JP2003209698A - Image processing device and method therefor, computer program, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable elimination of the need for image re-input, creation of encoded data which can effectively fall in a set size, and suppression of quality deterioration caused by a compression ratio. <P>SOLUTION: A judger 113 judges whether image data inputted from an input unit 101 is in a character area or in a half-tone area. An encoder 102 quantizes and encodes the input image data according to a judgement result and a parameter set in an encoding sequence unit 108 with use of any of character and half- tone quantized matrixes, and stores it in a first memory 104. The encoding sequence controller 108, when judging that the quantity of code generated in the encoder 102 reached a set value, sets the parameter to make a compression ratio higher, and continues the subsequent encoding. A re-encoder 109 re-encodes previously-encoded data according to a new parameter and stores it in the first memory 104. <P>COPYRIGHT: (C)2003,JPO

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 for compressing and encoding color image data, a control method thereof, a computer program, and a computer-readable storage medium.

[0002]

2. Description of the Related Art Conventionally, as a still image compression method, a JPEG method using discrete cosine transform and a method using Wavelet transform have been widely used. Since this type of encoding method is a variable length encoding method, the code amount changes for each image to be encoded.

In the JPEG method, which is an international standardization method,
Only one set of quantization matrices can be defined for an image. Therefore, the code amount cannot be adjusted without pre-scanning, and there is a risk of memory over when used in a system that stores in a limited memory.

In order to prevent this, when the code amount exceeds the planned code amount, the compression ratio is changed to read the original again, or the code amount is estimated in advance by prescan to adjust the code amount. In order to do so, methods such as resetting the quantization parameter have been adopted.

As a code amount control system for performing prescan, for example, there is a system in which precompressed data is put into an internal buffer memory, decompressed, the compression parameter is changed, main compression is performed, and the data is output to an external storage. . At this time, in the main compression, the compression rate is higher than in the pre-compression.

Further, for example, there is known a method of Huffman coding a coefficient in which a DCT coefficient is level-shifted n times in order to obtain an allowable code quantity for each pixel block and reduce the code quantity. It is determined from the allowable code amount.

[0007]

However, in the past, as a compression buffer, a compression buffer more than the target compression was required, and in order to prevent the overflow of the buffer used intermediately, there is a capacity enough to record the original image data. What is needed is inevitable.

Further, in the method of repeating the encoding process,
Since a process of decoding and recompressing all the compressed data is included, there is a problem that the speed of continuous processing does not increase.

The present invention has been made in view of the above conventional example, does not require re-image input, can effectively generate coded data within a set size, and deteriorates image quality with respect to compression rate. It is intended to provide an image processing apparatus, a control method therefor, a computer program, and a storage medium that can be reduced in size.

[0010]

In order to solve such a problem, for example, an image processing apparatus of the present invention has the following configuration. That is, an image processing device for compression-encoding image data, comprising a storage unit for storing the compression-encoded data,
Determination means for determining image area information of input image data,
First compression coding means for compressing and coding image data based on a parameter related to a quantization step and a judgment result of the judgment means, and image data compressed based on a parameter related to a quantization step and a judgment result of the judgment means. A second compression encoding unit that encodes, decodes the code data compressed by the first compression encoding unit, and recompresses it, and monitors a code amount generated by the first compression encoding unit. In addition, the code amount monitoring means for determining whether or not the code data amount has reached the predetermined amount, and the first and second compressed codes when the code amount monitoring means determines that the predetermined amount has been reached. Setting means for setting a parameter to increase the quantization step in the quantization means, and the first compression code when the parameter is changed by the parameter setting means The code data previously generated by the means is re-encoded by the second compression encoding means, and the re-encoded code data is the code data after the parameter change of the first compression encoding means. Is stored in the storage means as
And a control unit for storing the encoded data generated by the compression encoding unit as the subsequent encoded data in the storage unit.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the basic part will be described.

FIG. 1 is a functional block configuration diagram of an image processing apparatus 100 to which the embodiment is applied. Hereinafter, each part of the figure will be briefly described.

The image processing apparatus 100 has an input unit 101 for inputting an image from an image scanner or the like. The image scanner includes a well-known image area separation processing unit, and, for example, attribute flag data for identifying whether or not a pixel constitutes a black character portion in a document image is generated for each pixel. Although it is determined whether or not the pixel is a black character, in the case of a character line drawing, the change in density is steeper than in a halftone image. Therefore, first, it is determined whether or not the density change (brightness or density difference between adjacent pixels) is larger than a predetermined threshold value, and it is larger than the threshold value, and the RGB values are substantially equal to each other. If it is (achromatic), it can be determined that it is a black character pixel. Further, not only whether it is a black character (black character line drawing) but also whether it is a color character, whether it is a halftone dot area, whether it is a vector graphics area, etc. may be included. In this case, bits may be assigned to each attribute.

In the above description, the input unit 101 inputs from the image scanner and the image area separation processing unit is included in the image scanner. However, if the image scanner does not have the processing unit, The above determination process may be provided on the device side. Further, the input unit 101 is not limited to an image from an image scanner, and may input image data from page description language rendering or the like, or may be realized by reading an image file stored in a storage medium. In some cases, it may be received from the network. In particular, when the page description language data is received from the host computer and rendered, what kind of attribute each pixel has is indicated by the page description language, so that the determination is easy. Furthermore, when the image scanner does not include the image area separation processing unit, a processing unit that determines the above attribute may be provided on the apparatus side.

In any case, the image input from the input unit 101 is temporarily stored in the compressed block line buffer 111. In the block line buffer 111, the image is divided into tiles (the tile size is M × N),
For each tile M × N pixels, coding is performed by dividing into discrete old ginseng transform coding (JPEG) which is coding of a color image and line length coding which is coding of attribute flag data information.

However, M and N must be multiples of the window size for discrete cosine transform coding.
In the JPEG compression method used in the present embodiment, the window size for compression is set to 8 × 8 pixels.
= N = 32, the 32 × 32 pixel tile is further divided into 16 8 × 8 pixels, and JP is divided into 8 × 8 pixel units.
EG compression is performed. Hereinafter, in the embodiment, M = N = 32 will be described, but of course, the present invention is not limited to this.

