JP4035475B2 - Image processing apparatus, control method therefor, computer program, and storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for encoding image data.
[0002]
[Prior art]
Conventionally, as a still image compression method, a JPEG method using discrete cosine transform (hereinafter abbreviated as DCT) and a method using Wavelet transform are often used. Since this type of encoding method is a variable-length encoding method, the code amount changes for each image to be encoded.
[0003]
In the JPEG method, which is an international standardization method, only one set of quantization matrix can be defined for an image. Therefore, the code amount cannot be adjusted without pre-scanning and used in a system that stores in a limited memory. There was a danger of causing memory over.
[0004]
In order to prevent this, it is necessary to secure a sufficient memory capacity. However, the sizes of the input images are not always the same but may be different. Therefore, until now, it has been necessary to secure a memory having a capacity that can be adapted to the maximum size that can be input.
[0005]
[Problems to be solved by the invention]
However, in a device that secures a memory in accordance with the maximum size, it means that the memory is secured even when an image having a smaller size is input, and the memory is effectively used. I can't say that.
[0006]
Therefore, it is conceivable to match the memory capacity to be secured to a medium image, but this time, the code data obtained by the encoding process will exceed that.
[0007]
As a countermeasure in this case, when the code amount exceeds the planned code amount, in order to adjust the code amount by changing the compression rate and re-reading the document or estimating the code amount by pre-scanning in advance, A method of resetting the quantization parameter is known.
[0008]
Conventionally, as a code amount control method for performing pre-scan, for example, a method in which pre-compressed data is stored in an internal buffer memory, decompressed, changed in compression parameters, subjected to main compression, and output to an external storage is known . At this time, the main compression needs to have a higher compression rate than the pre-compression.
[0009]
Further, for example, in order to obtain an allowable code amount for each pixel block and reduce the code amount, a method of performing Huffman coding on a coefficient obtained by level-shifting a DCT coefficient n times is known. This shift amount n is an allowable code amount. Determined from.
[0010]
The present inventors have already proposed several techniques for reliably encoding an image within a single encoding processing time and with a small amount of memory. Although the details will be described later, in brief, when the code amount is likely to overflow the target memory capacity, the compression rate of the encoder is increased, and the data that has already been encoded is updated. Is re-encoded so that it is equivalent to being compressed at the compression rate set to.
[0011]
Although the above process is very effective, a high processing capability is required for the re-encoding unit that performs the re-encoding process. If the re-encoding processing capability is low, the compression code amount at the re-set compression rate may exceed the target value before the re-encoding is completed. This is because the encoding process cannot be started, and as a result, compression encoding fails.
[0012]
For the reasons described above, re-encoding requires a high processing capacity, but in fact, it is rare that such a situation occurs. Therefore, satisfying a high processing capacity for re-encoding is excessive, leading to an increase in cost.
[0013]
The present invention has been made in view of such problems, and with a relatively simple configuration, it is ensured that encoding is performed below the target code amount while image input is continued, and image quality is deteriorated. We intend to provide a technology that suppresses as much as possible.
[0014]
[Means for Solving the Problems]
In order to solve this problem, for example, an image processing apparatus of the present invention comprises the following arrangement. That is,
An image processing apparatus that compresses and encodes one page of image data,
First encoding means capable of changing the quantization step;
A second encoding unit that can change a quantization step and re-encodes the code data compressed by the first encoding unit;
First determination means for monitoring the amount of code data generated by the first encoding means and determining whether the amount of code data has reached a predetermined amount;
A prediction time T0 at which the encoding of one page of image data is completed, and a prediction time T1 at which the amount of code data generated by the first encoding means reaches the predetermined amount;
Condition 1: T0> T1-Δt1
(Where Δt1 is a predetermined positive value)
A second judging means for judging whether or not
Based on the amount of code data, the first encoding means is already generated according to the time T2 when the predetermined amount is reached when it is assumed that the first encoding means has performed compression encoding in the next quantization step, and the current quantization step. A re-encoding completion time T3 when it is assumed that the encoded data is re-encoded by the second encoding unit that has set the quantization step of the next stage;
Condition 2: T3> T2-Δt2
(Where Δt2 is a predetermined positive value)
A third determination means for determining whether or not
When it is determined that the predetermined amount has been reached by the first determination means, or when both the conditions 1 and 2 are satisfied by the second and third determination means, the first and second codes Setting means for setting the quantization step of the next stage in the conversion means;
When the quantization step is changed by the setting means, the encoding by the first encoding means is continued for the image data input after the quantization step change, and the already encoded code data before the quantization change Comprises control means for re-encoding by the second encoding means.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments according to the present invention will be described with reference to the accompanying drawings. First, basic portions will be described.
[0016]
FIG. 1 is a functional block configuration diagram of an image processing apparatus 100 to which the embodiment is applied. Hereafter, each part of the same figure is demonstrated easily.
[0017]
The image processing apparatus 100 includes an input unit 101 that inputs an image from an image scanner. The input unit 101 may input image data from means for rendering a page description language into a raster image, or may be realized by reading an image file stored in a storage medium. May be received from the network.
[0018]
The encoding unit 102 encodes input image data. The encoding method uses a known JPEG encoding method, DCT transforms image data with 8 × 8 pixels, and performs quantization and Huffman encoding processing using a quantization step described later.
[0019]
The first memory control unit 103 and the second memory control unit 105 use the encoded data (the same encoded data) output from the encoding unit 102 as the first memory 104 and the second memory 106. It controls to store each. Here, the first memory 104 is a network device or an image output device for connecting the encoded data finally determined (compressed to the data amount within the target value) outside the basic configuration of FIG. And a memory for holding the encoded data for output to a mass storage device or the like. The second memory 106 is a working memory that assists in the compression encoding process for forming the encoded data on the first memory.
[0020]
The counter 107 counts the data amount of the image data compressed and encoded by the encoding unit 102, holds the count value, and outputs it to the encoding sequence control unit 108 that controls the encoding sequence based on the count result. To do.
[0021]
The encoding sequence control unit 108 detects whether or not the count value of the counter 107 has reached a certain set value. When it is detected that the set value has been reached (exceeded the target value), it has been stored in the memory 104. A control signal is output to the first memory control unit 103 so as to discard the encoded data. The first memory control unit 103 discards the stored data by clearing the memory address counter or clearing the encoded data management table based on this control signal. At this time, the encoding sequence control unit 108 clears the first counter 107 to zero to match the data amount in the first memory 104 (the input from the input unit 101 is continued). Further, the encoding unit 102 is controlled to perform encoding at a higher compression rate than before. Specifically, the quantization step for quantizing the DCT transform coefficient is set to be doubled.
[0022]
Although the quantization step is simply doubled here, in the case of a color image, one luminance signal (luminance data) generated when color conversion is performed and two color difference signals (color difference data). Assign different quantization steps and double each one alternately.
[0023]
The encoded data after the compression rate change is also 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, as before. The The first memory 104 stores a code generated by encoding data input after the discard operation shift.
[0024]
When the count value of the counter 107 reaches a certain set value, the encoding sequence control unit 108 transfers the second memory control unit 105 to the second memory 106 so far in parallel with the control. The stored encoded data is read, and a control signal is output so that the encoded data is output to the re-encoding unit 109 serving as encoded data conversion means.
[0025]
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. The encoded data includes the first and second encoded data. The data is stored in the first and second memories 104 and 105 via the memory control units 103 and 105. At this time, the re-encoding quantization step in the re-encoding unit 109 is the same as the updated quantization step in the encoding unit 102. The code amount obtained by re-encoding by the re-encoding unit 109 is counted by the second counter 110.
[0026]
The second memory control unit detects whether or not the re-encoding process of the re-encoding unit 109 has been completed. That is, when there is no more data to be read for the re-encoding process, the encoding sequence control unit 108 is notified of the end of the re-encoding process. Actually, not only the reading process of the second memory control unit 105 but also the process of the re-encoding unit 109 is completed, the re-encoding process is completed.
