JPH0556271A - Reverse quantizing method and image data restoring device - Google Patents

Abstract

PURPOSE:To decrease the wasteful multiplying processing and initializing processing by extracting the effective coefficient from the number of the quantizing coefficients obtained by restoring the coding data, obtaining the effective matrix and performing reverse quantizing. CONSTITUTION:Image data coded by using an orthogonal converting system are decoded by a decoding means 101, and an effective coefficient address to show the position, in which the effective coefficient of the value except zero included in the quantizing coefficient matrix of respective blocks based on the decoding data is occupied at a quantizing coefficient matrix, is counted by an address counting means 111. The quantizing threshold in accordance with the address is multiplied to the effective quantizing coefficient by a quantizing means 112, stored in a conversion coefficient storing means 113, and an original image is restored by a reverse orthogonal converting means 102. By the system in which the effective quantizing coefficient only is the processing object, the wasteful multiplying processing and initializing processing are decreased and the high speed restoring processing can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dequantization method for dequantizing a quantized coefficient obtained by decoding code data in an image data decompression device for decompressing an original image from code data, and the dequantization method. The present invention relates to an image data restoration device to which the method is applied.

As a coding method for compressing the data amount of a multi-valued image such as a halftone image or a color image without deteriorating its characteristics, an adaptive discrete cosine transform coding method utilizing two-dimensional orthogonal transform (Adaptive Discrete Cosine). Transfo
rm, hereinafter referred to as ADCT method) is widely used.

In this ADCT method, a multi-valued image is divided into blocks each having a predetermined number of pixels (for example, 8 × 8 pixels), and the image data is orthogonally transformed for each block to obtain transform coefficients (hereinafter referred to as DCT coefficients). The data amount is compressed by quantizing each element of the matrix using a corresponding visual adaptation threshold value (described later) and then performing variable length coding.

[0004]

2. Description of the Related Art FIG. 10 shows the configuration of an image data compression apparatus to which a conventional ADCT method is applied. In addition, in FIG.
The example of the block obtained by dividing a multi-valued image is shown.

A multi-valued image read by an image reading device or the like is sequentially input to the DCT transform unit 611 for each block described above, and the two-dimensional discrete cosine transform (hereinafter referred to as DCT transform) by the DCT transform unit 611. By the processing, it is converted into a matrix of 8 rows and 8 columns (hereinafter, referred to as DCT coefficient D) including DCT coefficients corresponding to the spatial frequency components. FIG. 12 shows an example of the DCT coefficient D.

Each component of the DCT coefficient D is quantized by the linear quantizer 620 using the corresponding component of the quantization threshold value Q _TH . The above-mentioned quantization threshold Q _TH is
It is obtained from the visual adaptation threshold value corresponding to each spatial frequency and the quantization control parameter SF. This visual adaptation threshold value is determined in advance based on the experimental results regarding the visual sensitivity to each spatial frequency component, and is given as the quantization matrix V _TH (see FIG. 13). Further, the quantization control parameter SF is a coefficient that determines the quantization accuracy of the image, depending on the image quality required for the restored image,
It is set by the operator prior to the encoding process of the image data for one screen.

Here, the value of each component of the above-mentioned quantization matrix V _TH is, as shown in FIG. 13, the absolute value of the component corresponding to a low spatial frequency, depending on the spatial frequency characteristic of human visual sensitivity. On the contrary, the absolute value of the component corresponding to the high spatial frequency is set to a large value. Therefore, the quantization coefficient D _QU obtained by quantizing the DCT coefficient D by the linear quantization unit 620 is a component at the upper left corner of the matrix indicating the DC component (hereinafter referred to as the DC component), as shown in FIG.
In many cases, only a very small number of AC components around the DC component showing low spatial frequency components are effective coefficients having a value other than zero, and most AC components are invalid coefficients having a value of zero. ..

When the quantized coefficient D _QU obtained in this way is scanned using a scanning order called zigza scan shown in FIG. 15, a one-dimensional array in which a series of effective coefficients is followed by invalid coefficients is formed. Is obtained. The one-dimensional array is converted by the encoding unit 631 into a combination of the effective coefficient (index) and the continuous length (run) of the invalid coefficient that is continuous before this index, and each combination is converted based on the code table 632. The image data is compressed by replacing each with a code corresponding to the appearance frequency and performing variable length coding.

The coded data thus obtained is restored to image data by the image data restoration device shown in FIG. Decoding unit 711 of image data restoration device
Contrary to the above-mentioned code table 632, is provided with a decoding table 712 which indicates a combination of a run and an index corresponding to the code, and decodes sequentially input codes to obtain a combination of an index and a run. Input to the inverse quantizer 720.

