JPH1028224A - Image data processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image data processor for operating pixel density conversion and error diffusion processing, without increasing memory capacity. SOLUTION: A half-tone part 7 calculates the error data for each pixel to be stored in an error memory 8, according to the conversion ratio of pixel density in a pixel-density converting part 4 for the multilevel data of inputted pixels worth one line. Then, when the conversion ratio of the pixel density is less than '1', the half-tone part 7 calculates the error data for each pixel and stores the arithmetic result in the error memory 8. On the other hand, when the conversion ratio of the pixel density is more than '1', the half-tone part 7 calculates the average of the errors for every adjacently-inputted two pixels and stores the arithmetic result in the error memory 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data processing apparatus, and more particularly, to an image data processing apparatus for converting multi-value data into binary data by using an error diffusion method.

[0002]

2. Description of the Related Art Generally, facsimile, copy, OCR
The image data processing device used in the above-described apparatus converts an analog image signal input from a line sensor (sensor system) such as a CCD or a contact sensor into binary image data. Then, the facsimile transmits the converted binary image data to the destination via the modem. In copying, the converted binary image data is output to a printer to create a document. Also, OCR
Outputs the converted binary image data to a computer such as a personal computer.

In some cases, the pixel density of a sensor system such as a line sensor does not match the pixel density of a printing system such as a printer. For example, the image data obtained by the line sensor is 300 dpi, while the printer is 400 dpi.
Print with i. In this case, if the image data is output to the printer as it is, the displayed image is reduced.
Therefore, the image data processing device converts the pixel density of the data according to the pixel density of the printing system. For example, in the case of copying, the image data processing device enlarges the image data, that is, outputs the data of each input pixel twice, thereby doubling the number of pixels and increasing the pixel density.

In recent years, with the growing demand for natural and high-quality image display, error diffusion has been required to display multi-tone images on a binary display system (a printing system such as a printer capable of printing only binary values). The law has been used. The error diffusion method is known as a high-performance pseudo-gradation processing technique. Although the resolution is sacrificed macroscopically by using the error diffusion method, the multi-gradation is visually performed using a binary display system. Images can be obtained. In the image data processing by this error diffusion method, on / off (white / white) of a preset display or printing is set.
The difference (error) between the threshold value for determining black) and the multi-value data of the pixel to be displayed is temporarily stored for each pixel of the read one line. Then, the error is added to the multivalued data of the pixel for one line read next and the multivalued data of the pixel corresponding to the position of the pixel to be displayed and the multivalued data of the pixels around the pixel. After that, a comparison with a threshold value is performed to express a gradation.

[0005]

The pixel density conversion is performed prior to the error diffusion processing. Then, in the error diffusion process, an error for each pixel generated by the pixel density conversion is stored for each pixel. Therefore, when the pixel density is increased in the pixel density conversion, more error data must be stored as compared with the case where the density is not converted, so that a large-capacity memory is required and the device becomes large. There is.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an image data processing apparatus capable of performing pixel density conversion and error diffusion processing without increasing the memory capacity. Is to do.

[0007]

According to the first aspect of the present invention, image data composed of a plurality of lines is fetched in units of one line, and the image data of each line is quantized for each pixel and converted into multi-valued data. Then, the image data processing device converts the multi-valued data into binary data and outputs the binary data. The image data processing device calculates an average of multi-valued data of two adjacent pixels, and calculates the multi-valued data of the calculation result and A pixel density conversion circuit for selecting and outputting multi-valued data to convert the density of pixels constituting one line, and multi-valued data of the pixels whose density has been converted are sequentially input, and multi-valued data of each pixel A halftone circuit for converting and outputting binary data, calculating an error for each pixel, calculating an average of those errors for each two adjacent pixels, and outputting the calculation result as error data; Store the error data And gist that a error memory.

According to a second aspect of the present invention, in the image data processing apparatus according to the first aspect, the halftone circuit stores the error data of the preceding row stored in the error memory in the multi-value data of the pixel of interest. A first adder that performs an addition operation and outputs multi-value data of the operation result; multi-value data output from the first adder; multi-value data of the immediately preceding pixel is converted into binary data A second adder that adds error data generated during the conversion, and a clock signal that matches the input cycle of the multi-value data of the pixel, and outputs the second adder based on the clock signal. The multi-valued data to which the error data to be added is added to the multi-valued data until the multi-value data of the next pixel is input
A first register for holding the clock period, and converting the multi-valued data held in the first register into binary data and outputting the binary data; A binarization circuit that generates and outputs error data to be distributed to the next pixel and the next row of pixels, respectively;
An averaging circuit that holds the error data generated by the binarization circuit for one clock period, calculates an average of the held calculation result and the next input error data, and outputs the calculation result; The gist is to include

According to a third aspect of the present invention, in the image data processing device according to the second aspect, the halftone circuit receives the clock signal and outputs the clock signal from the binarization circuit based on the clock signal. A second register for holding the output error data for one clock period, an error operation of the error data output from the binarization circuit, and the error data held in the second register, and the operation result And a third adder that outputs the multivalued data of the above.

Therefore, according to the first aspect of the present invention,
The pixel density conversion circuit calculates the average of the multi-value data of two adjacent pixels, and selects and outputs the multi-value data of the calculation result and the multi-value data before the calculation to obtain the pixels of one line. Density is converted. The halftone circuit sequentially receives the multi-value data of the pixels whose density has been converted, converts the multi-value data of each pixel into binary data and outputs the binary data, calculates an error for each pixel, and calculates an error for each pixel. The average of those errors is calculated for each of the two pixels, the calculation result is output as error data, and stored in the error memory.

According to the second aspect of the present invention, the halftone circuit includes the first and second adders, the first register, the binarizing circuit, and the averaging circuit. The first adder performs an addition operation on the multi-value data of the target pixel with the error data of the previous row stored in the error memory, and outputs multi-value data of the operation result. In the second adder, error data generated when the multi-value data of the immediately preceding pixel is converted into binary data is added to the multi-value data output from the first adder. . In the first register, a clock signal that matches the input cycle of the multi-value data of the pixel is input, and based on the clock signal, the multi-value data to which the error data output from the second adder is added is Is held for one clock period until the multi-value data of the pixel is input. The binarization circuit converts the multi-valued data held in the first register into binary data and outputs the binary data. In addition, an error generated when converting the binary data into the binary data allows the next pixel and the pixel to be converted at a predetermined ratio. Error data to be distributed to the pixels in the next row is generated and output. The averaging circuit holds the error data generated by the binarization circuit for one clock period, calculates the average of the held calculation result and the next input error data, and outputs the calculation result. You.

According to the third aspect of the present invention, the halftone circuit further includes a second register and a third adder. A clock signal is input to the second register, and error data output from the binarization circuit is held for one clock period based on the clock signal. The error data output from the binarization circuit and the error data held in the second register are input to the third adder, added, and multi-valued data of the calculation result is output. .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic block circuit diagram of the image data processing device. The image data processing device 1 can be used for various applications such as facsimile. Image data processing device 1
Converts analog image signals from a CCD, a contact sensor, and the like into high-quality binary image data that expresses gradations in a pseudo manner.

The image data processing apparatus 1 includes an analog section 2,
A distortion correction unit 3, a pixel density conversion unit 4 as a pixel density conversion circuit, a gamma correction unit 5, a filter unit 6, a halftone unit 7 as a halftone circuit, an error memory 8, a binarization unit 9, a control circuit 10, And a register 11 integrated on one chip.

The line sensor divides a transmission original into a plurality of pixels in the main scanning direction, reads the density of each pixel, and outputs an image signal having a voltage corresponding to the density. The image signal input from the line sensor is input to the analog unit 2.
The image signal is an analog value, for example, a high voltage when the pixel is black, a low voltage when the pixel is white, and an intermediate voltage when the pixel is gray. The analog unit 2 includes an A / D converter having a predetermined number of bits (for example, 8 bits).
The image signal is quantized and converted into multi-value data of a plurality of gradations (256 gradations). The converted multi-value data has a value corresponding to the density of each pixel. Then, the converted multi-value data is output to the distortion correction unit 3.

The distortion correction unit 3 reads the distortion correction data stored in advance in a memory (not shown) and
The gradation correction is performed on the multi-value data of the line based on the distortion correction data, and the multi-value data of the correction result is output to the pixel density conversion unit 4. The distortion correction data (shading data) is data for numerically correcting distortion generated in the optical system.

The pixel density conversion unit 4 is provided for performing a density conversion process for converting the pixel density of each line on the data input from the distortion correction unit 3 using multi-value data. In the present embodiment, the pixel density conversion unit 4 increases the pixel density by “1/1”, “１ ／”, “2/3”, “3 /
It is set to convert to "2 times" or "2/1 times".

As shown in FIG. 3, one line of image data L1 read in the main scanning direction is composed of a plurality of pixels G. The pixel density conversion unit 4 calculates the average of the pixels G adjacent in the main scanning direction (the direction of the arrow in FIG. 3), and outputs the calculated result and the input multi-value data of the pixel G according to the density to be converted. As a result, the number of pixels is increased or decreased. In order to distinguish the calculation result from the input multi-value data of the pixel G, the input pixel is referred to as “input pixel G”.
1 ”, the pixel based on the multi-value data of the operation result
2 ".

For example, as shown in FIG. 4B, the pixel density converter 4 calculates an average for each two adjacent input pixels G1, and outputs only the multi-valued data of the pseudo pixel G2 resulting from the calculation. I do. That is, by outputting multi-value data of one pixel based on multi-value data of two pixels, the pixel density is reduced to “「 ”.
To "double".

Further, as shown in FIG. 4C, the pixel density conversion unit 4 outputs two adjacent input pixels G1 every other pixel.
And alternately outputs the multivalued data of one input pixel G1 that has not been calculated and the multivalued data of the pseudo pixel G2 that is the result of the calculation. That is, the pixel density is converted to "2/3 times" by outputting the multi-value data of two pixels based on the multi-value data of three pixels.

As shown in FIG. 4D, the pixel density conversion unit 4 calculates an average for each two adjacent input pixels G1, and calculates the multi-value data of the original two input pixels G1 and the calculated value. The resulting multi-value data of the pseudo pixel G2 is output. At this time,
The pixel density conversion unit 4 converts the multi-value data of the operation result into the original 2
Output during the multi-value data of the pixel. That is, the pixel density is converted to "3/2 times" by outputting the multi-value data of three pixels based on the multi-value data of two pixels.

Further, as shown in FIG. 4E, the pixel density conversion unit 4 calculates the average of two adjacent input pixels G1, and calculates the multi-value data of the input pixel G1 and the pseudo pixel G2 of the calculation result. And alternately output the multi-value data. That is, by inserting a pseudo pixel G2 that is an average of the two input pixels G1 between two adjacent input pixels G1, the pixel density is converted to “2/1”. FIG. 4A shows a case of no conversion, that is, a case of converting the pixel density to “1/1”, and the pixel density conversion unit 4 outputs the input pixel G1 as it is.

The pixel density converter 4 is provided with a register 1 to be described later.
1, the pixel density to be converted is switched based on control data written from outside. And
The multi-value data of the input pixel G1 and the pseudo pixel G2 output from the pixel density conversion unit 4 is output to the gamma correction unit 5.

The gamma correction unit 5 reads gamma correction data stored in a memory (not shown) in advance, and performs gamma correction on the multi-value data input from the pixel density conversion unit 4 based on the gamma correction data. Do. The gamma correction data is data for correcting a deviation between a photoelectric conversion characteristic of the line sensor and a change in light intensity that a person actually visually perceives. The gamma correction unit 5 outputs the multi-value data of the correction result to the filter unit 6. The gamma correction unit 5
Outputs the multi-value data of the correction result directly to the outside.

The filter unit 6 is a 3 × 3 matrix based on the multi-value data of two lines stored in a memory (not shown) and the multi-value data of pixels of one line input from the gamma correction unit 5. And outputs the filtered data to the halftone section 7 or the binarization section 9. This spatial filter is for performing filter processing such as edge enhancement on multi-value data of each pixel.

The halftone section 7 performs an error diffusion process on the input multi-valued data of each pixel, and creates binary data representing pseudo-halftones. Error diffusion processing
In order to express multi-valued data as binary data, an error generated when binarizing multi-valued data of an arbitrary pixel is added to multi-valued data of pixels around the pixel. .

As shown in FIG. 5, an arbitrary pixel on the current line La is defined as a pixel Ga, and a pixel input after the pixel Ga is defined as a next pixel Gb. Further, the line input next to the current line La is the next line Lb, and the pixels at the position corresponding to the pixel Ga in each pixel of the next line Lb are the pixels Gc and Gd. In this case, an error occurring in an arbitrary pixel Ga is caused by a pixel Gb next to the current line La and pixels Ga, G
The pixels are distributed to the pixels Gc and Gd on the next line Lb corresponding to the position b. The ratio of distribution to each of the pixels Gb, Gc, Gd is set in advance at a predetermined ratio with the total being “1”. For example, 1/2 of the error is in the pixel Gb, and 1 of the error is
/ 4 are distributed to the pixels Gc and Gd on the next line Lb. In FIG. 5, each error data EA, EB, EC is
These are indicated by arrows for the pixels Gb, Gc, and Gd, respectively.

The operation of the halftone section 7 is switched according to the conversion ratio of the pixel density conversion section 4. For example,
The halftone section 7 has a conversion ratio of “1” in the pixel density conversion section 4.
In the following cases, the error data is calculated for each pixel, the calculation result is stored in the error memory 8, and when the conversion ratio exceeds “1”, the error data is calculated for each pixel and the error of the adjacent pixel is simultaneously calculated. An average value of the data is calculated, and the average data is stored in the error memory 8.

The image data La of a specific line (referred to as a current line to distinguish it from other lines) is shown in FIG.
As shown in (e), the pixel density conversion unit 4 is configured by the input pixel G1 or the pseudo pixel G2 according to the conversion ratio.
Here, as an example when the conversion ratio is “1” or less, “1”
Considering the case of "/ 2 conversion", as shown in FIG. 4B, the current line is composed of only the pseudo pixel G2.

At this time, the halftone section 7 calculates error data of each pseudo pixel G2 constituting the current line, and stores the calculation result in the error memory 8. For example, as shown in FIG. 6, when attention is paid to an arbitrary pixel on the current line La (hereinafter, referred to as a pixel Gn to distinguish it from other pixels), the halftone unit 7 sets the multi-value data of the pixel Gn as A deviation (error) from a preset threshold value is calculated. At this time, the halftone unit 7 adds the error data EA of the pixel Gn-1 inputted one pixel before the pixel Gn to the focused pixel Gn. Then, the halftone unit 7 calculates
The error data EA, EB, and EC of the pixel Gn are calculated.

Further, the error data EB of the pixel Gn and the error data EC of the pixel Gn-1 one pixel before the pixel Gn are distributed to the pixels on the next line corresponding to the position of the pixel Gn. Therefore, the halftone section outputs the error data EB of the pixel Gn.
And the error data EC of the previous pixel Gn-1 are added, and the calculation result is used as the error data EM for the next line.
And stored in the error memory 8.

Similarly, when calculating the error data of the pixel Gn + 1, the halftone section 7 adds the error data EA of the pixel Gn to the multi-value data of the pixel Gn + 1, and based on the calculation result, the pixel Gn + 1 Are calculated. Then, the halftone section 7 performs an addition operation on the error data EB of the calculation result and the error data EC of the pixel Gn, and stores the calculation result in the error memory 8 as error data EM for the next line of the pixel Gn + 1.

When an arbitrary pixel Gn is the first pixel of one line, there is no pixel before the first pixel.
Therefore, the halftone section 7 stores the error data EB calculated based on the first pixel and the threshold value in the error memory 8 as error data EM for the next line.

On the other hand, as an example of the case where the conversion ratio of the pixel density exceeds “1”, in the case of “2/1 conversion”, as shown in FIG.
And the pseudo pixel G2 are alternately arranged. At this time, the halftone section 7 calculates error data of the input pixel G1 and the pseudo pixel G2 constituting the current line. Furthermore,
The halftone section 7 calculates the average of the error data of the adjacent input pixel G1 and the pseudo pixel G2. And the halftone part 7
The average value of the calculation results is calculated by using the input pixel G1 and the pseudo pixel G2.
Is stored in the error memory 8 as the error data.

For example, as shown in FIG.
When attention is paid to an arbitrary input pixel G1 or a pseudo pixel G2 (in FIG. 7, the input pixel G1 is an arbitrary pixel Gn), the halftone section 7 is set in advance as multi-value data of the pixel Gn. Calculate the deviation (error) from the threshold. At this time, the halftone unit 7 assigns the pixel Gn to the pixel Gn of interest.
Error data EA of the pixel Gn-1 input one pixel before
Is added. Then, the halftone section 7 calculates each error data EA, EB, EC of the pixel Gn based on the calculation result.

The error data EB of the pixel Gn and the error data EC of the pixel Gn-1 which is one pixel before the pixel Gn are distributed to the pixels on the next line corresponding to the position of the pixel Gn. Therefore, the halftone section outputs the error data EB of the pixel Gn.
And the error data EC of the pixel Gn−1 one pixel before the pixel Gn is added to generate error data ED. Further, the halftone section 7 outputs the error data EB of the next pixel Gn + 1.
And the error data EC of the pixel Gn one pixel before the pixel Gn + 1 is added to generate error data ED. Then, the halftone section 7 further calculates the average of the generated error data ED of both pixels Gn and Gn + 1, and calculates the calculated result as the error data EM for the next line of both pixels Gn and Gn + 1.
And stored in the error memory 8.

Similarly, the halftone section 7 calculates error data ED of the pixel Gn + 2 and error data ED of the pixel Gn + 3. Then, the halftone section 7 outputs both pixels Gn + 2 and Gn +
Then, the average of the error data ED of the three pixels Gn + 2 and Gn + 3 is stored in the error memory 8 as error data EM for the next line.

That is, when the conversion ratio of the pixel density conversion unit 4 exceeds “1”, the halftone unit 7 calculates the average of error data of both pixels for every two input pixels, and compares the calculation result. The error data is stored in the error memory 8 as pixel error data. Therefore, the error memory 8 stores error data of の of the number of pixels input to the halftone section 7.
Is the same as the conventional (when the pixel density conversion is not performed).

The pseudo pixel G2 is generated based on the adjacent input pixel G1, that is, the input pixel G1 before and after (in FIG. 7, right and left) the pseudo pixel G2 input to the halftone section 7. Therefore, the error data ED of the input pixel G1 (pixels Gn, Gn + 2 in FIG. 7) and the pseudo pixel G2
(In FIG. 7, the error data ED of the pixels Gn + 1, Gn + 3) becomes substantially equal. Further, both pixels Gn, Gn +
1 (Gn + 2, Gn + 3), the average of the error data ED is calculated, and the calculation result is calculated for both pixels Gn, Gn + 1.
(Gn + 2, Gn + 3) error data EM.
As a result, the error data EM includes both pixels Gn and Gn + 1.
(Gn + 2, Gn + 3) are substantially equal to the respective error data ED. Therefore, the error data EM is transferred to the next line L
b corresponding pixels Gn, Gn + 1 (Gn + 2, Gn +
Even when the addition process is performed for 3), no change is visually perceived as compared with the case where the error data ED of each pixel Gn to Gn + 3 is added.

The halftone section 7 selects and outputs the error data of each pixel and the average error data of adjacent pixels according to the conversion ratio of the pixel density of the input multi-valued data. With this configuration, by storing error data for each pixel when the conversion ratio is equal to or less than “1”, it is possible to perform high-quality error diffusion processing. By storing the average error data of adjacent pixels, an error memory with a small capacity can be used.

The binarizing section 9 converts the input multi-value data into binary data based on a preset threshold value. The binary data is, for example, “1” when the multi-valued data is larger than the threshold, and “0” when the multi-valued data is smaller than the threshold. When the binary data is "0", the output document is white, and when the binary data is "1", the document is black.

The binary data output from the halftone section 7 and the binarization section 9 are output to the outside via the switch SW. The switch SW is switched by a control circuit 10, which will be described later, according to an image area including the output binary data. The image area is an area composed of characters and the like,
There is an area composed of photographs and the like. The character area includes white data and black data. In this case, by switching the switch SW to the binarizing unit 9, binary data with a clear edge can be obtained. On the other hand, in the case of a photograph area, it is composed of halftone multi-value data. In this case, by switching the switch SW to the halftone section 7, binary data capable of expressing error-diffused shades is obtained.

The control circuit 10 and the register 11 are
To 9 are provided. The register 11 stores various conversion ratio data input from a controller for controlling the entire system such as a facsimile. The control circuit 10 outputs a control signal to each of the units 2 to 9 based on various data stored in the register 11,
Each of the units 2 to 9 operates based on a control signal.

Next, the configuration of the halftone section 7 will be described in detail. FIG.
, The halftone section 7 includes adders 21, 22, 2
3, a register 24, 25, a binarizing circuit 26, an averaging circuit 27, and a selecting circuit 28.

One input terminal of the adder 21 receives the multi-value data of the input pixel G1 and the pseudo pixel G2 constituting each line, and the other input terminal receives the previous line stored in the error memory 8 in the other input terminal. The error data EM carried over from is input. The adder 21 receives the input pixel G1 or the pseudo pixel G2
Is added to the error data EM, and the calculation result is output to the adder 22.

The operation result of the adder 21 is input to one input terminal of the adder 22, and the error data EA generated by the binarizing circuit 26 described later is input to the other input terminal. The error data EA is generated by a pixel immediately before the input pixel G1 or the pseudo pixel G2 input to the halftone unit 7 at that time. The adder 22 performs an addition operation on the operation result of the adder 21 and the error data EA,
The calculation result is output to the register 24.

The clock signal CLK is input to the register 24. The clock signal CLK is generated as a pulse signal corresponding to the input timing of the pixel to be converted,
Is entered. The register 24 operates in synchronization with the clock signal CLK, and holds the operation result of the adder 22 for one clock period.

A predetermined threshold value is set in the binarization circuit 26 in advance. The binarization circuit 26 compares the threshold with the multi-value data of each pixel input from the register 24, converts the multi-value data into binary data based on the comparison result, and outputs the binary data DO. And output to the outside. The binary data DO is output to the outside of the image data processing device 1 via the switch SW as described above.

The binarizing circuit 26 distributes the difference between the multi-valued data of each pixel before conversion and the threshold value generated at the time of conversion into binary data at a predetermined ratio, and distributes the error data EA, E
B and EC are generated and output. These error data EA ~
The ratio of EC is set in advance as a ratio with the total being “1”. Error data EA distributed from the current pixel (pixel Ga in FIG. 5) to the next pixel (pixel Gb in FIG. 5) on the same line is supplied to the adder 22, and the adder 2
At 2, the multi-value data of the next pixel is added. A pixel at the same position on the next line from the current pixel (pixel Gc in FIG. 5)
The error data EB distributed to the next line is supplied to the adder 23, and the error data EC distributed to the next pixel of the next line (pixel Gd in FIG. 5) is supplied to the register 25.

Clock signal CLK is input to register 25. The clock signal CLK is generated as a pulse signal corresponding to the input timing of the pixel to be converted,
Is entered. The register 25 operates in synchronization with the clock signal CLK, and holds the error data EC input from the binarization circuit 26 for one clock period.

The error data EC held by the register 25 is input to one input terminal of the adder 23, and the error data EB output from the binarization circuit 26 is input to the other input terminal. . The adder 23 performs an addition operation on the two error data EB and EC, and outputs the operation result to the averaging circuit 2.
7 is output. That is, the adder 23 calculates error data for a pixel on the next line corresponding to a pixel at an arbitrary position.

The averaging circuit 27 includes a register 31, an adder 32, and a divider 33. The error data output from the adder 23 is input to the register 31. The register 31 has a clock signal CL.
K is input. The register 31 has a clock signal CLK.
, And holds the error data input from the adder 23 for one clock period. The output signal of the register 31 is input to one input terminal of the adder 32, and the error data output from the adder 23 is input to the other input terminal. The adder 32 performs an addition operation on the error data input from the adder 23 and the error data held by the register 31 for one clock period. The error data held for one clock period is the error data (error data ED in FIG. 7) of the pixel immediately before the error data input from the adder 23 at that time. Therefore, the adder 32
Error data of two adjacent pixels are input, respectively, and they are added.

The output signal of the adder 32 is input to the divider 33. The divider 33 divides the input signal by “2”, that is, halves the input signal and outputs the signal. The input signal is a result of adding error data of two adjacent pixels. Therefore, the divider 33, that is, the averaging circuit 27
Performs averaging of the error data ED of two adjacent pixels, and outputs the result to the selection circuit 28.

In the averaging circuit 27, the average value of the error data ED of two adjacent pixels is calculated for each cycle of the clock signal CLK, and the same number of average values as the error data ED is calculated. . Therefore, at the time of writing to the error memory 8, の of the average value is thinned out. More specifically, the enable signal for permitting writing has a cycle twice as long as that of the clock signal CLK. As shown, the number of error data EM is を of the number of error data ED.
I am trying to be.

The operation result of the averaging circuit 27 is input to the selection circuit 28. The selection circuit 28 includes an adder 2
The error data ED, which is the operation result of No. 3, is directly input.
Further, a selection signal SEL is input to the selection circuit 28. The selection signal SEL corresponds to the density of the pixel to be converted. That is, the selection signal SEL is
Error data ED input from the adder 23 based on
And the signal input from the averaging circuit 27, and outputs the selection result to the error memory 8 as the error data EM at that time.

That is, there is a case where it is not necessary to calculate the average depending on the conversion ratio of the pixel density. In this case, the average signal is passed through the averaging circuit 27, that is, the output signal of the adder 23 is directly used as the error data EM. Output to the memory 8.

Accordingly, the error data of each pixel or the average of the error data of adjacent pixels is input to the error memory 8 according to the conversion ratio of the pixel density.
Is stored. Then, the error data stored in the error memory 8 is read out when the error diffusion process is performed on the pixels of the next line, and the error is distributed to each pixel.

As described above, the present embodiment has the following advantages. (1) The halftone section 7 calculates the error data of each pixel stored in the error memory 8 based on the input pixel density of one line. The halftone unit 7 receives the input 1
When the conversion ratio of the pixel density for the line is equal to or less than “1”, error data is calculated for each pixel, and the calculation result is stored in the error memory 8. On the other hand, when the conversion ratio of the pixel density for one line exceeds “1”, the halftone unit 7 calculates the average of the error of every two pixels that are input adjacently, and stores the calculation result in the error memory 8. Stored. As a result, when the pixel density is increased in the pixel density conversion, it is not necessary to store many errors as compared with the case where the density is not converted, so that the pixel density conversion and the error diffusion can be performed without increasing the memory capacity. Processing can be performed. Further, since a large-capacity memory is not required, the size of the image data processing apparatus 1 can be prevented.

The present invention may be carried out as follows in addition to the above embodiment. (1) In the above embodiment, the error of an arbitrary pixel is distributed to the next pixel of the pixel and the two pixels of the next line. For example, the error of an arbitrary pixel is distributed to the next pixel. By appropriately changing the number of pixels to distribute the error, such as distributing to one pixel of the next line, or distributing an error of an arbitrary pixel to the next two pixels of the current line and three pixels of the next line. May be implemented.

(2) In the above embodiment, the ratio of distributing pixel errors may be changed as appropriate. (3) In the above embodiment, the halftone unit 7 outputs average error data and stores it in the error memory 8 when the conversion ratio of the pixel density exceeds “1” according to the pixel density. However, the average error data may always be output and stored in the error memory 8.

While the embodiments of the present invention have been described above, technical ideas other than the claims that can be grasped from the embodiments will be described below together with their effects. (A) In the image data processing apparatus according to claim 2,
The halftone section further includes a selection circuit that inputs the calculation result output from the averaging circuit and the calculation result of the third adder, and selects and outputs them according to the pixel density. Image data processing device provided. According to this configuration, high-quality error diffusion processing can be performed by selecting error data to be stored in the error memory according to the pixel density.

[0062]

As described above in detail, according to the present invention, it is possible to provide an image data processing apparatus capable of performing pixel density conversion and error diffusion processing without increasing the memory capacity.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image data processing apparatus according to an embodiment.

FIG. 2 is a block diagram of a halftone section.

FIG. 3 is an explanatory diagram showing pixels for which pixel density conversion is performed.

FIGS. 4A to 4E are explanatory diagrams showing pixel density conversion.

FIG. 5 is an explanatory diagram showing pixels performing error diffusion.

FIG. 6 is an explanatory diagram showing pixels and an error memory in error diffusion.

FIG. 7 is an explanatory diagram showing pixels and an error memory in error diffusion.

[Explanation of symbols]

 Reference Signs List 4 Pixel density conversion section as pixel density conversion circuit 7 Halftone section as halftone circuit 8 Error memory 21 First adder 22 Second adder 23 Third adder 24 First register 25 Second Register 26 Binarization circuit 27 Averaging circuit CLK Clock signal

[Procedure amendment]

[Submission date] July 16, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

According to a first aspect of the present invention, there is provided an image data which is continuous in units of one line and constitutes one screen.
Multi-valued data obtained by quantization for each pixel from
An image data processing device for taking in , sequentially converting to binary data, outputting an average value of multi-value data of two adjacent pixels, multi-value data of the calculation result, and multi-value data before calculation And respond to the selected clock of the predetermined pattern.
The number of pixels per line is desired by selectively outputting
A pixel density conversion circuit for converting the number of, the pixel density variations
The multi-value data whose pixel density has been converted by the conversion circuit is sequentially input.
When converting each multi-valued data to binary data and outputting it,
Calculate the binarization error for each pixel,
Calculate the average of those binarization errors for each pixel of
The binarization error or the binarization error after averaging is the pixel density
A gist of the present invention includes a halftone circuit that selectively outputs a signal according to a conversion ratio of a conversion circuit, and an error memory that is output from the halftone circuit .

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

Therefore, according to the first aspect of the present invention,
The pixel density conversion circuit is continuous in one line unit and one screen
Is obtained by quantizing each pixel from the image data constituting
Input multi-valued data, and multi-valued data of two adjacent pixels are input.
The average value of the data is calculated, and the multi-valued data
The multi-value data before the operation is the selected clock of the predetermined pattern
Is selectively output in response to
The prime numbers are converted to the desired numbers. The halftone circuit has a pixel
The density-converted multi-value data is sequentially input, and each multi-value data is
When the data is converted to binary data and output,
A binarization error is calculated and every two adjacent pixels
The average of those binarization errors is calculated, and the binary
The binarization error or the binarization error after averaging is
It is selectively output according to the conversion ratio and stored in the error memory.

Claims (3)

[Claims] An image data comprising a plurality of lines is fetched on a line-by-line basis, the image data of each line is quantized for each pixel and converted into multi-value data, and the multi-value data is converted into binary data. An image data processing device for calculating and averaging multi-valued data of two adjacent pixels, selecting multi-valued data of the operation result and multi-valued data before the operation, and outputting the selected line. A pixel density conversion circuit (4) for converting the density of the pixels constituting the pixel, and multi-value data of the pixels whose density has been converted are sequentially input, and the multi-value data of each pixel is converted into binary data and output. And a halftone circuit (7) for calculating an error for each pixel, calculating an average of the errors for two adjacent pixels, and outputting the calculation result as error data, and an error for storing the error data. And a memory (8). Image data processing device. 2. The image data processing device according to claim 1, wherein the halftone circuit (7) adds an error data of a previous row stored in an error memory to multi-value data of a target pixel, A first adder (21) for outputting multi-valued data of the operation result; and multi-valued data output from the first adder (21) are added to the multi-valued data of the immediately preceding pixel. A second adder (22) for adding error data generated when the data is converted to data
And a clock signal that matches the input cycle of the multi-valued data of the pixel. Based on the clock signal, the multi-valued data to which the error data output from the second adder (22) has been added is A first register (24) for holding for one clock period until multi-valued data of the pixel is input, and converting the multi-valued data held in the first register (24) into binary data for output A binarization circuit (26) for generating and outputting error data for distributing an error generated when converting the binary data to the next pixel and the next row of pixels at a predetermined ratio; The error data generated by the value conversion circuit (26) is held for one clock period, an average of the held calculation result and the next input error data is calculated, and an averaging circuit ( 27) and Image data processing apparatus according to claim. 3. The image data processing device according to claim 2, wherein the halftone circuit (7) receives the clock signal (CLK) and performs the binarization based on the clock signal (CLK). A second register (25) for holding the error data output from the circuit (26) for one clock period, error data output from the binarization circuit (26),
A third adder (23) for performing an addition operation on the error data held in the second register (25) and outputting multi-valued data of the operation result; Processing equipment.