JP2002135583A - Image processing apparatus, image processing method and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus, an image processing method and a storage medium that can vary an error spread coefficient depending on an output resolution, especially its error spread range so as to preferably generate an output dot arrangement thereby obtaining an image with high quality even when any output resolution is employed. SOLUTION: The image processing apparatus is provided with a spread coefficient revision section 18 that conducts control of revising an error spared coefficient in response to the output resolution, that is, decreasingly controls the error spread range when the output resolution is low or increasingly controls the error spread range when the output resolution is high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, an image processing method, and a storage medium, and more particularly, to a method for outputting an image to an output device having a smaller number of tones than an input image. The present invention relates to an image processing device that performs conversion, an image processing method, and a storage medium.

[0002]

2. Description of the Related Art Conventionally, an error diffusion method has been widely used as a pseudo halftone processing method having high tone reproducibility in image processing apparatuses such as printers, copiers, and facsimile machines. The error diffusion method was described by Floyd and Steinberg in 1975 as “An Adaptive.
Algorithm for Spatial Gr
ay Scale "SID 75 Digest, which binarizes the multi-valued image data of the pixel of interest and sets a predetermined error in the error between the binarization level and the multi-valued image data before binarization. The weight is added to the data of the pixels near the target pixel.

[0003]

However, the above-mentioned prior art has the following problems. That is, the error diffusion coefficient of the error diffusion method, especially the error diffusion range is constant even if the output resolution is different.
Even if the output can be preferably performed at the output resolution of PI (Dot Per Inch), it is not always possible to preferably output at other resolutions. The main factor is that the error diffusion range on the output paper is different because the error diffusion range of the error diffusion method is constant despite the change in output resolution.

[0004] For this reason, it is often encountered that the dot arrangement that is preferably output at a certain output resolution disturbs the dot arrangement at the moment when the output resolution is changed, resulting in a significant reduction in image quality. That is, to obtain an image quality equivalent to 300 DPI at an output resolution of 600 DPI, for example, the error diffusion range of the error diffusion method must be doubled as compared with the case of 300 DPI. In other words, the error diffusion range of the error diffusion method must be varied in proportion to the output resolution. In the above case, the error diffusion range of 5 pixels × 2 pixels at 300 DPI is set to 10 pixels × 4 pixels at 600 DPI. There was a problem that had to be done.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and preferably generates an output dot arrangement by changing an error diffusion coefficient, particularly an error diffusion range, according to an output resolution. It is an object of the present invention to provide an image processing device, an image processing method, and a storage medium that can obtain a high-quality image with respect to resolution.

[0006]

According to an aspect of the present invention, there is provided an image processing apparatus having a function of performing image quantization based on an error diffusion method. Characterized in that it has a diffusion coefficient changing means for changing the diffusion coefficient.

In order to achieve the above object, the invention according to claim 2 is characterized in that the diffusion coefficient changing means switches an error diffusion coefficient according to an output resolution.

In order to achieve the above object, the invention according to claim 3 is characterized in that the diffusion coefficient changing means reduces the error diffusion range when the output resolution is low, and decreases the error diffusion range when the output resolution is high. It is characterized in that it is increased.

In order to achieve the above object, the invention according to claim 4 further includes a storage unit for storing a quantization error, an addition unit for adding the quantization error to input pixel data, and the quantization unit. A quantizing unit that compares the pixel data after the error addition with a preset quantization threshold to determine an output pixel value; and a quantizer corresponding to a difference between the pixel data after the quantization error addition and the output pixel value. And an error diffusion means for performing an error diffusion process based on the error diffusion coefficient change by the diffusion coefficient change means.

In order to achieve the above object, the invention according to claim 5 is characterized in that it can be applied to a printer, a copying machine, or a facsimile having a function of performing image quantization based on the error diffusion method.

In order to achieve the above object, an invention according to claim 6 is an image processing method applied to an image processing apparatus having a function of performing image quantization based on an error diffusion method,
The method further comprises a diffusion coefficient changing step of changing an error diffusion coefficient according to the output resolution.

In order to achieve the above object, the invention according to claim 7 is characterized in that in the diffusion coefficient changing step, an error diffusion coefficient is switched according to an output resolution.

In order to achieve the above object, the invention according to claim 8 is characterized in that in the diffusion coefficient changing step, the error diffusion range is reduced when the output resolution is low, and the error diffusion range is reduced when the output resolution is high. It is characterized in that it is increased.

In order to achieve the above object, the invention according to claim 9 further includes a storing step of storing a quantization error, an adding step of adding the quantization error to input pixel data, and A quantizing step of comparing the pixel data after the error addition with a preset quantization threshold to determine an output pixel value; and a quantization step corresponding to a difference between the pixel data after the quantization error addition and the output pixel value. And an error diffusion step of performing an error diffusion process based on the error diffusion coefficient change in the diffusion coefficient change step.

