JPH1198365A - Device and method for processing image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compress inputted image data less than a prescribed code amount by providing a monitoring means for monitoring the generated code amount of image data compressed by a compressing means, and repeatedly executing smoothing due to a smoothing means and compressing due to the compressing means to the image data based on this monitored result. SOLUTION: A code amount controller 21 compares the generated code amount of raster image data compressed by a compressor 16 with a setting value 22. When that code amount is less than the setting value 22, the compressed raster image data are stored in a compression memory 17 as they are. When that code amount is more than the setting value, on the other hand, the raster image data stored in a band memory 14 are inputted to a smoothing processing circuit 20 and smoothing processing to a binary image is performed at this circuit. Next, the caster image data, to which smoothing processing is performed, are inputted through a switcher 15 to the compressor 16 and compressed. Then, the generated code amount of the compressed caster image data is compared with the setting value 22 again by the code amount controller 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing apparatus and method for compressing input image data.

[0002]

2. Description of the Related Art Conventionally, as an encoding method for binary image data, an encoding method for encoding binary image data in raster units is generally known. For example, in coding methods such as MH, MR, and MMR coding used in FAX, binary image data is converted based on the length (run length) of continuous white or black pixels in the binary image data. Encode.

[0003]

However, since the code encoded by the above-mentioned conventional encoding method is a variable-length code whose encoding amount varies depending on the contents of the binary image data, the compression rate is controlled. Compression rate (constant memory capacity)
It was difficult to keep below. On the other hand, the above MH
The compression rate is better than encoding methods such as encoding method,
2. Description of the Related Art There is known an encoding method which combines arithmetic coding and arithmetic coding which can compress a pseudo halftone image such as a dither image or an error diffusion image. However, even with this encoding method, the compression ratio cannot be increased for the following images. (1) Image with strong randomness or error diffusion image (2) Dither image with very fine pattern The present invention has been made in view of the above problems, and compresses input image data to a predetermined code amount or less. It is an object of the present invention to provide an image processing apparatus and a method thereof that can perform the processing.

[0004]

An image processing apparatus according to the present invention for achieving the above object has the following arrangement.
That is, an image processing device that compresses input image data, a compression unit that compresses the input image data, a monitoring unit that monitors a generated code amount of the image data compressed by the compression unit, A smoothing unit capable of smoothing the image data with a plurality of types of smoothing degrees; and, based on the monitoring result of the monitoring unit, repeating the smoothing of the image data by the smoothing unit and the compression by the compression unit. An image processing apparatus comprising: an execution unit that executes the image processing.

Preferably, the input image data is binary image data. Preferably, the compression unit divides the image data into predetermined units and compresses the image data. Also, preferably, as a result of monitoring by the monitoring means, when the generated code amount of the image data compressed by the compression means is larger than a predetermined code length, the execution is performed until the generated code amount becomes equal to or less than the predetermined code amount. The means switches the degree of smoothing of the smoothing means, and repeatedly executes the smoothing of the image data by the smoothing means and the compression by the compression means.

Preferably, the executing means increases the degree of smoothing of the smoothing means every time the number of times of repeating the smoothing by the smoothing means and the compression by the compressing means is updated. Switch the degree of smoothing. Preferably, the compression unit compresses the image data by performing predictive coding on the image data.

Preferably, when the number of executions of the execution unit is different for each image data obtained by dividing the image data for one page for each predetermined unit, the execution unit is provided with a predetermined number of execution times. The execution means is executed again for each of the divided image data. An image processing method according to the present invention for achieving the above object has the following configuration. That is, an image processing method for compressing input image data, a compression step of compressing the input image data, and a monitoring step of monitoring a generated code amount of the image data compressed in the compression step, A smoothing step capable of smoothing image data with a plurality of types of smoothing degrees, and smoothing of the image data by the smoothing step and compression by the compression step are repeated based on the monitoring result of the monitoring step. And an execution step of executing.

