JP2001157050A - Image-processing method, image processor and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing method, an image processor and its controlling method for n-ary coding at high speed, using a simple constitution. SOLUTION: This method/device has an adder 104 for adding a propagating error based on the binarizing errors of plural peripheral pixels, which are already binarized to the input value of an image element under consideration to be a processing object, a comparator 101 for comparing the input value added with the propagating error by the adder 104 with a prescribed threshold and outputting binary data, a subtracter 105 for calculating the error of the input value and output value of the comparator 101, and a propagating error table 103 for relating and storing the combination of an n-ary error as the output of the subtracter 105, concerning plural peripheral pixels and the propagating error corresponding to the combination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for converting image data of a first gradation number m into image data of a second gradation number n smaller than the first gradation number m by using an error diffusion method. The present invention relates to an image processing method, an image processing apparatus, and a control method for converting a value into a value.

[0002]

2. Description of the Related Art Conventionally, an image processing apparatus using such an error diffusion method has been configured as shown in FIG. In the figure, reference numeral 1101 denotes a comparator for comparing an input value with a threshold value to determine an n-value output value, and 1102 stores a difference between an output value and an input value on which an error is superimposed. Is an error buffer. 1103 is the error buffer 11
02 is a propagation error calculation unit for performing a product-sum operation of the error stored in 02 and a predetermined diffusion matrix, and is configured to perform a product-sum operation by a combination of a plurality of multipliers and adders. . Reference numeral 1104 denotes an adder for adding the propagation error calculated by the propagation error calculation unit 1103 to the input image data, and reference numeral 1105 denotes a subtractor for calculating a difference between input and output of the comparator 1101.

When image data f (x, y) of a target pixel located at (x, y) is input, an error buffer 1102
, The n-valued errors of a plurality of peripheral pixels at a predetermined position are read out and input to the propagation error calculating unit 1103.

The propagation error calculation unit 1103 calculates a propagation error to be added to the input image data f (x, y) based on the following equation.

[0005]

(Equation 1)

Here, e (x + i, y + j) is a peripheral pixel (x + i, y +) existing around the pixel of interest (x, y).
j) is an n-ary error. Further, w (i, j) is a coefficient for weighting the binarization error of the peripheral pixel by the distance from the target pixel. However, to save the average concentration,

[0007]

(Equation 2) It is a relationship.

[0008] The propagation error A is obtained by adding the weighted n-valued errors over peripheral pixels existing around the target pixel.

In the adder 1104, the sum of the propagation error A and the input value f (x, y) is obtained, and the result f '(x,
y) is input to the comparator 1101. The comparator 1101 checks the magnitude relationship between the input value and a preset threshold value, and converts the value into n-values (n is an integer of 2 or more and smaller than the number of gradations of the input value) according to the result. Value g
(X, y) is output. Finally, the output g (x, y) of the comparator 1101 and the input value f ′ (x,
The difference e (x, y) from y) is calculated with a predetermined bit precision, and the result is stored in an error buffer.

[0010]

However, according to the above-described conventional technique, the propagation error calculation unit 1103 requires
Since the calculation of equation (1) is performed for all n-valued errors for each pixel, the processing is complicated and the processing speed is slow.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and it is an object of the present invention to provide an image processing method and an image processing apparatus capable of high-speed n-value conversion with a simple configuration and its control. It is to provide a method.

[0012]

In order to achieve the above object, according to the present invention, image data of the first number of gradations m is
Using an error diffusion method, the second gradation number smaller than the first gradation number m
An image processing apparatus for converting an n-value into n-valued image data into an n-valued image data, comprising: An input value obtained by adding the propagation error to the input value, comparing the input value with a predetermined threshold value, and outputting n values, the input value of the comparing means And an error calculating means for calculating an error between the output values, a combination of an n-valued error as an output of the error calculating means for the plurality of peripheral pixels, and the propagation error corresponding to the combination. Storage means for storing.

[0013] The image processing apparatus may further include temporary storage means for temporarily storing the n-valued errors of the plurality of peripheral pixels calculated by the error calculation means.

The storage means is an LUT using, as an address, a sequence formed by serially arranging n-value errors of the plurality of peripheral pixels stored in the temporary storage means.

[0015] Further, there is provided calculating means for calculating a propagation error based on the n-value errors of a plurality of peripheral pixels which have already been n-valued, and a part of the n-value errors is input to the calculating means. Calculating a part of the propagation error, deriving the remaining part of the propagation error by referring to the storage means from the remaining part of the n-valued error, and combining the output of the calculation means and the output of the storage means. Then, a total propagation error is obtained and input to the adding means.