In order to achieve the above object, the invention according to claim 10 is characterized in that it can be applied to a printer, a copying machine or a facsimile having a function of performing image quantization based on the error diffusion method.

According to another aspect of the present invention, there is provided a computer which stores a program for executing an image processing method applied to an image processing apparatus having a function of performing image quantization based on an error diffusion method. A readable storage medium, wherein the image processing method includes a diffusion coefficient changing step of changing an error diffusion coefficient according to an output resolution.

In order to achieve the above object, a twelfth aspect of the present invention is characterized in that in the step of changing the diffusion coefficient, the error diffusion coefficient is switched according to the output resolution.

According to a thirteenth aspect of the present invention, in the diffusion coefficient changing step, the error diffusion range is reduced when the output resolution is low, and the error diffusion range is reduced when the output resolution is high. It is characterized in that it is increased.

In order to achieve the above object, the invention according to claim 14 further includes a storing step of storing a quantization error, an adding step of adding the quantization error to input pixel data, and A quantization step of comparing the pixel data after error addition with a preset quantization threshold to determine an output pixel value; and a quantization step corresponding to a difference between the pixel data after the quantization error addition and the output pixel value. A calculation step of calculating a quantization error, and an error diffusion step of performing an error diffusion process based on the change of the error diffusion coefficient by the diffusion coefficient change step.

In order to achieve the above object, the invention according to claim 15 is characterized in that it can be applied to a printer, a copying machine or a facsimile having a function of performing image quantization based on the error diffusion method.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a main part of an image processing apparatus according to an embodiment of the present invention. The image processing device according to the embodiment of the present invention has a pixel data input terminal 1
0, cumulative error adder 11 (adder), fixed threshold setting terminal 12, quantizer 13 (quantizer), image data output terminal 14, error calculator 15 (calculator), error diffusion unit 1.
6 (error diffusion means), a cumulative error memory 17 (storage means), and a diffusion coefficient changing unit 18 (diffusion coefficient changing means).

The pixel data input terminal 10 is a terminal to which pixel data is input. The cumulative error adder 11 adds a value corresponding to a pixel position of the cumulative error memory 17 to the pixel data input from the pixel data input terminal 10. The fixed threshold setting terminal 12 is a terminal for setting a quantization threshold. The quantization unit 13 compares the pixel data after error addition by the cumulative error addition unit 11 with a threshold value set via the fixed threshold value setting terminal 12 to determine an output pixel value. Image data output terminal 14
Is a terminal to which the processed image data is output.

The error calculator 15 calculates a difference (quantization error) between the pixel data after the error addition by the cumulative error adder 11 and the output pixel value. The error diffusion unit 16 performs an error diffusion process based on the error diffusion coefficient change by the diffusion coefficient change unit 18. The cumulative error memory 17 has the configuration shown in FIG. 3, and stores the cumulative quantization error.
The diffusion coefficient changing unit (diffusion coefficient switching unit) 18 changes the error diffusion coefficient (especially, the error diffusion range) according to the output resolution. When the output resolution is low, the error diffusion range is reduced. If the output resolution is high, control is performed to increase the error diffusion range.

FIG. 6 is an explanatory diagram showing a conceptual example in which a program for executing the image processing method of the present invention and related data are supplied from a storage medium to the apparatus. A program for executing the image processing method of the present invention and related data are supplied by inserting a storage medium 61 such as a floppy disk or a CD-ROM into a storage medium drive insertion slot 63 provided in a device 62 such as a computer. . Thereafter, the program for executing the image processing method of the present invention and related data are stored in the storage medium 6.
By installing from 1 to the hard disk and loading from the hard disk to RAM, or loading directly to RAM without installing to the hard disk,
The program and related data can be executed.

In this case, in the image processing apparatus according to the embodiment of the present invention, when executing a program for executing the image processing method of the present invention, for example, the image is processed according to the procedure described with reference to FIG. By supplying the program and related data to the processing device, or storing the program and related data in the image processing device in advance,
Program execution becomes possible.

FIG. 5 is an explanatory diagram showing a configuration example of the storage contents of a storage medium storing a program for executing the image processing method of the present invention and related data. The storage medium includes storage contents such as volume information 51, directory information 52, a program execution file 53, and a program-related data file 54. A program for executing the image processing method of the present invention is a program code based on a flowchart of FIG. 2 described later. Note that the processing shown in the flowchart of FIG. 2 is executed under the control of a CPU provided in the image processing apparatus.

Next, the operation of the image processing apparatus according to the embodiment of the present invention configured as described above will be described in detail with reference to FIGS.