A computer readable memory according to the present invention for achieving the above object has the following configuration. That is,
A computer-readable memory storing a program code of image processing for compressing input image data,
A program code of a compression step of compressing the input image data, and a program code of a monitoring step of monitoring a generated code amount of the image data compressed in the compression step,
Based on a program code of a smoothing step capable of smoothing image data with a plurality of types of smoothing degrees and a monitoring result of the monitoring step, smoothing of the image data by the smoothing step and compression of the image data by the compression step And a program code for an execution step of repeatedly executing compression.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The above-mentioned image whose compression ratio cannot be increased has the following features. (1) Images with strong randomness such as error diffusion images Such images are dequantized and dithered,
It is known that a high compression rate can be obtained by performing compression by predictive coding. (2) Dither image with very fine pattern It is known that even a dither image with a strong periodicity, if the pattern is too fine, the compression ratio will decrease. It is known that a high compression ratio can be obtained for such an image by performing compression by predictive coding after inverse quantization and dither processing.

The present invention is realized based on the above features.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of an image processing system according to an embodiment of the present invention. FIG. 1 is an overall block diagram when applied to a page printer. A host computer (hereinafter, referred to as a host) 10 stores PDL data (for example, a line drawing command, a rectangle drawing command, etc.) written in a page description language in an intermediate memory 12 through an I / F circuit 11.

When the transfer of one page of PDL data is completed, the rendering circuit 13 develops the raster image on the band memory 14. Here, the raster image is expanded in band units when the raster memory for one page is provided with an A4 size 400 dp.
This is because i requires a large capacity memory of 2 MB and 600 dpi requires 4 MB.

The processing executed by each component connected to the subsequent stage of the band memory 14 is processing of a raster image that has been expanded into bands. The switch 15 inputs the raster image data of the band memory 14 to the compressor 16 and performs compression. The code amount controller 21 compares the generated code amount of the raster image data compressed by the compressor 16 with the set value 22. If the generated code amount is equal to or smaller than the set value 22, the compressed raster image data is stored in the compression memory 17 as it is. The set value 22 is set to a value that can achieve 1/4 to 1/8 compression.

When the compressed raster image data for one page is stored in the compression memory 17, the raster image data compressed by the decoder 18 is decoded, and the decoded raster image data is sent to the page printer 19.
Print with. A typical example of using the above-described path is an image processing system using a page printer in which printing cannot be interrupted, in which the rendering speed cannot keep up with the printing speed of the page printer. In this case, the compressed raster image data is stored in a limited compression memory, and is simultaneously decoded in real time and printed on a page printer.

On the other hand, when the code amount controller 21 determines that the generated code amount of the compressed raster image data is equal to or larger than the set value, the raster image data stored in the band memory 14 is smoothed by a smoothing processing circuit. 20 to perform a smoothing process on the binary image. Next, the smoothed raster image data is input to the compressor 16 through the switch 15 and compressed. Then, the code amount controller 21 compares the generated code amount of the compressed raster image data with the set value 22 again. As a result of the comparison, if the generated code amount is equal to or larger than the set value 22, the smoothing processing circuit 20
, The smoothing parameter indicating the degree of smoothing is increased by one step, a smoothing process is performed, and the above process is repeated until the generated code amount becomes equal to or less than the set value. Then, when the generated code amount becomes equal to or less than the set value 22, the above-described processing after the compression memory 17 is executed.

Next, a detailed configuration of the smoothing processing circuit 20 will be described with reference to FIG. FIG. 2 is a diagram showing a detailed configuration of the smoothing processing circuit according to the embodiment of the present invention. 30
Denotes an inverse quantizer, which inversely quantizes the input binary raster image data into multi-value raster image data.
This inverse quantization converts the binary raster image data to N × N
By counting the number of dots in each block for each block (inverse quantization matrix), the binary raster image data is inversely quantized into multi-value raster image data. Also, as shown in FIGS. 3A to 3C, the inverse quantizer 30 includes, for example, 2
Three types of × 2 blocks, 4 × 4 blocks, and 8 × 8 blocks are prepared. Then, as the size of the block is larger, a smoothing process with a larger smoothing parameter can be executed.

