JPH09191411A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of gradation and resolution of a full color image and to suppress the deterioration of the image in an image forming device executing a dither processing by means of a systematic dither method and forming the full color image. SOLUTION: In a color processing operation part 101, an image processing such as masking and mapping is executed on the input image signals of R (red), G (green) and B (blue) and the output signals of M (Magenta), C (cyanogen), Y (yellow) and B (black) are obtained. A shifter 102 compresses data and data for one line are stored in a line buffer 103. Then, the dither processing is executed by using a threshold matrix given by a dither processing circuit 104. At that time, the different threshold matrixes are prepared for respective inputted colors and the appropriate threshold matrix is selected in accordance with the gradation of the respective colors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, Y, M,
The present invention relates to an image forming apparatus applicable to a color hard copy apparatus that processes color image signals such as C and K, and more particularly to an image forming apparatus that performs image processing using a systematic dither method.

[0002]

2. Description of the Related Art In recent years, a system for handling a color image using a computer has been actively developed in response to a demand for colorization of printed matter and the like. In addition, an electrophotographic color printer has been developed as a computer hard copy device, and due to higher performance of the host computer and the controller that is the image generation unit of the printer, not only conventional monochrome printing but also color images are handled. Printing is becoming practical and widespread.

There are several methods such as a dither method, a density pattern method, an error diffusion method, and a pulse width modulation method as a method for printing a full-color image with gradation using such a color printer. In particular, the systematic dither method has received attention because of its relatively simple hardware configuration.

FIG. 18 is a block diagram showing a schematic configuration of a conventional general image forming 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.

[0007]

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

That is, a color hard copy apparatus normally prints with four colors of cyan (C), magenta (M), yellow (Y), and black (K), but the gradation that can be reproduced for each color is not constant. However, using a single threshold matrix may reduce the overall gradation.

In the case of printing with the above-mentioned four colors, if a threshold matrix is created so that both gradation and resolution are compatible, when printing on a transparent original such as an OHP sheet, a single matrix is created due to the effect of transmitted light. An image may be difficult to see when a threshold matrix is used.

Further, in the case of printing with the above four colors, if a dot concentration type threshold matrix is used to obtain gradation, the resolution is lowered, and a dot dispersion type threshold matrix is used to increase the resolution. To solve the problem at the same time for images in which character characters such as black characters and color characters that require resolution and natural images that require gradation are mixed. Is ruthlessly difficult.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an image forming apparatus capable of preventing deterioration in gradation and resolution of a full-color image.

Further, according to the present invention, it is possible to prevent the image from becoming difficult to see, and to maintain the gradation for an image such as a natural image which requires gradation, and to obtain a high resolution of character data or the like. It is an object of the present invention to provide an image forming apparatus capable of performing high-resolution processing on an image that needs to be processed and having less image deterioration.

[0013]

An image forming apparatus according to the present invention is configured as follows.

(1) In an image forming apparatus for forming a color image by performing a dithering process by the systematic dither method, a generating means for generating color image information based on input information, and a plurality of colors of the generated color image information. Color conversion means for converting the frame sequential image information, compression means for compressing the converted frame sequential image information, and information conversion means for converting the pixel value of the compressed image information into a predetermined value.

(2) In the image forming apparatus of the above (1), the information converting means uses an nxn (n is a positive integer) spatial filter to convert the information into a predetermined value.

(3) In the image forming apparatus of (2), the spatial filter has a plurality of different threshold matrices, and a specific threshold matrix is selected and used according to the characteristics of the image.

(4) In the image forming apparatus of (2), the spatial filter has a plurality of different threshold matrices, and a specific threshold matrix is selected and used by a control signal from the outside.

(5) In the image forming apparatus of the above (2), the spatial filter has a plurality of different threshold matrices having an information amount of m bits (m is a positive integer) per pixel, and the spatial filter has a plurality of threshold value matrices depending on the characteristics of the image. A specific threshold matrix is selected and used.

(6) In the image forming apparatus according to the above (2), the spatial filter has a plurality of different threshold matrices each having an information amount of m (m is a positive integer) bits per pixel, and is controlled by an external control signal. A specific threshold matrix is selected and used.

(7) In the image forming apparatus according to (3) or (4), the spatial filter has a plurality of threshold matrices having different sizes.

(8) In the image forming apparatus of the above (7), the plurality of threshold matrices having different sizes are such that the number of rows and the number of columns of the maximum size matrix are integer multiples of the number of rows and the number of columns of other matrices, respectively. I tried to be.

(9) In the image forming apparatus of (4) or (6), the external control signal is a signal for determining the type of recording paper.

(10) In an image forming apparatus for forming a color image by performing dither processing by the systematic dither method,
Generating means for generating color image information based on input information,
Color conversion means for converting the generated color image information into frame sequential image information of a plurality of colors; compression means for compressing the converted frame sequential image information; storage means for storing the compressed image information; Further, it is provided with a discriminating means for discriminating character data from the image information and an information converting means for converting the pixel value of the compressed image information into a predetermined value.

(11) In the image forming apparatus of the above (10), the discrimination means discriminates the character data by detecting the white data from the image information stored in the storage means.

(12) In the image forming apparatus according to (10) or (11) above, the information converting means uses an nxn (n is a positive integer) spatial filter to convert the information into a predetermined value.

(13) In the image forming apparatus according to (12), the spatial filter has a plurality of different threshold matrices, and a specific threshold matrix is selected and used according to the discrimination result of the discriminating means.

(14) In the image forming apparatus according to the above (12), the spatial filter has two kinds of threshold matrices having different resolutions.

[0028]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings.
A case where the color printer is applied to a color printer will be described in detail.

(First Embodiment) FIG. 1 is a block diagram showing the arrangement of a processing system according to the first embodiment of the present invention. In the figure, reference numeral 101 denotes a color processing operation unit (color conversion means) for converting color image information generated based on print information into frame sequential image information corresponding to each of a plurality of colors of developer, and an input signal (R,
G, B) are subjected to image processing such as masking, UCR, inking, direct mapping, etc., and output signals (C, M,
Y, K). Reference numeral 102 denotes a shifter (compressing means) that compresses the recording pixels of the frame sequential image information to a required accuracy.
Data is thinned from the signal output from the color processing calculation unit 101 to a required output accuracy. Reference numeral 103 denotes a line buffer (recording means) for storing the compressed image information, and stores data for one line. Reference numeral 104 denotes a dither processing circuit (information conversion means) that converts the recording pixels of the compressed color image information into a predetermined value, and performs dither processing using a given threshold matrix.

Next, the operation of this embodiment will be described. The color processing calculation unit 101 performs color processing such as masking, UCR, blacking, and direct mapping on the input R, G, B data, and outputs the data to the shifter 102. The shifter 102 performs thinning processing on the input data and compresses the bit width to the required output accuracy. This is performed in order to reduce the capacity of the line buffer by dropping extra bits because the maximum number of gradations that can be reproduced is defined by the size of the threshold matrix and the number of gradations that one pixel has. .

[0031]

[Equation 1]

The decimated input values are stored in the line buffer 103 and input to the dither processing circuit 104. In the dither processing circuit 104, the input data is binarized using the nxm dither matrix for each color by the color select signal CSEL, and the output value is obtained.

Next, the processing in the dither processing circuit 104 will be described in detail. FIG. 2 shows the dither processing circuit 104.
FIG. In the figure, 201 is a main scanning direction counter, which counts in synchronization with an image clock (not shown) and resets when the count output is m. 202
Is a sub-scanning direction counter, which counts in synchronization with a horizontal synchronizing signal (not shown) and resets when the count output is n.

Reference numeral 203 denotes a ROM which sets an address according to the output data of the main scanning direction counter 201, the sub scanning direction counter 202 and the color select signal CSEL, and outputs a predetermined value stored in advance. 20
A digital comparator 4 compares the input signals P and Q, and when P> Q, the output becomes "H". Reference numeral 205 is a driver, and 206 is a NOT circuit.

The operation will be described below. For simplification of description, the dither matrix is 4x as shown in FIG.
4 (n = m = 4) spatial filters and the case where the input data is 8 bits will be described.

First, the input image data of magenta /
DO7 to / DO0 are input to the P input terminal of the comparator 204 via the NOT circuit 206. The output value of the main scanning direction counter 201 is A1 to A of the ROM 203.
The output value of the sub-scanning direction counter 202 is RO at port 0.
The color select signal (00) is input to the A5 to A4 ports of the ROM 203 to the A3 to A2 ports of the M203, and the ROM 203 is set with the address by the data input to the A5 to A0 ports, and the data stored at the address is set. Is input to the Q input terminal of the comparator 204 and compared with the input image data.

At this stage, the value of the image data is "00".
"H" indicates the lowest concentration, and "FFH" indicates the highest concentration. Therefore, the output of the comparator 204 becomes "H" when the input image data is in the ROM 203.
This is a case where the density is higher than the set value of. Then, the output of the comparator 204 is output as an 8-bit signal “FFH” or “00H” via the driver 205.

When the processing for one screen of magenta is completed by the above operation, the input image data of cyan / D07
~ DO0 is the comparator 20 via the NOT circuit 206
4 is input to the P input terminal. Then, similarly to the above, the output value of the main scanning direction counter 201 is A1 of the ROM 203.
The output value of the sub-scanning direction counter 202 is R at the A0 port.
The color select signal (01) is input to the A5 to A4 ports of the ROM 203 to the A3 to A2 ports of the OM 203, and the ROM 203 is set with the address by the data input to the A5 to A0 ports, and the data stored at that address is stored. Is input to the Q input terminal of the comparator 204, is compared with the input image data, and the driver 2
It is output via 05.

When the processing for one cyan screen is completed,
Next, the yellow input image data / DO7 to / DO0 is N
It is input to the P input terminal of the comparator 204 via the OT circuit 206. The output value of the main scanning direction counter 201 is output to the A1 to A0 ports of the ROM 203, and the output value of the sub scanning direction counter 202 is A3 to A2 of the ROM 203.
The color select signal (10) is output to the ROM 203 to the port.
Input to the A5 to A4 ports of the
An address is set by the data input to the A0 port, the data stored at the address is input to the Q input terminal of the comparator 204, is compared with the input image data, and is output via the driver 205. It

When the processing of the yellow 1 screen portion is completed, the next black input image data / D07 to / D0O is input.
Is input to the P input terminal of the comparator 204 via the NOT circuit 206. Then, the main scanning direction counter 20
The output value of 1 is the A1 to A0 ports of the ROM 203, and the output value of the sub-scanning direction counter 202 is the A3 to A3 of the ROM 203.
Color select signal (11) is sent to ROM2 at port A2
03 is input to the A5 to A4 ports, and the ROM 203 is A
The address is set by the data input to the ports 5 to A0, the data stored at the address is input to the Q input terminal of the comparator 204, the input image data is compared, and the data is input via the driver 205. Is output.

The dither processing for one screen is performed by the above-described four-step operation for each color. By this operation,
Since the dither matrix data for each color is stored in the ROM 203, it is possible to set a dither matrix that takes into consideration the gradation of each color instead of a single dither matrix. Is difficult to determine, it is possible to arbitrarily set the number of output gradations. FIG. 4 schematically shows an example of the dither pattern.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In the first embodiment,
The input image is processed for the color with low gradation by changing the threshold value without changing the size of the dither matrix for each color by the dither processing circuit 104. In addition to the first embodiment, a large dither matrix is used for a color having a high gradation and a small dither matrix is used for a color having a low gradation.

At this time, the size of the large dither matrix is nxm, and the size of the small dither matrix is p.
If xq, p and q are divisors of n and m, respectively, and the small dither matrix has a period (p,
It is repeated in q). As an example, n = m = 4, p
The dither matrix for the case of = q = 2 is shown in (a) and (b) of FIG.

According to the second embodiment, a small matrix size is used for a color having low gradation by setting the small matrix size to a matrix size that takes a divisor of the large matrix size. By doing so, the number of output gradations of each color can be arbitrarily set.

(Third Embodiment) In the first and second embodiments, the case where the input image is converted into the binary output data by the dither processing has been described. The dither processing circuit 104 is changed to a multi-value instead of a binary one, and an operation of arbitrarily setting the depth direction of the dither matrix according to the gradation of each color is performed.

FIG. 6 is a block diagram of the dither processing circuit 104 in the third embodiment. In the figure, reference numeral 301 denotes a main scanning direction counter which counts in synchronization with an image clock (not shown) and resets when the count output is m. A sub-scanning direction counter 302 counts in synchronization with a horizontal synchronization signal (not shown), and the count output is n.
Reset with.

Reference numeral 303 denotes a ROM which sets an address according to the output data of the main scanning direction counter 201, the sub scanning direction counter 202 and the color select signal CSEL and outputs a predetermined value stored in advance. 30
Reference numeral 4 denotes a plurality of digital comparators, which compare the input signals P and Q, and when P> Q, the output becomes "H". A ROM 305 sets an address based on the output data of the digital comparator 304 and the output data of the color select signal CSEL, and outputs a predetermined value stored in advance. 306 is a NOT circuit.

The operation will be described below. For simplification of description, for example, as shown in FIG. 7, the dither matrix of each color is 4 × 4 (n = m = 4), and a maximum of 2 bits (4 dither matrices per color) are input in the depth direction of the dither matrix. The case where the data is 8 bits will be described.

First, the magenta input image data /
DO7 to / DO0 are each input to the P input terminal of the comparator 304 via the NOT circuit 306. An address is set in the ROM 303 by the output value of the main scanning direction counter 301, the output value of the sub scanning direction counter 302, and the color select signal (00), and the threshold value of the matrix for the depth direction stored at the address is set. Data (32 bits in this example) is read out and input to the Q input terminal of the comparator 304 by 8 bits, respectively, and compared with the input image data.

At this stage, the value of the image data is "00".
"H" indicates the lowest concentration, and "FFH" indicates the highest concentration. Therefore, the output of the comparator 304 becomes “H” when the input image data has a higher density than the set value of the ROM 303.

Further, an address is set in the ROM 305 by the output value of each comparator 304 and the color select signal (00), and the predetermined value stored in the address is output. By this operation, the output image data is determined by the comparison result with the threshold value of the dither matrix input to the four comparators 304.

When the processing for one magenta screen is completed by the above-mentioned operation, the cyan input image data / DO7
~ / DO0 passes through the NOT circuit 306 to the comparator 3
04 input to the P input terminal. Then, similar to the above, the output value of the main scanning direction counter 301, the output value of the sub scanning direction counter 302, and the color select signal (01)
By the ROM 303, the address is set, the threshold value matrix data for the depth direction stored at the address is read out, and is input to the Q input terminal of the comparator 304 by 8 bits, respectively, and is input to the input image data. A comparison is made.

Further, an address is set in the ROM 305 by the output value of each comparator 304 and the color select signal (01), and the predetermined value stored in the address is output.

When the processing for one cyan screen is completed,
Next, the yellow input image data / DO7 to / DO0 is N
It is input to the P input terminal of the comparator 304 via the OT circuit 306. Then, the main scanning direction counter 30
The output value of 1, the output value of the sub-scanning direction counter 302, and the color select signal (10) set the address in the ROM 303, and the threshold value matrix data for the depth direction stored at the address is read out. 8 bits each are input to the Q input terminal of the comparator 304,
The comparison with the input image data is performed.

Further, an address is set in the ROM 305 by the output value of each comparator 304 and the color select signal (10), and the predetermined value stored in the address is output.

When the processing for one yellow screen is completed, the next black input image data / DO7 to / DO0 is input.
Are input to the P input terminal of the comparator 304 via the NOT circuit 306. Then, the output value of the main scanning direction counter 301, the output value of the sub scanning direction counter 302,
And the ROM 303 according to the color select signal (11)
Address setting is performed, the threshold value matrix data for the depth direction stored at the address is read out, and input to the Q input terminal of the comparator 304 by 8 bits each, and the comparison with the input image data is performed. Be seen.

Further, an address is set in the ROM 305 by the output value of each comparator 304 and the color select signal (11), and the predetermined value stored in the address is output.

The multi-value dither processing for one screen is performed by the above-described four-step operation for each color. By this operation, the data of the dither matrix is stored in the ROM 303 for each color, and the data of the ROM 305 can be controlled by the color select signal CSEL. Therefore, a comparator for the maximum depth direction of the dither matrix is prepared. Since it is possible to determine whether the output data of each comparator is valid or invalid, the depth direction of the dither matrix can be set arbitrarily according to the gradation of each color. FIG. 8 schematically shows an example of the dither pattern.

(Fourth Embodiment) FIG. 9 is a block diagram showing the arrangement of a processing system according to the fourth embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same constituent elements. In the figure, 1
Reference numeral 01 is a color processing operation unit, which performs image processing such as masking, UCR, blacking, and direct mapping on an input signal (R, G, B) to obtain an output signal (C, M, Y, K).
Reference numeral 102 is a shifter, which thins out data from the signal output from the color processing calculation unit 101 to a required output accuracy. 1
A line buffer 03 stores data for one line. A dither processing circuit 104 performs dither processing using a given threshold matrix.

Next, the operation of this embodiment will be described. Since the operation of this embodiment is similar to that of the first embodiment of FIG. 1, detailed description thereof will be omitted. However, in the dither processing circuit 104, the input data is nx for each color by the transparent original detection signal OHP.
Binarization is performed using the m dither matrix to obtain an output value.

FIG. 10 is a block diagram of the dither processing circuit 104 of FIG. 9, and the same reference numerals as those in FIG. 2 indicate the same components. The operation of this circuit is the same as that of the circuit of FIG. 2, and thus a detailed description thereof will be omitted. However, the ROM 203 sets an address based on the output data of the main scanning direction counter 201, the sub scanning direction counter 202, and the transparent original detection signal OHP. , Outputs a predetermined value stored in advance. Further, when it is assumed that the dither processing as shown in FIG. 3 is performed, the transparent original detection signal OHP is input to the A4 port of the ROM 203. This transparent original detection signal OHP
Is "H" when the output sheet is a transparent original and "L" when it is a normal original. Then, the dither processing for one screen is performed in the same manner as the above-described embodiment.

According to the operation of this embodiment, since the data of the dither matrix according to the type of the original is stored in the ROM 203, it is possible to set the dither matrix considering the type of the output original instead of the single dither matrix. As a result, since the OHP is the detection signal of the transparent original, it is difficult to judge the gradation due to the scattered light of the toner due to the transmitted light, but it is possible to make an arbitrary setting such as reducing the number of output gradations.

(Fifth Embodiment) In the above-described fourth embodiment, the input image is changed by the dither processing circuit 104 by changing the threshold value without changing the size of the dither matrix for each color. Was processed for
In this embodiment, in addition to the above-mentioned fourth embodiment, a large dither matrix is used for a normal document and a small dither matrix is used for a transparent document.

According to the second embodiment, for example, a dither matrix as shown in FIG. 5 is used, and the small matrix size is set to a matrix size that takes a divisor of the size of the large matrix. The output gradation number can be arbitrarily set by using a small matrix size for transparent originals such as.

(Sixth Embodiment) In the fourth and fifth embodiments, the case where the input image is converted into the binary output data by the dither processing has been described. The dither processing circuit 104 is changed to a multi-value instead of a binary, and an operation of arbitrarily setting the depth direction of the dither matrisk according to the type of the output document is performed.

FIG. 11 is a block diagram of the dither processing circuit 104 in the sixth embodiment, and the same symbols as those in FIG. 6 indicate the same components. ROM 303 in this circuit
Is a main scanning direction counter 201 and a sub scanning direction counter 2
02 and the output data of the transparent original detection signal OHP, an address is set, and a predetermined value stored in advance is output. Further, the ROM 305 is a digital comparator 3
An address is set by the output data from 04 and the output data of the transparent original detection signal OHP, and a predetermined value stored in advance is output.

The operation will be described below. The operation of this embodiment is similar to that of the embodiment of FIG. 6, and assuming that the dither processing as shown in FIG. 7 is performed, first, the input image data /
DO7 to / DO0 are each input to the P input terminal of the comparator 304 via the NOT circuit 306. Then, the ROM 303 is set with an address by the output value of the main scanning direction counter 301, the output value of the sub scanning direction counter 302, and the transparent original detection signal OHP, and the threshold value data of the matrix for the depth direction stored at the address. (32 bits in this example) is read out and the comparator 304
8 bits are respectively input to the Q input terminals of the above, and are compared with the input image data.

At this stage, the value of the image data is "00".
"H" indicates the lowest concentration, and "FFH" indicates the highest concentration. Therefore, the output of the comparator 304 becomes “H” when the input image data has a higher density than the set value of the ROM 303.

Further, an address is set in the ROM 305 by the output value of each comparator 304 and the transparent original detection signal OHP, and the predetermined value stored in the address is output. At this time, the transparent original detection signal OHP is
When the output paper is a transparent original, "H" is output, and when it is a normal original, "L" is output. By this operation, the output image data is determined by the comparison result with the threshold value of the dither matrix input to the four comparators 304.

In this way, the multi-valued dither processing for one screen is performed, but according to the operation of this embodiment, the data of the dither matrix according to the type of the output document is stored in the ROM 303.
Since it is possible to control the data stored in the ROM 305 by the transparent original output signal OHP, the comparator for the maximum depth direction of the dither matrix is prepared and the output data of each comparator is enabled or disabled. You can decide what to do. Therefore, the depth direction of the dithermat risk can be arbitrarily set according to the type of the output document. FIG. 12 schematically shows an example of the dither pattern.

(Seventh Embodiment) FIG. 13 is a block diagram showing the arrangement of a processing system according to the seventh embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same constituent elements. In the figure,
Reference numeral 101 denotes a color processing calculation unit which performs image processing such as masking, UCR, blacking, and direct mapping on an input signal (R, G, B) to obtain an output signal (C, M, Y, K). Reference numeral 102 is a shifter, which thins out data from the signal output from the color processing calculation unit 101 to a required output accuracy. A line buffer 103 stores data for n lines. A dither processing circuit 104 and a character detection unit (determination means) 105 determine whether a predetermined area of the data output from the line buffer 103 is character data and output a determination signal. Then, the dither processing circuit 104 selects a threshold matrix by the discrimination signal output from the character detection unit 105 and performs dither processing.

Next, the operation of this embodiment will be described. Since the operation of this embodiment is the same as that of the embodiment of FIG. 1, detailed description thereof will be omitted. However, assuming that the number of pixels of the image in the main scanning direction is W, the line buffer 103 has image data of a rectangular area size of n × W. Memorize Then, the image data stored in the line buffer 103 is input to the character detection unit 105, where it is determined whether or not it is a character, and the character determination signal IMG / CHR is output. This discrimination signal is input to the dither processing circuit 104 together with the image data.

In the dither processing circuit 104, when the input data is discriminated by the character discrimination signal IMG / CHR, the input data is binarized by the dot dispersion type nxm dither matrix. When it is determined that the character is not a character, binarization is performed by the dot concentrated nxm dither matrix, and the output value is obtained.

Next, the processing in the character detection unit 105 will be described in detail. This character detection utilizes the fact that the print area is smaller than the image image when there is character data, and the determination is made by counting the number of pixels of data that is not printed, that is, color data.

FIG. 14 is a block diagram showing the structure of the character detection unit 105. In the figure, 401 is a comparator that compares input data with white data, 402 is a counter that counts the number of pixels of white data, 403 is a counter that counts the number of pixels of color data, and 404 and 405 are input data and setting, respectively. A comparator that compares the value,
406 is a latch.

The operation will be described below. The input data input to the character detection unit 105 is input to the comparator 401. The comparator 401 sorts the input data into color data and white data for each pixel by comparing the input data with white data that is a reference value, and the sorting result is used for the white data counter 402 and the color data. Counter 403
Output to The white data counter 402 counts the number of pixels of white data, and counts the count value by the comparator 4
04. Further, the color data counter 403 is
The number of pixels of color data is counted, and the count value is output to the comparator 405.

The comparators 404 and 405 determine whether or not it is a character by comparing a preset reference value (threshold value) with the input count value, and send the determination result to the latch circuit 406. Then, the latch circuit 406 outputs the character discrimination signal IMG / CHR. The white data corresponds to the actual background color as the background color, and for example, there are light cream and blue portions.

Next, the operation of the character detecting section 105 will be described in more detail with reference to the flowchart of FIG. As shown in FIG. 14, the character detection unit 105 includes a comparator 401 and counters 402 and 403. When character data is present, the fact that the printing area is smaller than that of an image image is used, and data not printed is used. That is, whether or not it is a character is determined by counting the number of pixels of color data with the white data counter 402.

First, the white data counter 402 and the color data counter 403 are reset (step S101,
S102), the comparator 401 checks whether the input data is white (step S103). When the input data is white, the count value W of the white data counter 402 is incremented by +1 (step S104), and the white The comparator 404 checks whether the count value of the data counter 402 is greater than or equal to the threshold value (step S105).

Then, if the count value of the white data counter 402 exceeds the threshold value set in advance in the comparator 404 of the counter circuit, it is judged to be a character (step S106), and the character detection unit 105 outputs the character discrimination signal IM.
G / CHR (H) is output. Also, step S103
If the input data is not white, the count value X of the color data counter 403 of the counter circuit is incremented by +1 (step S107), and it is confirmed whether the next input data is white (step S108). If the input data is not white, the operations from step S107 to step S108 are repeated.

When the input data is white in step S108, the comparator 405 confirms whether the count value X of the color data counter 403 is equal to or more than the threshold value (step S108).
109), if the count value exceeds a threshold value set in advance in the comparator 405 of the counter circuit, it is determined as an image (step S110), and the character detection unit 105
To output a character discrimination signal IMG / CHR (L). If the count value of the color data counter 403 does not exceed the threshold value in step S109, the color data counter 403 is reset (step S111), and step S111 is performed.
The operation from 103 is performed.

FIG. 16 is a block diagram of the dither processing circuit 104 of FIG. 13, and the same symbols as those in FIG. 2 indicate the same components. The operation of this circuit is the same as that of the circuit of FIG. 2, and thus detailed description thereof will be omitted, but the ROM 203 sets an address by the output data of the main scanning direction counter 201, the sub scanning direction counter 202, and the character discrimination signal IMG / CHR. Then, the predetermined value stored in advance is output.
The character discrimination signal is input to the A4 port of the ROM 203. When the character discrimination signal is "H", that is, when the input data is character data, the ROM 203 stores A4 to A0.
An address is set by the data input to the port, the dot dispersion type dither matrix data stored at the address is selected, input to the Q input terminal of the comparator 204, and compared with the input image data. Be seen.

When the character discrimination signal is "L", that is, when the input data is image data, the ROM 203
Address setting is performed by the data input to the A4 to A0 ports, the dot concentration type dither matrix data stored at the address is selected and input to the Q input terminal of the comparator 204, and the input image data and Are compared.

At this stage, the value of the image data is "00".
"H" indicates the lowest concentration, and "FFH" indicates the highest concentration. Therefore, the output of the comparator 204 becomes “H” when the input image data has a higher density than the set value of the ROM 203.

FIG. 17 shows an example of a dot concentrated type and a dot dispersed type dither matrix used here. The dot concentration type dither matrix is of a type generally called a fatning type. The dot dispersion type dither matrix is of a type generally called Bayer type, and the threshold distribution is arranged diagonally so as to have a screen angle of 45 degrees to double the apparent resolution in the vertical and horizontal directions. It was done. The output of the comparator 204 is output as an 8-bit signal "FFH" or "00H" via the driver 205.

With the above operation, the processing for one screen is completed. According to the present embodiment, the data of a plurality of dither matrices is stored in the ROM 203, the character data and the image data are discriminated by controlling the character discrimination signal, and the dither matrix can be selected based on the result, so that the image has Appropriate dither processing can be performed depending on the property.

[0087]

As described above, according to the present invention,
By preparing a different dither matrix for each input color and arbitrarily setting it according to the gradation of each color, it is possible to prevent deterioration of the gradation and resolution of a full-color image.

Further, according to the present invention, it is possible to prevent a full-color image or the like from being unsightly by preparing different dither matrices depending on the type of the output document.

Further, according to the present invention, the characteristics of the image in the input region are detected by preparing different dither and scan for the input data, and for the image requiring the gradation reproducibility. Selects a matrix with excellent gradation reproducibility, and selects a matrix with excellent resolution for images that require resolution, so that for images that require gradation such as natural images. In contrast, it maintains gradation and performs high-resolution processing for images that require high resolution, such as character data,
It is possible to perform dither processing with little image deterioration.

[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 a block diagram of the dither processing circuit of FIG.

FIG. 3 is a schematic diagram of a formed image after dithering in the first embodiment.

FIG. 4 is a schematic diagram of a dither pattern in the first embodiment.

FIG. 5 is a schematic diagram of a dither pattern in the second embodiment of the present invention.

FIG. 6 is a configuration diagram of a dither processing circuit according to a third embodiment of the present invention.

FIG. 7 is a schematic diagram of a dither pattern in the third embodiment.

FIG. 8 is a schematic diagram of a dither pattern in the third embodiment.

FIG. 9 is a block diagram showing a configuration of a fourth exemplary embodiment of the present invention.

FIG. 10 is a block diagram of the dither processing circuit of FIG.

FIG. 11 is a configuration diagram of a dither processing circuit according to a sixth embodiment of the present invention.

FIG. 12 is a schematic diagram of a dither pattern in the sixth embodiment.

FIG. 13 is a block diagram showing the configuration of a seventh embodiment of the present invention.

FIG. 14 is a block diagram showing the configuration of the character detection unit shown in FIG.

FIG. 15 is a flowchart showing the operation of the character detection unit of FIG.

16 is a block diagram of the dither processing circuit of FIG.

FIG. 17 is a schematic diagram of a dither pattern in the seventh embodiment.

FIG. 18 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

 Reference Signs List 101 color processing calculation unit (color conversion unit) 102 shifter (compression unit) 103 line buffer (storage unit) 104 dither processing circuit (information conversion unit) 105 character detection unit (determination unit)

Claims (14)

[Claims] 1. In an image forming apparatus for forming a color image by performing a dithering process by the systematic dither method, a generation means for generating color image information based on input information, and the generated color image information of a plurality of colors. A color conversion unit for converting the frame sequential image information, a compression unit for compressing the converted frame sequential image information, and an information conversion unit for converting the pixel value of the compressed image information into a predetermined value. A characteristic image forming apparatus. 2. The information converting means is nxn (n is a positive integer)
The image forming apparatus according to claim 1, wherein the image is converted into a predetermined value by using the spatial filter. 3. The image forming apparatus according to claim 2, wherein the spatial filter has a plurality of different threshold matrices, and a specific threshold matrix is selected and used according to the characteristics of the image. 4. The image forming apparatus according to claim 2, wherein the spatial filter has a plurality of different threshold matrices, and a specific threshold matrix is selected and used by a control signal from the outside. 5. The spatial filter has a plurality of different threshold matrices having an information amount of m bits (m is a positive integer) per pixel, and a specific threshold matrix is selected and used according to the characteristics of an image. The image forming apparatus according to claim 2, which is characterized in that. 6. The spatial filter has a plurality of different threshold matrices having an information amount of m bits (m is a positive integer) per pixel, and a specific threshold matrix is selected and used by a control signal from the outside. The image forming apparatus according to claim 2, which is characterized in that. 7. The image forming apparatus according to claim 3, wherein the spatial filter has a plurality of threshold matrices having different sizes. 8. The plurality of threshold matrices having different sizes are characterized in that the number of rows and the number of columns of the maximum size matrix are integer multiples of the number of rows and the number of columns of other matrices, respectively. Image forming apparatus. 9. The image forming apparatus according to claim 4, wherein the control signal from the outside is a signal for determining the type of recording paper. 10. An image forming apparatus for forming a color image by performing a dither process by the systematic dither method, a generation unit for generating color image information based on input information, and the generated color image information of a plurality of colors. Color conversion means for converting into frame sequential image information, compression means for compressing the converted frame sequential image information, storage means for storing the compressed image information,
An image forming apparatus comprising: a discriminating unit that discriminates character data from stored image information; and an information converting unit that converts a pixel value of the compressed image information into a predetermined value. 11. The image forming apparatus according to claim 10, wherein the discrimination unit discriminates the character data by detecting white data from the image information stored in the storage unit. 12. The image forming apparatus according to claim 10, wherein the information converting means converts the information into a predetermined value using an nxn (n is a positive integer) spatial filter. 13. The image forming apparatus according to claim 12, wherein the spatial filter has a plurality of different threshold matrices, and a specific threshold matrix is selected and used according to the discrimination result of the discriminating means. 14. The image forming apparatus according to claim 13, wherein the spatial filter has two types of threshold matrices having different resolutions.