The encoding unit 102 receives the input 32 × 32
The well-known DCT transform is applied to the 16 8 × 8 pixel windows included in the tile image of pixels to perform quantization. The quantization coefficient (referred to as a quantization matrix) used at this time can be set by switching for each tile by a method described later.

The determination unit 113 inputs the attribute flag information of 32 × 32 pixels corresponding to the image data to be encoded, performs the determination process described later, and according to the result, outputs the quantization coefficient selection signal to the encoding unit 102. Output to. The attribute flag data is attached to each pixel,
Since the encoding method in the M × N pixel tile is constant as in the present embodiment, the attribute data in the tile is analyzed and
It is necessary to determine the attribute that represents the tile (details will be described later).

The encoding unit 102 encodes the input image data based on the determination result from the determination unit 113 and the instruction from the encoding sequence 108. A known JPEG encoding method is used as an encoding method, image data corresponding to a unit of 8 × 8 pixels is orthogonally transformed, and quantization and Huffman encoding processing using a quantization step described later are performed. . Also, the encoding unit 102 performs run-length encoding on the representative attribute value of the tile and outputs it.

The first memory control unit 103 and the second memory control unit 105 receive the encoded data (encoded image data and encoded attribute data) output from the encoding unit 102, respectively. The control is performed so that the data is stored in the first memory 104 and the second memory 106. Here, the first memory 104 stores the finally determined encoded data (compressed to a data amount within a target value) in a network device and an image output device connected to the outside of the basic configuration of FIG. 1. Or a memory for holding the encoded data for output to a mass storage device or the like. In addition, the second memory 106
Is a working memory that assists the compression coding process for forming the coded data on the first memory.

The counter 107 counts the amount of image data compressed and coded by the coding unit 102, holds the count value, and controls the coding sequence based on the count result. To 108. The code amount of the attribute data may be counted, but it is excluded in the embodiment. The reason is that one attribute data is for one tile (a region composed of a plurality of pixels), so the amount of information for the entire image is originally very small and a high compression rate can be expected. However, it goes without saying that it may be counted.

The encoding sequence control unit 108 detects whether or not the count value of the counter 107 has reached a certain set value, and when it has reached that set value (even if it exceeds the target value). Then, a control signal is output to the first memory control unit 103 to discard the stored data in the memory 104. The first memory control unit 103 discards the stored data by clearing the memory address counter or the encoded data management table for image data based on the control signal. Further, at this time, the coding sequence control unit 108
Clears the first counter 107 to zero (input unit 1
The input from 01 continues) and the encoding unit 10
2 is controlled so that encoding is performed at a higher compression rate than before. That is, the data amount of the coded data generated in the coding process of the present apparatus is controlled so as to finally become, for example, 1/2. It should be noted that although it is set to 1/2 here, it can be set arbitrarily.

The coded data after the compression rate change is also
As before, it is stored in the first memory 104 and the second memory 106 via the first memory control unit 103 and the second memory control unit 105, respectively.

Further, the coding sequence control unit 108
Reads the encoded data stored in the second memory 106 so far to the second memory control unit 105,
A control signal is output to the re-encoding unit 109 which is the encoded data conversion means so as to output the encoded data.

The re-encoding unit 109 decodes the input encoded data, performs re-quantization to reduce the amount of data, and then performs the encoding process again, and the encoding unit whose compression rate is changed. The data amount having the same compression ratio as 102 is output to the second counter 110.

The encoded data output from the re-encoding unit 109 passes through the first memory control unit 103 and the second memory control unit 105, and the first memory 10 respectively.
4 and the second memory 106.

Whether or not the re-encoding process has been completed is determined by the second
Is detected by the memory control unit. That is, when there is no more data to read for the re-encoding process, the encoding sequence control unit 108 is notified of the end of the re-encoding process. Actually, the encoding process is completed after not only the reading process of the second memory control unit 105 but also the process of the re-encoding unit 109.

The count value obtained by the second counter 110 is obtained by the first counter 10 after the re-encoding process is completed.
It is added to the counter value held in 7. This addition result represents the total amount of data in the first memory 104 immediately after the re-encoding process is completed. That is, at the time when the encoding process of the encoding unit 102 and the re-encoding unit 109 for one screen is completed, the counter value held by the first counter 107 after the addition is for one screen. Represents the total amount of data generated in the case of encoding (details will be described later).

The encoder 102 terminates the re-encoding process /
Regardless of whether it is not finished, the encoding process is continued as long as the image data from the input unit 101 to be encoded remains.

Whether or not the count value of the counter 107 has reached a certain set value is repeated until the encoding process (encoding and re-encoding) of the image data for one page input from the input unit 101 is completed. The encoding and re-encoding processing is performed under the control according to the detection result obtained here.

A flow chart showing the flow of processing in the configuration of FIG. 1 is shown in FIG. 8. First, for simplification of description, description will first be made according to the simplified flow chart of FIG.

As described above, the image processing apparatus 100 of the present invention uses the input unit 101 such as a scanner to input the image
This is a device that compresses and encodes page image data to a predetermined data amount or less. In order to realize the encoding process, in addition to the input unit 101, an encoding unit 102 and a re-encoding unit 10
9, a first memory 104, a second memory 106, and the like. Encoding processing is performed using these functional blocks based on the flowchart shown in FIG.

The flowchart of FIG. 3 is roughly divided into the following three processing phases. (1) Encoding phase (2) Encoding / re-encoding phase (3) Transfer phase In each of the above processing phases, how image data, encoded data, etc. are processed by flow, FIG. 4 shows visually whether it is stored or not.
Through FIG. 7.

FIG. 4 shows the initial state of the encoding phase corresponding to steps S303 and S305 in the flowchart of FIG. 3 (however, the encoded data of the attribute data is omitted). 5 shows the processing state of the encoding / re-encoding phase corresponding to steps S307 to S315, FIG. 6 shows the processing state of the transfer phase corresponding to step S317, and FIG. 7 shows the processing state of the encoding phase after the transfer phase. Indicates the processing status. Each phase will be described below.

<< Encoding Phase >> The encoding process of one page of image data starts from the initial setting of encoding parameters (step S301). Here, the upper limit value of the encoded data amount that is uniquely determined from the image size to be encoded (the paper size read from the input unit 101 such as a scanner) and the encoding unit 102 (here, a known JPEG encoding method is used). The quantization step parameter (Q1) applied to

The encoding unit 102 follows the quantization step parameter Q1 and the determination result of the 32 × 32 pixel block from the determination unit 113 and determines the target pixel block (=
32 × 32 pixels) are quantized and encoded using either the black character region quantization matrix Q1a or the halftone image quantization matrix Q1b. Although details will be described later, since it is important whether or not the character portion is legible as a character, it is preferable that the quantization step is smaller than that of the halftone image. The quantization matrix Q1a for the black character area,
The halftone image quantization matrix Q1b has such a difference. Further, as will be described later, when the quantization step parameter Q2 is set, encoding is performed using either of the quantization matrices Q2a and Q2b,
When the quantization step parameter Q3 is set,
Encoding is performed using either the quantization matrix Q3a or Q3b. Details of this will be described later, and FIG.
Continue to explain.

In step S303, the first counter 1
07 is the actual encoding process (J is performed for each 8 × 8 pixel unit of the image).
(PEG compression) is performed, and the data amount of the encoded data to be output is cumulatively counted.

Next, in step S305, it is detected whether the count value of the data amount exceeds the upper limit value, and if not, the JPE of step S303.
The G encoding process is continued. This is the initial encoding phase.

The encoded data output from the encoding unit 102 is stored in both the first memory 104 and the second memory 106 as shown in FIG. The area indicated by vertical stripes represents the stored code.

The encoding unit 102 also compression-encodes the attribute data for each tile, which is the determination result from the determination unit 113, and outputs it to the first and second memories, respectively. The structure related to the compression of the attribute data in 102 is as shown in FIG.

The figure shows the structure of only the portion related to the attribute data compression encoding in the encoding unit 102.

In the figure, the determination unit 310 determines whether the previous value and the current value of the input attribute flag data are the same. If they are the same, the RL code generation unit 311 is used. If they are different, the LT code generation unit 311 is used. Switch to send data to 312. The RL code generation unit 311 counts the number of times the same as the previous data until different data appears,
Finally, the repeated data is output. The LT code generation unit 312 counts the number of cases in which the data is different from the previous pixel, and outputs the code word corresponding to the count number and the minimum number of bits constituting the actual data for the count number. The synthesizing unit 313 synthesizes the output data of the RL unit and the output data of the LT unit and outputs the synthesized data as a code 315. It should be noted that this configuration is one example, and may be realized by another configuration.

<< Encoding / Re-Encoding Phase >> When the encoding process of the encoding unit 102 progresses and the count value of the data amount exceeds the set upper limit value, the first step is performed in step S307. The encoded data in the memory 104 of the above is discarded, and at the same time, in step S309, the encoding unit 1
The quantization step parameter of 02 is changed to Q2 (thus, the encoding unit 102 performs encoding using either of the quantization matrices Q2a and Q2b according to the determination result of the determination unit 113).

The fact that the count value of the data amount of the encoded data exceeds the set upper limit value means that the data amount after compression does not fall within the target value. Therefore, it is meaningless to continue the encoding process using the same quantization step, so that the quantization step parameter is set to Q2 (the quantization step is larger than that in the case of Q1) so that the data amount becomes smaller than before. ) Will be changed to.

After changing the quantization step parameters,
In step S311, the encoding process of the encoding unit 102 is restarted, and the encoded data is stored in the second memory 1 as shown in FIG.
Only stored in 06. In parallel with this, step S31
3 re-encoding processing is performed. In the re-encoding process, the encoded data (both the image encoded data and the attribute encoded data) stored in the second memory 106 is read out, and the re-encoding unit 109 performs the re-encoding process. The data is stored in the two memories 104 and 106. Then, the encoding process and the re-encoding process are continued until all the codes of the vertical stripes are re-encoded. In addition, the re-encoding unit 109 includes the encoding unit 102.
Using the same new quantization step parameter set for, according to the attribute obtained by decoding, re-encoding will be performed using the optimum quantization matrix. Specifically, in this re-encoding process, , Huffman coding is performed again after bit shift processing that gives the same result as the result of dividing these coded data by 2 ⁿ for each quantized value after Huffman decoding the coded data. Will be realized. This method enables high-speed re-encoding processing in that the quantization step is changed only by bit shifting and that inverse orthogonal transformation or re-orthogonal transformation processing is not performed. Step 31
At 5, the end of the re-encoding process is detected.

Since the data amount after re-encoding becomes smaller than the data amount of the encoded data before re-encoding, as shown in FIG. 5, data is re-encoded in the memory area where the code before re-encoding is stored. The encoded data after encoding can be stored so as to be overwritten. When the re-encoding process is completed, the data amount of the coded data of vertical stripes is reduced to the data amount of the coded data of diagonal stripes shown in FIG.

Steps S307 to 315 described above
Is a process performed in the encoding / re-encoding phase.

<< Transfer Phase >> When the re-encoding process is completed, the transfer process is performed in step S317.
In the transfer processing, as shown in FIG. 6, the diagonal stripe coded data stored in only the second memory 106 in the coding / recoding phase is converted into the diagonal line coded data in the first memory 104. Transfer to the address linked to and store. On the other hand, the diagonal stripes are coded so that the coded data of the diagonal stripes and the coded data of the diagonal stripes, which are dispersed in the second memory 106, are continuously stored in the first memory 104. The encoded data of the second memory 106
Transfer within and connect. This is the process performed in the transfer phase.

When the transfer phase is completed, the process returns to the encoding phase of steps S303 and S305, and the code of the diagonal stripe is output from the encoding unit 102 and stored in the two memories 104 and 106 as shown in FIG. This coding phase is slightly different from the coding phase in the initial state (FIG. 4), and the quantization step at the time of coding by the coding unit 102 is changed from Q1 to Q2, and the two memories 104 and 106 are also used. The encoded data stored in is also a collection of codes processed in various phases. If these differences are ignored, the coding phase immediately after the transfer phase and the coding phase in the initial state can be regarded as the same.

Therefore, by repeating the three phases of the encoding phase, the encoding / re-encoding phase and the transfer phase, the code obtained by finally compressing the image data of one page to the data amount set value or less is stored in the first memory. Can be stored in. Moreover, the input unit 101 only continues the input until the series of processing is completed. That is, it is not necessary to input the image again from the beginning.

The flow chart shown in FIG. 3 describes only the processing corresponding to each phase shown in FIGS. 4, 5 and 6 for easy understanding of the description. However, in reality, the input of the image data of one page ends in some phase. Therefore, depending on which phase the process is completed, the subsequent actions are slightly different. FIG. 8 is a flowchart showing the flow in consideration of this. The flow chart of FIG. 8 considers the relationship between the completion of inputting one page of image data and the various processes described in FIG. 3, and here, in the flow chart of FIG.
1, S803, S805, and S807 are added.

Steps S801, S803, S805
Detects that the input of the image data for one page from the input unit 101 is completed in the encoding phase, the encoding / re-encoding phase, and the transfer phase, respectively.

When it is detected that the input of the image data for one page is completed in the encoding phase and the transfer phase (steps S801 and S805), the process proceeds to step S807, the compression encoding process of the page is terminated, and If there is one or more pages of image data to be processed, the compression encoding process of the next one page of image data is started, and if there is none, the process enters the stopped state.

On the other hand, when the input end of the image data for one page is detected in the encoding / re-encoding phase (step S803), the encoding unit 102 operates once until there is no image data to be re-encoded. Therefore, the re-encoding process for passing the encoding process of step S311 and suppressing the image data already encoded by the encoding unit 102 to a predetermined encoded data amount in step S313. Only continue. If all the re-encoding processing is completed and the subsequent transfer processing is not completed, the encoded data of the entire image data for one page cannot be collected in the first memory, and the input of the image data for one page is completed. After that, the re-encoding process and the subsequent transfer process need to be continuously performed. In this case, when it is detected in step S315 that all the re-encoding processing has been completed, encoding /
During the re-encoding phase, the encoded data stored only in the second memory 106 is transferred to the first memory (step S317), and then in the next step S805, the image data for one page is input. When the end is detected, step S80
I will move to 7.

The above is the operation and is also an explanation of the operation in FIG.

<Modification of Memory Storage Method> FIGS. 9 and 10
FIG. 9 is a diagram showing a modification of the memory storage method shown in the conceptual diagrams of FIGS. 5 and 6.

In the conceptual diagram of FIG. 5, in the encoding / re-encoding phase, the encoded data output from the encoding unit 102 is stored only in the second memory 106.
As shown in, during the encoding / re-encoding phase, the encoded data output from the encoding unit 102 is directly stored in both the first and second memories.

From the viewpoint of the encoding unit 102, the encoded data which is encoded and output in any phase is stored in both memories. Also, unlike the conceptual diagram of FIG. 6, as shown in FIG. 10, data transfer between memories is not necessary in the transfer phase. In the case of this modification,
In the re-encoding phase, the encoded data and the re-encoded data are sequentially stored in the order sent to the first memory 104. Therefore, there is a problem that two types of data are mixed.

Therefore, in the case of this modification, in order to cope with this, the encoded data is divided into certain units and managed as files or packets. In particular,
A file management table or a packet management table is separately created and managed.

As one method, when the data from the encoding unit 102 is stored in the first memory 104, an appropriate unit (for example, 32.times.i because the unit of the orthogonal transformation is a 32.times.32 pixel block). A management number is assigned from the beginning of the image data for each (i = 1, 2 ... Line data), and the storage start address of the encoded data corresponding to each management number and the encoded data amount are Create a management table that can be stored in order of management numbers.

The encoding unit 102 and the re-encoding unit 109 hold the management number of the data being processed, and based on the management number, the start address and the encoded data amount at the time of storing the encoded data are stored in the management table. Write. By doing so, even if the encoded data processed by the encoding unit 102 and the re-encoding unit 109 is stored at random, the management table is accessed in the order of the management numbers, and the start address and the encoded data to be read at that time are read. The first encoded data based on the quantity
If the data is read from the memory 104, the encoded data can be read in order from the beginning of the image. If such a management mechanism is provided, there is no need to store continuous data on the image in the memory so as to be continuous.

The encoding phase after the transfer phase in the conceptual diagram of FIG. 10 is almost the same as the two encoding phases described so far (FIGS. 4 and 7), and the storage state of the code in the first memory. Are only slightly different as shown in FIG. Therefore, the above description and this modification are 3
There is no change in processing one phase repeatedly.

As a result of the above, according to the embodiment, when an existing document is read and it is determined that the target value is reached during encoding, the subsequent steps are performed according to the newly set quantization step parameter. It is compression encoded at a higher compression rate. When it is determined that the target value has been reached, the code data that has already been compression-encoded before that is temporarily
It is decoded and re-encoded according to the newly set quantization step parameter. Therefore, even if the generated code data amount exceeds the target value during reading the original, the code amount can be suppressed within the target value while continuing the reading.

<Quantization Matrix> As described above, when the quantization step parameter Qi (i = 1, 2, ...) Is set, the encoding unit 102 in the embodiment uses the quantization matrix QiaQib. Using one of the
The transform coefficient after the orthogonal transform is quantized, and entry Py coding (Huffman coding) is performed. Hereinafter, description will be given with reference to FIGS. 18 and 19.

FIG. 18A shows a document image to be read, in which a character area and a halftone image area are mixed as shown. In the embodiment, the determination unit 113 has 32 ×
The attribute representative of the pixel block is determined in units of 32 pixel blocks. Specifically, if even one of the pixel blocks has the attribute of being a character pixel, the pixel block is determined as a character area. In other words, the halftone is determined when all the pixels in the pixel block have the attribute indicating the halftone pixel (however, when there are two or more pixels that are characters, it may be a character area. However, the present invention is not limited by the number).

FIG. 18C shows that only the portion determined to be the character area in FIG. 18B is extracted. On the contrary, FIG. 3D shows a portion that is determined to be a halftone region with a hatched portion for distinction.

As described above, since it is important that the character can be read in the character image portion, it is desirable that the quantization step (particularly, the medium and high frequency components) is smaller than that in the halftone area. In other words, the halftone region has less effect on the whole even if the quantization step is larger than that of the character region.

For example, FIG. 19 shows an example of the halftone area quantization matrix and the character area quantization matrix for the quantization step parameter Q1. T1 is an example of a quantization matrix applied to a halftone region such as a photograph that does not include characters, and T2 is an example of a quantization matrix applied to a tile that includes characters and line drawings.

The DCT coefficient is normally DC at the upper left of the matrix.
The quantization step is for the component, and the quantization step for the high-frequency component is expressed as it goes to the right or the bottom. The smaller the number, the smaller the quantization step. That is, it means that the information of the original image is stored. T
In the case of 2, the numerical value in the upper left area is larger than that in T1, and the numerical value becomes smaller toward the right or the lower side. That is, the information of the high frequency component is stored while slightly sacrificing the low frequency component, so that the compression deterioration of the character image can be reduced.

As a result, although the quantization step parameter changes to Q1, Q2, Q3 ... Each time the set data amount is reached, the first memory 104 has a code according to one quantization step parameter. The encoded image data and the encoded attribute data are stored.

For example, when the coded data stored in the first memory 104 is used to print with a printer (not shown), the data (coded image data and coded data stored in the first memory 104 The attribute data) is stored as a file in a hard disk or the like, and the image data and the attribute flag data stored in the hard disk are read out, and are decoded and output in the following procedure.

First, data of M × N (32 × 32 in the embodiment) pixels of the compressed and stored attribute flag data is read and the attribute flag is decoded.

Next, the image data decoding process is performed by switching the image data decoding parameter (inverse quantization matrix in the present invention) according to the attribute flag data decoding result.
The result is output to the output buffer.

At this time, first, the attribute flag data is decoded, and the attribute flag data in the decoded M × N pixels is subjected to the same analysis and determination processing as the determination unit 101, and the corresponding M × N
An inverse quantization matrix for decoding the image data of N pixels is set and decoded. The image scanner and the page description language rendering unit make exactly the same determination, and the attribute flag data is compressed by a lossless compression method such as run length encoding that does not deteriorate the data. The determination results corresponding to the same tile are exactly the same. Therefore, even if each tile is quantized with a different quantized coefficient, an appropriate inverse quantized coefficient is set at the time of decoding, so that correct decoded image data can be obtained.

As described above, according to the first embodiment, even if the set value is exceeded during image input, the code is set so that the input value is kept within the target set value while continuing the input. Can be performed. Further, by using two quantization matrices in accordance with the image area attribute information, the compression rate of the halftone area can be set to be slightly higher than that in the case of one, and the image quality deterioration of the character area can be suppressed accordingly. As a result, 1 can be allocated for
Compared to the two cases, it is possible to further suppress the image quality deterioration with respect to the compression rate.

<Second Embodiment> The second embodiment according to the present invention will be described below. FIG. 2 shows the basic configuration of the image processing apparatus.

A major difference from the image processing apparatus 100 shown in FIG. 1 is that two coding units for coding first exist in parallel. In the image processing apparatus 200, the image data input from the input unit 201 is coded in parallel by the first coding unit 202 and the second coding unit 205, and two types of coded data having different compression rates are obtained. To generate. Also in this example,
A known JPEG encoding method is used as the encoding method, and 8 × 8 is used.
The image data corresponding to a pixel unit is orthogonally transformed, and quantization and Huffman coding processing using a quantization step described later is performed.

In this example, the compression rate applied by the second coding unit 205 is set to be higher than that by the first coding unit 202. Specifically, in the initial state, the quantization step parameter set in the first coding unit 202 is Q1, and the quantization step parameter set in the second coding unit 205 is Q2. That is, as the quantization step parameter set in the second encoding unit 205, a parameter having a higher one-rank compression rate than that of the first encoding unit 202 is always set. The first and second encoding units 202 and 205 select, quantize, and encode an optimum quantization matrix for orthogonally transformed data according to the set parameters and the determination result from the determination unit 213. .

The first counter 208 has a coding unit 202.
The amount of encoded data output from the counter is counted and held, and at the same time, the encoding sequence control unit 2
Also output to 09.

On the other hand, the encoded data encoded by the encoding unit 205 is stored in the second memory 207 via the second memory control unit 206. At this time, the second counter 210 counts the data amount of the encoded data output from the encoding unit 205 and holds it.

Furthermore, when the encoded data stored in the second memory 207, which will be described later, is transferred to the first memory 204, at the same time, the count value is transferred to the first counter 208.

Now, the first counter 208 is the encoding unit 2
When the count value reaches a certain set value while counting the data amount of the encoded data output from 02, the encoding sequence control unit 209 controls the memory control as in the first embodiment described above. Memory 204 for unit 203
Issue a control signal to discard the data stored in.

Then, the coding sequence control unit 209
Memory control so that the encoded data (encoded image data and encoded attribute data) stored in the second memory 207 is read out, transferred to the first memory 204, and stored in the first memory 204. Unit 206 and memory control unit 20
The control signal is output to 3. As a result, the second counter 2
The count value of 10 is transferred to the first counter 208,
The value is loaded (overwritten) as the count value of the first counter. Further, the second counter 210 is cleared to zero and starts counting the encoded data amount of the image data input thereafter.

In short, since the count value of the second counter 210 represents the data amount of the encoded data stored in the second memory 207, the count value and the encoded data correspond to each other. So that the attachment does not change,
It may be considered that the data is copied to the first counter and the first memory as it is.

Further, the coding sequence control 209 is
A control signal is issued to the first encoding unit 202 and the second encoding unit 205 so that encoding is performed so that the encoded data becomes smaller than ever.

For example, when it is judged that the set value is exceeded first, the first coding unit 202 and the second coding unit 2
The quantization step parameters set to 05 are Q1 and Q2.
Change from Q2 to Q3. As a result, the first encoding unit 202 inherits the quantization step parameter Q2 in the second encoding unit 205 immediately before that, and the second encoding unit 205 has a larger quantization step Q3. Is used to perform encoding processing with a higher compression rate in preparation for the next overflow.

However, when it is determined that the set value is exceeded,
Since the data encoded according to the quantization step parameter Q2 so far is stored in the second memory 207, it is necessary to update this data with the code data for the newly set quantization step parameter Q3. There is.
Therefore, when the re-encoding unit 211 determines that the set value is exceeded, it reads the previous code data (coded image data and coded attribute data), decodes the coded data, and according to the newly set quantization step parameter Q3, It is encoded again and stored again in the second memory 207 via the second memory control unit 206. At this time, the third counter 212 is counting the amount of data re-encoded by the re-encoding unit 211, and when the re-encoding of the previous encoded data is completed,
The count value is added to the second counter 210. Therefore, when this addition is completed, the second counter 210
Is transparent that the second encoding unit 205 counts the amount of data encoded by the quantization step parameter Q3 from the beginning of the input image.

If the image data from the input unit 201 to be encoded still remains, the encoding process by the two encoding units 202 and 205 is continued regardless of whether the re-encoding process is completed or not. Do it. Then, the counter 208
The monitoring of whether or not the count value has reached a certain set value is repeated until the encoding process (encoding, re-encoding) of the image data for one page input from the input unit 201 is completed, and the above-described encoding is performed. The re-encoding process and the re-encoding process are executed under control according to the detection result obtained here.

FIG. 12 is a flowchart showing the flow of processing in the configuration of FIG.

When there are two encoding units as described with reference to FIG. 2, the image data for one page is encoded based on the flowchart shown in FIG. Note that the description of FIG. 12 is mostly similar to FIG. 8 which is the flowchart in the case where there is one encoding unit, and those skilled in the art can fully understand the features of the second embodiment from the above description. Since it can be understood, the processing will be described in three phases as in the case of one encoding unit, and the points different from FIG. 8 will be mainly described.

The biggest difference between the above-described flow of FIG. 8 and the flow of this embodiment is that the transfer process of step S317 is moved between step S307 and step S309. In short, it may be considered that the encoding / re-encoding phase and the transfer phase are exchanged (the exception is the processing of discarding encoded data in step S307).

In the initial setting of the coding parameter in step S301, the quantization step parameter Q1 is set in the first coding section 202 and the quantization step parameter Q2 is set in the second coding section 205.

In the encoding phase, steps S801,
S303 and S305 are repeatedly executed. Step S8
01 and step S305 are the same processes as in the case where there is one encoding unit, but only the encoding process of step S303 is different as shown in FIG.

The encoded data to be stored in the first memory 204 is encoded with the quantization step parameter Q1 having the lowest compression rate in order to increase the compression rate stepwise. The encoded data stored in the second memory 207 is the data encoded with the quantization step parameter Q2 having a compression ratio one rank higher than that of the encoded data.

When the amount of data being stored in the first memory 204 exceeds the set upper limit value (step S3
05), immediately, the encoded data held in the first memory 204 is discarded (step S307), and the encoded data having a high compression rate held in the second memory 207 is
The data is transferred to the first memory 204 (step S317, see FIG. 14). As a result, the appropriate second candidate coded data that does not exceed the upper limit can be promptly obtained without waiting for the end of the first re-encoding process described in the first embodiment (FIG. 1). Can be stored in the memory 207. This is the greatest advantage of applying FIG. 2 with two encoders to FIG.

In the second embodiment, two memories 20 are provided.
Since it is wasteful that the coded data of 4 and 207 have the same compression rate, the second memory 207 has coded data with a higher compression rate than the coded data stored in the first memory 204. Is stored. Therefore, the subsequent processing is also performed based on this idea, and the processing of transferring the encoded data in the second memory 207 to the first memory 204 (transfer phase)
After the above, the encoded data in the second memory 207 is re-encoded so as to retain the encoded data having a higher one-step compression rate.

Specifically, first, as shown in FIG. 15, in the encoding / re-encoding phase subsequent to the transfer phase, it is applied to the two encoding units 202 and 205 before the re-encoding. The quantization step parameters Q1 and Q2 are changed to Q2 and Q3, respectively (step S309), and if the input of the image data of one page continues without being completed (step S803), the subsequent image data will be replaced by a new quantum. The input data is encoded by the two encoding units to which the encoding steps are set (step S311), and the corresponding memories 204, 2
It is stored in 07. Then, the encoded data stored in the second memory (transferred to the first memory 204) in parallel with the encoding process is compressed one step higher than the encoded data in the first memory. In order to change the encoded data to the rate, the re-encoding unit 211 performs re-encoding processing (S313) so that data encoded using the quantization step Q3 is obtained, and the re-encoded data is converted into the first encoded data. The data is stored again in the second memory 207.

In the second embodiment, as in the first embodiment, in the re-encoding process, these values are set to 2 for each quantized value after Huffman decoding the encoded data once.
It is realized by performing Huffman coding again after performing a bit shift process that produces a result similar to the result divided by ⁿ . This method enables high-speed re-encoding processing in that the quantization step is changed only by bit shifting and that inverse orthogonal transformation or re-orthogonal transformation processing is not performed.

When there are two encoders as in the second embodiment, the encoded data and the re-encoded data are mixed in the second memory 207 as shown in FIG. There is a situation where it is stored. Therefore, as described above, it is also necessary for the second memory 207 to divide the encoded data into certain units and manage them as files or packets. For that purpose, for example, a configuration similar to that of the modification of the first example may be provided.

In FIG. 12, when the end of the re-encoding process is detected in step S315, the process proceeds to the encoding phase (steps S801 and S303). In the encoding phase after the encoding / re-encoding phase, as shown in FIG. 16, not only the encoded data held in the two memories 204 and 207 have different compression rates but also mixed encoded data. The method (address) is also quite different. Therefore,
Again, when the data amount of the first memory 204 exceeds the set value, the encoded data (the code of the + horizontal stripe area) held in the second memory 207 is transferred to the first memory 204. Will need to be done. Considering these points, it is necessary to manage the encoded data as a file or packet not only in the second memory 207 but also in the first memory 204. Therefore, the first memory 204 also needs a management mechanism using the above-mentioned management table.

The state of the encoding phase shown in FIG. 16 is different from that of the encoding phase in the initial state except that the method of mixing the quantization step and the encoded data is different before and after the re-encoding process. (Fig. 13). Therefore, by repeating the encoding phase, the transfer phase, and the encoding / re-encoding phase, it is possible to ensure that the encoded data obtained by compressing the image data of one page to the set upper limit value or less is finally stored in the first memory. It can be stored in 204.

Since the arrangement order of the transfer phase and the encoding / re-encoding phase is opposite to that of the first embodiment, the image data for one page, which was performed after the transfer processing in FIG. 8, is performed. Input end detection (step S80
5) is the detection of the end of inputting one page of image data performed in the encoding / re-encoding phase (step S803),
The timing is almost the same. Further, the two detection processes are functionally the same as step S805 and are the same in timing as step S803. Therefore, these two steps detect the end of input of a new page of image data. Are integrated as steps to be performed, and are referred to as step S1201.

In the first and second embodiments described above,
The first memory and the second memory have been described as being physically different memories. This is advantageous because the access to the two memories can be independent, and is a feature of the present invention. However, the case where the first memory and the second memory are not physically separate memories is also included in the scope of the present invention. Two areas corresponding to the first memory and the second memory are physically secured on one memory, and the first memory is the first memory area and the second memory is the second memory. It can be understood that the present invention can be realized by a single memory, by re-reading the description given so far as a region.

Further, when the above embodiments are implemented by one memory, some of the data transfer processing described in the transfer phase becomes unnecessary. The details are omitted because they can be easily imagined each time. However, when the two areas are strictly separated from each other, the data transfer processing is required as in the case of physically having two memories. Two
If the same data is shared between the two areas, not only the data transfer processing becomes unnecessary, but also the storage capacity can be reduced.

For example, when the encoded data held in the second memory area is transferred to the first memory area, two pieces of information, that is, the head address where the encoded data is stored and the data size, are stored in the second information. Only by transferring from the second memory control unit to the first memory control unit, the same effect as the transfer of the encoded data can be obtained.

When the encoded data is stored in the file format or the packet format, the information transferred between the memory control units is slightly increased and it is necessary to transfer the management table information related to the encoded data. is there. Nevertheless, it is more efficient than transferring the encoded data.

According to the above-described image processing apparatus, when the input image data is encoded, even if the input image data exceeds the target size, the input size is kept and the input size is kept within the target size. The process can be continued. Moreover, in the first and second embodiments,
Quantization step parameters are not uniformly set to the same quantization step, but are encoded using a quantization matrix suitable for each of the character area and the halftone area, so high compression rate and minimum deterioration of image quality are achieved. It becomes possible to limit it.

In the embodiment, when the attribute data is compressed, it is stored in each of the first and second memories, but the attribute data of the determination results of the determination units 113 and 213 is the image of one page. Therefore, the re-encoding unit 211 stores the data in a common memory (for example, the first memory) and, when the re-encoding unit 211 re-encodes, refers to the common memory and re-encodes. You may choose to do this.

Further, as described above, the present invention can be realized by an application program that operates on a general-purpose device, so the present invention also includes a computer program. The computer program is usually a floppy (registered trademark) disk or CDRO.
This is performed by setting a storage medium such as M in the apparatus and copying or installing the storage medium, and thus such a storage medium is naturally included in the scope of the present invention.

Further, in the embodiment, the image data is input from the scanner, but it may be applied to a printer driver operating on a host computer.
When applied to a printer driver, when data to be printed is received from a higher-level process (application, etc.), it is of course possible to determine at that point whether the data is a halftone image or a character / line drawing. It is possible to omit the configuration related to the region information generation processing or to simplify the configuration.

The present invention can also be applied to a combination of a computer program and appropriate hardware (encoding circuit etc.).

[0112]

As described above, according to the present invention, re-image input is unnecessary, coded data can be effectively generated within a set size, and image quality deterioration with respect to a compression rate is reduced. It will be possible.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an image processing apparatus according to a first embodiment.

FIG. 2 is a block configuration diagram of an image processing apparatus according to a second embodiment.

3 is a flowchart showing a simplified process in the configuration of FIG.

FIG. 4 is a diagram showing a data flow and a memory content in an encoding phase in an initial state.

FIG. 5 is a diagram showing a data flow and a memory content in an encoding / re-encoding phase.

FIG. 6 is a diagram showing a data flow and a memory content in a transfer phase.

FIG. 7 is a diagram showing a data flow and a memory content in an encoding phase after a transfer phase.

FIG. 8 is a flowchart showing details of processing in the configuration of FIG.

9 is a diagram showing a data flow and a memory content in an encoding / re-encoding phase in the modified example of the configuration of FIG.

10 is a diagram showing a data flow and a memory content in a transfer phase in the modified example of FIG.

11 is a diagram showing a data flow and a memory content in an encoding phase after a transfer phase in the modified example of FIG.

12 is a flowchart showing a processing procedure in the configuration of FIG.

13 is a diagram showing a data flow and a memory content in an encoding phase in an initial state in the configuration of FIG.

14 is a diagram showing a data flow and a memory content in a transfer phase in the configuration of FIG.

15 is a diagram showing a data flow and a memory content in an encoding / re-encoding phase in the configuration of FIG.

16 is a diagram showing a data flow and a memory content in the encoding phase after the encoding / re-encoding phase in the configuration of FIG.

FIG. 17 is a diagram showing a configuration of a processing unit relating to encoding of attribute data applied by the embodiment.

FIG. 18 is a diagram showing a relationship between a document image and a character area and a halftone area in the embodiment.

FIG. 19 is a diagram showing an example of a quantization matrix adopted in the embodiment.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenichi Ota             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Tadayoshi Nakayama             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Hidefumi Osawa             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F term (reference) 5C059 KK08 KK11 MA00 MA23 MC11                       MC38 ME02 ME05 PP01 PP15                       PP20 RC12 RC40 SS20 TA46                       TB06 TC02 TC18 TC24 TC38                       TD05 TD07 TD09 TD12 TD17                       UA02 UA32 UA35 UA36 UA38                       UA39                 5C078 AA04 BA57 CA03 CA27 CA31                       DA01 DA06                 5J064 AA01 AA02 BC01 BC16 BC25                       BD06

Claims (9)

[Claims] 1. An image processing apparatus for compression-encoding image data, comprising: storage means for storing compression-encoded data; determination means for determining image area information of input image data; and parameters relating to quantization steps. And first compression encoding means for compressing and encoding image data based on the determination result of the determining means, and compression encoding of the image data based on the parameter relating to the quantization step and the determination result of the determining means,
Second compression coding means for decoding and recompressing coded data compressed by the first compression coding means, and monitoring the code amount generated by the first compression coding means, and Code amount monitoring means for determining whether or not the data amount has reached a predetermined amount, and when the code amount monitoring means determines that the predetermined amount has been reached, the quantum in the first and second compression encoding means Setting means for setting a parameter so as to increase the encoding step, and when the parameter is changed by the parameter setting means, the code data previously generated by the first compression encoding means is converted into the second compression encoding means. And re-encode the encoded data after the re-encoding, and store the re-encoded encoded data in the storage unit as encoded data after the parameters of the first compression encoding unit are changed. An image processing apparatus, comprising: a control unit that causes the storage unit to store the encoded data generated by the first compression encoding unit after the data change as subsequent encoded data. 2. The determination means determines whether a character / line drawing area or a halftone area, and the first and second compression / encoding means determines the character / line drawing for one parameter according to the determination result. The image processing apparatus according to claim 1, wherein the image processing apparatus is quantized and coded using one of the quantization matrices for each of the region and the halftone image region. 3. An image processing method for compression-encoding image data, comprising a determination step of determining image area information of input image data, an image based on a parameter relating to a quantization step and a determination result of the determination step. A first compression encoding step of compressing and encoding data, and compression encoding of image data based on a parameter related to a quantization step and a determination result of the determination step,
A second compression encoding step of decoding and recompressing the code data compressed in the first compression encoding step, and monitoring the code amount generated in the first compression encoding step and A code amount monitoring step of determining whether or not the data amount has reached a predetermined amount, and if the code amount monitoring step determines that the predetermined amount has been reached, the quantum in the first and second compression encoding steps A parameter setting step of setting a parameter so as to increase the encoding step; and when the parameter is changed in the parameter setting step, the code data previously generated in the first compression encoding step is converted into the second compression encoding. The data is re-encoded by the process, and the re-encoded code data is stored in a predetermined storage unit as the code data after the parameter change of the first compression encoding process. Both image processing method characterized by comprising the control step of the encoded data generated by the first compression encoding step after parameter change, it is stored in the storage means as a subsequent code data. 4. A computer program for an image processing apparatus, which compresses and encodes image data, comprising: determining means for determining image area information of input image data; parameters relating to a quantization step and determination results of the determining means. A first compression encoding means for compressing and encoding image data based on, and compression encoding the image data based on the parameter relating to the quantization step and the determination result of the determination means,
Second compression coding means for decoding and recompressing coded data compressed by the first compression coding means, and monitoring the code amount generated by the first compression coding means, and Code amount monitoring means for determining whether or not the data amount has reached a predetermined amount, and when the code amount monitoring means determines that the predetermined amount has been reached, the quantum in the first and second compression encoding means Setting means for setting a parameter so as to increase the encoding step, and when the parameter is changed by the parameter setting means, the code data previously generated by the first compression encoding means is converted into the second compression encoding means. And re-encode the encoded data after the re-encoding by storing the encoded data in the predetermined storage means as the encoded data after the parameter change of the first compression encoding means. A computer program that functions as a control unit that causes the storage unit to store the encoded data generated by the first compression encoding unit after the meter has been changed, as subsequent encoded data. 5. A computer-readable storage medium storing the computer program according to claim 4. 6. An image processing device for compression-encoding image data, comprising: storage means for storing compression-encoded data; determination means for determining image area information of input image data; and parameters relating to quantization steps. And first compression encoding means for compressing and encoding image data based on the determination result of the determining means, and compression encoding of the image data based on the parameter relating to the quantization step and the determination result of the determining means,
Operating in parallel with the first compression encoding means,
Second compression coding means for compressing at a compression rate higher than that of the compression coding means, and the code amount generated by the first compression coding means are monitored and A code amount monitoring means for determining whether or not a fixed amount has been reached, and when the code amount monitoring means determines that the predetermined amount has been reached, the first compression is performed using the conventional parameter of the second compression encoding means. Parameter setting means for setting the encoding means and setting new parameters in the second compression encoding means, and when the parameters are changed by the parameter setting means, the first compression encoding means previously generates the parameters. The coded data processed by the second compression coding means instead of the coded data stored in the storage means is stored in the storage means as coded data after the parameters of the first compression coding means are changed. Both the image processing apparatus, characterized in that it comprises a control means for the encoded data generated by the first compression encoding means after parameter change, is stored in the storage means as a subsequent code data. 7. An image processing method for compression-encoding image data, comprising a determination step of determining image area information of input image data, an image based on a parameter relating to a quantization step and a determination result of the determination step. A first compression encoding step of compressing and encoding data, and compression encoding of image data based on a parameter related to a quantization step and a determination result of the determination step,
Operating in parallel with the first compression encoding step,
The second compression encoding step of compressing at a compression rate higher than the compression rate of the compression encoding step and the amount of code generated by the first compression encoding step are monitored, and the amount of code data is determined. A code amount monitoring step of determining whether or not the quantity has become constant, and when it is determined that the predetermined amount has been reached by the code amount monitoring step, the first compression is performed using the parameter used in the second compression encoding step. A parameter setting step of setting an encoding step and setting a new parameter in the second compression encoding step, and when the parameter is changed by the parameter setting step, the parameter is previously generated in the first compression encoding step. In place of the encoded data, the encoded data that has been subjected to the second compression encoding process is stored in the predetermined storage means as the encoded data after the parameter change of the first compression encoding process. Together, an image processing method characterized by comprising the control step of the encoded data generated by the first compression encoding step after parameter change, it is stored in the storage means as a subsequent code data. 8. A computer program for an image processing apparatus, which compresses and encodes image data, comprising: determination means for determining image area information of input image data; parameters relating to a quantization step and determination results of the determination means. A first compression encoding means for compressing and encoding image data based on, and compression encoding the image data based on the parameter relating to the quantization step and the determination result of the determination means,
Operating in parallel with the first compression encoding means,
Second compression coding means for compressing at a compression rate higher than that of the compression coding means, and the code amount generated by the first compression coding means are monitored and A code amount monitoring means for determining whether or not a fixed amount has been reached, and when the code amount monitoring means determines that the predetermined amount has been reached, the first compression is performed using the conventional parameter of the second compression encoding means. Parameter setting means for setting the encoding means and setting new parameters in the second compression encoding means, and when the parameters are changed by the parameter setting means, the first compression encoding means previously generates the parameters. The code data processed by the second compression coding means instead of the coded data stored in the second compression coding means is stored in a predetermined storage means as code data after the parameters of the first compression coding means are changed. With a computer program that functions encoded data generated by the first compression encoding means after parameter change, as control means for causing stored in the storage means as a subsequent code data. 9. A computer-readable storage medium storing the computer program according to claim 8.