Reference numeral 33 denotes a matrix control signal, which is input from the code amount controller 21 to the smoothing processor 20 and can control smoothing parameters for smoothing processing applied to raster image data. In general, the compression ratio of raster image data tends to be low when the frequency is high, and the compression ratio tends to increase when the frequency is low. Therefore, the smoothing parameter is controlled according to the contents of the raster image data.

Reference numeral 31 denotes an interpolation processing circuit for interpolating the number of pixels of the raster image data which has been inversely quantized into the number of pixels of the raster image data before inverse quantization. For example, when the inverse quantization matrix is 2 × 2, the number of pixels becomes half the length and width, and the interpolation processing circuit 31 performs double linear interpolation processing. Similarly, when the inverse quantization matrix is 4 × 4, quadruple linear interpolation is performed, and when the inverse quantization matrix is 8 × 8, eight-fold linear interpolation is performed. A re-dithering circuit 32 dithers the interpolated raster image data.

Next, a detailed configuration of the compressor 16 will be described.
This will be described with reference to FIG. FIG. 4 is a diagram showing a detailed configuration of the compressor according to the embodiment of the present invention. Reference numeral 60 denotes a reference pixel when each pixel of the raster image data is compressed by predictive coding. “*” Is the position of the encoding target pixel to be encoded. The reference pixels for the encoding target pixel are a total of 10 pixels, that is, four pixels on the same line as the encoding target pixel and eight pixels away from the pixel on the same line and four pixels on one line. In this manner, by setting the reference pixel of the encoding target pixel to the pixel located 4 pixels to the left of the encoding pixel and 8 pixels away from the encoding pixel, 4 × 4 dither and 8 pixels
Highly efficient compression utilizing the periodicity of × 8 dither can be realized.

Then, a predicted value is generated according to the content of the pixel to be encoded ("0" or "1"),
1 is stored. Next, the prediction value 65 stored in the RAM 61 is read and input to the prediction conversion circuit 62 together with the pixel value of the encoding target pixel. The prediction conversion circuit 62 generates a match signal 68 indicating “0” if the pixel value matches the prediction value and “1” otherwise.

The arithmetic parameter 66 of the arithmetic encoder 63 is read from the RAM 61, and the arithmetic parameter 66 is read.
Is arithmetically coded by the arithmetic coder 63 using The arithmetic coding performed by the arithmetic encoder 63 can use, for example, an internationally standardized QM-coder. An update signal 67 generated based on the coincidence signal 68 is output from the arithmetic encoder 63 to the update circuit 64, and the update circuit 64 updates the predicted value and the arithmetic parameter. Then, the update circuit 64 stores the updated predicted value and the arithmetic parameter in the RAM 61. Thereby, adaptive coding can be realized.

Next, the processing executed by the image processing system according to the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing processing executed in the image processing system according to the embodiment of the present invention. First, in step 101, the raster image data stored in the band memory 14 is compressed by the compressor 16. Next, step S102
Then, it is determined whether or not the generated code amount of the compressed raster image data is equal to or smaller than a set value. If it is equal to or smaller than the set value (YES in step S102), the process ends. On the other hand, if it is larger than the set value (N in step S102)
O), and proceed to step S103.

Next, in step S103, the smoothing parameter of the smoothing processing circuit 20 is increased by one step. Next, in step S104, the raster image data stored in the band memory 14 is read into the smoothing processing circuit 20. Next, in step S105, the read raster image data is inversely quantized using a 2 × 2 inverse quantization matrix. Then, after the interpolation processing is performed on the dequantized raster image data, the raster image data is re-dithered. Then, the re-dithered raster image data is compressed by the compressor 1.
Then, the process returns to step 102.

In the above processing, if the processing in step S102 is not satisfied, the smoothing parameter is increased by one step every time the processing is repeated, and the processing is repeated until the processing in step S102 is satisfied. In the embodiment, although it is not possible to do more than the smoothing process using the prepared 8 × 8 inverse quantization, compression of 1/4 to 1/8 can be performed for most images by itself.