In the inverse quantizing unit 720, the array restoring unit 721 restores the above-mentioned one-dimensional array from the input index and run, and the respective components of this one-dimensional array are sequentially input to the multiplier 722. It Further, the quantization threshold value holding unit 723 holds the quantization threshold value Q _TH , and the corresponding quantization threshold value is sent to the multiplier 722 in synchronization with the input of the quantization coefficient to the multiplier 722. There is. In this way, the multiplier 723 dequantizes each component of the quantized coefficient D _QU using the corresponding quantization threshold, and D
The CT coefficient D is restored.

Next, the DCT coefficient D is input to the inverse DCT conversion unit 731, and the inverse DCT conversion unit 731 performs the inverse D.
The image data of the corresponding block is restored by performing the CT conversion process.

[0012]

By the way, in the above-mentioned conventional method, the inverse quantization processing is performed by multiplying all the quantization coefficients by the quantization threshold value. However, the multiplication process of the invalid coefficient having a value of zero and the quantization threshold is a useless process in which the multiplication result is known in advance. That is, conventionally, 64 times of multiplication processing is performed for the dequantization processing of the quantized coefficient D _QU of one block, regardless of whether it is useless processing. It took a long time to process.

The present applicant has already filed Japanese Patent Application No. 1-316708 "Image Data Restoration Method" as a technique for speeding up inverse quantization processing by eliminating such wasteful processing. .. FIG. 17 shows a schematic configuration of an inverse quantization processing unit according to this technique.

According to this technique, the address calculation unit 724 obtains the address of the corresponding effective coefficient from the value of the input run, and the quantization threshold holding unit 723 causes the multiplier 722 to obtain the quantization threshold value corresponding to this address. By sending out and multiplying this quantization threshold value and index by the multiplier 722, only effective coefficients are selectively dequantized.
In this case, the multiplier 72 corresponds to the above-mentioned address.
By holding the multiplication result by 2 in the DCT coefficient holding unit 725, the DCT coefficient D of 8 rows and 8 columns is restored.

In this technique, in the inverse quantization processing of each block, the inverse quantization result is written only in the address corresponding to the effective coefficient of the DCT coefficient holding unit 725, so that
Before performing the inverse quantization process for the next block, it is necessary to perform an initialization process for clearing the DCT coefficient obtained by the inverse quantization process for the previous block.

For example, the initialization process may be performed by writing zero as an initial value in each address of the DCT coefficient holding unit 725. However, since the content of the address corresponding to the invalid coefficient of the previous block is zero, writing zero again by the initialization process is a wasteful process.
Therefore, irrespective of whether or not each address corresponds to the effective coefficient, if the writing process is performed on all 64 addresses, the time required for such a wasteful writing process is wasted. The time-saving effect of the inverse quantization process due to the reduction of the multiplication process is lost.

An object of the present invention is to provide a dequantization method and a dequantization device that can reduce useless multiplication processing and wasteful initialization processing.

[0018]

FIG. 1 shows the principle of the inverse quantization method of the present invention. According to a first aspect of the present invention, an original image is orthogonally transformed for each of a plurality of blocks each including a plurality of pixels to obtain a coefficient matrix including transform coefficients, and each component of the coefficient matrix is quantized by a corresponding quantization threshold value. When decompressing the original image from the coded data obtained by coding the quantized coefficient matrix obtained as described above, the coefficient corresponding to each block The effective coefficient having a value other than zero is extracted from the quantization coefficient matrix, multiplied by the quantization threshold value corresponding to each effective coefficient, and the obtained multiplication result is set as the effective coefficient address indicating the position where the effective coefficient occupies in the quantization coefficient matrix. Accordingly, the coefficient matrix is restored by being retained respectively, and the initialization processing is selectively performed on the effective coefficient address before the inverse quantization processing of the quantized coefficient corresponding to the next block. The features.