[0027]
The count value obtained by the second counter 110 is added to the counter value held by the first counter 107 after the re-encoding process is completed. This addition is performed when the encoding sequence unit 108 receives a re-encoding completion notification from the second memory control unit 105. As a result of this addition, the first counter 107 holds a count value representing the total amount of data in the first memory 104. That is, at the time when the encoding process of the encoding unit 102 and re-encoding unit 109 for one screen (page) is completed, the counter value held by the first counter 107 after the addition is one screen. This represents the total amount of data generated when this apparatus encodes minutes (for one page) (details will be described later).
[0028]
The encoding unit 102 continues the encoding process as long as image data from the input unit 101 to be encoded remains, regardless of whether the re-encoding process is completed or not.
[0029]
The detection of whether or not the count value of the first counter 107 has reached a certain setting value is repeated until the encoding process (encoding and re-encoding) of image data for one page input from the input unit 101 is completed. Thus, the encoding and re-encoding processes described above are executed under control according to the detection result obtained here.
[0030]
The above processing contents will be described in a more easy-to-understand manner as follows. The following is about monochrome image encoding.
[0031]
The image data input from the input unit 101 is compressed and encoded by the encoding unit 102 in accordance with the quantization parameter Q1 at the initial stage. The generated compressed code data is written into the first memory 104 and the second memory 106, respectively. At this time, the first counter 107 counts the amount of code data to be generated. When the compression encoding process is completed while the amount is less than or equal to the set amount, the data stored in the first memory 104 is externally stored. If there is a subsequent image (image of the next page), the counters 107 and 110 are reset and input.
[0032]
On the other hand, when the encoding sequence control unit 108 detects that the amount of encoded data to be generated has reached the set value while encoding a certain page, the data in the first memory 104 is discarded. Then, the quantization parameter Q2 at the next stage is set so that the compression rate becomes higher for the encoding unit 102, and the input of the image data is continued. At this time, the first counter 107 is reset. As a result, the image data input after it is determined that the set value has been reached is encoded at a higher compression rate. Also, the encoded data (data encoded with the quantization parameter Q1) before the encoded data amount reaches the set value is stored in the second memory 106. Therefore, this data is re-encoded by the re-encoding unit 109 and the result is stored in the first memory 104 and the second memory 106, respectively. The quantization parameter at the time of re-encoding by the re-encoding unit 109 is the same as the quantization parameter Q2 of the encoding unit 102 after the setting change. When the re-encoding for the previous encoded data stored in the second memory 106 is completed, the code amount is held in the second counter 110, so that it is added to the first counter 107.
[0033]
As a result, the first memory 104 and the second memory 106 store the encoded data compressed with the quantization parameter Q2 from the top of one page. When it is determined that the value of the counter 107 has reached the set value again during compression encoding with the quantization parameter Q2, the quantization parameter Q3 is re-established with the encoding unit 102 and the re-encoder to achieve a higher compression rate. The above processing is performed by setting in the encoding unit 109. When it is determined that the set value is reached even with the quantization parameter Q3, the quantization parameter is set to Q4.
[0034]
The quantization step is increased by m times (m> 1) (Q2 = Q1 × m, Q3 = Q2 × m, Q4 = Q3 × m,... (Not necessarily equal). When the quantization step is increased, the frequency component value at the time of DCT conversion can be expressed with a small value, that is, with a small number of bits, and thus the data amount can be reduced.
[0035]
FIG. 8 is a flowchart showing the process flow in the configuration shown in FIG. 1, but for the sake of simplicity, description will be given first according to the simplified flowchart shown in FIG.
[0036]
As described above, the image processing apparatus 100 of the present invention is an apparatus that compresses and encodes one page of image data input from the input unit 101 such as a scanner 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, a re-encoding unit 109, a first memory 104, a second memory 106, and the like are provided. Using these functional blocks, encoding processing is performed based on the flowchart shown in FIG.
[0037]
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 and processed in the memory FIG. 4 to FIG. 7 show whether the data is stored visually.
[0038]
FIG. 4 shows an initial state of the encoding phase corresponding to steps S303 and S305 in the flowchart of FIG. 5 shows the processing state of the encoding / recoding 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 encoding phase after the transfer phase. Indicates processing status. Hereinafter, each phase will be described.
[0039]
<< Encoding Phase >>
Encoding processing of image data for one page starts from initial setting of encoding parameters (step S301). Here, the quantization step Q1 to be applied to the encoding unit 102 is set based on the upper limit value of the encoded data amount uniquely determined from the image size to be encoded (paper size read from the input unit 101 such as a scanner).
[0040]
In step S303, the first counter 107 performs actual encoding processing (JPEG compression of the image in units of 8 × 8 pixels) and cumulatively counts the amount of encoded data to be output.
[0041]
Next, in step S305, it is detected whether the count value of the data amount has exceeded the upper limit value. If not, the JPEG encoding process in step S303 is continued. This is the initial encoding phase.
[0042]
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. A region indicated by vertical stripes represents the stored code.
[0043]
<< Encoding / Recoding Phase >>
When the encoding process of the encoding unit 102 proceeds and the count value of the data amount exceeds the set upper limit value, in step S307, the encoded data in the first memory 104 is discarded and the step In S309, the quantization parameter of the encoding unit 102 is changed to Q2.
[0044]
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, since it is meaningless to continue the encoding process using the same quantization step, it is changed to the quantization step Q2 having a larger quantization step width than Q1 so that the data amount is smaller than before. is there.
[0045]
After changing the quantization step and the contents of the quantization operation, in step S311, the encoding process of the encoding unit 102 is resumed, and the encoded data is stored only in the second memory 106 as shown in FIG. In parallel with this, the re-encoding process in step S313 is performed. In the re-encoding process, the encoded data stored in the second memory 106 is read out, re-encoded by the re-encoding unit 109, and 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 (1) are re-encoded.
[0046]
Specifically, in this re-encoding process, after the Huffman decoding of the encoded data, each quantized value is subjected to a bit shift process that produces a result similar to the result obtained by dividing these values by 2 ⁿ This is realized by performing Huffman coding again (when m = 2). This method enables high-speed re-encoding processing in that the quantization step is changed only by bit shift and that inverse orthogonal transformation or re-orthogonal transformation processing is not performed. In step 315, the end of the re-encoding process is detected.
[0047]
Since the amount of data after re-encoding is smaller than the amount of encoded data before re-encoding, as shown in FIG. 5, after re-encoding in the memory area where the code before re-encoding was stored Can be stored so as to be overwritten. When the re-encoding process is completed, the data amount of the encoded data of the vertical stripes (1) decreases to the data amount of the encoded data of the diagonal stripes (1) shown in FIG.
[0048]
Steps S307 to 315 described above are processes performed in the encoding / recoding phase.
[0049]
<< Transfer Phase >>
When the re-encoding process is completed, a transfer process is performed in step S317. In the transfer process, as shown in FIG. 6, encoded data of diagonal stripes (2) stored only in the second memory 106 in the encoding / re-encoding phase is converted into diagonal lines ▲ in the first memory 104. It is transferred to the address linked to the encoded data 1) and stored. On the other hand, the encoded data of the diagonal stripe {circle around (1)} and the encoded data of the diagonal stripe {circle around (2)} dispersed on the second memory 106 are continuously stored on the first memory 104. Similarly, the encoded data of the diagonal stripe {circle around (2)} is transferred in the second memory 106 and connected. This is processing performed in the transfer phase.
[0050]
When the transfer phase ends, the process returns to the encoding phase of steps S303 and S305, and the code of the diagonal stripe (4) is output from the encoding unit 102 and stored in the two memories 104 and 106 as shown in FIG. This encoding phase is slightly different from the encoding phase in the initial state (FIG. 4), the quantization step at the time of encoding by the encoding unit 102 is changed from Q1 to Q2, and the two memories 104 and 106 The encoded data stored in is also a collection of codes processed in various phases. If these differences are ignored, the encoding phase immediately after the transfer phase and the initial encoding phase can be regarded as the same.
[0051]
Therefore, by repeating the encoding phase, the encoding / re-encoding phase, and the transfer phase, a code in which one page of image data is finally compressed to a set code amount or less is stored in the first memory. I can do it. In addition, the input unit 101 simply continues input until a series of processing is completed. That is, it is not necessary to input the image again from the beginning.
[0052]
The flowchart shown in FIG. 3 describes only the processing corresponding to each phase shown in FIGS. 4, 5, and 6 so that the explanation can be easily understood. In practice, however, the input of image data for one page ends in some phase. Therefore, the correspondence after that is slightly different depending on which phase it is completed. FIG. 8 is a flowchart showing the flow considering this. The flowchart in FIG. 8 considers the relationship between the completion of input of image data for one page and the various processes described with reference to FIG. 3. Here, steps S801, S803, S805, and S807 are added to the flowchart in FIG. It has been added.
[0053]
Steps S801, S803, and S805 detect that the input of image data for one page from the input unit 101 has been completed in the encoding phase, the encoding / recoding phase, and the transfer phase, respectively.
[0054]
When it is detected that the input of image data for one page has been completed in the encoding phase and the transfer phase (steps S801 and S805), the process proceeds to step S807 to end the compression encoding process for the page, and then the compression process If there is image data to be processed, compression encoding processing of image data for the next one page is started (respective counters are reset and quantization parameters are set to initial values).
[0055]
On the other hand, when the end of input of image data for one page is detected in the encoding / re-encoding phase (step S803), the encoding unit 102 needs to stop operation until there is no image data to be re-encoded. Therefore, the encoding process of step S311 is passed, and in step S313, only the re-encoding process for suppressing the image data encoded by the encoding unit 102 so far to a predetermined encoded data amount is continued. And do it. When all the re-encoding processes are completed and the subsequent transfer process is not completed, the encoded data of the entire image data for one page is not collected on the first memory, so 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 performed continuously. In this case, when it is detected in step S315 that all the re-encoding processes have been completed, the encoded data stored only in the second memory 106 is stored in the first memory during the encoding / re-encoding phase. After the transfer to the memory (step S317), in the next step S805, the input end of the image data for one page is detected, and the process proceeds to step S807.
[0056]
The above is the operation, and is also the operation description of FIG.
[0057]
<Modification of memory storage method>
9 and 10 are diagrams showing modifications of the memory storing method shown in the conceptual diagrams of FIGS.
[0058]
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. However, as shown in FIG. During the re-encoding phase, the encoded data output from the encoding unit 102 is directly stored in both the first and second memories.
[0059]
When viewed from the encoding unit 102, encoded data to be encoded and output in any phase is stored in both memories. Further, unlike the conceptual diagram of FIG. 6, as shown in FIG. 10, it is not necessary to transfer data between memories in the transfer phase. In the case of this modification, the encoded data and the re-encoded data are sequentially stored in the order in which they are sent to the first memory 104 in the encoding / re-encoding phase. Therefore, there is a problem that two types of data are mixed.
[0060]
Therefore, in the case of this modification, the encoded data is divided into certain units and managed as a file or a packet in order to cope with this. Specifically, a file management table or a packet management table is created and managed separately.
[0061]
As one method, when data from the encoding unit 102 is stored in the first memory 104, an appropriate unit (for example, 8 × i (i = 1 because the unit of the orthogonal transform is an 8 × 8 block). 2) (integer) for each line), a management number is assigned from the top of the image data, and the storage start address of the encoded data corresponding to each management number and the amount of the encoded data are stored in the order of the management number. Create a management table that can be used.
[0062]
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, write the start address and the encoded data amount when storing the encoded data in the management table. In this way, even if the encoded data processed by the encoding unit 102 and the re-encoding unit 109 is randomly stored, the management table is accessed in the order of the management number, and the head address and the encoded data to be read at that time are read. If the encoded data is read from the first memory 104 based on the amount, the encoded data can be read sequentially from the top of the image. Providing such a management mechanism eliminates the need to store continuous data on the image so as to be continuous on the memory.
[0063]
The encoding phase after the transfer phase in the conceptual diagram of FIG. 10 is almost the same as the two encoding phases described above (FIGS. 4 and 7), and the code storage state in the first memory is shown in FIG. It is only slightly different as shown in. Therefore, the above description and this modification are the same in that the three phases are repeated.
[0064]
<Second example>
Next, a second example (the configuration described so far is referred to as the first example) for performing a characteristic encoding process in the present invention will be described with reference to FIG.
[0065]
FIG. 2 is a block diagram of the image processing apparatus 200 in the second example.
[0066]
A significant difference from the image processing apparatus 100 in the first example of FIG. 1 is that two encoding units that perform encoding first exist in parallel. The image processing apparatus 200 encodes image data input from the input unit 201 in parallel with the first encoding unit 202 and the second encoding unit 205, and two types of encoded data having different compression rates. Is generated. Also in the second example, a known JPEG encoding method is used as the encoding method, image data is DCT-converted in units of 8 × 8 pixel blocks, and quantization and Huffman encoding processing using a quantization step described later is performed. Is to do.
[0067]
In this example, a case where the compression rate applied by the second encoding unit 205 is set higher than that of the first encoding unit 202 will be described. Specifically, the quantization parameter in the first encoding unit 202 is Q1, and the quantization parameter of the second encoding unit 205 is Q2 (the Q2 quantization step is larger than the Q1 quantization step). .
[0068]
The encoded data output from the encoding unit 202 is stored in the first memory 204 via the first memory control unit 203. At this time, the first counter 208 counts the amount of encoded data output from the encoding unit 202, holds this, and also outputs it to the encoding sequence control unit 209.
[0069]
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 described later is transferred to the first memory 204, the count value of the second counter 210 is transferred to the first counter 208 at the same time.
[0070]
When the first counter 208 counts the data amount of the encoded data output from the encoding unit 202 and the count value reaches a certain set value, the encoding sequence control unit 209 As in the example, a control signal is issued to the memory control unit 203 so as to discard the data stored in the first memory 204.
[0071]
Then, the encoding sequence control unit 209 reads the encoded data stored in the second memory 207, transfers it to the first memory 204, and stores it in the first memory 204. A control signal is output to the control unit 203. As a result, the count value of the second counter 210 is transferred to the first counter 208, and the value is loaded (overwritten) as the count value of the first counter.
[0072]
In short, since the count value of the second counter 210 represents the amount of encoded data stored in the second memory 207, the encoded data corresponding to the count value is directly used as the first value. It can be considered that the data has been copied to the counter and the first memory.
[0073]
Further, the encoding sequence control 209 outputs a control signal to the second encoding unit 205 so as to perform encoding so that encoded data is smaller than before. On the other hand, for the first encoding unit 202, the setting is changed so as to inherit the quantization parameter Q2 in the second encoding unit 205 until just before.
[0074]
For example, the quantization step in the second encoding unit 205 is switched to twice. As a result, the first encoding unit 202 performs encoding processing with a higher compression ratio in preparation for the next overflow using the second encoding unit 205 using a larger quantization step Q3. The encoded data output from the switched encoding units 202 and 205 is stored in the corresponding memories 204 and 207 via the corresponding memory control units 203 and 206, respectively.
[0075]
Here, although the magnification ratio of the quantization step is set to double, it is not limited to this, and needless to say, it can be arbitrarily set. For example, in the case of a color image, separate quantization steps are assigned to one luminance signal (luminance data) generated at the time of color conversion and two color difference signals (color difference data), and each one is doubled alternately. By making it, it becomes possible to make finer settings.
[0076]
Then, the encoding sequence control 209 reads out the encoded data already stored in the second memory 207 and sends a control signal to the re-encoding unit 211 to the memory control unit 206. The re-encoding unit 211 performs re-encoding processing of encoded data in the same manner as the re-encoding unit 109 in FIG.
[0077]
The third counter 212 counts the amount of data output from the re-encoding unit 211, is reset to zero immediately before starting the re-encoding process, and counts the output data amount during the re-encoding process. When the re-encoding process is completed, the counter 212 transfers the count value obtained there to the second counter 210.
[0078]
The second counter 210 adds the transferred data amount count value to the counter value held in the second counter 210 to thereby store the code stored in the memory 207 during the re-encoding process. The total data amount of the encoded data and re-encoded data is calculated. That is, the amount of data stored in the memory 207 matches the count value of the counter 210.
[0079]
Regardless of whether the re-encoding process is completed or not, if the image data from the input unit 201 to be encoded remains, the encoding process by the two encoding units 202 and 205 is continued. Then, monitoring whether the count value of the counter 208 has reached a certain set value is repeated until the encoding process (encoding, re-encoding) of image data for one page input from the input unit 201 is completed, The encoding and re-encoding processes described above are executed under control according to the detection result obtained here.
[0080]
To summarize the above operations, the second encoding unit 205 performs encoding at a compression rate that is one higher than that of the first encoding unit 202. When the code amount generated by the first encoding unit 202 reaches the set amount, the quantization parameter of the first encoding unit 202 is set to be the same as that of the second encoding unit 205 immediately before. Also, the quantization parameter of the second encoding unit 205 is set to be a higher compression rate. Then, the data in the first memory 204 is discarded, the data stored in the second memory 207 is transferred to the first memory 204, and the value of the second counter 210 is transferred to the first counter 208. Write. Then, in order to re-encode the data in the second memory at a higher compression rate, the re-encoding unit 211 is made the same as the quantization parameter newly set in the second encoding unit 205. As a result, the data in the second memory 207 stores code data equivalent to the data compressed with the newly set quantization parameter from the top of the page.
[0081]
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 a flowchart in the case of one encoding unit, and those skilled in the art will fully understand the features of the second example from the above description. Since it will be possible, the process will be described in three phases as in the case of one encoding unit, and the differences from FIG. 8 will be mainly described.
[0082]
The biggest difference between the flow of FIG. 8 described above and the flow of this example is that the transfer processing in step S317 is moved between step S307 and step S309. In short, it can be regarded that the encoding / re-encoding phase and the transfer phase are switched (the exception is the discarded processing of the encoded data in step S307).
[0083]
In the initial setting of the encoding parameter in step S301, the quantization parameter Q1 is set in the first encoding unit 202, and the quantization parameter Q2 is set in the second encoding unit 205. However, the quantization step represented by the quantization parameter Q2 is larger than Q1.
[0084]
In the encoding phase, steps S801, S303, and S305 are repeatedly executed. Steps S801 and S305 are the same processing as in the case of one encoding unit, but only the encoding processing in step S303 is different as shown in FIG.
[0085]
In order to increase the compression rate of the encoded data stored in the first memory 204 in a stepwise manner, the encoded data stored first stores data encoded with the quantization parameter Q1 having the lowest compression rate. The encoded data stored in the second memory stores data encoded with the quantization parameter Q2.
[0086]
When the amount of data stored in the first memory 204 exceeds the set upper limit value (step S305), the encoded data held in the first memory 204 is immediately discarded (step S307). The encoded data having a high compression rate held in the second memory 207 is transferred to the first memory 204 (step S317, see FIG. 14). As a result, without waiting for the end of the first re-encoding process described in the first example, the appropriate second candidate encoded data that does not exceed the upper limit value is quickly stored in the first memory 207. Can be stored. This is the greatest advantage of applying FIG. 2 with two encoders over FIG.
[0087]
In this second example, since it is a wasteful idea to have encoded data having the same compression rate in the two memories 204 and 207, the second memory 207 has the encoding stored in the first memory 204. The encoded data having a higher compression rate than the data is stored. Accordingly, the subsequent processing is also performed based on this concept, and after the processing (transfer phase) for transferring the encoded data in the second memory 207 to the first memory 204 is completed, the second processing is performed. The encoded data in the memory 207 is re-encoded so as to hold encoded data with a higher one-stage compression rate.
[0088]
Specifically, first, as shown in FIG. 15, in the encoding / re-encoding phase subsequent to the transfer phase, each quantization applied to the two encoding units 202 and 205 before the re-encoding. The parameters Q1 and Q2 are changed to Q2 and Q3, respectively (step S309). If the input of one page of image data is not completed (step S803), the subsequent image data is set by a new quantization step. The input data is encoded by the two encoded units (step S311) and stored in the corresponding memories 204 and 207. The encoded data (transferred to the first memory 204) stored in the second memory in parallel with the encoding process is compressed one step higher than the encoded data in the first memory. In order to change to rate encoded data, the re-encoding unit 211 performs a re-encoding process (S313) so that data encoded using the quantization parameter Q3 is obtained, and the re-encoded data is 2 is stored again in the second memory 207.
[0089]
In the second example, as in the first example, the re-encoding process is the result of dividing these values by 2 ⁿ for each quantized value after the encoded data is once Huffman-decoded. This is realized by performing a Huffman coding again after performing a bit shift process that produces a similar result. This method is capable of high-speed re-encoding processing in that the quantization step is changed only by bit shift and the inverse orthogonal transformation or re-orthogonal transformation processing is not performed.
[0090]
Further, when there are two encoding units as in the second example, as shown in FIG. 15, a situation in which encoded data and re-encoded data are mixedly stored in the second memory 207. Will occur. Therefore, as described above, it is necessary for the second memory 207 to manage the encoded data as a file or a packet by dividing the encoded data into a certain unit. For this purpose, for example, a configuration similar to that of the modification of the first example may be provided.
[0091]
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) again. In the encoding phase after the encoding / re-encoding phase, as shown in FIG. 16, the encoded data held in the two memories 204 and 207 not only have different compression ratios but also a mixture of encoded data. The way (address) is also quite different. Accordingly, when the data amount of the first memory 204 again exceeds the set value, the encoded data held in the second memory 207 (the code of the horizontal stripe region of (6) + (8)) Need to be transferred to the first memory 204. Considering these, it is necessary to manage the encoded data as a file or a packet not only in the second memory 207 but also in the first memory 204. Therefore, the first memory 204 also requires a management mechanism using the above-described management table.
[0092]
The state of the encoding phase shown in FIG. 16 is the encoding phase in the initial state (FIG. 13) except that the method of mixing the quantization parameter and the encoded data is different before and after the re-encoding process. Is the same. Therefore, by repeating the encoding phase, the transfer phase, and the encoding / re-encoding phase, the encoded data that is finally compressed to be equal to or less than the set upper limit value of the image data for one page is surely stored in the first memory. 204 can be stored.
[0093]
Since the arrangement order of the transfer phase and the encoding / re-encoding phase is opposite to that of the first example, the input end detection of one page of image data performed after the transfer process in FIG. S805) is almost the same timing as the input end detection of image data for one page (step S803) performed in the encoding / recoding phase. The two detection processes are functionally the same as step S805 and the timing is the same as step S803. Therefore, these two steps detect the end of input of image data for a new page. Are integrated as a step to be performed and described as step S1201.
[0094]
In the first and second examples described above, the first memory and the second memory have been described as physically separate memories. This is because it is advantageous that the accesses to the two memories are independent. 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 secured on one physical memory, 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 with a single memory by re-reading the above description by rephrasing the area.
[0095]
Further, when each of the above examples is realized with one memory, some of the data transfer processes described in the transfer phase are unnecessary. The details can be easily imagined each time, so the explanation will be omitted. However, when the two areas are used strictly separated, data transfer processing is necessary as in the case of physically having two memories. If the same data is shared between the two areas, not only the data transfer process becomes unnecessary, but also the storage capacity can be reduced.
[0096]
For example, when the encoded data held in the second memory area is transferred to the first memory area, two pieces of information of the head address and the data size in which the encoded data is stored are stored in the second memory. The same effect as that obtained by transferring the encoded data can be obtained only by transferring the data from the control unit to the first memory control unit.
[0097]
When the encoded data is stored in a file format or a 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. Nevertheless, it is more efficient than transferring encoded data.
[0098]
<First Embodiment>
In the above first and second examples, if the re-encoding capability of the re-encoding unit 109 or 211 is low, the code amount by the first encoding unit 202 is completed before the re-encoding is completed. May reach the target value again. In such a situation, the encoding process cannot be continued, and the original image must be read again.
[0099]
The first embodiment of the present invention provides a control method for solving the above problem in the configuration of FIG.
[0100]
In the first embodiment, the first and second counters 107 and 110 not only measure the amount of code data generated, but also count the number of symbols of code data. The reason for measuring the number of symbols is to obtain the time required for the re-encoding process by the re-encoding unit 109 with high accuracy. That is, since re-encoding in the re-encoding unit 109 requires a certain time (cycle) per symbol, once the number of symbols is determined, the time required for the entire re-encoding can be calculated easily and accurately. Because. For example, when it takes one cycle per symbol, the time required for re-encoding the code data of 300 symbols can be calculated as 300/1 symbol / cycle = 300 cycles, and time information with high calculation accuracy can be obtained. However, if the accuracy is not so required, the relationship between the number of symbols and the amount of codes is approximately proportional, so that the time required for the re-encoding process may be calculated.
[0101]
FIG. 17A shows the relationship between the amount of image data input on the horizontal axis and the amount of code on the vertical axis.
[0102]
In FIG. 9A, input of image data from the input unit 101 is started at time t0, the encoding unit 102 starts encoding at the initial quantization step Q1, and is counted by the first counter 107 at time t1. This shows a case where the amount of encoded data reaches the upper limit value. At time t1, the encoding unit 102 is set to discard the data stored in the first memory 104 and to encode image data input thereafter thereafter in the quantization step Q2. At this time, the counter 107 is cleared to zero. As a result, the encoding unit 102 continues the encoding in the newly set (updated) quantization step Q2 for the image data input after time t2. When the code data encoded in the quantization step Q1 is re-encoded in the quantization step Q2, it is not necessary to decode from the code data to the image data. What is necessary is just to re-encode using encoding step Q2. If there is a relationship of quantization step Q2 = Q1 × 2, the DCT transform coefficient may be simply shifted down by 1 bit.
[0103]
In addition, since the data compression-encoded in the quantization step Q1 before time t1 remains in the second memory 106, the re-encoding unit 109 performs a decoding process once and re-encodes in the quantization step Q2 this time. It will become. Accordingly, the amount of encoded data that must be re-encoded by the re-encoding unit 109 at time t1 is substantially equal to the set upper limit value, and gradually decreases as the re-encoding is performed. Therefore, the re-encoding process is performed until the data to be re-encoded becomes zero. In the figure, the re-encoding process by the re-encoding unit 109 is completed at time t2. When re-encoding is completed, the amount of code data and the number of symbols after re-encoding are counted by the second counter 110, and these values are added to the first counter 107. Then, it is determined that the upper limit value has been reached again at the final time t3, and the above processing is repeated.
[0104]
When following the above sequence, no particular problem occurs. The reason is that time t2 ≦ t3. In other words, the re-encoding process of the re-encoding unit 109 is completed before the amount of data stored in the first memory 103 reaches the upper limit again.
[0105]
On the other hand, it will be understood that when time t2> t3, normal encoding processing can no longer be realized. FIG. 5B shows a situation where t2> t3.
[0106]
In order to avoid such a situation, the re-encoding unit 109 starts re-encoding at the time t1 ′ that is earlier than the time t1 when the amount of encoded data reaches the upper limit first. The time for completing the process is to be before time t3.
[0107]
Since the time required for re-encoding is determined by the number of symbols as described above, when a certain time Ta is set, the number of symbols held in the first counter 107 at that time Ta is set. By calculating the time Tb obtained by multiplying the number of cycles per symbol number, the re-encoding completion time t2 = Ta + Tb is obtained.
[0108]
On the other hand, the ratio of the code amount when the same image data is encoded in the quantization step Q2 and the quantization step Q1 is experimentally obtained for several sample images, and the average value α12 is stored in the table. Keep it. This is the same for the other quantization steps Q3, Q4..., And is stored as the respective code amount ratios α13, α14. In addition, you may make it memorize | store as an arithmetic expression instead of a table.
[0109]
Accordingly, when the code amount at the quantization step Q1 at time Ta is V1 (actual value), the predicted code amount V2a at the quantization step Q2 at the same time can be calculated by V2a = V1 × α12. Therefore, when the coordinate is {time, code amount}, the predicted time t3 when the time at which the extension line connecting {t0, 0} and {ta, V2a} intersects the upper limit value reaches the second upper limit value is It can be seen that it can be calculated.
[0110]
Therefore, in the first embodiment, as shown in FIG. 17B, during the encoding in the quantization step Q1, the time t3 when the second target value is reached is predicted and calculated. At that time, the time t2 when the re-encoding is completed is predicted from the number of symbols,
t2> t3−Δt (Δt is a positive value, and is a predetermined value obtained empirically in advance)
When the above condition is satisfied, even if the upper limit value is not reached, the same processing as when the upper limit value is reached is started.
[0111]
The above example is an example in which the encoding unit 102 performs the encoding in the quantization step Q1 and the next quantization step to be used is Q2. However, the present invention is not limited to the above example. It is clear that the present invention can be applied during encoding with Qn (the next quantization step is Qn + 1).
[0112]
In order to realize such processing, the processing shown in FIG. 18 or FIG. 19 may be performed instead of the processing shown in FIG. 3 described above (the processing shown in FIGS. The encoding sequence control unit 108 performs this).
[0113]
3 and 18 and FIG. 8 and FIG. 19 is that step S318 is added.
[0114]
That is, even if it is determined in step S305 that the code amount has not reached the upper limit value, the process proceeds to step S315, where the predicted time t3 when the encoding is performed in the next quantization step reaches the upper limit value. And the predicted time t2 when the re-encoding with the number of symbols M at that time is completed,
t2> t3-Δt (1)
It is determined whether or not the relationship is established. If this relationship is established, the process proceeds to step S307 to perform the same process as when the code amount reaches the upper limit value. The other processes are the same as those in the first example described above, and need not be described.
[0115]
According to the above description, the re-encoding process can be completed before the generated encoded data amount reaches the upper limit again, and the image data encoding process proceeds smoothly.
[0116]
By the way, in the situation shown in FIG. 17B, the time at which the input of the image data for one page ends may be before t1. In this case, even if the encoding is continued in the quantization step Q1, the encoding of one page is completed before the upper limit value is reached, so it is not necessary to start the re-encoding process. Further, if re-encoding is performed, it should be originally encoded in the quantization step Q1, but re-encoding is performed in a larger quantization step Q2. This means that unnecessary image quality deterioration processing is caused, and it is desirable to avoid such a situation.
[0117]
Therefore, the calculation is performed in consideration of the expression (1), which is the above condition indicating whether it is the timing to start re-encoding in step S318 in FIG. 18 and FIG. It will be necessary.
[0118]
The encoding unit 102 in the embodiment performs JPEG encoding on a block basis of 8 × 8 pixels. In other words, every time encoding of one block is completed, the next block is input and encoding is performed. Here, an average time for encoding pixel data of one block is Tb. If the total number of blocks in one page is M (uniquely determined by the input image size), the current encoding block is Nth, and the current time is Tc, the prediction of the end of encoding for one page is completed. Time Te is
Te = Tc + (MN) × Tb
Can be calculated as In order to calculate this time Te, the first counter 107 not only counts the amount of encoded data and the number of symbols, but also counts the encoded data output from the encoding unit 102 in units of blocks. become. However, it goes without saying that the number of blocks being counted is reset at the start of encoding of one page, and is not reset (zero cleared) even if the code amount reaches the upper limit.
[0119]
On the other hand, when the encoded data size counted by the first counter 208 at the current time Tc is Vc, the past code amount ΔV per block can be calculated as Vc / N. Assuming that the upper limit value is Vmax, the predicted time T1 when the encoded data amount counted by the first counter 208 reaches the upper limit value Vmax when the encoding process in the encoding unit 102 is continued is as follows:
T1 = Tc + {(Vmax−Vc) / ΔV} × Tb
Can be calculated as Therefore,
Te ≦ T1
In this case, it is not necessary to start the re-encoding process. However, since it is necessary to ensure safety, if the tolerance is ε (> 0),
Te ≦ T1-ε
If the condition is satisfied, re-encoding is not performed.
[0120]
In short, in step S318 in FIG. 18 and FIG. 19, the process proceeds to step S307 to start re-encoding.
Te> T1-ε (3)
t2> t3-Δt (4)
The two conditions (3) and (4) are satisfied. If at least one of these two conditions is not satisfied, the encoding process is continued with the currently set quantization step. Since Te and T1 both include a Tc component, Tc may be excluded from the calculation target. In this case, Te indicates the time from the present until the encoding of one page is completed, and T1 indicates the time from the present until the upper limit is reached.
[0121]
As described above, image quality deterioration is minimized, and encoding is performed within the target encoded data amount with a single input of image data without interruption of a series of encoding processes. It becomes possible.
[0122]
Although it is not necessary to explain, the time Te at which the encoding of one page of image data is completed is the time at which the reading of the image data of one page is completed when the image is read by an image scanner or the like. Is substantially the same.
[0123]
In the above example, the time at which the upper limit value is first reached is compared with the time at which the encoding of one page of image data is completed, but the upper limit value is reached after the second time after re-encoding. It is clear that the same is true for the time and the time when the encoding of one page of image data is completed, and there is no correction to FIGS.
[0124]
<Second Embodiment>
The first embodiment is based on the configuration of FIG. 1, but an example based on FIG. 2 will be described below as a second embodiment.
[0125]
The difference between FIG. 1 and FIG. 2 is that the two encoding units perform compression encoding in parallel as described above.
[0126]
In the first embodiment, when compression coding is performed in the quantization step Qn, it is assumed that the code amount in the quantization step Qn + 1 is estimated and compression coding is performed in the quantization step Qn + 1. The time t3 when reaching the upper limit value of was predicted.
[0127]
On the other hand, in the second embodiment, the first encoding unit 202 performs compression encoding at the quantization step Qn, and the second encoding unit 205 performs compression encoding at the quantization step Qn + 1. That is, the time t3 at which the upper limit value in the quantization step Qn + 1 is reached can be calculated based on the actual code data amount, so that the accuracy can be made higher than in the first embodiment. In other words, Δt in the first embodiment can be further reduced, and the timing for starting re-encoding can be delayed.
[0128]
First, when applied to FIG. 2, the first counter 208 only needs to count the amount of data encoded by the encoding unit 202, and does not need to count the number of symbols. Instead, the second counter 210 and the third counter 212 count the amount of encoded data and the number of symbols.
[0129]
Hereinafter, an outline of the operation in the second embodiment will be described.
[0130]
The first encoding unit 202 performs compression encoding processing based on the quantization step Q1 in the initial state, and the generated encoded data is stored in the first memory 204. The second encoding unit 205 performs compression encoding at a quantization step Q2 that is one step larger than that, and the result is stored in the second memory 207. The first counter 208 cumulatively counts the amount of code data output from the first encoding unit 202, and the second counter 210 accumulates the amount of encoded data output from the second encoding unit 205. Count.
[0131]
If the code amount counted by the first counter 208 is within the set value when the input of the image of one page is completed, the encoded data stored in the first memory 204 is used as the final compressed encoded data. Output to the outside.
[0132]
On the other hand, the case where the code amount output from the first encoding unit 202 reaches the set value during image input for one page will be described with reference to FIGS. .
[0133]
In FIG. 20A, it is now assumed that the code data amount counted by the first counter 208 has reached the set upper limit value at time t1. At this time, the data in the first memory 204 is discarded, the data in the second memory 207 is transferred to the first memory 204, and the quantization step used by the first encoding unit 202 is Updating is performed at the quantization step Q2 used by the second encoding unit 205 at the time. As a result, a configuration equivalent to one page of the image being compressed from the beginning in the quantization step Q2 is obtained. Further, the quantization step Q3 is set for the second encoding unit 205 so that the compression rate is higher, and the image data input after the time t1 is compressed and encoded at the quantization step Q3. . However, since the encoded data stored in the second memory 207 at time t1 is encoded data based on the quantization step Q2, it is necessary to re-encode it in the quantization step Q3. This re-encoding is performed by the re-encoding unit 211.
[0134]
The time t2 at which the re-encoding at the quantization step Q3 is completed is before the time t3 at which the code amount by the first encoding unit 202 that has started the encoding at the quantization step Q2 reaches the upper limit again. It needs to be.
[0135]
That is, it is necessary to start the re-encoding in the re-encoding unit 211 at a timing before the time t1 ″ in FIG.
[0136]
In the first embodiment, it is necessary to start re-encoding just before the time t1 ′ of FIG. 20, but by using the configuration of FIG. 2, a time margin is generated only by the time t1 ″ −t1 ′. .
[0137]
Further, as can be seen from FIG. 5A, the re-encoding target of the re-encoding unit 211 may be performed on the encoded data in the second memory 207, and the first encoding unit 202 It is not directly related to the code amount. Therefore, although the second counter 210 and the third counter 212 need to count the amount of code data and the number of symbols, the first counter 208 only needs to count the amount of code data.
[0138]
In the case of FIG. 9A, since the quantization steps set in the first encoding unit 202 and the second encoding unit 205 are updated at the timing t1, in practice, at the time t1. The re-encoding process of the re-encoding unit 211 is started. The above is an example when the upper limit value is reached first, but for the second and subsequent times, only the quantization steps set in the encoding units 202 and 210 and the re-encoding unit 211 are different, and the processing contents are the same. It is.
[0139]
FIG. 20B shows the code amount in the quantization step Q2 even if re-encoding by the re-encoding unit 211 is started at time t1 when the amount of code data counted by the first counter 208 reaches the upper limit value. This shows a state in which the re-encoding process cannot be completed within the time t3 when it reaches the upper limit again. That is, the processing of the re-encoding unit 211 needs to be started before the time t1 ″ in FIG.
[0140]
In this determination, the time t2 required for the re-encoding process of the re-encoding unit 211 based on the number of symbols held in the second counter 210 is calculated, and the upper limit value is set again based on the code amount at that time. A predicted time t3
t2> t3-Δt
If the first counter 208 does not reach the upper limit value, the first counter 208 may be processed as having reached the upper limit value.
[0141]
Note that, according to FIG. 20B, the time at which the re-encoding needs to be started is t1 ″, but it can also be seen that there is a time margin than time t1 ′ in the first embodiment.
[0142]
As described above, in order to realize the above processing, for example, the processing shown in FIG. 21 may be performed instead of the processing in FIG. The difference from FIG. 12 is that step S318 is added.
[0143]
That is, even if it is determined in step S305 that the code amount has not reached the upper limit value, the process proceeds to step S315, and the quantization step in the next stage is performed based on the code amount and the number of symbols held in the second counter 210. Between the predicted time t3 when reaching the upper limit when encoding is performed and the predicted time t2 when the re-encoding by the number of symbols at that time is completed,
t2> t3-Δt
It is determined whether or not the relationship is established. If this relationship is established, the process proceeds to step S307 to perform the same process as when the code amount reaches the upper limit value. The other processes are the same as those in the first example described above, and need not be described.
[0144]
When realizing the functions of the second embodiment, the encoding sequence unit 209 also refers to the information held in the second counter 210 (encoded data amount and number of symbols in the embodiment). Therefore, it becomes the structure shown in FIG. 22 instead of FIG. The difference between FIG. 22 and FIG. 2 is only that the coding sequence control unit 209 can directly refer to the data of the second counter 210 as described above, and need not be described in detail. Will.
[0145]
According to the above description, the same operational effects as those of the first embodiment can be achieved. In the case of the second embodiment, since two encoding units perform encoding processing in parallel, a time margin is generated in the re-encoding processing by using the configuration. Therefore, it is convenient when the process corresponding to FIG. 2 is realized by a computer program. This is because, for example, when image data is input and compressed and encoded by a personal computer or the like, an unexpected process may occur in another task or the like, and therefore, a process with sufficient time is desirable. The time required for the re-encoding process may be the amount of code data, but the time can be calculated with high accuracy by using the number of symbols.
[0146]
However, in the second embodiment as well, as in the first embodiment described above, it is determined whether re-encoding should be performed in consideration of the encoding end time of one page of image data. Is desirable.
[0147]
That is, in the situation shown in FIG. 20B, that is, when the encoding end time Te of one page is before the time t1, it is determined that re-encoding is unnecessary. When conforming to the second embodiment, the two encoding units 202 and 205 are different from the first embodiment in that they are encoded in parallel, but the principle is the same.
[0148]
That is, the average time for encoding the pixel data of one block of the encoding unit 202 is Tb. If the total number of blocks in one page is M (uniquely determined by the input image size), the current encoding block is Nth, and the current time is Tc, the prediction of the end of encoding for one page is completed. Time Te is
Te = Tc + (MN) × Tb
Calculate as
[0149]
On the other hand, when the encoded data size counted by the first counter 208 at the current time Tc is Vc, the past code amount ΔV per block can be calculated as Vc / N. Assuming that the upper limit value is Vmax, the predicted time T1 when the encoded data amount counted by the first counter 208 reaches the upper limit value Vmax when the encoding process in the encoding unit 102 is continued is as follows:
T1 = Tc + {(Vmax−Vc) / ΔV} × Tb
Can be calculated as Therefore,
Te ≦ T1
In this case, it is not necessary to start the re-encoding process. However, since it is necessary to ensure safety, if the tolerance is ε (> 0),
Te ≦ T1-ε
If the condition is satisfied, re-encoding is not performed.
[0150]
Therefore, in step S318 in FIG. 21, the process proceeds to step S307 to start re-encoding, as in <Improvement of first embodiment>.
Te> T1-ε (3)
t2> t3-Δt (4)
The two conditions (3) and (4) are satisfied. If at least one of the two conditions is not satisfied, the encoding process may be continued with the currently set quantization step.
[0151]
As described above, as in the first embodiment, image quality degradation is minimized, and the target code can be input by inputting image data once without interrupting a series of encoding processes. It becomes possible to encode within the encoded data amount.
[0152]
In the first and second embodiments, a monochrome image is input. However, in the case of a color image, finer adjustment is possible. When a color image is encoded, luminance data (Y) and two color difference data (C) are obtained by known color conversion, so that the following relationship can be obtained. Become. In the following, Y means luminance, C means color difference, QYi (i = 1, 2, 3...) Is a quantization step for luminance components, and QCi (i = 1, 2, 3...) Is color difference. The quantization step for the component is shown, and the quantization step increases as i increases.
Previous quantization step Quantization step candidate
(QY1, QC1) → (QY1, QC2), (QY2, QC2), (QY2, QC3), (QY3, QC3) ...
(QY1, QC2) → (QY2, QC2), (QY2, QC3), (QY3, QC3), (QY3, QC4) ...
(QY2, QC2) → (QY2, QC3), (QY3, QC3), (QY3, QC4), (QY4, QC4) ...
:
Further, in the embodiment, an example in which the quantization step is increased in order to improve the compression rate has been described. However, the present invention can be applied to any coding in which the compression rate is variable by changing parameters. Obviously, it is not necessarily limited to the quantization step. For example, according to JPEG2000, compression can be performed in units of layers when entropy encoding is performed after quantization. The higher the layer, the more dominant the image quality, so the compression rate can be changed by cutting off i layers from the lowest layer.
[0153]
Further, as described above, the present invention can be realized by an application program that runs on a general-purpose device, and therefore the present invention includes a computer program. In particular, when realized by a computer program, the processing capability of the computer will vary, so that “ε” and “Δt” in the above formulas (3) and (4) can be freely changed by the user. desired.
[0154]
Further, since the computer program is normally performed by setting or copying or installing a storage medium such as a floppy (registered trademark) disk or CDROM in the apparatus, such a storage medium is naturally included in the scope of the present invention.
[0155]
The present invention can also be applied to a combination of a computer program and appropriate hardware (such as an encoding circuit).
[0156]
【The invention's effect】
As described above, according to the present invention, with a relatively simple configuration, it is ensured that encoding is performed below the target code amount while image input is continued, and image quality degradation is possible. As long as it can be suppressed.
[Brief description of the drawings]
FIG. 1 is a block diagram of an image processing apparatus according to a first example which is a premise of the present invention.
FIG. 2 is a block configuration diagram of an image processing apparatus in a second example.
FIG. 3 is a flowchart showing a simplified process in the configuration of FIG. 1;
FIG. 4 is a diagram illustrating a data flow and memory contents in an encoding phase in an initial state.
FIG. 5 is a diagram showing a data flow and memory contents in an encoding / re-encoding phase.
FIG. 6 is a diagram illustrating a data flow and memory contents in a transfer phase.
FIG. 7 is a diagram illustrating a data flow and memory contents in an encoding phase after a transfer phase.
FIG. 8 is a flowchart showing details of processing in the configuration of FIG. 1;
9 is a diagram showing a data flow and memory contents in an encoding / re-encoding phase in the modification of the configuration of FIG. 1; FIG.
10 is a diagram showing a data flow and memory contents in a transfer phase in the modification of FIG. 9;
11 is a diagram showing a data flow and memory contents in an encoding phase after a transfer phase in the modification of FIG.
12 is a flowchart showing a processing procedure in the configuration of FIG. 2;
13 is a diagram showing a data flow and memory contents in an encoding phase in an initial state in the configuration of FIG.
14 is a diagram showing a data flow and memory contents in a transfer phase in the configuration shown in FIG.
15 is a diagram illustrating a data flow and memory contents in an encoding / re-encoding phase in the configuration of FIG.
16 is a diagram illustrating a data flow and memory contents in an encoding phase after an encoding / re-encoding phase in the configuration of FIG. 2;
FIG. 17 is a diagram for explaining the principle of setting the re-encoding process start timing in the first embodiment.
FIG. 18 is a flowchart showing a processing procedure in the first embodiment.
FIG. 19 is a flowchart showing a processing procedure in the first embodiment.
FIG. 20 is a diagram for explaining the principle of setting the re-encoding processing start timing in the second embodiment.
FIG. 21 is a flowchart showing a processing procedure in the second embodiment.
FIG. 22 is a block configuration diagram of an image processing apparatus according to a second embodiment.

Claims (10)

An image processing apparatus that compresses and encodes one page of image data,
First encoding means capable of changing the quantization step;
A second encoding unit that can change a quantization step and re-encodes the code data compressed by the first encoding unit;
First determination means for monitoring the amount of code data generated by the first encoding means and determining whether the amount of code data has reached a predetermined amount;
A prediction time T0 at which the encoding of one page of image data is completed, and a prediction time T1 at which the amount of code data generated by the first encoding means reaches the predetermined amount;
Condition 1: T0> T1-Δt1
(Where Δt1 is a predetermined positive value)
A second judging means for judging whether or not
Based on the amount of code data, the first encoding means is already generated according to the time T2 when the predetermined amount is reached when it is assumed that the first encoding means has performed compression encoding in the next quantization step, and the current quantization step. A re-encoding completion time T3 when it is assumed that the encoded data is re-encoded by the second encoding unit that has set the quantization step of the next stage;
Condition 2: T3> T2-Δt2
(Where Δt2 is a predetermined positive value)
A third determination means for determining whether or not
When it is determined that the predetermined amount has been reached by the first determination means, or when both the conditions 1 and 2 are satisfied by the second and third determination means, the first and second codes Setting means for setting the quantization step of the next stage in the conversion means;
When the quantization step is changed by the setting means, the encoding by the first encoding means is continued for the image data input after the quantization step change, and the already encoded code data before the quantization change And an image processing apparatus comprising control means for re-encoding by the second encoding means. The image processing apparatus according to claim 1, wherein the number of symbols included in the amount of code data based on which the third determination unit determines. The second compression encoding means re-encodes after reconstructing the data format of the frequency component without decoding the encoded data to be re-encoded into image data. 2. The image processing apparatus according to 2. A method for controlling an image processing apparatus that compresses and encodes one page of image data,
A first encoding step in which the quantization step can be changed;
A second encoding step in which the quantization step can be changed, and the code data compressed in the first encoding step is re-encoded;
A first determination step of monitoring the amount of code data generated by the first encoding step and determining whether the amount of code data has reached a predetermined amount;
A prediction time T0 at which encoding of one page of image data is completed and a prediction time T1 at which the amount of code data generated in the first encoding step reaches the predetermined amount;
Condition 1: T0> T1-Δt1
(Where Δt1 is a predetermined positive value)
A second determination step of determining whether or not
Based on the code data amount, the first encoding step is already generated according to the current quantization step and the time T2 when the predetermined amount is reached assuming that the first encoding step is compression encoded in the next quantization step. Re-encoding completion time T3 when it is assumed that the encoded data is re-encoded in the second encoding step in which the quantization step of the next stage is set,
Condition 2: T3> T2-Δt2
(Where Δt2 is a predetermined positive value)
A third determination step for determining whether or not
When it is determined that the predetermined amount has been reached in the first determination step, or when both of the conditions 1 and 2 in the second and third determination steps are satisfied, the first and second codes A setting process for setting a quantization step of the next stage in the conversion process;
When the quantization step is changed by the setting step, the encoding by the first encoding step is continued for the image data input after the quantization step change, and the already encoded code data before the quantization change And a control step of re-encoding by the second encoding step. A computer program that functions as an image processing apparatus that compresses and encodes one page of image data,
First encoding means capable of changing the quantization step;
A second encoding unit that can change a quantization step and re-encodes the code data compressed by the first encoding unit;
First determination means for monitoring the amount of code data generated by the first encoding means and determining whether the amount of code data has reached a predetermined amount;
A prediction time T0 at which the encoding of one page of image data is completed, and a prediction time T1 at which the amount of code data generated by the first encoding means reaches the predetermined amount;
Condition 1: T0> T1-Δt1
(Where Δt1 is a predetermined positive value)
A second judging means for judging whether or not
Based on the amount of code data, the first encoding means is already generated according to the time T2 when the predetermined amount is reached when it is assumed that the first encoding means has performed compression encoding in the next quantization step, and the current quantization step. A re-encoding completion time T3 when it is assumed that the encoded data is re-encoded by the second encoding unit that has set the quantization step of the next stage;
Condition 2: T3> T2-Δt2
(Where Δt2 is a predetermined positive value)
A third determination means for determining whether or not
When it is determined that the predetermined amount has been reached by the first determination means, or when both the conditions 1 and 2 are satisfied by the second and third determination means, the first and second codes Setting means for setting the quantization step of the next stage in the conversion means;
When the quantization step is changed by the setting means, the encoding by the first encoding means is continued for the image data input after the quantization step change, and the already encoded code data before the quantization change Functions as control means for re-encoding by the second encoding means. A computer-readable storage medium storing the computer program according to claim 5. An image processing apparatus that compresses and encodes one page of image data,
First encoding means capable of changing the quantization step;
A second encoding unit that can change a quantization step and encodes at least a quantization step larger than the quantization step of the first encoding unit;
A third encoding unit that can change a quantization step and re-encodes the code data compressed by the second encoding unit;
Monitoring means for monitoring the amount of code data generated by the first and second encoding means for the image data being input;
First determination means for determining whether or not the amount of code data by the first encoding means monitored by the monitoring means has reached a predetermined amount;
A prediction time T0 at which the encoding of one page of image data is completed, and a prediction time T1 at which the amount of code data generated by the first encoding means reaches the predetermined amount;
Condition 1: T0> T1-Δt1
(Where Δt1 is a predetermined positive value)
A second judging means for judging whether or not
Based on the amount of code data by the second encoding means monitored by the monitoring means, the predicted time to continue the encoding by the second encoding means and reach the predetermined amount is T2, the second Re-encoding when it is assumed that the code data already generated according to the current quantization step of the encoding means is re-encoded by the third encoding means in which the quantization step of the next stage is set. Calculate completion time T3,
Condition 2: T3> T2-Δt2
(Where Δt2 is a predetermined positive value)
A third determination means for determining whether or not
When it is determined that the predetermined amount has been reached in the first determination step, or when it is determined that both the conditions 1 and 2 in the second and third determination steps are satisfied, the first code The quantization step of the encoding means is updated with the quantization step set by the second encoding means, and the quantization step of the second and third encoding means is updated to a higher quantization step. Update step update means;
When updating the quantization step by the quantization step updating means, the previous encoded data of the first encoding means is updated with the previous encoded data previously generated by the second encoding means, An image processing apparatus comprising: control means for re-encoding and updating the previous code data by the second encoding means by the third encoding means. A method for controlling an image processing apparatus that compresses and encodes one page of image data,
A first encoding step in which the quantization step can be changed;
A second encoding step in which the quantization step can be changed, and at least a quantization step larger than the quantization step of the first encoding step is encoded;
A third encoding step that can change the quantization step and re-encodes the code data compressed in the second encoding step;
A monitoring step of monitoring the amount of code data generated in the first and second encoding steps for the image data being input;
A first determination step of determining whether or not the amount of code data by the first encoding step monitored in the monitoring step has reached a predetermined amount;
A prediction time T0 at which encoding of one page of image data is completed and a prediction time T1 at which the amount of code data generated in the first encoding step reaches the predetermined amount;
Condition 1: T0> T1-Δt1
(Where Δt1 is a predetermined positive value)
A second determination step of determining whether or not
Based on the amount of code data in the second encoding step monitored in the monitoring step, the predicted time to continue the encoding in the second encoding step and reach the predetermined amount is T2, the second Re-encoding when it is assumed that the code data already generated according to the current quantization step of the encoding step is re-encoded in the third encoding step in which the quantization step of the next step is set. Calculate completion time T3,
Condition 2: T3> T2-Δt2
(Where Δt2 is a predetermined positive value)
A third determination step for determining whether or not
When it is determined that the predetermined amount has been reached in the first determination step, or when it is determined that both the conditions 1 and 2 in the second and third determination steps are satisfied, the first code The quantization step of the encoding step is updated with the quantization step set in the second encoding step, and the quantization step of the second and third encoding steps is updated to a higher quantization step. Update step update process,
When updating the quantization step in the quantization step updating step, the previous encoded data of the first encoding step is updated with the previous encoded data previously generated by the second encoding step, And a control step of re-encoding and updating the previous encoded data in the second encoding step in the third encoding step. A computer program that functions as an image processing apparatus that compresses and encodes one page of image data,
First encoding means capable of changing the quantization step;
A second encoding unit that can change a quantization step and encodes at least a quantization step larger than the quantization step of the first encoding unit;
A third encoding unit that can change a quantization step and re-encodes the code data compressed by the second encoding unit;
Monitoring means for monitoring the amount of code data generated by the first and second encoding means for the image data being input;
First determination means for determining whether or not the amount of code data by the first encoding means monitored by the monitoring means has reached a predetermined amount;
A prediction time T0 at which the encoding of one page of image data is completed, and a prediction time T1 at which the amount of code data generated by the first encoding means reaches the predetermined amount;
Condition 1: T0> T1-Δt1
(Where Δt1 is a predetermined positive value)
A second judging means for judging whether or not
Based on the amount of code data by the second encoding means monitored by the monitoring means, the predicted time to continue the encoding by the second encoding means and reach the predetermined amount is T2, the second Re-encoding when it is assumed that the code data already generated according to the current quantization step of the encoding means is re-encoded by the third encoding means in which the quantization step of the next stage is set. Calculate completion time T3,
Condition 2: T3> T2-Δt2
(Where Δt2 is a predetermined positive value)
A third determination means for determining whether or not
When it is determined that the predetermined amount has been reached in the first determination step, or when it is determined that both the conditions 1 and 2 in the second and third determination steps are satisfied, the first code The quantization step of the encoding means is updated with the quantization step set by the second encoding means, and the quantization step of the second and third encoding means is updated to a higher quantization step. Update step update means;
When updating the quantization step by the quantization step updating means, the previous encoded data of the first encoding means is updated with the previous encoded data previously generated by the second encoding means, A computer program that functions as a control unit that re-encodes and updates the previous encoded data by the second encoding unit by the third encoding unit. A computer-readable storage medium storing the computer program according to claim 9.

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