First, in the image processing apparatus, the output resolution is obtained from a printer driver or the like (step S21).
The diffusion coefficient changing unit 18 sets an error diffusion coefficient for each output resolution prepared in advance according to the output resolution (step S22). FIG. 4 shows an example of the error diffusion coefficient for each output resolution. FIG. 4A shows an output resolution of 300 DPI.
FIG. 4B is an explanatory diagram showing an error diffusion coefficient having an output resolution of 600 DPI. From FIG. 4, it can be seen that the error diffusion range of the error diffusion coefficient of 600 DPI is twice that of the case of 300 DPI.
However, the reason why the error diffusion coefficient used for 600 DPI is often 0 is to avoid a reduction in processing speed as compared with the case of 300 DPI.

The input image is sequentially scanned by an image scanning unit (not shown), and each pixel data is input from the pixel data input terminal 10 (step S23). The scanning of the image starts from the upper left pixel of the image area and proceeds rightward one pixel at a time, and when it reaches the right end, it proceeds rightward sequentially from the leftmost pixel one pixel below, to the lower right pixel. Next, in the cumulative error adding unit 11,
The pixel data input from the pixel data input terminal 10 includes
A value corresponding to the pixel position of the accumulated error memory 17 is added (Step S24). As shown in FIG. 3, the accumulated error memory 17 has one storage area E0 and storage areas E (x) (x = 1 to W) equal in number to the horizontal pixels W of the image.
The quantization error is stored by a method described later. It is assumed that the accumulated error memory 17 has been all initialized to the initial value 0 before the processing is started.

The cumulative error adder 11 adds the value of the storage area E (x) of the cumulative error memory 17 corresponding to the horizontal pixel position x to the input pixel data. That is, if the input pixel data is I and the pixel data after error addition is I ', then I' = I + E (x). Next, the quantization unit 13 compares the pixel data I ′ after the error addition with a threshold value set via the fixed threshold value setting terminal 12 to determine an output pixel value (step S25).

The threshold value is usually set to a median value between the maximum input pixel value and the minimum input pixel value. That is, if the input pixel value is an integer in the range of 0 to 255, the threshold T is 127
To 128. The output pixel value O is determined by the following equation.

O = 0 (I ′ <T) O = 255 (I ′ ≧ T) Next, the error calculator 15 calculates the difference between the pixel data I ′ after error addition and the output pixel value, that is, the quantization error. E is calculated (step S26).

E = I'-O Next, the error diffusion unit 16 performs an error diffusion process based on the error diffusion coefficient change by the diffusion coefficient change unit 18 (step S27). Thus, the processing for one pixel is completed.

As described above, according to the image processing apparatus according to the embodiment of the present invention, the control for changing the error diffusion coefficient according to the output resolution, that is, when the output resolution is low, the error diffusion range Is provided, and the diffusion coefficient changing unit 18 that performs control to increase the error diffusion range when the output resolution is high is provided.

In the above configuration, in order to vary the error diffusion coefficient, particularly the error diffusion range according to the output resolution,
The output dot arrangement is preferably generated, and as a result, there is an effect that a high-quality image can be obtained for any output resolution.

[Other Embodiments] In the above-described embodiment of the present invention, a specific example of the image processing apparatus has not been particularly described. However, the present invention relates to various image processing apparatuses such as a printer, a copying machine, and a facsimile. It is possible to apply to the device.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. A storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus is stored in a medium such as a storage medium. It goes without saying that this can also be achieved by reading and executing the program code.

In this case, the program code itself read from a medium such as a storage medium realizes the functions of the above-described embodiment, and the medium such as a storage medium storing the program code constitutes the present invention. Will be. Examples of a medium such as a storage medium for supplying the program code include a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, and a network. For example, download via the Internet can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS and the like running on the computer are actually executed based on the instructions of the program code. It goes without saying that a part or all of the above-described processing is performed, and the functions of the above-described embodiments are realized by the processing.

Further, after the program code read out from a medium such as a storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the program code is read out. It is needless to say that a CPU or the like provided in the function expansion board or the function expansion unit performs part or all of the actual processing based on the above, and the functions of the above-described embodiments are realized by the processing.

[0042]

As described above, according to the image processing apparatus according to the first to fifth aspects, in an image processing apparatus having a function of performing image quantization based on an error diffusion method, an error of an image is determined according to an output resolution. Diffusion coefficient changing means for changing the diffusion coefficient is provided.The diffusion coefficient changing means performs control to reduce the error diffusion range when the output resolution is low and to increase the error diffusion range when the output resolution is high. That is, in order to vary the error diffusion coefficient, particularly the error diffusion range according to the output resolution, an output dot arrangement is preferably generated,
As a result, there is an effect that a high-quality image can be obtained for any output resolution.

According to the image processing method of the present invention, by executing the image processing method in the image processing apparatus, the output dot arrangement is preferably generated in the same manner as described above. There is an effect that a high-quality image can be obtained even at a high output resolution.

According to the storage medium of the present invention, the image processing method is read from the storage medium and executed by the image processing apparatus, so that the output dot arrangement is preferably generated similarly to the above. As a result, there is an effect that a high-quality image can be obtained for any output resolution.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating an operation of the image processing apparatus according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a configuration example of a cumulative error memory of the image processing device according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an example of an error diffusion coefficient with respect to each output resolution of the image processing apparatus according to the embodiment of the present invention; FIG. 4 (a) is an explanatory diagram showing an error diffusion coefficient with an output resolution of 300 DPI; FIG. 4B is an explanatory diagram illustrating an error diffusion coefficient having an output resolution of 600 DPI.

FIG. 5 is an explanatory diagram showing a configuration example of storage contents of a storage medium storing a program for executing the image processing method of the present invention and related data.

FIG. 6 is an explanatory diagram showing a conceptual example in which a program for executing an image processing method of the present invention and related data are supplied from a storage medium to an apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Pixel data input terminal 11 Cumulative error addition part 12 Fixed threshold value setting terminal 13 Quantization part 14 Image data output terminal 15 Error calculation part 16 Error diffusion part 17 Cumulative error memory 18 Diffusion coefficient change part

Claims (15)

[Claims] An image processing apparatus having a function of performing image quantization based on an error diffusion method, comprising: a diffusion coefficient changing unit that changes a diffusion coefficient of an error according to an output resolution. apparatus. 2. The image processing apparatus according to claim 1, wherein said diffusion coefficient changing unit switches an error diffusion coefficient according to an output resolution. 3. The diffusion coefficient changing unit according to claim 1, wherein the error diffusion range is reduced when the output resolution is low, and the error diffusion range is widened when the output resolution is high. Image processing device. 4. A storage means for storing a quantization error, an addition means for adding the quantization error to input pixel data, and a pixel data after the addition of the quantization error and a predetermined quantization. And a calculating means for calculating a quantization error corresponding to a difference between the pixel data after the addition of the quantization error and the output pixel value, and a calculating means for calculating the diffusion coefficient. 4. The image processing apparatus according to claim 1, further comprising an error diffusion unit configured to perform an error diffusion process based on a change in an error diffusion coefficient by the unit. 5. The image processing apparatus according to claim 1, wherein the image processing apparatus is applicable to a printer, a copying machine, or a facsimile having a function of performing image quantization based on the error diffusion method. 6. An image processing method applied to an image processing device having a function of performing image quantization based on an error diffusion method, comprising a diffusion coefficient changing step of changing an error diffusion coefficient according to an output resolution. An image processing method comprising: 7. The image processing method according to claim 6, wherein in the diffusion coefficient changing step, an error diffusion coefficient is switched according to an output resolution. 8. The diffusion coefficient changing step, wherein the error diffusion range is reduced when the output resolution is low, and the error diffusion range is increased when the output resolution is high. Image processing method. 9. A storage step of storing a quantization error, an addition step of adding the quantization error to input pixel data, and a step of adding the pixel data after the addition of the quantization error to a predetermined quantization. A quantization step of comparing an output pixel value with a threshold value of the pixel data, calculating a quantization error corresponding to a difference between the pixel data after the addition of the quantization error and the output pixel value, and changing the diffusion coefficient. 9. The image processing method according to claim 6, further comprising: an error diffusion step of performing an error diffusion process based on a change in an error diffusion coefficient in the step. 10. A printer, a copying machine, or a facsimile having a function of performing image quantization based on the error diffusion method.
The image processing method according to any one of the above. 11. A computer-readable storage medium storing a program for executing an image processing method applied to an image processing apparatus having a function of performing image quantization based on an error diffusion method, wherein the image processing method includes the steps of: Comprises a diffusion coefficient changing step of changing a diffusion coefficient of an error according to an output resolution. 12. The storage medium according to claim 11, wherein in the diffusion coefficient changing step, an error diffusion coefficient is switched according to an output resolution. 13. The diffusion coefficient changing step according to claim 11, wherein the error diffusion range is reduced when the output resolution is low, and the error diffusion range is increased when the output resolution is high. Storage media. 14. A storage step of storing a quantization error, an addition step of adding the quantization error to input pixel data, and a step of adding the pixel data after the addition of the quantization error to a predetermined quantization. A quantization step of comparing the threshold value with the threshold value to determine an output pixel value; an operation step of calculating a quantization error corresponding to a difference between the pixel data after the addition of the quantization error and the output pixel value; 14. The storage medium according to claim 11, further comprising: an error diffusion step of performing an error diffusion process based on a change in an error diffusion coefficient by the step. 15. The storage medium according to claim 11, wherein the storage medium is applicable to a printer, a copying machine, or a facsimile having a function of performing image quantization based on the error diffusion method.