The n-valued error is divided into a predetermined number of upper bits and the remaining lower bits, and one of the upper bits and the lower bits is input to the storage medium, and the other is input to the calculating means. It is characterized by being performed.

In an image processing apparatus for converting an input value into an output having a smaller bit width, an error diffusion means for performing error diffusion processing, an organized dither means for performing systematic dither processing, the error diffusion means, A storage means capable of storing information referred to by the systematic dither means, a combination of n-valued errors for a plurality of peripheral pixels, and a propagation error corresponding to the combination stored in advance. When performing an error diffusion process, a propagation error LUT is created in the storage unit based on the contents of the first nonvolatile memory, and the error is stored in the storage unit. When the diffusion means performs the error diffusion processing with reference to the propagation error LUT stored in the storage means and performs the tissue dither processing,
A threshold LUT is created based on the contents of the non-volatile memory, and the systematic dithering means performs systematic dither processing with reference to the threshold LUT stored in the storage means. Switching means for switching contents.

An image processing method for converting image data of a first gradation number m into n-valued image data of a second gradation number n smaller than the first gradation number m using an error diffusion method. And already n
An addition step of adding a propagation error based on the n-valued error of the plurality of peripheral pixels that have been converted to the input value of the target pixel to be processed, and an input value obtained by adding the propagation error in the addition step. Comparing a predetermined threshold value and outputting n values; an error calculating step of calculating an error between the input value and the output value of the comparing step; and A combination of the n-ary error as an output in the error calculation step, and the propagation error corresponding to the combination;
And a control step of controlling a storage means storing the propagation error corresponding to the combination of the n-valued errors.

Error diffusion means for performing error diffusion processing, systematic dither means for performing systematic dither processing, storage means capable of storing information referred to by the error diffusion means and the systematic dither means, N for a plurality of peripheral pixels in advance
A control method for an image processing apparatus, comprising: a first nonvolatile memory storing a combination of a binarization error and a propagation error corresponding to the combination, and a second nonvolatile memory storing a threshold table in advance. In performing the error diffusion process, a propagation error LUT is created in the storage unit based on the contents of the first nonvolatile memory, and the error diffusion unit refers to the propagation error LUT stored in the storage unit to determine an error. When performing a diffusion process and performing a tissue dither process, a threshold LUT is created in the storage unit based on the contents of the second nonvolatile memory, and the systematic dither unit is configured to store the threshold LUT stored in the storage unit. And controlling the image processing apparatus so as to perform organized dither processing with reference to FIG.

An image processing program for converting the image data of the first gradation number m into image data of the second gradation number n smaller than the first gradation number m by using an error diffusion method is stored. A computer-readable memory, wherein the image processing program adds a propagation error based on an n-value error of a plurality of peripheral pixels that have already been n-valued to an input value of a target pixel to be processed. And a program code of a comparing step of comparing the input value obtained by adding the propagation error in the adding step with a predetermined threshold value and outputting n values, and the input code of the comparing step A program code of an error calculation step of calculating an error between a value and an output value, a combination of an n-ary error as an output in the error calculation step for the plurality of peripheral pixels, and the propagation error corresponding to the combination. And controls the storage means for storing in association with, characterized in that it comprises a program code reading control step the propagation error corresponding to a combination of the n-valued error.

Error diffusion means for performing error diffusion processing; systematic dither means for performing systematic dither processing; storage means capable of storing information referred to by the error diffusion means and the systematic dither means; N for a plurality of peripheral pixels in advance
A control program for an image processing apparatus, comprising: a first non-volatile memory storing a combination of a binarization error and a propagation error corresponding to the combination, and a second non-volatile memory storing a threshold table in advance Wherein the control program creates a propagation error LUT in the storage means based on the contents of the first non-volatile memory when performing the error diffusion processing, and the error diffusion means Propagation error L stored in the means
A program code of an error diffusion process for controlling to perform an error diffusion process with reference to a UT, and when performing a tissue dither process, a threshold LUT is created in the storage unit based on the contents of the second nonvolatile memory. And a program code for an organized dither processing step of controlling the organized dither means to perform the organized dither processing with reference to the threshold value LUT stored in the storage means.

[0022]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the relative arrangement of components described in this embodiment, formulas, numerical values, etc., unless otherwise specified,
It is not intended to limit the scope of the present invention only to them.

(First Embodiment) First, FIGS.
The printer according to the first embodiment of the present invention will be described with reference to FIG. In the present embodiment, for example, 25
A case in which binarization processing is performed on multi-level image data of six gradations will be described.

FIG. 2 is a block diagram showing a schematic configuration of a printer to which the present embodiment can be applied. Printer 200
Are the print controller 201 and the print engine 2
And converts vector data such as figures and characters input from the host computer 203 into raster data composed of a set of pixels (dots).
The data is expanded in the page memory 205 for one page. And
When the raster data is output from the page memory 205, the conversion unit 204 binarizes the raster data, and based on the converted binary data, performs printing by causing the print engine 202 to attach toner or ink to the recording material. .

FIG. 1 is a diagram schematically showing the internal configuration of the conversion unit 204.

In the figure, reference numeral 101 denotes a comparator for comparing an input value with a threshold value to determine a binary output value.
An error buffer 2 temporarily stores a binarization error which is a difference between the output value and the input value on which the error is superimposed. Reference numeral 103 denotes a propagation error table for obtaining a propagation error from the output from the error buffer 102, and is configured by an LUT. 104 is an adder that adds the propagation error calculated by the propagation error table 103 to the input image data, and 105 is a subtractor that calculates the difference between the input and output of the comparator 101.

The propagation error table 103 stores the 2
This LUT has a combination of a binarization error as an address, and a value of a propagation error when the binarization error of a peripheral pixel is the combination.

For example, using a matrix as shown in FIG. 3, the image data f of the pixel of interest located at (x, y)
Assuming that the propagation error based on the binarization error of the peripheral pixels indicated by 0 to 7 is added to (x, y), first, the binarization error of the eight peripheral pixels is e (x + i, y + j) (−2 ≦ i, j ≦ 0; execpti = j = 0) (3)

A sequence a (8p bits) in which such binarization errors (p bits) are arranged in order from peripheral pixel 0 to peripheral pixel 7 is as follows:

[0030]

(Equation 3) Becomes This sequence becomes the address of the propagation error table 103.

Then, the position information of the eight peripheral pixels is represented by l
(0-7), the propagation error A (a) of address a
Is

[0032]

(Equation 4) Becomes

That is, the propagation error table 103 stores a propagation error A (a) having address a.

When the image data f (x, y) of the pixel of interest located at (x, y) is input, the binarization errors of a plurality of peripheral pixels (0 to 7) are read from the error buffer 102. .

The binarization errors of the peripheral pixels (0 to 7) read from the error buffer 102 are input to the propagation error table 103 in the form of a sequence a.
Is read from the propagation error A (a). Further, the adder 10
4, the sum of the propagation error A (a) and the input value f (x, y) is calculated, and the resulting f ′ (x, y) is compared with the comparator 1101.
Is input to The comparator 1101 checks the magnitude relationship between the input value and a preset threshold value, and converts the value into n-values (n is an integer of 2 or more and smaller than the number of gradations of the input value) according to the result. The value g (x, y) is output. Finally, the difference e (x, y) between the output g (x, y) of the comparator 1101 and the input value f ′ (x, y) on which the propagation error is superimposed.
Is calculated with p-bit precision, and the result is stored in the error buffer.

As described above, without calculating for each pixel,
Since a propagation error is obtained by reading from the LUT, n-value can be quickly converted to a simple value with a simple configuration.

In the ordinary processing, when the input value f has 8-bit precision, the error precision p is generally 8-bit. At this time, if the above principle is used as it is, a table having a considerably large address space is required (in the above example, a 64-bit address space is required). In an environment where resources such as RAM capacity are limited, each error may be thinned out when creating the above-mentioned address sequence (for example, in the above-described example,
If the error is reduced to 2 bits, the required address space becomes 16
Reduced to a bit). When this method is applied, data to be stored in the propagation error table 103 is obtained as follows. (However, it shall be decimated from p bits to m bits.)

[0038]

(Equation 5) (However, applying the 2 ⁿ is divisible by 2 ⁿ represents the n-bit left shift denote the n-bit right shift.) The second embodiment (second embodiment) the present invention FIG.
This will be described with reference to FIG.

In the first embodiment, all of the binarization errors are input to the propagation error table, and the propagation errors are obtained with reference to the table. In the present embodiment, the binarization errors are calculated. The division is performed, a part of which is input to the propagation error table, and the rest is input to the propagation error calculation unit, and the outputs are combined to determine the propagation error. The configuration is the same as that of the first embodiment except that the propagation error calculation section 304 is provided in parallel with the propagation error table 303. Therefore, the same components are denoted by the same reference numerals and description thereof will be omitted.

In the figure, reference numerals 303 and 304 denote a propagation error table and a propagation error calculation unit, respectively.
Reference numeral 04 denotes a product-sum operation unit. In this configuration, error data used for calculating a propagation error is divided into upper n bits and lower m bits, and input to the propagation error table 303 and the propagation error calculator 304, respectively. Assuming that the diffusion window shown in FIG. 3 is used, the propagation error table contains

[0041]

(Equation 6) here,

[0042]

(Equation 7) The following value A (a) is stored at each address a. Therefore, by adding the value A output from the propagation error table 303 and the result B obtained by calculating the lower m-bit error in the propagation error calculation unit 304 using the expression (1) using the following expression, the final value is obtained. A propagation error A 'is obtained.

A ′ = 2 ^mA + B (10) After that, normal error diffusion processing can be performed using the value calculated by equation (10).

In this embodiment, in order to calculate a propagation error, the error is divided into upper n bits and lower m bits, and a product sum operation is performed with lower m bits by referring to a table with the upper n bits. In addition, it is possible to prevent the processing accuracy from deteriorating due to the thinning out of the error, and at the same time, reduce the bit width of the product-sum operation unit included in the propagation error calculation unit, thereby reducing the operation scale.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG.

In the first embodiment, only the error diffusion processing is performed on the input image data and the image data is binarized and output. However, in the present embodiment, the error diffusion processing and the systematic dithering are performed. Processing and can be selected.

In the figure, reference numeral 401 denotes the error diffusion processing unit described in the first and second embodiments. The error diffusion processing unit 401 uses the RAM 40
5 is used. Reference numeral 402 denotes an organized dither processing unit that performs organized dither processing, and a RAM is used as a threshold table.
405 is used. The ROMs 403 and 404 always hold a propagation error table used for error diffusion processing and a threshold table used for systematic dither processing, respectively.

That is, in this embodiment, the RAM 405 is shared by two different processes. When the error diffusion process is performed, the switches 406, 407, and 408 in FIG.
And the stored propagation error table is loaded from the ROM 403 into the RAM 405.
When the tissue dither processing is performed, each switch is connected to the B side, and the stored threshold table is loaded from the ROM into the RAM 405. Thus, processing using the selected method becomes possible. In the present embodiment, the error diffusion processing and the tissue dither processing are configured to be performed using the same RAM resource. That is, the effect of reducing costs is produced.

[0049]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (a computer) of the system or apparatus. It is needless to say that the present invention can also be achieved by a CPU or an MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Also,
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the operating system (OS) running on the computer based on the instructions of the program code.
It goes without saying that a case where the functions of the above-described embodiments are implemented by performing some or all of the actual processing, and the processing performs the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. Needless to say, the CPU included in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0052]

As described above, in the image processing apparatus which performs the error diffusion processing as described above, the following effects are produced by using the storage means for calculating the propagation error.

The processing speed is improved because a complicated product-sum operation is not required.

By setting the capacity of the table as needed, it is possible to perform a design in which parameters such as processing accuracy, apparatus cost, and processing speed are optimized.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a configuration of a printer to which the image processing apparatus according to the present invention can be applied.

FIG. 3 is a diagram illustrating an example of an error diffusion window.

FIG. 4 is a diagram illustrating a configuration of an image processing apparatus according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration of an image processing apparatus according to a third embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration of a conventional image processing apparatus.

[Explanation of symbols]

 101 Comparator 102 Error buffer 103, 303 Propagation error table 104 Adder 105 Subtractor 304 Propagation error calculation unit 401 Error diffusion processing unit 402 Systematic dither processing unit 403, 404 ROM 405 RAM 406, 407, 408 Switch

Claims (10)

[Claims] An image processing apparatus for converting image data having a first gradation number m into image data having a second gradation number n smaller than the first gradation number m using an error diffusion method. Adding means for adding a propagation error based on the n-value error of a plurality of peripheral pixels that have already been n-valued to an input value of a pixel of interest to be processed; A comparing unit that compares the added input value with a predetermined threshold value and outputs n values; an error calculating unit that calculates an error between the input value and the output value of the comparing unit; Storage means for storing a combination of an n-valued error as an output of the error calculation means for the peripheral pixel of and a propagation error corresponding to the combination, apparatus. 2. The image processing apparatus according to claim 1, further comprising a temporary storage unit for temporarily storing the n-valued errors of the plurality of peripheral pixels calculated by the error calculation unit. 3. The storage device according to claim 2, wherein the storage means is an LUT using, as an address, a sequence formed by serializing the n-valued errors of the plurality of peripheral pixels stored in the temporary storage means. The image processing device according to claim 1. 4. A calculating means for calculating a propagation error based on n-value errors of a plurality of peripheral pixels which have already been n-valued, wherein a part of the n-value error is provided to the calculating means. Input, calculate a part of the propagation error, derive the remaining part of the propagation error by referring to the storage means from the remaining part of the n-valued error, output the calculation means and the output of the storage means By combining
2. The image processing apparatus according to claim 1, wherein a total propagation error is obtained and input to said adding means. 5. The n-valued error is divided into a predetermined number of upper bits and the remaining lower bits, one of the upper bits and the lower bits is input to the storage medium, and the other is the calculating means. The image processing apparatus according to claim 4, wherein the image is input to the image processing apparatus. 6. An image processing apparatus for converting an input value to an output having a smaller bit width, comprising: an error diffusion unit for performing an error diffusion process; an organized dither unit for performing an organized dither process; A storage unit capable of storing information referred to by the systematic dither unit; a combination of n-ary errors for a plurality of peripheral pixels and a propagation error corresponding to the combination stored in advance. A first non-volatile memory, a second non-volatile memory in which a threshold table is stored in advance, and when performing an error diffusion process, a propagation error LUT is created in the storage means based on the contents of the first non-volatile memory; When the error diffusion means performs error diffusion processing with reference to the propagation error LUT stored in the storage means and performs tissue dither processing, the second nonvolatile memory A threshold LUT is created based on the content of the threshold, and the systematic dithering means stores the threshold LUT stored in the storage means.
An image processing apparatus comprising: a switching unit that switches contents of the storage unit so as to perform systematic dither processing with reference to a UT. 7. An image processing method for converting image data having a first gradation number m into image data having a second gradation number n smaller than the first gradation number m using an error diffusion method. An addition step of adding a propagation error based on an n-value error of a plurality of peripheral pixels that have already been n-valued to an input value of a pixel of interest to be processed; A comparing step of comparing the added input value with a predetermined threshold value and outputting n values; an error calculating step of calculating an error between the input value and the output value in the comparing step; Controlling the storage means for storing a combination of the n-valued error as an output in the error calculation step for the peripheral pixel and the propagation error corresponding to the combination in association with the n-valued error. Controlling the reading of the propagation error corresponding to the combination of Image processing method comprising and. 8. An error diffusion means for performing error diffusion processing, an organized dither means for performing systematic dither processing, a storage means capable of storing information referred to by the error diffusion means and the systematic dither means. A first nonvolatile memory in which a combination of n-valued errors for a plurality of peripheral pixels and a propagation error corresponding to the combination are stored in advance, and a second nonvolatile memory in which a threshold value table is stored in advance In the method for controlling an image processing apparatus having the following, when performing an error diffusion process, a propagation error LUT is created in the storage unit based on the content of the first nonvolatile memory;
When the error diffusion means performs error diffusion processing with reference to the propagation error LUT stored in the storage means and performs tissue dither processing, a threshold LUT is stored in the storage means based on the contents of the second nonvolatile memory. And controlling the image processing apparatus so that the organized dither means performs an organized dither process with reference to a threshold LUT stored in the storage means. . 9. An image processing program for converting image data having a first gradation number m into image data having a second gradation number n smaller than the first gradation number m using an error diffusion method. Wherein the image processing program adds a propagation error based on an n-value error of a plurality of peripheral pixels that have already been n-valued to an input value of a target pixel to be processed. A program code of an adding step, a program code of a comparing step of comparing the input value obtained by adding the propagation error in the adding step with a predetermined threshold value, and outputting n values, A program code for an error calculation step of calculating an error between the input value and the output value; a combination of an n-valued error as an output in the error calculation step for the plurality of peripheral pixels; and the propagation corresponding to the combination Mistake If, by controlling the storage means for storing in association with, a computer-readable memory, characterized in that it comprises a program code for reading control step the propagation error corresponding to a combination of the n-valued error. 10. An error diffusion means for performing error diffusion processing, an organized dither means for performing systematic dither processing, a storage means capable of storing information referred to by the error diffusion means and the systematic dither means. A first nonvolatile memory in which a combination of n-valued errors for a plurality of peripheral pixels and a propagation error corresponding to the combination are stored in advance, and a second nonvolatile memory in which a threshold value table is stored in advance A computer-readable memory storing a control program for an image processing apparatus, comprising: a control unit that, when performing an error diffusion process, transmits a propagation error LUT to the storage unit based on contents of the first nonvolatile memory. make,
A program code for an error diffusion step for controlling the error diffusion means to perform an error diffusion process by referring to a propagation error LUT stored in the storage means; and a content of the second nonvolatile memory for performing a tissue dither process. Generating a threshold LUT in the storage means based on the threshold value, and controlling the systematic dither means to perform the systematic dither processing with reference to the threshold LUT stored in the storage means. A computer readable memory comprising: