JP4194216B2 - Image processing apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus that compresses an input image.
[0002]
[Prior art]
Conventionally, various compression methods have been proposed. For example, there are MR, MMR, MH, JBIG, JPEG and the like. Among them, the JPEG compression method is one of techniques frequently used particularly for images such as photographs.
[0003]
In the JPEG compression method, there is a parameter held in the quantization table, and the compression rate can be changed by changing this parameter. However, there is a close relationship between the compression rate and the image quality after decompression, and when the compression rate is increased, the image quality after decompression tends to deteriorate.
[0004]
For this reason, conventionally, a method of specifying a compression level (quantization table) according to a document read by a user has been used.
[0005]
[Problems to be solved by the invention]
However, in a copying machine, a scanner, or the like that can select the reading resolution of an original, there is a problem that it is difficult for the user to select an optimal compression parameter corresponding to the resolution from the viewpoint of image quality and compression rate.
[0006]
The present invention has been made in view of the above-described problems, and an object of the present invention is to efficiently calculate quantization parameters suitable for compression without being aware of the detailed relationship between the reading resolution and the quantization table. It provides a good and selectable device.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, an image processing apparatus according to the present invention includes a reading unit that reads a document as image data, a resolution specifying unit that specifies a reading resolution by the reading unit from among a plurality of resolutions, and JPEG compression. From the storage means for storing a plurality of quantization tables used in the compression processing by the method and the plurality of quantization tables stored in the storage means, the resolution designated by the resolution designation means as a candidate for designation by the user selection means for selecting a plurality of quantization tables are related in advance, from among the selected quantization table by the selection unit, a receiving unit that receives any one of the given quantization table from the user, Using the quantization table received by the receiving means, a pressure for compressing the image data by the JPEG compression method. Reduction processing means, and when the first resolution is selected by the resolution designation means, the selection means first, second, from a plurality of quantization tables stored in the storage means. A quantization table corresponding to a third compression rate (first compression rate> second compression rate> third compression rate) is selected as the designation candidate, and is higher than the first resolution by the resolution designation unit. When the second resolution is selected, the second, third, and fourth compression ratios (third compression ratio> fourth compression ratio) are selected from the plurality of quantization tables stored in the storage unit. A corresponding quantization table is selected as the designation candidate .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
Hereinafter, an image processing apparatus according to a first embodiment of the present invention will be described with reference to the drawings.
[0010]
<Process outline>
FIG. 1 is a block diagram showing the configuration of the image processing apparatus according to the present embodiment.
[0011]
An image reading unit 109 includes a lens 101, a CCD sensor 102, and an analog signal processing unit 103. A document image 100 formed on the CCD sensor 102 via the lens 101 is converted into an analog electric signal by the CCD sensor 102. The converted image information is input to an analog signal processing unit, subjected to analog-digital conversion (A / D conversion) after being subjected to sample & hold, dark level correction, and the like. The digital signal thus converted is input to the image processing unit 104.
[0012]
The image processing unit 104 performs correction processing necessary for the reading system such as shading correction and γ correction, smoothing processing, edge enhancement, JPEG compression / decompression processing, and the like, and outputs the result to the printer unit 105.
[0013]
The printer unit 105 includes an exposure control unit (not shown) composed of a laser or the like, an image formation unit (not shown), a transfer control unit (not shown) for transfer paper, and the like, and records an input image signal on the transfer paper.
[0014]
The CPU circuit unit 110 includes a CPU 106, a ROM 107, a RAM 108, and the like, and controls the image reading unit 109, the image processing unit 104, the printer unit 105, the operation unit 113, and the like, and comprehensively controls the sequence of the apparatus. .
[0015]
A RAM 111 and a ROM 112 are prepared in advance in the operation unit 113, and characters can be displayed on the user interface and information set by the user can be stored.
[0016]
Information set by the operation unit 113 by the user is sent to the image reading unit 109, the image processing unit 104, the printer unit 105, and the like via the CPU circuit unit 110.
[0017]
<Image processing unit>
Next, the image processing unit 104 will be described. The image processing unit 104 shown in FIG. 2 is a block diagram showing only the main part of the present invention.
[0018]
The digital image signal output from the analog signal processing unit 103 in FIG. 1 is input to the shading correction unit 201. The shading correction unit 201 corrects variations in sensors for reading a document and light distribution characteristics of a document illumination lamp.
[0019]
The corrected image luminance signal is input to the JPEG compression unit 202 for compression, and compression using parameters held in a predetermined quantization table is performed. The parameters of this quantization table are important parameters for performing compression, and are set by the CPU circuit unit 110. Since this setting is a point according to the present embodiment, details will be described later.
[0020]
The signal compressed by the JPEG compression unit 202 is sent to and stored in a hard disk (hereinafter abbreviated as HDD) 203. A signal read from the HDD 203 is input to the JPEG decompression unit 204.
[0021]
The JPEG decompression unit 204 is configured to decompress the compressed signal and output it to the luminance / density conversion unit 205. The luminance / density conversion unit 205 performs log conversion of the input luminance signal into density data.
[0022]
Although not shown, the signal output from the luminance / density conversion unit 205 is subjected to various processing such as gamma correction, filter processing, and dither processing, and is output to the printer.
[0023]
Next, setting of the operation unit according to the present embodiment will be described.
[0024]
<Operation unit>
FIG. 3 shows an operation unit according to the present embodiment.
[0025]
The image processing apparatus starts scanning at a resolution set in 301 to 303 by pressing a copy button (not shown).
[0026]
Here, only main parts according to the present embodiment will be described, and description of other parts will be omitted.
[0027]
Reference numerals 301, 302, and 303 are buttons for switching the reading resolution when performing a copy operation.
[0028]
For example, when 150 dpi (301) is specified as the reading resolution, the resolution is digitally converted in the main scanning direction (not shown) (direction parallel to the image reading CCD), and the sub scanning direction (perpendicular to the image reading CCD) is obtained. For (direction), resolution conversion is performed by changing the scanning speed. As an example, when the resolution of the CCD is 600 dpi, the sub-scanning direction can be converted to a resolution of 150 dpi by increasing the scan speed by four times.
[0029]
Of course, the resolution may be converted digitally in both the main scanning direction and the sub-scanning direction, but in that case, resolution conversion is performed using a zero-order interpolation method, a primary interpolation method, a bicubic method, or the like.
[0030]
When 300 dpi (302) is specified as the reading resolution, similarly to the case of 150 dpi, resolution conversion is performed by digitally converting the resolution in the main scanning direction and changing the scanning speed in the sub-scanning direction. . Needless to say, when the resolution of 600 dpi is designated and the resolution read from the scanner is converted to 300 dpi, the image size is halved.
[0031]
When 600 dpi (303) is designated as the reading resolution, the CCD resolution is set to 600 dpi, so that the same size reading is performed.
[0032]
Next, 304, 305 and 306 are buttons for switching the compression rate.
[0033]
In this embodiment, JPEG compression will be described as an example.
[0034]
A high-quality button 304 is for setting a low compression rate with priority on image quality. That is, the size of the read file increases. In this case, the area where the image data occupies the HDD or memory increases, but the data can be compressed with good image quality.
[0035]
On the other hand, reference numeral 306 denotes a button for setting a high compression rate at the expense of image quality. This is prepared for use when it is desired to store a large amount of image data in the HDD or memory even if the image quality is a little worse. This mode is said to be suitable for data transfer using a network or a medium because the compression rate of image data is high, that is, the file size after compression is small.
[0036]
A normal button 305 is used to set an intermediate compression ratio between the high image quality 304 and the low image quality 306. In this case, it is possible to make a setting that balances the image quality and the compression rate to some extent.
[0037]
These compressions have been described using JPEG compression as an example as described above, but since this JPEG compression technique is known, only the use of the quantization table according to the present invention will be described in the present embodiment.
[0038]
<Quantization table used for JPEG compression>
4A and 4B are quantization tables used in the present embodiment. The luminance information is shown in FIG. 4A, and the saturation information is shown in FIG. 4B.
[0039]
In both figures, the vertical axis is called a q factor, and is composed of 64 numbers in order to perform compression processing with an 8 × 8 pixel block. The horizontal axis is called a quantization table. The larger the number, the higher the image quality can be compressed. However, in that case, the compression rate is lowered.
[0040]
In the present embodiment, 401, 402, 403, 404, 405, 406, 407, 408, 409, and 410 shown by the network are actually used quantization tables.
[0041]
When these tables are used in compression, the luminance information shown in FIG. 4A and the saturation information shown in FIG. 4B are used in pairs. For example, a 401/406 pair, a 402/407 pair, a 403/408 pair, a 404/409 pair, a 405/410 pair, and the like.
[0042]
<Relationship between image mode and Q table>
Next, the relationship between the quantization table described above and the designated reading resolution, which is a point in the present embodiment, will be described with reference to FIGS. 5 (a) to 5 (c).
[0043]
FIG. 5A is a diagram when the reading resolution is specified to be 501 and 150 dpi.
[0044]
When 150 dpi is specified in 501, the quantization tables described in FIGS. 4A and 4B are assigned to the image quality selection buttons 502, 503, and 504.
[0045]
For example, 403 and 408 are assigned to the high-quality button 502, 402 and 407 are assigned to the normal button 503, and 401 and 406 are assigned to the low-quality button 504. Needless to say, when the low image quality button 504 is selected, the compression rate is the highest among them. That is, the file size is reduced.
[0046]
On the other hand, when a reading resolution of 300 dpi is selected at 505, the result is as shown in FIG.
[0047]
When 300 dpi is selected, the quantization tables in FIGS. 4A and 4B are assigned to the image quality selection buttons 506, 507, and 508, as described above.
[0048]
However, the difference from the above is that the quantization table selected for each designated reading resolution is different. That is, when the reading resolution is 300 dpi, 404 and 409 are assigned to the high-quality button 506, 403 and 408 are assigned to the normal button 507, and 402 and 407 are assigned to the low-quality button 508. It is characterized by.
[0049]
As described above, by preparing the optimum quantization table option for each reading resolution, it is possible to compress a read image using a more optimum quantization table.
[0050]
In the above-mentioned 150 dpi and 300 dpi, 300 dpi potentially contains more information up to high frequency components. Therefore, in the case of 300 dpi resolution, a quantization table that can be compressed while maintaining up to high frequency components. Assigned.
[0051]
Based on the same idea, since the reading resolution of 600 dpi shown in FIG. 5C includes a high frequency component because the reading resolution is high, a quantization table that can be compressed while maintaining the high frequency component is allocated. Yes. That is, 405 and 410 are assigned to the 510 high image quality button, 404 and 409 are assigned to the 511 normal button, and 403 and 408 are assigned to the 512 low image quality button.
[0052]
With this allocation method, the compression parameter can be efficiently specified without the user being aware of the detailed relationship between the resolution and the compression parameter.
[0053]
As described above, by assigning an optimal quantization table to the image quality setting buttons 304 to 306 for each designated reading resolution, it is possible to simplify the designation of a compression rate that tends to be complicated.
[0054]
[Second Embodiment]
The configuration of the apparatus according to the second embodiment is substantially the same as the configuration of the apparatus according to the first embodiment, and the same reference numerals are given to the same configuration parts, and description thereof is omitted.
[0055]
The representation method of the high image quality / normal / low image quality buttons shown in FIGS. 5A to 5C shown in the first embodiment is not limited to the first embodiment. The same applies to the method of expressing the options of large / medium / small file sizes indicated by reference numerals 601, 602, 603, 604, 605, 606, 607, 608 and 609 in FIGS. Needless to say. Furthermore, the same expression method is used for low speed / medium speed / high speed (not shown).
[0056]
By assigning the quantization tables of FIG. 4A and FIG. 4B described above to these options, processing similar to that of the first embodiment can be performed.
[0057]
Further, the number of options is not limited to three as shown in the present embodiment, and even if the number of options is five, seven,... Needless to say, you can do it.
[0058]
The quantization table to be assigned is not limited to that shown in the present embodiment, and it goes without saying that the same effect can be obtained even if other tables are assigned.
[0059]
In addition, it goes without saying that these processes can obtain similar effects not only for color images but also for black and white images.
[0060]
In the first embodiment, for each resolution indicated by 301 to 303 in FIG. 3, the smaller value of the quantization table shown in FIGS. 4A and 4B is applied to the lower resolution of 150 dpi (301). It was set. This is because, as described in the first embodiment, there are potentially fewer high-frequency components when data is read at a lower resolution.
[0061]
That is, when reading at a high resolution containing a lot of high-frequency components, the file size tends to increase because compression is performed using a quantization table that holds the high-frequency components as such. For this reason, when reading at a high resolution, the file size becomes large, and the compression parameters used are those with a low compression rate, so that the file size tends not to become too small.
[0062]
Therefore, in the image processing apparatus according to the second embodiment of the present invention, when reading at a high resolution with a large file size, the high-frequency component is positively applied contrary to the one shown in the first embodiment. Let's use an automatic quantization table. As a result, the file size can be set so as not to change greatly depending on the reading resolution.
[0063]
For example, when 150 dpi in FIG. 3 is set, the quantization tables 404 and 409 are selected, when 300 dpi is set, the quantization tables 403 and 408 are selected, and when 600 dpi is set, the quantization table 402 is selected. And 407 are selected.
[0064]
Needless to say, as in the case of the first embodiment, it is also possible to provide ranks of high image quality / normal / low image quality and assign a quantization table to each rank.
[0065]
[Other Embodiments]
Note that the present invention can be applied to a system (for example, a copier, a facsimile machine, etc.) consisting of a single device even when applied to a system composed of a plurality of devices (for example, a host computer, interface device, reader, printer, etc.). You may apply.
[0066]
Another object of the present invention is to supply a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (or CPU or CPU) of the system or apparatus. Needless to say, this can also be achieved by the MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.
[0067]
Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. It goes without saying that the CPU or the like provided in the expansion card 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.
[0068]
【The invention's effect】
As described above, according to the present invention, it is possible to select several quantization tables suitable for compression for each reading resolution on the operation unit, so that the details of the reading resolution and the quantization table can be selected. There is an effect that a quantization parameter suitable for compression can be efficiently selected without being aware of the relationship.
[0069]
In addition, it is possible to set a quantization table suitable for holding a high-frequency component for an image containing a lot of high-frequency components, or conversely, a quantization table that actively holds high-frequency components By doing so, it is possible to select whether to give priority to image quality or to give priority to reducing the file size.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image processing apparatus according to first and second embodiments of the present invention.
FIG. 2 is a diagram illustrating a configuration of an image processing unit in the image processing apparatus according to the first and second embodiments.
FIG. 3 is a diagram illustrating an operation unit according to the first and second embodiments.
FIG. 4A is a JPEG quantization table (for luminance information) used in the image processing apparatuses according to the first and second embodiments.
FIG. 4B is a JPEG quantization table (for saturation information) used in the image processing apparatuses according to the first and second embodiments.
FIG. 5 is a diagram illustrating an example of an operation unit in the image processing apparatus according to the first embodiment.
FIG. 6 is a diagram illustrating an example of an operation unit in the image processing apparatus according to the second embodiment.

Claims (4)

Reading means for reading a document as image data;
Resolution designation means for designating the resolution of reading by the reading means from among a plurality of resolutions ;
Storage means for storing a plurality of quantization tables used in compression processing by the JPEG compression method ;
A plurality of quantization tables stored in the storage means, as a designated candidate user, and selection means for a plurality of quantization tables previously associated with the specified resolution to select by the resolution designation unit,
Receiving means for receiving designation of any one quantization table from the quantization tables selected by the selection means ;
Compression processing means for compressing the image data by JPEG compression using the quantization table received by the receiving means;
Have
When the first resolution is selected by the resolution specifying unit, the selection unit selects the first, second, and third compression rates (first level) from the plurality of quantization tables stored in the storage unit. When a quantization table corresponding to compression rate> second compression rate> third compression rate) is selected as the designation candidate, and a second resolution higher than the first resolution is selected by the resolution designation unit Includes a quantization table corresponding to the second, third and fourth compression ratios (third compression ratio> fourth compression ratio) from the plurality of quantization tables stored in the storage means. An image processing apparatus characterized by being selected as Furthermore, when the third resolution higher than the second resolution is selected by the resolution designating means, the selection means selects the third, fourth, and fourth from the plurality of quantization tables stored in the storage means. The image processing apparatus according to claim 1 , wherein a quantization table corresponding to a fifth compression ratio (fourth compression ratio> fifth compression ratio) is selected as the designation candidate . An image processing method for performing compression processing on image data read by a reading unit,
A resolution designating step of designating a resolution of reading by the reading unit from a plurality of resolutions ;
A reading step of reading a document as image data by the reading unit;
From the storage unit for storing a plurality of quantization tables used in the compression process by the JPEG compression method, as specified candidate by the user, a plurality of quantization tables that are associated in advance in the resolution specified by the resolution specifying step a selection step to select,
An accepting step of accepting designation of any one quantization table from the quantization table selected in the selection step;
A compression processing step for compressing the image data by a JPEG compression method using the quantization table received by the reception step;
Have
In the selecting step, when the first resolution is selected in the resolution specifying step, the first, second, and third compression rates (the first compression rate) are selected from the plurality of quantization tables stored in the storage unit. When a quantization table corresponding to compression rate> second compression rate> third compression rate) is selected as the designation candidate, and a second resolution higher than the first resolution is selected in the resolution designation step Includes a quantization table corresponding to the second, third, and fourth compression rates (third compression rate> fourth compression rate) from the plurality of quantization tables stored in the storage unit. An image processing method characterized by selecting as A computer-readable recording medium that records a program for causing a computer to execute a document reading process by a reading unit and a compression process on the read image data .
A resolution designating step of designating a resolution of reading by the reading unit from a plurality of resolutions;
A reading step of reading a document as image data by the reading unit;
From the storage unit that stores a plurality of quantization tables used in the compression processing by the JPEG compression method, a plurality of quantization tables associated in advance with the resolution specified by the resolution specifying step are specified as candidates specified by the user. A selection step to select;
An accepting step of accepting designation of any one quantization table from the quantization table selected in the selection step;
A compression processing step of compressing the image data by a JPEG compression method using the quantization table received in the reception step;
To the computer,
In the selecting step, when the first resolution is selected in the resolution specifying step, the first, second, and third compression rates (the first compression rate) are selected from the plurality of quantization tables stored in the storage unit. When a quantization table corresponding to compression rate> second compression rate> third compression rate) is selected as the designation candidate, and a second resolution higher than the first resolution is selected in the resolution designation step Includes a quantization table corresponding to the second, third, and fourth compression rates (third compression rate> fourth compression rate) from the plurality of quantization tables stored in the storage unit. A recording medium characterized by being selected as:

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