FIG. 2 shows the configuration of the image data restoration device according to the second and third aspects. According to a second aspect of the present invention, an original image is orthogonally transformed for each of a plurality of blocks each including a plurality of pixels to obtain a coefficient matrix including transform coefficients, and each component of the coefficient matrix is quantized by a corresponding quantization threshold value. The coded data obtained by coding the quantized coefficient matrix obtained as a result is input, the coded data is decoded, and the decoding means 101 for outputting the decoded data representing the quantized coefficient matrix, and the decoding means 101 for each block based on the decoded data. Address calculation means 111 for respectively obtaining an effective coefficient address indicating a position occupied by an effective coefficient having a value other than zero included in the quantized coefficient matrix in the quantized coefficient matrix, and quantization indicated by the effective coefficient and the corresponding effective coefficient address. Inverse quantization means 112 that multiplies a threshold value and outputs as a conversion coefficient, and conversion coefficient storage means 11 that stores the conversion coefficient in correspondence with the effective coefficient address. And,
Address holding means 1 for sequentially holding valid coefficient addresses
14 and an inverse orthogonal transform unit 102 that restores image data by performing an inverse orthogonal transform on a coefficient matrix made up of transform coefficients stored in the transform coefficient storage unit 113, and at the end of the inverse orthogonal transform process by the inverse orthogonal transform unit 102. Accordingly, a writing unit 115 for writing a predetermined initial value is provided at the storage location of the conversion coefficient storage unit 113 indicated by the effective coefficient address held by the address holding unit 114.

According to a third aspect of the present invention, in the image data restoration device according to the second aspect, the transform coefficient storage means 113 is
A plurality of areas having a capacity corresponding to the coefficient matrix for one block are switched to store the coefficient matrix corresponding to consecutive blocks, and the address holding unit 114
The effective coefficient address is held in correspondence with the coefficient matrix stored in each area of the transform coefficient storage means 113, and the writing means 115 corresponds to the coefficient matrix of each area held in the address holding means 114. It is characterized in that the initial value is written according to the effective coefficient address.

FIG. 3 shows the configuration of the image data restoration device according to claims 4 and 5. According to a fourth aspect of the present invention, in the image data restoration device according to the second aspect, the DC block represented by only the DC component is detected based on the number of effective coefficients included in the quantization coefficient matrix corresponding to each block. Then
The present invention is characterized by including a block detection means 121 for providing the detection result to the inverse orthogonal transformation processing by the inverse orthogonal transformation means 102.

According to a fifth aspect of the present invention, in the image data restoration device according to the second aspect, an invalid block that does not include an effective coefficient is determined based on the number of effective coefficients included in the quantized coefficient matrix corresponding to each block. The present invention is characterized by including block detection means 131 for detecting and providing the detection result to the inverse orthogonal transformation processing by the inverse orthogonal transformation means 102.

[0023]

According to the present invention, only the effective coefficient is extracted from the quantized coefficient matrix corresponding to each block and multiplied by the quantization threshold value, and the obtained transform coefficient is held according to the effective coefficient address. Therefore, the coefficient matrix is restored, and the initialization processing is selectively performed on the above-mentioned effective coefficient address before performing the inverse quantization processing of the next block. Can be reduced.

According to a second aspect of the present invention, the address calculation means 1 is based on the decoded data obtained by the decoding means 101.
11 calculates the effective coefficient address and stores the multiplication result by the inverse quantization means 112 in the conversion coefficient storage means 113 according to this effective coefficient address, thereby omitting the useless multiplication processing of the invalid coefficient and the quantization threshold value. Thus, the coefficient matrix of each block can be obtained. Further, the effective coefficient addresses obtained by the address calculation means 111 are held in the address holding means 114, and the writing means 115 corresponds to these effective coefficient addresses in accordance with the end of the inverse orthogonal transform processing by the inverse orthogonal transform means 102. Conversion coefficient storage means 113
By writing the initial value to the storage location of, the useless initialization process for the address corresponding to the invalid coefficient can be omitted.

According to a third aspect of the present invention, the transform coefficient storage means 11 is provided.
The process of storing the transform coefficient in any one of the plurality of regions 3 and the inverse orthogonal transform process for the coefficient matrix stored in the other region can be performed in parallel. Further, since the address holding means 114 holds the effective coefficient address corresponding to each area, the writing means 115 causes the writing area 115 to move to another area in parallel with the processing of storing the conversion coefficient in any one of the plurality of areas. The process of writing an initial value to can be performed.

According to a fourth aspect of the invention, the block detecting means 12 is provided.
Since the DC block is detected by 1, the inverse orthogonal transforming means 102 can perform the processing adapted to the DC block according to the detection result by the block detecting means 121.

According to a fifth aspect of the invention, the block detecting means 13 is provided.
Since the invalid block is detected by 1, the inverse orthogonal transforming unit 102 can perform the processing adapted to the invalid block according to the detection result of the block detecting unit 131.

[0028]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 4 shows the configuration of an embodiment of the image data restoration device of claim 2.

