values A0 and A1, the quantization code = 00 is assigned. When the pixel A is larger than the threshold values A0 and A1, the quantization code = 11 is assigned. Further, when the pixel A is between the threshold values A0 and A1, the allocation code is different when the right pulse (right phase) or the left pulse (left phase), and when the right pulse series is allocated, the quantization code = 01 Is assigned, and quantization code = 10 is assigned when the left pulse sequence is assigned.
[0044]
Phase generation is also basically performed for the remaining pixels B to P in FIG. 10 (1), 6 × 6 pixels aa to ff in FIG. 10 (2), and 8 × 8 pixels aa to hh in FIG. 10 (3). By taking the threshold value into consideration and downloading it to the RAM 6-10, a pulse code is generated based on the same definition.
[0045]
FIG. 11 shows the configuration and processing of the binary / error diffusion processing unit 6-11. First, a fixed threshold value or a variation threshold value Tij (dither and error diffusion matrix RAM 6-10) is used as a quantization threshold value for an addition result Sij obtained by adding the product-sum result from the error weighted product-sum operation unit 105 by the addition unit 101. Is selected by the threshold value switching circuit shown in FIG. When the fluctuation threshold value Tij is used, the fluctuation threshold value Tij that is repeated in a certain block unit is set in the RAM 6-10.
[0046]
FIG. 11 (2) shows an example of the threshold value Tij in the 8 × 8 pixel fluctuation region in the case of binary values. Note that the texture can be reduced by changing the threshold Tij within the block. Further, by mixing the fixed threshold value and the variation threshold value Tij in the 8 × 8 pixel matrix region, the balance between edge preservation and gradation reproducibility can be adjusted. In the case of multivalue, the quantization code is changed with a plurality of threshold values Tij for one pixel in the matrix. Separately, the phases are rearranged according to the density distribution in the main scanning direction.
[0047]
Then, the 8-value / quaternarization / ternarization / binarization unit 102 compares the value Sij from the addition unit 101 with the variation threshold value Tij to obtain an 8-value / quaternarization / ternarization / binarization. Is done. Further, the error Eij between the data Gij after the 8-level / quaternary / ternarization / binarization and the data Sij before the processing is calculated by the error calculation unit 103 and stored in the error memory 104. Next, the error weighted product-sum operation unit 105 multiplies this error by a coefficient of 5 × 2 (actually 5 + 3), adds each multiplication result, and applies the product-sum operation result to the addition unit 101. Note that the 5 × 2 coefficient matrix of the error weighted product-sum operation unit 105 and the coefficient distribution shown in FIG. 11A are examples.
[0048]
In the fixed threshold / variation threshold switching circuit shown in FIG. 12, the multiplexer 112 is switched via the system bus in accordance with the setting mode to select the variation threshold or the fixed threshold (register 111), and the RAM 6-10 via the comparison unit 113. Output to. As for the fluctuation threshold value, in the case of error diffusion, the threshold value for referring to the setting value in the RAM 6-10 in the main scanning direction and the sub-scanning direction and the multi-value level is controlled. In the case of simple binarization, a threshold value set by the spatial filter unit 5 and subjected to density correction is used. The fixed threshold value is not a hardware fixed value, but a value set in the register 111 by the CPU 11 is used as the fixed threshold value, and can be changed according to the mode and the image characteristics.
[0049]
Returning to FIG. 1, the subsequent PWM (pulse width modulation) modulation unit 8 performs pulse width modulation of image data for the writing laser of the writing unit 9. For this reason, in conjunction with the phase control in the gradation processing unit 7 in the preceding stage and this pulse width modulation, gradation is expressed by smoothly performing dot aggregation and dispersion. The subsequent writing unit 9 reproduces an image on a transfer sheet by a known electrophotographic process such as image formation, transfer, and fixing on a photoconductor with a laser. When the writing unit 9 is a developing system such as an ink jet, the configuration of the PWM modulation unit 8 and below is different, but the configuration is the same up to the phase control for dot reproduction.
[0050]
Setting of gradation processing, switching of density correction, and the like are linked to the operation mode from the operation unit 14, and a processing mode is selected according to a picture-based document, a character-based document, or the like, and according to a thin document or a dark document. Change the density correction parameter. In actual system control, the CPU 11 sets the RAM 12 via the system bus 10 or sets the path of the processing path to each block according to the operation mode.
[0051]
【The invention's effect】
As explained above Book According to the invention, Since binarization is performed based on the variation threshold, an image processing mode corresponding to the document type is provided. be able to.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention.
FIG. 2 is an explanatory diagram showing a scanner γ correction table and a density correction table of the scanner γ correction unit in FIG. 1;
FIG. 3 is a block diagram illustrating in detail a scanner γ correction unit in FIG. 1;
4 is a block diagram illustrating in detail a spatial filter processing unit in FIG. 1; FIG.
5 is a block diagram illustrating in detail an isolated point detection unit in FIG. 4;
6 is a block diagram illustrating in detail an isolated point detection unit in FIG. 4;
7 is a block diagram illustrating in detail a threshold value setting unit in FIG. 4;
FIG. 8 is a block diagram illustrating in detail a density correction unit and a gradation processing unit in FIG. 1;
FIG. 9 is an explanatory diagram showing data when the dither and error diffusion matrix RAM in FIG. 8 is used as a binary data matrix;
10 is an explanatory diagram showing data when the dither and error diffusion matrix RAM in FIG. 8 is used as a multi-value data matrix. FIG.
11 is an explanatory diagram showing in detail a binary multi-value error diffusion processing unit in FIG. 8;
FIG. 12 is a block diagram showing a fixed threshold value / variable threshold value switching circuit.
[Explanation of symbols]
1 Reading unit (scanner)
2 Shading correction part
3 Scanner γ correction unit
4 Main scanning electric zoom
5 Spatial filter processing section
5-3 MTF correction unit
5-4 Isolated point detector
5-4-1, 5-4-2, 5-4-3 Matrix
5-5 Smoothing processing unit
5-6 Edge detector
5-7 Isolated point removal unit
5-10 Threshold setting unit
6a, 6b Density correction unit
6-10 Matrix RAM
6-11 Binary / Multilevel Error Diffusion Unit
6-18 Multi-level conversion unit
6-20 Binary / Multilevel Dither Processing Unit
7 Gradation processing section
8 PWM modulator
9 Writing part

Claims (2)

MTF correction means for performing MTF correction on input image data and outputting MTF correction data;
Smoothing means for smoothing input image data and outputting smooth data;
Edge detection means for detecting an edge signal based on input image data;
Selecting means for selecting the MTF correction data when the edge signal detected by the edge detecting means indicates an edge, and selecting the smoothed data as output data when indicating the non-edge ;
A threshold setting means for selecting in accordance with one of the fixed threshold or the smoothing data predetermined on whether an edge signal indicating the non-edge or represents an edge, and sets the selected value as a variable threshold,
First γ conversion means for performing γ conversion with reference to the first γ correction table with respect to the variation threshold set by the threshold setting means;
Second γ conversion means for performing γ conversion on the output data selected by the selection means with reference to a second γ correction table;
Binarization means for binarizing the output data converted by the second γ conversion means based on the fluctuation threshold value converted by the first γ conversion means ;
An image processing apparatus comprising: The image processing apparatus according to claim 1 , wherein the threshold setting unit includes a level determination unit that determines a value of smooth data based on a result of comparison between the smooth data and a predetermined value .

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