JP2003051940A - Image processing method and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing method and its device that can enhance color reproducibility in an entire output image, without increasing a processing load. SOLUTION: A resolution conversion circuit 201 converts a pixel density of multi- valued image data in image processing where the pixel density of received multi-valued image data is converted and the multi-valued image data are converted into binary image data in the main scanning direction, using an output color table for outputting binary image data of a plurality of lines whose pixel density is converted in the subscanning direction, by using the multi-valued image data of each pixel subjected to pixel density conversion in the main scanning direction for an address converts the multi-valued image data into the binary image data (205, 209, 210), and employing an output point table for outputting the multi-valued image data corresponding to a dot pattern output of the binary image data of a plurality of lines, by using the multi-valued image data of each pixel subjected to pixel density conversion in the main scanning direction can spread output error between the dot pattern, on the basis of the binary image data and the multi-valued image data subjected to pixel density conversion in the main scanning direction in the adjacent binarized pixels (204, 206 to 208, 212, 213).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and an apparatus thereof, and more particularly to an image processing method and an apparatus thereof for performing high color reproduction at high speed.

[0002]

2. Description of the Related Art Conventionally, when converting multivalued data having a low pixel density into binary data having a high pixel density, and when the processing speed is emphasized, it is possible to obtain a high density like a density pattern method. A method of performing binarization while executing pixel density conversion (enlargement) processing is used. On the other hand, when the emphasis is placed on the image quality, a binarization method is used in which, after enlarging the multivalued data, one pixel of the multivalued data is also one pixel as in the error diffusion method. Has been.

However, when converting multivalued data of low pixel density into binary data of high pixel density as in the above-mentioned conventional example, binary data for one pixel of multivalued data like the density pattern method is used. 2 using a binarization method that allocates multiple pixels
When the binarization is performed, the binarization can be performed at high speed, but the error that occurs during binarization cannot be propagated and the gradation expression is limited. The problem remains.

Further, as in the error diffusion method, one pixel of binary data is assigned to one pixel of multi-valued data and the error generated at the time of binarization is diffused to realize binarization excellent in gradation expression. When binarization is performed using the method, it is possible to binarize with high image quality, but a lot of time-consuming processing such as error diffusion processing is required, so much time is required for binarization. Further, there is a drawback that the processing time is very long because the enlarging processing must be performed.

The JCD method is known as a means for compensating for the above-mentioned drawbacks (see Japanese Patent Laid-Open No. 7-38766). The JCD method is a combination of the density pattern method and the error diffusion method, and has both the high speed of the density pattern method and the high image quality of the error diffusion. However, as the output image, the resolution of the output device has not been sufficiently brought out.

Another method is as follows. Many conventional output devices that output a color image express a color by combining binary primary colors, and color printers and color displays are known as specific examples. In an image processing apparatus that performs image processing for such a binary output apparatus, first, for input color image data, a conversion relationship between an input color space created by these data and an output color space included in the output apparatus is adjusted. The input color image data is converted to yellow (Y), magenta (M), cyan (C), or each primary color component obtained by adding black (K) to these, or red (R). ), Green (G), and blue (B) primary color components. Then, it is general to output a binary image obtained by performing pseudo gradation expression processing on the color component data obtained by this color correction.

However, in the above-described conventional image processing, since the colors to be output are obtained in pixel units, in the binary output device as described above in which the combinations of colors that can be output are small, the colors actually output and the input image data are The problem that the error with the corresponding color becomes large, and in the binary output device, since the pseudo gradation expression processing is performed independently for each color component, the finally output color matches the predicted color. There was a problem that I did not do it.

On the other hand, among the color combinations reproducible by the output device, the distance in the color space is calculated for each color of the combination so that the color closest to the color in the input image data is associated. A technique capable of improving the high-speed processing and the color reproducibility by realizing the configuration in which the smallest color combination is selected and the above-described color difference is diffused to other pixels by a small-scale circuit (CD method: Color Difference Diffu
sion) is disclosed in JP-A-11-55535.

Although the processing of the CD method itself can be sufficiently speeded up, since it is necessary to have a buffer for the input multi-valued data for a plurality of lines in order to interpolate the input multi-valued data, it takes a long time to write, and each input There is a demerit that it is necessary to have a large capacity memory for buffering multi-valued input data for color, and the minimum time required for memory access regulates the total processing time.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to improve color reproducibility in the entire output image without increasing the processing load. An object of the present invention is to provide an image processing method and an apparatus therefor.

[0011]

In order to solve this problem, an image processing method according to the present invention is an image processing method for converting binary density image data while converting the pixel density of input multilevel image data. That is, the pixel density conversion step of converting the pixel density of the multi-valued image data in the main scanning direction, and the multi-valued image data subjected to the pixel density conversion in the main scanning direction, in pixel units in the sub-scanning direction A binarization step of converting the converted binary image data, and an output error between the dot pattern based on the binary image data and the multivalued image data whose pixel density has been converted in the main scanning direction are binarized. And an error diffusion step of diffusing in the vicinity of the pixel.