In FIG. 4, the decoding section 711 and the decoding table 71 are shown.
2 is equivalent to the decoding means 101, and similarly to the conventional case, the combination of the corresponding index and run is searched from the decoding table 712 according to the input of each code, and the obtained search result is the decoded data. Is sent to the inverse quantization unit 210.

In the dequantizer 210, the above-mentioned decoded data is separated into a run and an index by the demultiplexer 201 and sent to the address calculation means 111 and the dequantization means 112, respectively.

The address calculating means 111 is composed of an integrating circuit 211 and a block detecting section 212,
The integrating circuit 211 is configured to sequentially integrate the value of the run by adding the numerical value "1". A run is input to the block detection unit 212, and a detection signal indicating that the end of the block has been detected is output according to the input of the run " _REOB " indicating the end of the block, and the integration circuit 2
The integrated value of 11 is reset to the initial value "0".

In this way, the scanning order by zigzag scanning is obtained as the integration result corresponding to each index. This scanning order is the 8 × 8 quantized coefficient D _QU.
Indicates the position occupied by the effective coefficient corresponding to each index. Therefore, it suffices to send out this scanning order obtained by the integrating circuit 211 as an effective coefficient address.

In FIG. 4, the inverse quantization means 112 is composed of a multiplier 221 and a quantization threshold holding unit 222, and this quantization threshold holding unit 222 corresponds to the scanning order by zigzag scanning. , A quantization threshold value corresponding to each DCT coefficient is held. Therefore, in response to the input of the address obtained by the address calculation unit 111, the quantization threshold holding unit 222 sends the corresponding quantization threshold to the multiplier 221, and the multiplier 221 determines the index to be input. By performing multiplication with this quantization threshold value, the effective coefficient indicated by the index can be dequantized to obtain the DCT coefficient.

Here, here, the demultiplexer 201
Thus, the run and the index are separated in advance and are input to the address calculating means 111 and the dequantizing means 112, respectively. However, the address calculating means 111 and the dequantizing means 112 respectively execute the run and the dequantized data from the decoded data. It may be configured by including means for extracting the index.

Further, in FIG. 4, the DCT coefficient obtained by the above-mentioned inverse quantizing means 112 is inputted to the buffer 232 via the multiplexer 231. This buffer 232 corresponds to the transform coefficient storage means 113, and this buffer 232 receives the input DC.
By storing the T coefficient corresponding to the above-mentioned effective coefficient address, the DCT coefficient D of 8 rows and 8 columns is restored.

In this way, only effective coefficients are extracted from the quantized coefficients D _QU, only the extracted effective coefficients are selectively dequantized, and 8 rows and 8 lines corresponding to one block of image data are extracted.
The DCT coefficient D of the column can be restored.

Further, in response to the detection signal from the block detection unit 212 described above, the timing control unit 252 causes the DC
The inverse DCT conversion unit 73 indicates that the restoration process of the T coefficient D is completed.
1 may be notified and the start of the inverse DCT conversion process may be instructed.

In response to this start instruction, the inverse DCT converter 7
31 is the DC stored in the buffer 232 as in the conventional case.
By performing the inverse DCT conversion process on the T coefficient, 1
The block of image data is restored.

Next, a method of selectively initializing only the address corresponding to the effective coefficient of the buffer 232 will be described. In FIG. 4, the memory 241 and the counter 242 form an address holding unit 114,
The counter 242 is configured to increment the count value by “1” each time an effective coefficient address is input to the memory 241. In addition, the memory 241 uses the counter 242.
The effective coefficient address described above is held at the address indicated by the count value of.

For example, effective coefficient addresses corresponding to the effective coefficients shown by hatching in FIG. 5 (a) are stored in the addresses of the memory 241 corresponding to the input order as shown in FIG. 5 (b). It

Further, in FIG. 4, the multiplexer 23
1, the zero generator 251, the timing control unit 252, and the read circuit 253 correspond to the writing unit 115,
The timing control unit 252 is configured to instruct the multiplexer 231 to select the output of the zero generator 251 when performing the initialization process of the contents of the buffer 232. The timing control unit 252 causes the multiplexer 231 to generate the zero generator 251 in response to the end signal indicating that the inverse DCT conversion processing for one block by the inverse DCT conversion unit 731 is completed.
It suffices to indicate the selection of the output of.

Further, the timing control section 252 is arranged to instruct the read circuit 253 to read the effective coefficient address in response to the end signal, and the read circuit 253 responds to this instruction. The effective coefficient address is sequentially read from each address of the memory 241 described above,
The write address is sent to the buffer 232.

