JPH09191402A - Picture processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To preserve resolution in a picture area where resolution is required and to provide gradation in an area where tone reproducibility is requested in a picture processor executing a binarization processing by a systematic dither method. SOLUTION: Two kinds of matrixes of the same size different in resolution are prepared as threshold matrixes for the binarization processing. The specified matrix is selected and used in accordance with a characteristic requested for a picture from them. When resolution is requested, the matrix of the higher resolution is selected, and the matrix of lower resolution is selected when tone reproducibility is requested, for example. At that time, an average value generation circuit 101 obtains the average value of picture data. A threshold comparison part 103 compares the average value with a prescribed threshold, and switches the threshold matrix in accordance with the compared result. A dither processing part 101 executes the binarization processing by using the switched threshold matrix.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus using a systematic dither processing method applicable to a hard copy apparatus.

[0002]

2. Description of the Related Art FIG. 14 is a block diagram showing a schematic configuration of a conventional general image processing apparatus which performs binarization processing by the systematic dither method in a hard copy apparatus. In the figure, 1 is a γ conversion unit that performs γ correction, and 2 is a dither processing unit that performs dither processing (binarization processing).

In the above structure, when the density input value is given, the γ conversion unit 1 refers to the γ conversion table to convert the data. This conversion is performed in order to correct the non-linearity existing in the input / output relationship of the hard copy device and ensure the linearity between the input density value and the final output density value.

Next, the area ratio data output from the γ conversion unit 1 is sent to the dither processing unit 2 where binarization processing is performed. Specifically, the output pixel value is determined by comparing the area ratio with the corresponding element (value) in the preset threshold matrix.

[0005]

However, in the conventional image processing apparatus as described above, since the dither processing is performed using a single threshold matrix, there are the following problems. It was

(1) If a dot concentration type threshold matrix is used to obtain gradation, the resolution is lowered.

(2) If a dot dispersion type threshold matrix is used to increase the resolution, gradation reproducibility deteriorates.

These problems will be described with reference to FIG. FIG. 12 shows a typical input / output characteristic of the hard copy device when two threshold matrices different in dot growth method are used. In the figure, the horizontal axis is the normalized dot area ratio, which shows what percentage of the unit half-tone cell area formed by the threshold matrix is on, and the vertical axis is the output density normalized by the maximum density. Is shown.

Characteristic A shown in FIG. 12 represents a dot concentration type characteristic, and characteristic B represents a dot dispersion type characteristic. FIG. 13 shows examples of these threshold matrices, where (a) is a fatting type (dot concentrated type) matrix, and (b) is a Bayer type (dot dispersion type) matrix.

As shown in FIG. 12, it can be seen that the dot concentration type is superior in gradation reproducibility. This difference in gradation reproducibility is due to the fact that the hard copy device cannot completely reproduce isolated dots, and is generally greatly affected by the printing process of the hard copy device. Depending on the process conditions,
This is particularly noticeable in the case of a device using an electrophotographic method. Note that, here, the horizontal axis of FIG. 12 is defined as the dot area ratio, but as is clear from the above description, this is not the area ratio actually output, but the color material control amount given to the hard copy device. It is more accurate to interpret.

As described above, it is extremely difficult to solve the problems (1) and (2) at the same time with only one matrix.

The present invention has been made in view of the above problems, and it is possible to maintain the resolving power in the region where the resolving power is required and to obtain the necessary tone reproducibility in the region where the tone reproducibility is required. It is an object of the present invention to provide an image processing device that can be used.

It is another object of the present invention to provide an image processing apparatus capable of improving gradation while maintaining sufficient resolution for an image requiring high resolution such as halftone characters and patterns.

[0014]

The image processing apparatus according to the present invention is configured as follows.

(1) In an image processing apparatus that performs image processing using the systematic dither method, a plurality of threshold matrices having different resolving powers for dither processing are prepared. A control means is provided for selecting and using a specific threshold matrix.

(2) In the image processing apparatus of (1) above, two types of matrices of the same size having different resolving powers are prepared as threshold matrices, and a dot concentration type matrix is adopted as the lower resolving power matrix, The control means compares the average value of the image data included in the matrix immediately before the print data with a predetermined threshold value, and when the average value is smaller than the threshold value, selects the matrix having the higher resolution, and when the average value is greater than the threshold value. Selects the dot-concentrated matrix having the lower resolution.

(3) In the image processing apparatus of (1) above, the control means sets the threshold value based on the average value of the image data included in the matrix immediately before the print data and the maximum value and the minimum value of the image data. I decided to do it.

(4) In the image processing apparatus of (2) or (3), when the matrix having the higher resolution is selected, the difference between the maximum value and the minimum value of the image data included in the matrix immediately before the print data is selected. When is smaller than the predetermined value, the matrix is switched to the dot concentrated type matrix.

(5) In an image processing apparatus that performs image processing using the systematic dither method, a plurality of threshold matrices having different resolutions for dither processing are prepared, and a specific threshold matrix is selected for each matrix from these. The control means to be used later was provided.

(6) In the image processing apparatus of the above (5), two types of matrices of the same size having different resolving powers are prepared as threshold matrices, and a dot concentration type matrix is adopted for the lower resolving power matrix, A dot-dispersion type matrix is adopted for the matrix with higher resolution.

(7) In the image processing apparatus of (5), the control means selects two types of matrices for each matrix.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. In the figure, 101 is a dither processing unit for performing dither processing by the systematic dither method, and 102.
Is an average value generation circuit for obtaining an average value of image data included in the dither matrix immediately before the currently input data, 103 is a preset threshold value and an average value generated by the average value generation circuit 102. The dither processing unit 101 has a control means for performing dither processing on the input data by switching between two dither matrices according to the comparison result of the threshold comparing unit 103.

Here, as a preparation before the description of the operation, the real coordinates (X, Y) and the block coordinates (U, V) are introduced, and the relationship between them will be described with reference to FIG. If the size of the threshold matrix used here is n rows and m columns (nxm), the figure shows the relationship between the real coordinates and the block coordinates when n = m = 4. As is clear from the figure, the relationship between (U, V) and (X, Y) is

[0024]

[Equation 1]

Is given by However, floor (A) represents the maximum integer not exceeding A.

Based on the above description, the operation will be described below with reference to FIG.

As shown in FIG. 3, (U, V) = (0,0)
Is dithered by one of the two prepared dither matrices which is set in advance. Also, (U, V) = (1,0) is (0,
The average value of the input data in 0) is generated, and one of the two dither matrices is selected according to the result of comparing the average value (average density) with a preset threshold value to perform the dither processing.

Similarly, (U, Y) = (2,0) becomes (1,
One of the two dither matrices is determined by comparing the average value of 0) with the threshold value. Also, (U, V) =
One of (0,1) is determined from two dither matrices by comparing the average value of (0,0) with a threshold value.

In this way, the dither processing is performed by repeating the sequential operation. FIG. 4 shows an example of the dither matrix.

That is, when the average value generated by the average value generation circuit 102 of FIG. 1 is lower than a preset threshold value, the Bayer matrix shown in FIG. When the average value generated by the average value generation circuit 102 is higher than the set threshold value, the fatting type dither matrix of FIG. 4A in which importance is attached to the resolution is used.

Next, the dither processing section 101 will be described with reference to the block diagram of FIG. FIG. 5 shows an example of a concrete circuit configuration of this embodiment.

In the circuit of FIG. 5, the input data is input to the average value processing unit 111, and the average value processing unit 111 calculates the average value of the input data included in the dither matrix immediately before the data to be printed or 1 LINE before, The value is output to the threshold comparison unit 112.

The threshold comparison unit 112 is an average value processing unit 111.
The average value calculated in step 1 is compared with a preset threshold value, and if the average value is larger than the threshold value, "H" is output, and if the average value is smaller than the threshold value, "L" is output to the table ROM 112.

Further, the average value processing unit 111 has a timing controller circuit for adjusting the time required for the average value processing, the threshold value processing and the table ROM conversion of the input data, and the input data is subjected to the timing adjustment. It is output to the comparator circuit 114.

The table ROM 113 has an X count circuit 1 for counting the matrix size in the X direction.
15, and a Y count circuit 116 for counting the matrix size in the Y direction is connected, and the bank is switched by the bank switching signal from the threshold comparison unit 112 to switch the dither matrix, and the coefficient in the dither matrix is set to X. Switching is performed by the count circuit 115 and the Y count circuit 116.

At this time, the bank switching signal from the threshold value comparing section 112 and the count signals from the X counting circuit 115 and the Y counting circuit 116 are table-converted by the table ROM 113 and output to the comparator circuit 114 as a dither matrix signal.

The comparator circuit 114 compares the input signal (8 bits) whose timing is adjusted by the average value processing unit 111 and the dither matrix signal (8 bits) table-converted by the table ROM 113, and dither-converts it into a 1-bit signal. Output.

As described above, by obtaining the average density of the input data included in the dither matrix immediately before the data to be printed or before 1 LINE, the dither matrix is a Bayer type with emphasis on gradation and a fatting type with emphasis on resolution. By switching to, high-quality printing becomes possible.

Further, in the present embodiment, the number of thresholds is one and the number of matrix patterns is two, but it is also possible to have a plurality of thresholds and switch a plurality of matrix patterns.

That is, a plurality of threshold matrices having different resolving powers are prepared, and a means for switching between them is provided. The switching means detects the characteristics of the image in the input area, and selects an image requiring gradation reproducibility. On the other hand, a matrix excellent in gradation reproducibility is selected, and a matrix excellent in resolution is selected for an image in which resolution is required.

(Second Embodiment) FIG. 6 is a block diagram showing the structure of the second embodiment of the present invention, and the same reference numerals as those in FIG. 5 denote the same constituent elements.

In the present embodiment, the maximum and minimum values of the data contained in the matrix pattern are added to the switching conditions in addition to the switching of the matrix pattern by the average value described in the first embodiment.

That is, in the first embodiment, when the average density is lower than the preset threshold value, the Bayer type dither matrix which unconditionally emphasizes the gradation is selected.
In this embodiment, by referring to the maximum value and the minimum value of the image data contained in the dither matrix, even if the average density is low, for example, in the case of a line drawing, the average density is low but resolution is required. In this case, it is possible to select a dither matrix that gives priority to the fatting type resolution and to perform high-quality printing.

In the circuit of FIG. 6, input data is input to the average value processing unit 111 and the maximum value / minimum value processing unit 117. The maximum value / minimum value processing unit 117 detects the maximum value and the minimum value of the image data included in the dither matrix immediately before the print data or before 1 LINE, and obtains the difference between them. Then, the difference is compared with a preset threshold value, and the maximum value −
When the minimum value is larger than the threshold value, “H” is output, and when the maximum value-minimum value is smaller than the threshold value, “L” is output to the determination unit 118 while controlling the timing with the average value processing unit 111.

FIG. 7 is a block diagram showing the configuration of the maximum / minimum value processing unit 117. In the figure, 171 is a maximum value detection unit, 172 is a minimum value detection unit, 173 is a maximum value-minimum value calculation unit that calculates the difference between them, and 174 is a threshold value comparison unit that compares the difference with a threshold value.

In addition to the threshold comparing unit 1 in the judging unit 118,
Twelve output terminals are also connected to obtain the comparison signal obtained by the method described in the first embodiment. Then, the determination unit 118
Performs the following processing with the comparison signal from the threshold value comparison unit 112 and the data width signal from the maximum / minimum value processing unit 117.

That is, when the output of the threshold value comparing unit 112 is "H", the "L" signal is output to the table ROM 113 regardless of the processing result of the maximum value / minimum value processing unit 117, and the fatting type in which resolution is prioritized. Dither conversion is performed using the dither matrix of.

Further, when the output of the threshold comparing section 112 is "L", that is, when the tone value-oriented request is output, the processing result of the maximum value / minimum value processing section 117 is referred to. And
When the output of the maximum value / minimum value processing unit 117 is “L”, that is, when the difference between the maximum value and the minimum value is smaller than the threshold value, it is regarded as a natural image or the like, and the signal of “H” is given to the table ROM as the gradation priority.
Output to 113. When the output of the maximum value / minimum value processing unit 117 is "H", the average density is low, and the difference between the maximum value and the minimum value is large, so it is regarded as a line drawing or the like, and the "L" signal is output to the table ROM 113 as the resolution priority. To do.

Table 1 collectively shows the operation of the above-mentioned determination unit 118, where a is a threshold for comparing the average densities of input images and b is a threshold for comparing the difference between the maximum value and the minimum value. The other points are the same as those in the first embodiment.

[0050]

[Table 1]

As described above, when the average density is low, by referring to the maximum value and the minimum value, the output of the line drawing or the like can be made higher in quality.

(Third Embodiment) FIG. 8 is a block diagram showing the configuration of the third embodiment of the present invention. In the figure, 2
Reference numeral 01 is a dither processing unit that performs the dithering process (1) that emphasizes gradation, 202 is a dither processing unit that performs the dither process (2) that emphasizes resolution, and 203 is dithered by the dither processing unit 201 and the dither processing unit 202. A selector circuit that selects and outputs one of the two output signals, and a control unit (control unit) 204 that outputs the select signal to the selector circuit 203 in matrix units.

Also in this embodiment, the actual coordinates (X, Y) and the block coordinates (U, V) are introduced as described above, and the relationship between them is described as having the relationship shown in FIG. .

The input image signal is input to the dither processing unit 201 and the dither processing unit 202, respectively. With respect to the input image signal, the dither processing unit 201 performs dither conversion with emphasis on gradation, and the dither processing unit 202 performs dither conversion with emphasis on resolution.

The input image signal processed by the dither processing unit 201 and the dither processing unit 202 is the selector circuit 20.
3 is input, and one is selected by a select signal from the control unit 204 and output. The control unit 204 has both main scanning direction and sub-scanning direction counting means, and switches the select signal in matrix units.

An image of the image thus processed is shown in FIG. Through the above-described processing, the dithered output signal is obtained using the dither matrix having different characteristics in matrix units as shown in FIG.

FIG. 10 shows a more specific circuit configuration of this embodiment. Further, for simplification of description, it is assumed that the input image signal is 8 bits, the dither matrix is 4 × 4, and the dither processing is 1-bit binary dither processing.

The main-scanning counter 213 and the sub-scanning counter 214 are connected to the address input terminals of the table ROM 211, respectively, and output the coordinate signals representing the respective coordinates in the dither matrix to the table ROM 211 and the control circuit 215. Further, the main scanning counter 213 and the sub scanning counter 214 output a carry signal indicating the final value of each scanning to the control circuit 215.

The control circuit 215 generates a select signal that is switched for each matrix from the coordinate signal and the carry signal, and outputs the highest address bi of the table ROM 211.
output to t. This select signal is a signal indicating the type of dither matrix. When it is “L”, it means that the dither matrix that emphasizes resolution is selected, and when it is “H”, the dither matrix that emphasizes gradation is selected. Represent
An example of this dither matrix is as shown in FIG.

The signals generated by the main scanning counter 213, the sub scanning counter 214 and the control circuit 215 are shown in FIG.
It is shown in FIG. As described above, the signals generated by the main scanning counter 213, the sub scanning counter 214, and the control circuit 215 are input to the address input terminal of the table ROM 211, and the dither matrix is selected by the select signal generated by the control circuit 215. , Each scan counter 213, 21
The coordinate is selected by the coordinate signal generated by 4,
The table ROM 211 performs table conversion into a corresponding dithering threshold value and outputs it to the comparator circuit 212.

The comparator circuit 212 compares the input image signal with the threshold value input from the table ROM 211,
The 1-bit signal is subjected to dither conversion and output.

As described above, printing is performed by switching the dither matrix having different characteristics for each matrix unit, so that it is possible to improve the gradation without lowering the resolution.

[0063]

As described above, according to the present invention,
Depending on the characteristics required for the image, for example, by referring to the average value and the maximum value and the minimum value of the image data included in the adjacent dither matrix and switching and using a plurality of threshold matrices having different resolutions, the resolution is improved. There is an effect that the resolving power can be maintained in a necessary area, and the necessary gradation reproducibility can be obtained in an area where gradation reproducibility in a low density area is required.

Further, according to the present invention, by switching the threshold matrices having different resolutions for each matrix,
It becomes possible to improve the gradation while maintaining a sufficient resolution for an image requiring a resolution.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between real coordinates and block coordinates.

FIG. 3 is an explanatory diagram showing a result of dither processing.

FIG. 4 is an explanatory view showing one column of a threshold matrix of a resolution-oriented type and a gradation-oriented type.

FIG. 5 is a block diagram showing a specific circuit configuration of the first embodiment.

FIG. 6 is a block diagram showing a configuration of a second exemplary embodiment of the present invention.

7 is a block diagram showing a configuration of a maximum / minimum value processing unit in FIG.

FIG. 8 is a block diagram showing a configuration of a third exemplary embodiment of the present invention.

9 is an explanatory diagram showing an image of an image processed by the circuit of FIG.

FIG. 10 is a block diagram showing a specific circuit configuration of a third embodiment.

FIG. 11 is an explanatory diagram showing signals reproduced by the respective parts of FIG.

FIG. 12 is an explanatory diagram showing input / output characteristics of the hard copy device.

FIG. 13 is an explanatory diagram showing an example of dot concentration type and dot fraction type threshold matrices.

FIG. 14 is a block diagram showing a schematic configuration of a conventional example.

[Explanation of symbols]

 Reference Signs List 101 dither processing unit (control means) 102 average value generation circuit 103 threshold value comparison unit 201 dither processing unit 202 dither processing unit 203 selector circuit 204 control unit (control means)

Claims (7)

[Claims] 1. An image processing apparatus that performs image processing using the systematic dither method, prepares a plurality of threshold matrices having different resolving powers for dither processing, and specifies from among these threshold matrices according to characteristics required for an image. An image processing apparatus comprising: a control unit that selects and uses the threshold matrix. 2. A threshold matrix is provided with two types of matrices of the same size having different resolving powers, and a dot concentration type matrix is adopted as the lower one of the resolving powers, and the control means is included in the matrix immediately before the print data. The average value of the image data to be compared is compared with a predetermined threshold value, and when the average value is smaller than the threshold value, the higher resolution matrix is selected. The image processing apparatus according to claim 1, wherein a matrix is selected. 3. The control means sets the threshold value based on the average value of the image data included in the matrix immediately before the print data and the maximum value and the minimum value of the image data. Image processing device. 4. When a matrix having a higher resolving power is selected and the difference between the maximum value and the minimum value of the image data included in the matrix immediately before the print data is smaller than a predetermined value, switching to a dot-concentrated matrix is performed. The image processing apparatus according to claim 2 or 3, characterized in that: 5. An image processing apparatus that performs image processing using the systematic dither method, prepares a plurality of threshold matrices having different resolving powers for dither processing, and selects a specific threshold matrix for each matrix from these. An image processing apparatus comprising a control unit used as the image processing apparatus. 6. A threshold matrix is provided with two types of matrices of the same size having different resolving powers, a dot concentration type matrix is adopted as the lower resolution matrix, and a dot dispersion type matrix is adopted as the higher resolution matrix. The image processing apparatus according to claim 5, wherein a matrix is adopted. 7. The image processing apparatus according to claim 5, wherein the control means selects two types of matrices for each matrix.