As described above, according to the present embodiment, the raster image data before compression is smoothed based on the generated code amount of the raster image data compressed by the compressor 16, and then compressed again. Can be. for that reason,
It is possible to realize the compression with the generated code amount equal to or larger than the set value. In the above-described embodiment, the number of times the smoothing process is performed until the value becomes equal to or less than the set value is not always the same in each band.

For example, FIG. 7A shows the generated code amount when one page of raster image data is divided into five bands (# 1 to # 5) and the raster image data corresponding to each band is compressed. Indicates the number of times the smoothing process was performed until the value became equal to or less than the set value. As shown in FIG. 7A, the number of times of smoothing processing of raster image data corresponding to bands # 1 to # 5 is 0, 1, 2, 1, 0. As described above, if the number of times of smoothing processing of the raster image data corresponding to the band obtained by dividing the raster image data for one page varies, the image quality of the output image may be degraded. For example, in FIG.
The degree of smoothing of the raster image data (the degree of blurring of the image) corresponding to band # 3 is large, and the degree of smoothing becomes lower toward the periphery. Therefore, the image quality of the entire output image deteriorates.

Therefore, as described above, when the number of times of smoothing processing of the raster image data corresponding to the band obtained by dividing the raster image data for one page is remarkably varied, it is shown in FIG. 7B. In this manner, the number of times of smoothing processing of raster image data corresponding to each band is unified to a predetermined number (here, two times). As a result, it is possible to reduce the possibility that the image quality of the entire output image is degraded due to variations in the number of times of the smoothing process.

The problem with the above processing is that
The raster image data corresponding to band # 2 is raster image data compressed after performing the smoothing process once. Therefore, if the raster image data stored in the band memory 14 cannot be restored, the raster image data having the same level as the raster image data corresponding to the band # 3 compressed after performing the smoothing process twice is generated. Will not be.

Therefore, as shown in FIG. 6, when performing smoothing processing of raster image data, the compressed raster image data stored in the compression memory 17 is decoded by the decoder 1.
Raster image data decoded in step 8
This is realized by connecting wires so that they are input to 0. Accordingly, as shown in FIG. 7A, the processing flow is to sequentially perform the smoothing processing of the raster image data corresponding to each band, compress each smoothed raster image data, and then perform the smoothing processing. The smoothing process is performed on the decoded raster image data for which the number of times of the smoothing process is insufficient, so that the number of times of the smoothing process is the same as that of band # 3.

The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but can be applied to a single device (for example, a copier, a facsimile) Device). Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and a computer (or CPU or MPU) of the system or apparatus to store the storage medium. Needless to say, this can also be achieved by reading and executing the program code stored in the program.

In this case, the program code itself read from the storage medium realizes the functions 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, a hard disk, an optical disk, a magneto-optical disk,
A CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the 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 based on the instruction of the program code. It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the above-described flowcharts. Each module shown will be stored in a storage medium. In other words, at least the program code of each of the “compression module”, “monitoring module”, “smoothing module”, and “execution module” may be stored in the storage medium.

The "compression module" compresses the input image data. The “monitoring module” monitors the generated code amount of the compressed image data. The “smoothing module” can smooth image data with a plurality of types of smoothing degrees. The “execution module” repeatedly executes smoothing and compression on the image data based on the monitoring result.

[0035]

As described above, according to the present invention,
An image processing apparatus and method capable of compressing input image data to a predetermined code amount or less can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an image processing system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a detailed configuration of a smoothing processing circuit according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of an inverse quantization matrix according to the embodiment of the present invention.

FIG. 4 is a diagram showing a detailed configuration of a compressor according to the embodiment of the present invention.

FIG. 5 is a flowchart illustrating a process executed by the image processing system according to the embodiment of the present invention.

FIG. 6 is a block diagram showing another configuration example of the embodiment of the present invention.

FIG. 7 is a diagram for describing processing executed when the number of times of smoothing processing according to the embodiment of the present invention varies for each raster image data corresponding to each band.