That is, the effective coefficient addresses held in the address holding means 114 are sequentially designated in the buffer 232 in accordance with the above-mentioned end signal, and the multiplexer 23 is operated.
The output "0" of the zero generator 252 is sequentially written to these addresses as an initial value via 1.

Further, the above-mentioned read circuit 253 is so constructed as to instruct the counter 242 to subtract the count value every time the effective coefficient address is read from the memory 241.
In addition, the counter 242 responds to the count value by "1".
The timing control unit 252 indicates that all effective coefficient addresses have been read when the count value becomes “0”.
It is configured to notify.

Therefore, the timing control section 252 judges that the initialization processing is completed in response to the notification from the counter 242, and instructs the multiplexer 231 to select the output of the inverse quantization means 112. ..

In this manner, the initial value "0" can be written and selectively initialized only in the address of the buffer 232 corresponding to the effective coefficient of the previous block. This makes it possible to reduce the initialization process for the address corresponding to the invalid coefficient of the previous block when selectively quantizing only the effective coefficient.

In this case, for example, the addresses of the buffer 232 corresponding to the nine effective coefficients shown by hatching in FIG. 5A are selectively initialized. As a result, the write processing for the 55 addresses corresponding to the invalid coefficient is reduced, and the initialization processing can be completed by performing the write processing 9 times. The time required for the initialization process can be significantly shortened as compared with the case where the initial value “0” is written and initialized.

As described above, by selectively dequantizing only the effective coefficients included in the quantized coefficient D _QU and selectively initializing only the addresses of these effective coefficients, the conventional inverse quantization processing is performed. By doing so, it is possible to reduce the time spent for useless processing and shorten the time required for the inverse quantization processing of the quantization coefficient D _QU for one block.

When a normal image is encoded by the ADCT method, a large number of quantization coefficients D _QU including a very small number of effective coefficients appear, so that the inverse quantization processing of each block is performed as described above. By reducing the time required, it is possible to significantly reduce the time required for restoration processing of the entire image.

Since the inverse quantization process of each block and the inverse DCT transform process of each block can be performed independently, the inverse quantization process and the inverse DCT transform process may be processed in parallel. Good.

FIG. 6 shows the construction of an embodiment of the dequantization section of the image data restoration device of the third aspect. In FIG. 6, the conversion coefficient storage unit 113 has two buffers 233a and 233.
b and a switching control unit 234, the switching control unit 234 alternately outputs the output of the multiplexer 231 to the two buffers 233a and 233b for each block. Further, in FIG. 6, two memories 241a and 241b and two counters 242a and 24b are provided.
2b forms an address holding unit 114, which corresponds to the two buffers 233a and 233b, respectively.
It is configured to hold the address of the effective coefficient included in the DCT coefficient D stored in each of the buffers 233a and 233b. Hereinafter, the buffers 233a and 233b will be simply referred to as the buffer 233 when collectively referred to.

Further, the image data restoration device is constructed by including a pipeline control section 235, and by this pipeline control section 235, the inverse quantization section 210 and the inverse DCT are performed.
It is configured to control the operation with the conversion unit 731.

In this case, the pipeline control unit 235 instructs the switching control unit 234 to switch the buffer 233 in response to the input of the detection signal from the block detection unit 212 of the address calculation unit 111 of the inverse quantization unit 210. At the same time, the decoding unit 711 may be instructed to start the decoding processing of the next block. As a result, the DCT coefficient D corresponding to the previous block can be held in one of the buffers 233 while the inverse quantization process of the next block can be performed. Further, at this time, the pipeline control unit 235 instructs the inverse DCT conversion unit 731 to start the inverse DCT conversion process by designating the above-mentioned buffer 233.
In response to the end notification from 31, the timing control unit 252
However, the start of the initialization process of the buffer 233 may be instructed. In addition, a notification that all valid coefficient addresses have been read from the counter 242 is input to the pipeline control unit 235, and the pipeline control unit 235 confirms the completion of the initialization processing by the writing unit 115 described above. It may be configured to.

Thus, the process of selectively dequantizing the effective coefficient, the process of selectively initializing the address corresponding to the effective coefficient, and the inverse DCT of the obtained DCT coefficient D
It becomes possible to execute the conversion process in parallel,
Image data restoration processing can be sped up.

By the way, the applicant of the present invention has proposed a technique for reducing the time required to restore the entire image in Japanese Patent Application No.
No. 290304 “Image data restoration system” has already been filed, and by implementing this technique together with the inverse quantization method of the present invention, it is possible to further speed up the restoration process of image data.

In Japanese Patent Application No. 1-290304 "Image Data Restoration Method", when the effective coefficient included in the quantized coefficient D _QU or DCT coefficient D is only the DC component, the block produces an effective AC component. Instead of executing the inverse DCT conversion process by determining that it is a DC block that does not have DC
By multiplying the components by a constant and obtaining the image data of the corresponding block, the restoration processing of the entire image is speeded up.

FIG. 7 shows the configuration of an embodiment of the image data restoration device of claim 4. 7, the image data restoration device has a configuration in which a comparator 261 corresponding to the block detection means 121 is added to the inverse quantization unit 210 shown in FIG. Further, in FIG. 7, the inverse DCT transform section 731, the shift circuit 262, and the multiplexer 263 form an inverse orthogonal transform means 102.

The above-mentioned comparator 261 is configured to compare the count value of the counter 242 of the address holding means 114 with the threshold value "1" in response to the input of the detection signal from the block detection unit 212, and shift the shift. The circuit 262 and the multiplexer 263 are configured to operate according to the comparison result.

Here, when the comparator 261 determines that the quantization coefficient D _QU contains one effective coefficient, this effective coefficient corresponds to the DC component of the DCT coefficient D. That is, the block corresponding to this quantized coefficient D _QU is a DC block that does not have a valid AC component, and the image data of this block is all DC described above.
It is a value obtained by dividing the component by a constant “8”, and can be obtained by shifting the DC component stored in the buffer 232 to the right by 3 bits by the shift circuit 262 described above.

That is, in this case, the inverse orthogonal transform means 10
2, the inverse DCT conversion processing by the inverse DCT conversion unit 731 can be replaced with the shift processing by the shift circuit 262.

As described above, the inverse quantizer 210 is provided with the block detector 121 to detect a DC block, so that the inverse orthogonal transformer 102 is adapted to the DC block having no effective AC component. The processing described above can be performed, and the time required for the restoration processing of the image data can be shortened as a whole.

In the case of the successive restoration method, since the quantized coefficient D _QU corresponding to each block always includes the DC component, the inverse quantized processing of the quantized coefficient D _QU of the next block is performed. In addition, the address corresponding to the DC component is always updated. Therefore, in this case, the initialization processing by the inverse quantization unit 210 may be skipped.

For example, when a DC block is detected by the comparator 261 described above, the timing control unit 25
2 clears the count value of the counter 242 instead of instructing the multiplexer 231 to select the output of the zero generator 251, and instructs the decoding unit 711 to input the quantization coefficient D _QU corresponding to the next block. It may be configured to. In this case, the dequantization unit 210 selectively dequantizes only the DC component and further skips the initialization process, so that the time required for the dequantization process can be further shortened.

Further, the dequantization method of the present invention may be applied to an image data restoration device of a hierarchical restoration system. FIG. 8 shows an embodiment configuration of a hierarchical restoration type image data restoration device to which the inverse quantization method of the present invention is applied.

In FIG. 8, the image data restoration device is the same as the image data restoration device shown in FIG.
It is configured by adding 0, and by the decoding unit 711, the dequantization unit 210, and the inverse DCT conversion unit 731 described above,
The image in each layer is restored from the input code data, and based on the obtained image and the image of the previous layer, the layer restoration processing unit 270 restores the image including all information up to the current layer. It is composed. The layer restoration processing unit 270 holds, for example, image data of the previous layer, adds this image data and the image data obtained by the inverse DCT conversion unit 731, and outputs all information up to the current layer. It may be configured to obtain image data including

When hierarchical reconstruction is performed, as a code for one block in each hierarchy, a code obtained by selectively encoding only a part of the components of the quantized coefficient D _QU in 8 rows and 8 columns is input. For example, in the spectral selection method, first, only the DC component of each block is selectively encoded and transmitted, and then the second and third components are subjected to zigzag scanning.
The components corresponding to higher spatial frequencies are selectively coded and transmitted in sequence, such as selecting the component to be scanned next. Therefore, the effective coefficients included in quantized coefficients D _QU obtained by decoding the encoded data of each layer is very low, the number of valid coefficients included in quantized coefficients D _QU of each layer about two to three Is often the case.

Therefore, as described above, by selectively dequantizing only the effective coefficients and selectively initializing only the addresses corresponding to these effective coefficients, the time required for the dequantization processing is greatly increased. It is possible to shorten and speed up the restoration processing of the image data of each block.