Here, in the binarizing step, the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction is used as an address, and the binary image of a plurality of lines whose pixel density has been converted in the sub scanning direction. The first table that outputs data is used. The output binary image data corresponds to a combination of color dots output on a plurality of lines.
In the error diffusion step, the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction is used as an address, and the pixel density is converted in the sub-scanning direction.
A second table for outputting multivalued image data corresponding to the dot pattern output of the value image data is used, and the multivalued image data of each pixel whose pixel density has been converted in the main scanning direction and the second table are output. The difference from the multi-valued image data is the error. Further, the first and second tables are one table in which the multi-valued image data of each pixel whose pixel density is converted in the main scanning direction is used as an address. The address is composed of a plurality of upper bits of multi-valued image data of each pixel whose pixel density is converted in the main scanning direction. Further, the first table is switched depending on the recording medium. Further, the second table is switched depending on the recording medium. At least one of the first and second tables is switched depending on the mode of the recording engine.

Further, the image processing apparatus of the present invention is an image processing apparatus for converting the pixel density of the input multi-valued image data into binary image data while converting the multi-valued image data in the main scanning direction. Pixel density conversion means for converting the pixel density of the pixel value and the multi-valued image data that has been subjected to the pixel density conversion in the main scanning direction.
Binarization means for converting into binary image data, and an output error between the dot pattern based on the binary image data and the multivalued image data subjected to pixel density conversion in the main scanning direction, in the vicinity of the binarized pixel. And an error diffusing means for diffusing the data.

Here, the binarizing means uses the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction as an address, and the binary image of a plurality of lines whose pixel density has been converted in the sub-scanning direction. It has a first table for outputting data. The output binary image data corresponds to a combination of color dots output on a plurality of lines. Further, the error diffusion means corresponds to the output of a plurality of lines of binary image data whose pixel density has been converted in the sub-scanning direction, using the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction as an address. Second output multi-valued image data
It has a table and a subtraction unit that uses a difference between the multi-valued image data of each pixel subjected to the pixel density conversion in the main scanning direction and the multi-valued image data output from the second table as an error. Further, the first and second tables are one table in which the multi-valued image data of each pixel whose pixel density is converted in the main scanning direction is used as an address. Further, there is further provided an address generation means for selecting a plurality of high-order bits of the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction and making the selected address the address. Further, a storage medium for storing the table is further provided with an attachable / detachable interface means, and a different table can be used by exchanging the storage medium. Further, it has a storage medium storing a plurality of different tables and uses a table selected based on a signal from the outside. Further, it further comprises a rewritable storage medium and means for downloading the table to the storage medium from the outside. In addition, the error diffusion means,
It further comprises an error storage medium for storing the error diffused from the already processed main scan line, and an interface means for the error storage medium.

Input means for inputting multi-valued image data, pixel density conversion means for converting the multi-valued image data into pixel density in the main scanning direction, and error data added to the pixel density converted data, Calculation means for calculating the error correction data, selection means for selecting a predetermined dot pattern based on the error correction data, and error calculation means for calculating the difference between the value of the selected dot pattern and the error correction data. And the dot pattern comprises a plurality of dot patterns in at least the sub-scanning direction.

Here, the dot pattern is a combination of color dots. Further, the dot pattern combination is switched depending on the recording medium. Further, a predetermined value for each dot pattern for calculating the difference from the error correction data is switched depending on the recording medium. Further, at least one of the dot pattern combination and the predetermined value for each dot pattern is switched depending on the mode of the recording engine. Further, the image processing apparatus is included in a color facsimile, and the image processing apparatus converts the received image into the resolution of the recording unit based on the received resolution information.

The storage medium of the present invention is a storage medium for storing a computer-readable image processing program for converting binary image data while converting pixel density of input multi-valued image data. The image processing program, a program module for controlling pixel density conversion for converting the pixel density of the multi-valued image data in the main scanning direction, and the multi-valued image data pixel density converted in the main scanning direction,
A program module for controlling binarization for converting into binary image data in which the pixel density is converted in the sub-scanning direction on a pixel-by-pixel basis, a dot pattern based on the binary image data, and a pixel density converted in the main-scanning direction. And a program module for controlling an error diffusion for diffusing an output error from the multi-valued image data in the vicinity of the binarized pixel. Further, a first table for outputting binary image data of a plurality of lines whose pixel density is converted in the sub-scanning direction, using the multi-valued image data of each pixel whose pixel density is converted in the main scanning direction as an address, and / or , Multi-valued image data corresponding to dot pattern output of binary image data of a plurality of lines with pixel density converted in the sub-scanning direction, using the multi-valued image data of each pixel converted in the main scanning direction as an address A second table for outputting

Further, the storage medium is attachable to and detachable from an image processing device for converting binary image data while converting the pixel density of input multi-valued image data, and the pixel density conversion is performed at least in the main scanning direction. A first table for outputting binary image data of a plurality of lines whose pixel density is converted in the sub-scanning direction, using the generated multi-valued image data of each pixel as an address;
And / or using the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction as an address, the multi-valued image data corresponding to the dot pattern output of a plurality of lines of binary image data whose pixel density has been converted in the sub-scanning direction. It is characterized by including a second table for outputting the value image data.

According to the above construction, the pixel density is increased by interpolation in the main scanning direction on the basis of multi-valued input color data, and at least in the sub scanning direction based on the input data in the sub scanning direction. To generate a data representing a plurality of pixels in a dot pattern. At this time, the color difference correction data in which the color difference generated by the binarization of the pixel is added is obtained, and the binary data is output by referring to the table based on the color difference correction data, so that the binary data is obtained in the image processing. In particular, the calculation for obtaining the correspondence between the multivalued color data and the binary data can be omitted, and the color difference is diffused in the entire output image.

[0020]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

<Example of Configuration of Image Processing Apparatus According to this Embodiment> FIG. 1 is a block diagram showing the configuration of the image processing apparatus according to one embodiment of the present invention.

In the figure, the CPU 101 is a ROM 10
According to the program stored in the image processing unit 6, the image processing of the present embodiment described later is executed and various functions of the image processing apparatus are controlled.

A reading unit 104 equipped with a CCD reads a document image and outputs R, G, and B color analog luminance data. The reading unit 104 may include a contact image sensor (CS) instead of the CCD, and the read data that is output may be for each of C, M, and Y colors. The image processing unit 103 includes a reading unit 104.
The analog data sent from is converted into digital data,
For example, 1 pixel of each color, 8 bits, and 256 gradations are converted into expressible digital data and stored in the RAM 107. Further, by writing this data in the binarization processing unit 102, the image processing of the present embodiment described later is performed, and the binary color data obtained by this is read out to the RAM.
It is stored in 107. And this stored data is
The recording operation is performed by the recording unit 111 when the recording unit 111 reaches the amount necessary for recording a predetermined amount.

Further, in the configuration shown in FIG. 1, the non-volatile RAM 108 is an SRAM backed up by a battery and can store data unique to the device. The operation unit 109 includes a copy key for monochrome copying and color copying, a mode key for specifying a mode such as resolution and image quality for copying, a stop key for stopping operation, a ten-key pad for inputting the number of copies, a registration key, and the like. It is configured. And CPU1
01 detects the pressed state of these keys, and controls each unit according to the pressed state.

The display unit 110 is provided with a dot matrix type liquid crystal display unit (LCD) and an LCD driver.
Various displays are performed under the control of the PU 101. Recording unit 1
Reference numeral 11 denotes a bubble jet (registered trademark) type inkjet head, a general-purpose IC, or the like.
Under the control of 01, the print data stored in the RAM 107 can be read and printed out as a hard copy. The driving unit 105 is the reading unit 1 described above.
04 and the recording unit 111, a stepping motor for driving the feeding and discharging rollers in the reading operation and the recording operation, a gear for transmitting the driving force of the motor,
Further, it is composed of a driver circuit for controlling the motor.

The sensor unit 112 is composed of a recording paper width sensor, a recording paper presence sensor, a document width sensor and a document presence sensor, and detects the condition of the document and the recording paper under the control of the CPU 101.

<Structural Example of Binarization Processing Unit 102 According to the Present Embodiment> FIG. 2 is a diagram showing the details of the binarization processing unit 102 shown in FIG. 1, which is a main part of the image processing apparatus of the present invention. FIG. As will be apparent from the description below, the binarization processing unit 102 directly corresponds to the binary Y, M, C, and K used by the recording unit 111 for the brightness data R, G, and B of each 8-bit input image. Perform processing to attach. In the present embodiment, for the sake of explanation, the resolution of the data read by the reading unit 104 is 300 × 300 dpi, and the resolution of the output printer is 600 × 600 dpi.

In the configuration shown in FIG. 2, the binarization processing unit 102 is roughly divided into preprocessing blocks (for example, 201, 202, 203, etc.) for performing preprocessing, and a CD method for performing output pattern and color difference diffusion. Block (eg 204
˜208) and an I / F block (for example, 209, 212, etc.) serving as an interface with various memories.

(Structural Example of Preprocessing Block of this Embodiment) R of 300 × 300 dpi read by the reading unit 104
Each brightness data of GB8bit is A in the image processing unit 103.
/ D conversion, shading correction, edge enhancement, noise removal, image area separation, etc. are performed as necessary, and are input to the resolution conversion circuit 201. The resolution conversion circuit 201 is a circuit that creates interpolation data from input luminance data, and converts 300 dpi read by the reading unit 104 into 600 dpi in accordance with the resolution of the printer in the main scanning direction. In this example, since the resolution is simply doubled from 300 dpi to 600 dpi, the resolution conversion circuit 201 can be configured by a bit shift and an addition circuit. Further, a known linear scaling circuit that performs scaling may be used instead.

The data whose resolution has been converted in the main scanning direction of 600 dpi is converted from the RGB space to the CMY space in the color space conversion circuit 202. Further, the converted data is input to a γ conversion circuit 203 for converting into an image that reflects the characteristics of the image processing apparatus and the user's preference. In the color space conversion circuit 202 and the γ conversion circuit 203, correspondence between input and output is often performed by a table (look-up table including RAM or ROM). is there.

(Structural Example of CD Method Block of this Embodiment) The corrected CMY data is added with color difference data from the previous line and color difference data from the previous pixel, which will be described later, in the color difference addition circuit 204. Next, an ink ejection method (CMYK) that allows the CMY data to which the color differences have been added to reproduce the closest color in the color space is selected. This correspondence is disclosed in JP-A-11-5.
Although the method according to the CD method disclosed in Japanese Patent No. 5535 is used, in the present embodiment, the ink ejection method (CMYK) of a plurality of lines is selected according to the resolution conversion magnification corresponding to the input data of one line. . The corrected CMY
It is preferable that the relation between the data and the ink ejection method (CMYK) is calculated in advance and stored in a table because the load of the processing on the mounting is small. Further, the calculation of the distance on the color space may use another color space (L, a *, b *) or (Y, Cb, Cr).

In the present embodiment, the upper 3 bits are cut out from each 8 bits of CMY in consideration of the effect on mounting.
Correspondence CMYK for input of bit (2 ⁹ = 512 types)
Create output data. This table is stored in the table memory 210, and the print patterns of a plurality of lines for the 9-bit data are stored in the RAM I / F unit 209.
To the output buffer unit 211. At this time,
An error occurs when the data is converted into fewer points than the input data. If this error is discarded, color reproduction becomes poor. Therefore, in the CD method, it is avoided that the generated error is diffused to the peripheral pixels of each color component and the color reproducibility is deteriorated.
A specific example will be described below.

The subtraction circuit 206 calculates the color difference between the density information of the input data and the density information of the selected output pattern. The density information of the selected output pattern used here is one that predicts the density when the print pattern is printed under a predetermined condition, and the one obtained experimentally by measurement as described later is used. The obtained data is stored in association with the output color table memory, and the color of the corresponding pixel output is obtained via the RAM I / F unit 209. The calculated color difference is the color difference distribution circuit 20.
At 7, it is distributed to each pixel.

That is, after the color difference is weighted, it is sent to the above-mentioned color difference adding circuit 204 to be added to the input image data of the next pixel, and also sent to the color difference integrating circuit 208 to be diffused to the pixels of the next line. . The color difference integration circuit 208 calculates the sum of color differences for each pixel corresponding to each pixel on the next line, and stores the previous line color difference storage memory 21.
It is stored in 3.

In the configuration example of FIG. 2, the RAM I / F units 209 and 212 are separated and the table memory 210 and the front line color difference storage memory 213 are described as different memories, but they are the same. RAM composed of storage media
It is also possible to have one I / F section. In this case,
It is necessary to control the timing when it is used as the table memory 210 and when it is used as the front line color difference storage memory 213.

<Example of Operation of Binarization Processing Unit 102 According to this Embodiment> FIG.
6 is a flowchart showing a binarization process, that is, a process for obtaining print data used in the recording unit 111. The processing will be described below step by step according to the flowchart shown in FIG.

Step S101: When color copying or color printing is executed, the front line color difference storage memory 21
The buffers in the 3 and 2 binarization processing units 102 are cleared.

Step S102: The counter PIX indicating the input pixel to be processed is initialized to 0.

Step S103: The image data which has been subjected to various kinds of preprocessing after reading is written in the registers allocated to R, G and B of the binarization processing section. It should be noted that the data format may be CMY or another color other than RGB as the color system. 300 dpi to 600 dpi
In the case of this embodiment in which i is converted to i, every two pixels (R0,
By inputting R1, G0, G1, B0, B1), the number of times of access and resolution conversion are improved.

As a method of managing the processing of the binarization processing unit 102, for example, a method of counting the number of clocks can be used. An optimum processing circuit can be designed by starting the counting by the system counter triggered by the writing of data by the CPU and controlling the processing timing by the number of clocks. Also,
Since it is a synchronous circuit, timing verification and the like are facilitated. As an example, in the process of step S103, the address R,
When writing data in the order of G and B, the system counter starts counting by being triggered by the writing of the data of address B, and counts every clock.
This counter is cleared by soft clear or when the next R data is written.

Step S104: R0 and R1 to Rc0
And Rc1 are generated. Since the conversion from 300 dpi to 600 dpi is a simple double interpolation, Rc0 is generated by the sum of the previous pixel and R0 bit-shifted, and Rc1 is generated by the sum of R0 and R1 bit-shifted. In this way, G and B data are similarly interpolated.

Step S105: 600 by the above interpolation
The data that has become dpi is RGB in the color space conversion circuit 202.
Converted from space to CMY. Conversion from RGB to CMY can be performed independently for each color. It may be converted to another color space if there is a margin in processing. The input data is C,
In the case of the ones represented by M and Y, it goes without saying that the color space conversion need not be performed.

Step S106: γ conversion for converting into an image that reflects the characteristics of the image processing apparatus and the user's preference. The input data generated by the above is Ci, Mi,
Yi.

Step S107: The front line color difference data CL to be diffused to the pixel to be processed is stored in the front line color difference storage memory 2
Read from 13. This color difference data will be described later.

Step S108: In the input data Ci obtained above, as described above, the color difference data CL read from the previous line color difference data storage memory 213 in correspondence with the pixels shown in FIG. The color difference data CP from the immediately preceding processed pixel is added by the adder circuit 203.

Step S109: (Ci + CL + CP) obtained by the above addition is stored in the buffer as data ILPC.
Memorize as. The ILPC has a signed 11-bit width (-512 to +512), and those exceeding 512 are rounded as 512 so as not to overflow, so that the adder circuit can be realized on a small scale within a range that does not affect the image. it can. Similar processing is performed in parallel for G and B to generate ILPM and ILPY. In this way, it is possible to obtain data in which the color difference in each of the predetermined pixel of the previous line and the immediately preceding processed pixel is added to the input image data.

Step S110: Based on the input data (ILPC, ILPM, ILPY) calculated by the above processing, an address (I
LPC ', ILRM', ILPY ') are created, and the output color table memory 210 shown in FIG.
The output color data (Cp, Mp, Yp) closest to the input data in the color space is read out and stored in the register.

The output color table memory 210 is constructed as follows.

Normally, in the color space, the colors (ILPC, ILPM, ILPY) indicated by the input data and the colors (Cp, Mp, Y) indicated by the measurement data actually recorded by the recording unit are shown.
p) distance L ² = (ILPC-Cp) ² + (ILPM-Mp) ² +
In the calculation of (ILPY-Yp) ² , the values of Yp, Mp, and Cp are changed within the range shown in the output color point table of FIG. 4, and Cp, Mp, and Yp when the value of L ² becomes the smallest A pair is obtained, and corresponding to the pair of Cp, Mp, and Yp in the relationship shown in FIG. 4, each of several bits (KO, CO, MO, Y) based on resolution conversion is obtained.
O) as input data (ILPC, ILPM, ILPY)
The relationship of the output color corresponding to is tabulated.

As described above, the calculation described above for obtaining the output color data for each pixel requires a great deal of software and hardware load and requires a long processing time. Then, by previously storing the above calculation result as a table, based on the input data (ILPC, ILPM, ILPY) in consideration of the color difference, the output color data (KO, KO,
CO, MO, YO) can be obtained at high speed.
Further, the table is constituted by a memory, and by having a plurality of optimum tables corresponding to the output device, the recording method such as ink and toner, and the recording medium such as paper, the optimum output color data (KO, CO, MO, YO) can be obtained. ) Can be obtained at high speed. Furthermore, by changing the table, it is possible to represent an image with a plurality of dots or dots of different sizes. In this case, the table may be changed by replacing the storage medium such as a memory card or a CD, or a plurality of tables may be prepared in one storage medium and this may be selected by an automatic or manual operation from the outside. May be. Further, since the plurality of tables can be changed by the control of the main and PC, the optimum table can be selected without changing the hardware. Alternatively, with the storage medium set in the image processing apparatus, the main and P
It can also be configured to download table data from C. Alternatively, an application for creating a table may be prepared in the storage medium and the table may be created by an external PC or the like.

Regarding the output color table described above, the input data (ILPC, ILPM, ILPY) is 11 bits each with a sign as described above, but the corresponding output color data is (KO, CO, MO, YO). Will correspond to each several bits. Therefore, in the present embodiment, the output color data is obtained with a smaller table by extracting the upper bits of the input data. More specifically, in step S109, as shown in FIG. 8, the upper 3 bits of each of the input data (ILPC, ILPM, ILPY) that have been coded are combined to form 9-bit address data (IL
If PC ', ILPM', ILPY '), then {512
(Address space) × 4 (KCMY color element) × n (number of bits)} bit table. In this way, by reducing the capacity of the table, it is possible to put this table on a storage medium mainly used for other purposes and use it without preparing a dedicated storage medium. It is also possible to prepare a large number of tables.

Step S111: Table memory 210
Output color data (KO, CO, MO, Y
O) is stored in the buffer circuit 211. Where C,
The number of accesses from the CPU to the binarization processing unit 102 can be reduced by allocating a register to each of M, Y, and K and performing reading when 8 pixels corresponding to the size of the data bus are stored. When the data processing method of the recording unit 111 is a main scanning line unit, the load of data rearrangement by software is reduced. Further, when the output data in the sub-scanning direction is for two pixels, the output bits can be divided and written in another register to be output to the recording unit 111 as data of another line.

If the CPU has a word (16-bit) unit transfer mode, two registers are allocated to each of C, M, Y, and K, and 16 pixels are stored and read out from the CPU. Good.

From the above, the data of 2 lines of output 2
The binarization is performed, the vertical position Y of the processed pixel is incremented, the process from step S102 is repeated, and the process from step S101 is repeated due to a page break.

Next, the color difference diffusion process that occurs during the binarization process described above will be described in detail with reference to the flowchart shown in FIG.

Step S201: The vertical position Y of the input pixel to be processed is initialized to 0.

Step S202: The horizontal position X of the input pixel to be processed is initialized to 0.

Step S203: Output color data (CO, CO obtained from the output color table memory 210 as described above).
MO, YO, KO), the output color point table 21 of FIG.
By referring to 0, multivalued data (Cp, Mp, Yp) is obtained.
Here, the data (Cp, Mp, Yp) indicates the density of each color when printing based on (CO, MO, YO, KO) as described above.

Step S204: Pixel (X,
The color difference E (Ce, Me, Ye) of Y) is converted into the input data (C
i, Mi, Yi) and output color point data (Cp, Mp, Y)
p) is obtained in the subtraction circuit 206 as follows.

Ce = Cp-Ci, Me = Mp-Mi, Y
e = Yp-Yi Step S205: In the color difference distribution circuit 207, the color difference E obtained above is added to neighboring input pixels at a predetermined ratio. Specifically, as shown in FIG. 6, the color difference is diffused to the four pixels of the lower left, lower, and lower right of the right and next line pixels of the pixel to be processed, and the color difference diffusion to the right is ,
The color difference data is sent to the color difference adding circuit 204, and the diffusion of the next line to the three pixels is achieved by sending the color difference data to the previous line color difference memory 213. That is, the color difference of the processed pixel (x, y) is (x-1, y + 1), 2/16 (x, y + 1), 5/16 (x + 1, y + 1), and 1/16 (x + 1, y). Are distributed at a rate of 8/16 (= 1/2). Note that the remainder when divided by 16 is (x
It is also possible to reflect the color difference information without losing it by distributing it to (+1, y).

As a result, the addition in the color difference addition circuit 204 is performed as follows. Yi (X + 1, Y) → Yi (X + 1, Y) + (Ye /
2) Mi (X + 1, Y) → Mi (X + 1, Y) + (Me /
2) Yi (X + 1, Y) → Ci (X + 1, Y) + (Ce /
2) Step 206: On the other hand, from the above, the color difference diffused to the processed pixel (x, y) is E (x, y) = 1/16 × E (x-1, y-1) + 5 /
15 × E (x, y−1) + 2/16 × E (x + 1, y−
1) + 8/16 × E (x-1, y), of which the data E of the previous line (y-1) is stored in the previous line color difference memory 213. In this case, as described above, the color difference integration circuit 208 uses the sum of the color differences for each pixel group in the previous line, CL = 1/16 × E (x-1, y-1) + 5/16 × E.
(X, y−1) + 2/16 × E (x + 1, y−1) will be stored. As a result, the RAM can be effectively used.

Further, by utilizing the RAM chip, the color difference stored to reduce the number of accesses is 8 bits (-12
8 to 128), the distribution shown in FIG. 6 may be set. Further, by further expanding the distribution area, more faithful color reproduction can be obtained. Further, since the color difference is distributed to the unprocessed pixels, if the processing directions are alternated to the left and right, the color difference is not reflected only in a specific direction, and an effect of suppressing moire can be suppressed.

After that, the horizontal position counter X is updated in step S207, and it is determined in step S208 whether or not the processing for one line is completed. When one line is completed, the vertical position counter Y is updated in step S209,
In step S210, it is determined whether or not the processing of all lines has been completed.

(Example of Creating Output Color Table in this Embodiment) Improving the reproducibility of input and output colors is one of the important matters in the system design such as the present apparatus provided with color reading and output.

First, the output color combination used in this system is determined. When generating output data of two pixels in the sub-scanning direction with respect to one pixel input, there are 8 (= 2 ³ ) ways even when both pixels are formed only by dots of a combination of the same color. An example in which two pixels are dots of different colors is shown in FIGS. 9 and 10.

First, consider the case where there are no Y dots and K dots. When (C, M) is (0, 0), neither dot is printed and it becomes white (color of the recording medium), and when (C, M) is (1, 0), only one pixel is C dot. Strike, (C,
When M) is (2, 0), C dots are printed for both pixels.
When (C, M) is (0, 1), only one pixel is M dots, and when (C, M) is (0, 2), both pixels are M dots. When (C, M) is (2, 2), C dot and M
Both dots are printed.

By generating this also for combinations of Y and C, M and Y, and respective colors and K, a color space corresponding to the number of combinations of Y and C, M and Y, and respective colors and K can be expressed. You can
Arithmetically, 3 ⁴ = 81 combinations are possible,
(C, M, Y, K) = (1, 1, 1, 2) Combinations that cannot be used due to restrictions such as colors that can be sufficiently reproduced even if they are replaced by other combinations in terms of color space, and ink ejection limit amount Exclude. The remaining output pattern combinations are printed as patches on the recording media that the user actually uses,
Measure the printed data.

Here, the measured CMY data and (C,
The patch is read from the reading unit 104 in order to associate (M, Y). Color space conversion circuit 2 for read data
The process of 02 is performed. At this time, (C, M, Y) becomes (C
p, Mp, Yp), and the data obtained from each patch is used as a table as shown in FIG. Then, using the formula for obtaining the distance described above, (C of the input ILP and each output patch
p, Mp, Yp), and the shortest one is made into a table as shown in FIG.

In the color difference diffusion method (CD method) of this embodiment, all the input colors are replaced with the closest input color among the used ink and the combination type, and the difference is diffused to the peripheral pixels. The method of dealing with this replacement is the basis for improving the color reproducibility of the color copy using the CD method.

In this embodiment, CMYK is used for ILP.
Since it is necessary to obtain (Yp, Mp, Cp) for CMYK, a table as shown in FIG. 11 is prepared.

The correspondence obtained above differs depending on the type of ink used and the type of paper. Therefore, if the table is changed according to the supported ink, paper, etc.,
High color reproducibility can be obtained. RAM does not have multiple types, and RAM is copied from ROM etc. each time copying or changing settings.
You may copy the table to. Of course, having an average table may simplify the table to have. It is also possible to optimize the selected recording medium such as paper and toner or ink by the following procedure.

In the present embodiment, in order to simplify the explanation, the tables in FIGS. 4, 8 and 11 are shown for the case where the resolution conversion is doubled, but in the case of other integer multiples,
Alternatively, it is possible for those skilled in the art to easily create what the tables of FIG. 4, FIG. 8, and FIG. 11 look like when they are not integral multiples, by knowing the description of the present embodiment. It goes without saying that other integer multiples and non-integer multiples are also included in the present invention.

Further, the present invention is applied to a system composed of a plurality of devices (for example, host computer, interface device, reader, printer, etc.), but is also applied to a device composed of one device (for example, copying machine, facsimile machine). You may.

According to this embodiment, in the color facsimile, the received data is output with good reproducibility. In the above-described embodiment, the description has been made based on color copying, but the input means may be color facsimile data received by a known method instead of a scanner. Color facsimile data is IT
The L, a *, b * color spaces defined in U-T T.42 are compressed by JPEG. Performing effective resolution conversion based on the resolution data in the header section by this method enables high-speed binarization with a small memory capacity.

In this embodiment, the printer of 600 dpi is used as the recording means, but the output of other resolution may be used. Further, a printer in which one pixel is generated from a plurality of dots can be similarly implemented by recreating the table.

Further, software for realizing the functions of the above-described embodiments is provided to a computer in an apparatus or system connected to the various devices so as to operate the various devices so as to realize the functions of the above-described embodiments. What is implemented by operating the above various devices according to the program supplied with the program code and supplied to the computer (CPU or MPU) of the system or apparatus is also included in the scope of the present invention.

Further, an object of the present invention is to supply a storage medium having a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to supply a computer (or CPU) of the system or apparatus.
Or MPU) reads and executes the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, magnetic tape, non-volatile memory card, ROM, etc. can be used.

Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) running on the computer based on the instruction of the program code. ) And the like perform some or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion board inserted in the computer or the function expansion unit connected to the computer, based on the instruction of the program code, This also includes a case where a CPU or the like included in the function expansion board or the function expansion unit performs some or all of the actual processing and the processing realizes the functions of the above-described embodiments.

When the present invention is applied to the above-mentioned storage medium, the storage medium stores program codes and tables for executing the processes corresponding to the above-mentioned flowcharts.

[0083]

As described above, it is possible to provide an image processing method and apparatus capable of improving the color reproducibility of the entire output image without increasing the processing load.

That is, by increasing the pixel density by interpolation in the main scanning direction and generating a print pattern consisting of a plurality of dots in the sub scanning direction, high definition image data is obtained in the main scanning direction. In the sub-scanning direction, there is an effect that the amount of data to be stored is compressed and the processing speed is increased. As a result, the processing load required to obtain the output color can be made extremely small, and the deterioration of image quality due to binarization can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a detailed configuration example of a binarization processing unit 102 shown in FIG.

FIG. 3 is a flowchart showing an example of a processing procedure of binarization processing by the binarization processing unit 102.

FIG. 4 is a diagram showing an example of an output color point table according to the present embodiment.

FIG. 5 is a flowchart showing an example of a color difference diffusion process that occurs during the binarization process of the present embodiment.

FIG. 6 is a diagram showing an example of error diffusion from a processed pixel according to the present embodiment.

FIG. 7 is a diagram showing an example of error diffusion to processed pixels according to the present embodiment.

FIG. 8 is a diagram showing an example of an output color table according to the present embodiment.

FIG. 9 is a diagram showing an example of correspondence between output color points of output color combinations according to the present embodiment.

FIG. 10 is a diagram showing a print example of output color combinations according to the present embodiment.

FIG. 11 is a diagram showing an example in which an output color point table and an output color table according to the present embodiment are integrated.

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Claims (28)

[Claims] 1. An image processing method for converting pixel density of input multi-valued image data into binary image data while converting the pixel density of the multi-valued image data, the pixel density converting the pixel density of the multi-valued image data in a main scanning direction. A conversion step; a binarization step of converting the multi-valued image data whose pixel density has been converted in the main scanning direction into binary image data whose pixel density has been converted in the sub-scanning direction on a pixel-by-pixel basis; An image processing including an error diffusion step of diffusing an output error between a dot pattern based on the data and the multivalued image data whose pixel density is converted in the main scanning direction in the vicinity of a binarized pixel. Method. 2. The binary image data of a plurality of lines in which the pixel density is converted in the sub-scanning direction using the multi-valued image data of each pixel whose pixel density is converted in the main scanning direction as an address in the binarizing step. The image processing method according to claim 1, wherein the first table for outputting is used. 3. The image processing method according to claim 2, wherein the output binary image data corresponds to a combination of color dots output on a plurality of lines. 4. In the error diffusion step, the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction is used as an address, and the binary image data of a plurality of lines whose pixel density has been converted in the sub-scanning direction. Using a second table that outputs multi-valued image data corresponding to dot pattern output, multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction and multi-valued image data output from the second table The image processing method according to claim 2 or 3, wherein a difference between and is defined as an error. 5. The table according to claim 4, wherein the first and second tables are one table having an address of multi-valued image data of each pixel subjected to pixel density conversion in the main scanning direction. Image processing method. 6. The address according to claim 2, wherein the address comprises a plurality of upper bits of multivalued image data of each pixel whose pixel density is converted in the main scanning direction. Image processing method. 7. The image processing method according to claim 2, wherein the first table is switched depending on a recording medium. 8. The image processing method according to claim 4, wherein the second table is switched depending on a recording medium. 9. The image processing method according to claim 2, wherein at least one of the first and second tables is switched depending on a recording engine mode. 10. An image processing device for converting pixel density of input multi-valued image data into binary image data while converting the pixel density of the multi-valued image data, the pixel density converting the pixel density of the multi-valued image data in a main scanning direction. Conversion means; binarization means for converting the multi-valued image data whose pixel density has been converted in the main scanning direction into binary image data whose pixel density has been converted in the sub-scanning direction on a pixel-by-pixel basis; Image processing characterized by having an error diffusion means for diffusing an output error between the dot pattern based on the data and the multi-valued image data whose pixel density has been converted in the main scanning direction in the vicinity of the binarized pixel. apparatus. 11. The binary image data of a plurality of lines in which the pixel density is converted in the sub-scanning direction by using the multi-valued image data of each pixel in which the pixel density is converted in the main scanning direction as an address. 10. The image processing apparatus according to claim 9, further comprising a first table for outputting 12. The image processing apparatus according to claim 11, wherein the output binary image data corresponds to a combination of color dots output on a plurality of lines. 13. The error diffusing unit uses, as an address, the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction, and stores the binary image data of a plurality of lines in which the pixel density has been converted in the sub-scanning direction. A second table for outputting multi-valued image data corresponding to the output, a difference between the multi-valued image data of each pixel subjected to the pixel density conversion in the main scanning direction and the multi-valued image data output from the second table 13. The image processing apparatus according to claim 11 or 12, further comprising subtraction means for calculating an error. 14. The table according to claim 13, wherein the first and second tables are one table having an address of multi-valued image data of each pixel whose pixel density is converted in the main scanning direction. Image processing device. 15. The method according to claim 11, further comprising an address generating unit that selects the upper bits of the multi-valued image data of each pixel whose pixel density has been converted in the main scanning direction and uses the selected upper bits as the address. The image processing device according to any one of 1. 16. The storage medium for storing the table further comprises a detachable interface means, and a different table can be used by exchanging the storage medium. The image processing device according to any one of claims. 17. A storage medium having a plurality of different tables stored therein, wherein a table selected based on an external signal is used. The image processing device described. 18. The image processing apparatus according to claim 11, further comprising a rewritable storage medium, and means for downloading the table to the storage medium from the outside. 19. The error diffusion means further comprises an error storage medium for storing the error diffused from the already processed main scanning line, and an interface means for the error storage medium. The image processing device described. 20. Input means for inputting multi-valued image data, pixel density conversion means for converting the multi-valued image data in pixel density in a main scanning direction, and error data added to the pixel density converted data,
Calculation means for calculating error correction data, selection means for selecting a predetermined dot pattern based on the error correction data, and error calculation means for calculating a difference between the value of the selected dot pattern and the error correction data. And an image processing apparatus, wherein the dot pattern comprises a plurality of dot patterns at least in the sub-scanning direction. 21. The image processing apparatus according to claim 20, wherein the dot pattern is a combination of color dots. 22. The image processing apparatus according to claim 21, wherein the dot pattern combination is switched depending on a recording medium. 23. The image processing apparatus according to claim 20, wherein a predetermined value for each dot pattern for calculating a difference from the error correction data is switched by a recording medium. 24. The at least one of the dot pattern combination and the predetermined value for each dot pattern is switched depending on a mode of a recording engine.
The image processing apparatus according to item 0. 25. The image processing apparatus is included in a color facsimile, and the image processing apparatus converts a received image into a resolution of a recording unit based on received resolution information. Image processing device. 26. A storage medium for storing a computer-readable image processing program for converting binary image data while converting pixel density of input multi-valued image data, wherein the image processing program is mainly A program module for controlling pixel density conversion for converting the pixel density of multi-valued image data in the scanning direction, and the multi-valued image data for which the pixel density conversion has been performed in the main scanning direction is converted in pixel units in the sub-scanning direction. A program module for controlling binarization for converting the binarized image data into a converted binary image data, and an output error between the dot pattern based on the binary image data and the multivalued image data whose pixel density has been converted in the main scanning direction. A storage medium including a program module that controls error diffusion that diffuses in the vicinity of a binarized pixel. 27. A first line for outputting binary image data of a plurality of lines, the pixel density of which is converted in the sub-scanning direction, using the multi-valued image data of each pixel whose pixel density is converted in the main scanning direction as an address. Corresponding to the dot pattern output of the table and / or the multi-valued binary image data in which the pixel density is converted in the sub-scanning direction, using the multi-valued image data of each pixel in the main scanning direction as the address. 27. The storage medium according to claim 26, further comprising a second table for outputting the multivalued image data to be output. 28. A storage medium attachable to and detachable from an image processing device for converting into binary image data while converting the pixel density of input multi-valued image data, wherein the pixel density conversion is at least in the main scanning direction. The first table that outputs the binary image data of a plurality of lines whose pixel density has been converted in the sub-scanning direction by using the generated multi-valued image data of each pixel as an address, and / or the pixel density conversion in the main scanning direction. 2 of a plurality of lines whose pixel density is converted in the sub-scanning direction using the multi-valued image data of each pixel as an address.
A storage medium comprising a second table for outputting multi-valued image data corresponding to dot pattern output of value image data.