FIG. 8 is a diagram showing a structure of a memory map of a storage medium storing a program code for realizing an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Host 11 I / F circuit 12 Intermediate memory 13 Rendering circuit 14 Band memory 15 Switch 16 Compressor 17 Compression memory 18 Decoder 19 Page printer 20 Smoothing processing circuit 21 Code amount controller 30 Dequantizer 31 Interpolation processing circuit 32 Re-dithering circuit

Claims (15)

[Claims] 1. An image processing apparatus for compressing input image data, comprising: compression means for compressing the input image data; and monitoring for monitoring a generated code amount of the image data compressed by the compression means. Means, smoothing means capable of smoothing image data with a plurality of types of smoothing degrees, and smoothing of the image data by the smoothing means and by the compression means based on the monitoring result of the monitoring means. An image processing apparatus comprising: an execution unit that repeatedly executes compression. 2. The image processing apparatus according to claim 1, wherein the input image data is binary image data. 3. The image processing apparatus according to claim 1, wherein the compression unit divides the image data into predetermined units and compresses the divided data. 4. When the generated code amount of the image data compressed by the compression unit is larger than a predetermined code length as a result of monitoring by the monitoring unit, the execution is performed until the generated code amount becomes equal to or smaller than the predetermined code amount. 2. The image processing apparatus according to claim 1, wherein the means switches the degree of smoothing of the smoothing means, and repeatedly performs smoothing on the image data by the smoothing means and compression by the compression means. 5. The smoothing unit according to claim 1, wherein the number of times of repeating the smoothing by the smoothing unit and the compression by the compressing unit is updated. The image processing apparatus according to claim 1, wherein the image processing apparatus is switched. 6. The image processing apparatus according to claim 1, wherein the compression unit compresses the image data by performing predictive encoding on the image data. 7. When the number of executions of the execution unit is different for each image data obtained by dividing one page of image data for each predetermined unit, the number of executions of the execution unit is equalized.
Again, for each image data divided for each predetermined unit,
The image processing apparatus according to claim 1, wherein the execution unit executes the execution unit. 8. An image processing method for compressing input image data, comprising: a compression step of compressing the input image data; and a monitoring step of monitoring a generated code amount of the image data compressed in the compression step. A smoothing step capable of smoothing the image data with a plurality of types of smoothing degrees; a smoothing process for the image data based on a monitoring result of the monitoring process; An image processing method comprising the step of repeatedly executing compression. 9. The image processing method according to claim 8, wherein the input image data is binary image data. 10. The image processing apparatus according to claim 8, wherein in the compression step, the image data is divided into predetermined units and compressed.
The image processing method according to 1. 11. When the generated code amount of the image data compressed in the compression step is larger than a predetermined code amount as a result of monitoring in the monitoring step, the execution is performed until the generated code amount becomes equal to or smaller than the predetermined code amount. 9. The image processing method according to claim 8, wherein in the step, the degree of smoothing in the smoothing step is switched, and smoothing of the image data by the smoothing step and compression by the compression step are repeatedly executed. 12. The smoothing step includes increasing the smoothing degree of the smoothing step each time the number of times of repeating the smoothing by the smoothing step and the compression by the compressing step is updated. 9. The method according to claim 8, wherein
The image processing method according to 1. 13. The image processing method according to claim 8, wherein in the compression step, the image data is compressed by performing predictive encoding on the image data. 14. When the number of executions of the execution step is different for each image data obtained by dividing one page of image data for each predetermined unit, the image data is divided for each predetermined unit so that the number of executions of the execution step is equal. 9. The method according to claim 8, wherein the execution step is executed again for each image data.
The image processing method according to 1. 15. A computer-readable memory storing a program code for image processing for compressing input image data, wherein: a program code for a compression step for compressing the input image data; A program code of a monitoring step of monitoring the generated code amount of the image data obtained, a program code of a smoothing step capable of smoothing the image data with a plurality of types of smoothing degrees, and a monitoring result of the monitoring step. And a program code for an execution step of repeatedly performing smoothing of the image data by the smoothing unit and compression by the compression unit.