The applicant has already filed Japanese Patent Application No. 2-180473 as a technique for shortening the time required for the restoration processing of the entire image data in the hierarchical restoration.
This technique detects an invalid block in which the quantized coefficient D _QU does not include a valid coefficient, omits the inverse DCT transform process and the image data update process for this invalid block, and speeds up the restoration process of the entire image data. It is intended to

FIG. 9 shows the main configuration of an embodiment of the image data restoration device according to the fifth aspect. 9, the image data restoration device has a configuration in which a comparator 271 corresponding to the block detection means 131 is added to the image data restoration device shown in FIG. 8, and the inverse DCT conversion unit 731 and the hierarchy restoration processing unit are included. The inverse orthogonal transform means 102 is constituted by 270.

Further, the comparator 271 described above responds to the input of the detection signal from the block detection unit 212, and the count value of the counter 242 of the address holding means 114 and the threshold value "0".
_Are compared, and when they match, an invalid block signal indicating that the quantized coefficient D _QU of the corresponding block does not include an effective coefficient is output.

For example, in the spectral selection method, since components corresponding to high spatial frequencies are sequentially transmitted as described above, there are cases where all selected components are invalid coefficients in a high-order hierarchy.

In such a case, as a code for one block, "E" indicating that the code for one block is completed
Only the "OB" code is input, and in response thereto, the invalid signal is output by the comparator 271 described above.

In this case, all the components of the quantized coefficient D _QU corresponding to the corresponding block are invalid coefficients.
Since all the components of the corresponding DCT coefficient D are also invalid coefficients, the inverse quantization process and the inverse DC for this block are performed.
The T conversion process is a useless calculation process. Further, in this case, since new information regarding the image of the current layer is not input, it is not necessary to update the image including the information up to the previous layer by the layer restoration processing unit 270 described above.

For example, the timing control section 252 may be configured to instruct the decoding means 101 to start the decoding processing of the coded data in accordance with the invalid block signal described above. In this case, since the count value of the counter 242 is “0”, the timing control unit 252 does not need to clear it again.

Further, the inverse DCT transform section 731 may skip the inverse DCT transform processing in response to the input of this invalid block signal, and notify the hierarchical restoration processing section 270 that it is an invalid block. .. Accordingly
The layer restoration processing unit 270 may skip the layer restoration process described above and output the image data of the previous layer as it is.

As described above, the inverse quantizing unit 210 is provided with the block detecting means 131 to detect an invalid block, so that the inverse orthogonal transforming means 102 adapts to an invalid block which does not include valid information. The processing described above can be performed, and the time required for the restoration processing of the image data can be shortened as a whole.

[0077]

As described above, the present invention selectively dequantizes effective coefficients and selectively initializes the addresses at which these effective coefficients are held, thereby making it possible to obtain an invalid coefficient and a quantization threshold value. It is possible to reduce useless multiplication processing of the above and useless initialization processing for an address corresponding to an invalid coefficient, so that the time required for the inverse quantization processing can be shortened, and the image data restoration processing can be speeded up. Can be planned.

Further, by performing the inverse quantization process and the initialization process and the inverse DCT transform process in parallel, the processing time per block can be shortened and the restoration process can be performed at a higher speed.

Further, by detecting the DC block and the invalid block and performing the processing adapted to these blocks in the inverse orthogonal transform means, the time required for the inverse quantization processing of each block is shortened and the entire image is restored. The time required for processing can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of an inverse quantization method according to the present invention.

FIG. 2 is a diagram showing a configuration of an image data restoration device according to claims 2 and 3;

FIG. 3 is a diagram showing a configuration of an image data restoration device according to claims 4 and 5;

FIG. 4 is a diagram showing a configuration of an embodiment of the image data restoration device of claim 2;

FIG. 5 is an explanatory diagram of effective coefficient addresses.

FIG. 6 is a diagram showing a main configuration of an embodiment of an inverse quantization unit of the image data restoration device according to the present invention.

FIG. 7 is a diagram showing a main configuration of an embodiment of an inverse quantization unit of the image data restoration device of claim 4;

FIG. 8 is a configuration diagram of an embodiment of an image data restoration device of a hierarchical restoration system to which the inverse quantization method of the present invention is applied.

FIG. 9 is a diagram showing a main configuration of an embodiment of the image data restoration device of claim 5;

FIG. 10 is a configuration diagram of a conventional image data compression device.

FIG. 11 is a diagram showing an example of a block.

FIG. 12 is a diagram showing an example of a DCT coefficient D.

FIG. 13 is a diagram showing a quantization matrix.

FIG. 14 is a diagram showing a quantization coefficient D _QU .

FIG. 15 is an explanatory diagram of zigzag scanning.

FIG. 16 is a configuration diagram of a conventional image data restoration device.

FIG. 17 is a schematic configuration diagram of a conventional inverse quantization processing unit.

[Explanation of symbols]

 101 Decoding Means 102 Inverse Orthogonal Transforming Means 111 Address Calculating Means 112 Inverse Quantizing Means 113 Transform Coefficient Storing Means 114 Address Holding Means 115 Writing Means 121, 131 Block Detecting Means 201 Demultiplexer (DMPX) 211 Integrating Circuits 212 Block Detecting Units 221 , 722 Multiplier 222,723 Quantization threshold holding unit 231,263 Multiplexer (MPX) 232,233 Buffer 234 Switching control unit 235 Pipeline control unit 241 Memory 242 Counter 251 Zero generator 252 Timing control unit 253 Read circuit 261,271 Comparator 262 Shift circuit 270 Hierarchical restoration processing unit 611 DCT conversion unit 620 Linear quantization unit 631 Encoding unit 632 Code table 711 Decoding unit 712 Decoding table 720 Inverse quantization unit 721 Distribution Restorer 724 address calculating unit 725 DCT coefficient holding unit 731 inverse DCT unit

Claims (5)

[Claims] 1. An original image is orthogonally transformed for each of a plurality of blocks each including a plurality of pixels to obtain a coefficient matrix including transform coefficients, and each component of the coefficient matrix is quantized by a corresponding quantization threshold value. In the dequantization method of obtaining the coefficient matrix from the quantized coefficients obtained by decoding the code data when restoring the original image from the code data obtained by encoding the quantized coefficient matrix, the quantum corresponding to each block An effective coefficient having a value other than zero is extracted from the quantized coefficient matrix, multiplied by a quantization threshold value corresponding to each of the effective coefficients, and the obtained multiplication result is indicated by the effective coefficient indicating the position occupied in the quantized coefficient matrix. The coefficient matrix is restored by holding it according to the coefficient address, and the effective coefficient address is selected before the inverse quantization process of the quantized coefficient corresponding to the next block. Inverse quantization method and performing initialization processing. 2. An original image is orthogonally transformed for each of a plurality of blocks each having a plurality of pixels to obtain a coefficient matrix composed of transform coefficients, and each component of this coefficient matrix is quantized by a corresponding quantization threshold value. Coded data obtained by coding the quantized coefficient matrix is input, the coded data is decoded, and the decoding means (101) for outputting the decoded data representing the quantized coefficient matrix; Address calculation means (111) for obtaining an effective coefficient address indicating a position in the quantized coefficient matrix, which effective coefficient having a value other than zero included in the quantized coefficient matrix of the block, respectively, and the effective coefficient and the corresponding effective coefficient. An inverse quantization means (112) for multiplying a quantization threshold value indicated by an address and outputting it as a transform coefficient, and the transform coefficient corresponding to the effective coefficient address. A conversion coefficient storage means (113) for storing the same, an address holding means (114) for sequentially holding the effective coefficient addresses, and a coefficient matrix composed of the conversion coefficients stored in the conversion coefficient storage means (113). Inverse orthogonal transformation means (102) for performing orthogonal transformation to restore the image data, and in accordance with the end of the inverse orthogonal transformation processing by the inverse orthogonal transformation means (102), the valid data held in the address holding means (114). An image data restoration device comprising: a writing means (115) for writing a predetermined initial value in a storage location of the conversion coefficient storage means (113) indicated by a coefficient address. 3. The image data restoration device according to claim 2, wherein the transform coefficient storage means (113) switches a plurality of areas having a capacity corresponding to a coefficient matrix for one block to correspond to consecutive blocks. The address holding means (114) holds the effective coefficient address corresponding to the coefficient matrix stored in each area of the transform coefficient storage means (113). And an address holding means (11)
4) An image data restoration device characterized in that the initial value writing process is performed according to the effective coefficient address corresponding to the coefficient matrix of each area held in 4). 4. The image data restoration device according to claim 2, wherein a DC block represented by only a DC component is detected based on the number of effective coefficients included in the quantization coefficient matrix corresponding to each block, The result of this detection is the inverse orthogonal transformation means (102).
Block detecting means (12
An image data restoration device comprising 1). 5. The image data restoration device according to claim 2, wherein an invalid block containing no effective coefficient is detected based on the number of effective coefficients included in the quantization coefficient matrix corresponding to each block, and this detection is performed. Block detection means (131) for providing the result to the inverse orthogonal transformation processing by the inverse orthogonal transformation means (102)
An image data restoration device comprising: