JP2887843B2 - Image data restoration method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] A multi-valued image is divided into blocks each including a plurality of pixels.
The present invention relates to an image data restoration device for restoring a signal of an encoded multi-valued image by an orthogonal transformation encoding method after orthogonally transforming pixels in a block. For this purpose, an original image is divided into blocks each including a plurality of N × N pixels, and for each of the blocks, a gradation value of the plurality of N × N pixels is subjected to a two-dimensional discrete cosine transform to obtain a plurality of spatial frequency distributions. In a device for obtaining a transform coefficient represented by, quantizing the obtained transform coefficient with a coefficient corresponding to the spatial frequency distribution, and restoring an image from code data obtained by coding the quantized coefficient obtained by the quantization, Decoding means for decoding the code data into quantized coefficients, inverse quantizing means for inversely quantizing the quantized coefficients decoded by the decoding means to obtain DCT coefficients, and inverse quantity by the inverse quantizing means. Conversely D The DCT coefficients
Inverse DCT transform means for performing CT transform, and the number of significant coefficients representing non-zero present in the quantized coefficients in the block decoded by the inverse decoding means are detected. Significant coefficient detection means for controlling the inverse quantization of the conversion means and the output as restored image data without performing the inverse DCT transformation of the inverse DCT transformation means.

[Industrial applications]

The present invention relates to a device for restoring a data-compressed image, and more particularly, to a multi-valued image to be divided into a block of a plurality of pixels, and the pixels in the block are orthogonally transformed and then encoded. The present invention relates to an image data restoration apparatus for restoring a signal according to the orthogonal transform coding method.

[Conventional technology]

As an efficient compression method for image data, for example, there is an adaptive discrete cosine transform coding method. Adaptive Discrete Cosine Transform: A
DCT), for example, divides an image into blocks of 8 × 8 pixels, converts image signals of each block into spatial frequency distribution coefficients by two-dimensional discrete cosine transform, and quantizes the coefficients with a threshold adapted to vision. In this method, quantization coefficients are encoded using a Huffman table statistically obtained.

FIG. 6 is a block diagram of an encoding circuit of the ADCT system.
Hereinafter, the encoding operation will be described in detail with reference to FIG.

The pixels are divided into blocks of 8 × 8 pixels shown in the original image signal table of FIG. In the two-dimensional DCT transform unit 32, the input image signal is orthogonally transformed by the DCT transform, and is transformed into the spatial frequency distribution coefficient shown in the DCT coefficient chart of FIG. Then, it outputs the result to the linear quantization unit 33.

FIG. 7 is a block diagram of a two-dimensional DCT transform unit. First, the input image signal is converted by the one-dimensional DCT conversion unit 32-1.
Then, the transposition unit 32-2 transposes the rows and columns, and again performs one-dimensional transposition.
The transform is performed by the DCT transform unit 32-3, and the transpose unit 32-4 similarly transposes the rows and columns. Two-dimensional DCT transformation is performed by these two one-dimensional DCT transformations. The one-dimensional DCT transform units 32-1 and 32-
Step 3 is performed using a conversion constant.

The linear quantization unit 33 divides the input DCT coefficient by a value of a quantization threshold holding unit (quantization matrix) 34 configured by a threshold value shown as a quantization threshold value for a general DCT coefficient in FIG. , Linearly quantize.

FIG. 13 is a chart of quantized DCT coefficients (quantized coefficients), and is a result of quantization using a constant shown in FIG. 12 as an example of a threshold value for DCT coefficients. As shown in FIG. 13, the DCT coefficient equal to or smaller than the threshold value becomes 0, and a quantized coefficient having only the DC component and a small amount of the AC component is generated.

The two-dimensionally arranged quantized coefficients are converted to one-dimensional by zigzag scan. FIG. 14 is an explanatory diagram of the above-described quantization coefficient scanning order (zigzag scanning). 1
When the block is set to 8 × 8, for example, dots are sequentially selected in the diagonal direction of the upper left, followed by the right and lower left,. The data selectively read sequentially by the zigzag scan is input to the variable-length coding unit 35, and is input to the variable-length coding unit 35.
35 performs variable length coding on the difference between the DC component at the head of each block and the DC component of the previous block. For the AC component, the length (run) of the value (index) of the significant coefficient (coefficient whose value is not 0) and the run length of the invalid coefficient (coefficient whose value is 0) so far are variable-length coded for each block. The DC and AC components are encoded using a code table 36 composed of Huffman tables created based on statistics for each image, and the obtained code data is sequentially output from a terminal 37.

On the other hand, the above-mentioned code data is restored to an image by the following method. FIG. 8 is a block diagram of a restoration circuit of the ADCT system. The code data input from the terminal 40 is input to the variable length decoding unit 41. The variable-length decoding unit 41 decodes the input code data into fixed-length data of an index and a run by using a decoding table 42 formed of a table opposite to the Huffman table of the above-described code table 36, Output to The inverse quantization unit 43 restores the DCT coefficient by multiplying the input quantization coefficient by the value stored in the inverse quantization matrix 44, and outputs the DCT coefficient to the two-dimensional inverse DCT transformation unit 45. The two-dimensional inverse DCT transform unit 45 orthogonally transforms the input DCT coefficients by inverse DCT transform, and converts the spatial frequency distribution coefficients into image signals.

More specifically, the two-dimensional inverse DCT transform unit 45 will be described. FIG. 9 is a block diagram of a two-dimensional inverse DCT transform unit. Terminal 40
The input DCT coefficient is subjected to a dimensional inverse DCT transform by a one-dimensional inverse DCT transform unit 41-1 and output to a transpose unit 41-2. Transposed part 41
At -2, the rows and columns of the coefficients in one block are exchanged and output to the one-dimensional inverse DCT transformer 41-3. One-dimensional inverse DCT converter 41
-3 performs one-dimensional inverse DCT on the input transposed coefficients again, and outputs the result to the transposed unit 41-4. The transposed part 41-4 is the transposed part 41
Similarly to -2, the rows and columns of the coefficients in one block are exchanged again. The signal obtained by the above operation is output from the terminal 46. That is, the image is restored. The one-dimensional inverse DCT transform units 41-1 and 41-3 convert using the inverse DCT transform constant.

 The above-mentioned restoration will be described in more detail.

FIG. 15 is a block diagram of a conventional restoration circuit (hierarchical restoration). A conventional hierarchical restoration method will be described with reference to FIG.
The code data is input from a terminal 51 to a variable length decoding unit 52.
Assuming that the scanning order of the DCT coefficients is X01, X02,... X64 (corresponding to 1 to 64 in FIG. 14), the variable length decoding unit 52 first converts the DCT coefficients of the first to n1st terms (n1 <64). The corresponding coded data is decoded into the quantized DCT coefficient using the decoding table 53. The decoded quantized coefficients are input to the inverse quantization unit 54,
54 dequantizes to DCT coefficients using a quantization matrix 55. The inversely quantized DCT coefficients are converted into image data by a two-dimensional inverse DCT transform unit 56. The obtained image data is added to the adder 57.
Are stored in the image memory 58 via the terminal 59 and output from the terminal 59. Next, the variable length decoding unit 52 calculates the n1 to n2 terms (n1 <n2
≤ 64) D is the quantized code data corresponding to the DCT coefficient
Decode to CT coefficients. The decoded quantized coefficient is inverse quantized.
It is output to 54 and inversely quantized to DCT coefficients. The inversely quantized DCT coefficients are converted into image data by a two-dimensional inverse DCT transform unit 56. Then, the adder 57 adds the obtained image data and the image data held in the image memory 58, stores the added image data again in the image memory 58, and outputs it from the terminal 59. Finally, the DCT coefficient buffer restores the DCT coefficients from the first term to the sixty-fourth term into image data and stores them in the image memory 58. in this way,
By sequentially adding the code data and finally transferring all the data, the hierarchical restoration for one screen is completed.

[Problems to be solved by the invention]

In the prior art, when restoring DCT coefficients to an image,
The DCT coefficients of the pixels in all blocks were subjected to inverse DCT.
However, the inverse DCT transform is an 8 × 8 matrix operation when one block is composed of 8 × 8 pixels.
One multiplication and seven additions, that is, conversion of one block of 64 pixels, requires 512 multiplications and 448 additions. For this reason, when the pixels of all the blocks of one screen are subjected to the inverse DCT transform, there is a problem that it is difficult to speed up image restoration. For example, when image data (difference data) is hierarchically restored for each DCT coefficient divided into a predetermined number, as shown in FIGS. 16 (A) and 16 (B),
The DCT coefficients are often zero, and the DCT coefficients in the newly restored block are all often zero. When the DCT coefficients in the block are all zero, the restored image data also becomes all zero, so that there is a problem in that unnecessary processing is frequently performed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image data restoring device capable of suppressing the increase in the number of circuits and increasing the speed.

[Means for solving the problem]

 FIG. 1 is a block diagram showing the principle of the present invention.

According to the present invention, an original image is divided into blocks each composed of a plurality of N × N images, and for each of the blocks, the tone values of the plurality of N × N pixels are represented by a plurality of spatial frequency distributions by performing a two-dimensional discrete cosine transform. An apparatus for obtaining a transform coefficient, quantizing the transform coefficient with a coefficient corresponding to the spatial frequency distribution, and restoring an image from code data obtained by coding the quantized coefficient obtained by the quantization.

 The decoding means 1 decodes code data into quantized coefficients.

The inverse quantization means 2 inversely quantizes the quantized coefficients decoded by the decoding means 1 to obtain DCT coefficients.

The inverse DCT transform unit 3 performs an inverse DCT transform on the DCT coefficient inversely quantized by the inverse quantization unit 2.

Significant coefficient detecting means 4 detects the number of significant coefficients present in the block decoded by the decoding means 1 and indicating that it is not 0, and when the significant coefficient does not exist, the inverse quantizing means 2 And performs control to output as reconstructed image data without performing inverse DCT transformation of the inverse DCT transformation means 3.

The image memory means 7 stores the image data which has been subjected to the inverse DCT transformation by the inverse DCT transformation means 3.

When image data is stored in the image memory unit 7, the adding unit 5 adds the image data stored in the image memory unit 7 and the image data subjected to the inverse DCT conversion by the inverse DCT conversion unit 3. , Stored in the image memory means 7.
This addition is not performed in the first stage, but is performed in the second and subsequent stages.

The selecting means 6 adds the output of the adding means 5 and the output of the inverse DCT transforming means 3 to select the output of the inverse DCT transforming means 3 in the first stage, which is a low frequency component, and After the second stage, which is the next frequency component region of the stage, the output of the adding means 5 is selected,
It is added to the image memory means 7.

[Action]

The input code data is decoded by the decoding means 1 and becomes a quantized coefficient. In one block, the number of significant coefficients present in the decoded quantized coefficient, which is not 0, is detected. If no significant coefficient exists, zero data is output as restored data. When there are significant coefficients, the inverse quantization means 2 and the inverse DCT transform means 3 are operated to restore the image.

Further, the restored image data is selected and stored in the image memory means 7 by the selecting means 6 in the first stage which is a low-frequency component, and the image data is stored in the second stage which is the next frequency component area of the first stage. The image data stored in the memory means 7 is added to the image data restored by the inverse DCT transform means 3, and the output is selected by the selecting means 6 and stored in the image memory means 7.

When the quantized coefficient has no significant coefficient in one block, the block address is advanced, and addition in the block is not performed.

This can reduce operations such as inverse quantization and addition of inverse DCT transform.

〔Example〕

FIG. 2A is a configuration diagram of the first embodiment of the present invention.

The code data input from the terminal 11 is input to the variable length decoding unit 12. The variable-length decoding unit 12 decodes the input code data into fixed-length data of an index and a run by using a decoding table 13 constituted by a table opposite to the Huffman table, and outputs the decoded data to the inverse quantization unit 14. The inverse quantization unit 14 determines the number of significant coefficients in the block, and outputs an invalid block signal ZERO to the two-dimensional inverse DCT transform unit 16 when there is no significant coefficient.
If a significant coefficient exists, the quantization matrix 15
Is multiplied by the input quantization coefficient by each value of
The T coefficient is restored and output to the two-dimensional inverse DCT transform unit 16. When the invalid block signal ZERO is input, the two-dimensional inverse DCT transform unit 16 outputs the invalid block signal ZERO to the terminal 18 without performing the two-dimensional inverse DCT transform. When the invalid block signal ZERO is not input, the input DCT coefficient is orthogonally transformed by the inverse DCT transform, the coefficient of the spatial frequency distribution is converted into an image signal, and output to the terminal 17.

By repeating the above processing, an image of one screen is restored.

FIG. 2 (B) is an operation flowchart of the present invention.
Execution starts when the decrypted data is input. First, the variable-length decoding process S1 is executed to obtain decoded data as quantization coefficients. Then, it is determined whether or not a significant coefficient exists S2. If there is a significant coefficient (YES), the quantization coefficient is then inversely quantized by inverse quantization processing S3 to obtain a DCT coefficient. Following the DCT coefficient, a two-dimensional inverse DCT transform S4 is performed, and a restored signal is output S5.

On the other hand, when there is no significant coefficient in discrimination S2 (N
ZERO output as an invalid block signal for O) (S
6). That is, all zero data is output. After processing S5 and processing S6, it is determined whether or not all blocks have been completed S7,
If the processing is not to be ended (NO), the processing is executed again from the above-described variable length decoding processing S1. When all the blocks have been completed (YES), the process ends.

As is clear from the above processing, if no significant coefficient exists, all zero data is output.
There is no need to execute the dimensional DCT transform processing S3, S4, and the processing can be sped up.

FIG. 3 is a block diagram of an invalid block signal generation circuit in the inverse quantization unit 14 according to the embodiment of the present invention, and FIG. 4 is an example diagram of a decoded data sequence.

Hereinafter, the calculation of the number of significant coefficients in the block will be described with reference to the block diagram of the invalid block signal generation circuit of the present invention shown in FIG.

The decoded data of the index and the run decoded from the code data by the variable length decoding unit 12 is input to the demultiplexer 21 from the terminal 10. According to the selection signal (CSL) from the timing control unit 25, the demultiplexer 21 alternately selects the decoded data of the index and the run from the input decoded data sequence, and sends the index (IDX) to the DCT coefficient restoration unit 28 by the run ( RUN) is output to the block end detection unit 22.

In the case of a block having only DC components (FIG. 4A), the first decoded data (D1) of DC components is selected by the demultiplexer 21 and output to the DCT coefficient restoration unit 28. Then, in accordance with the number count signal (ICN) from the timing controller 25, the significant coefficient number calculator 23 counts the number of significant coefficients “1” in the target block. Also, the significant coefficient selector
The address where the decrypted data (D1) exists in A26 (ADR = 0)
Is held. Next, the demultiplexer 21 is run (Reob)
Is selected and output to the block end detection unit 22. The block end detection unit 22 determines that the value of the input run (RUN) is (Reob)
Therefore, the coefficients of the remaining pixels in the block are all invalid coefficients, it is determined that the coefficients in the block have been completed, and a signal (BEN) instructing the timing control unit 25 to terminate the significant coefficients in the block is output. I do. And the timing control unit 2
5 instructs the significant coefficient number determination unit 24 to determine the number of significant coefficients in the block (BCN). Since the number of significant coefficients in the block is one, the significant coefficient number determination unit 24 determines that the target block has a significant coefficient, and outputs the invalid block signal ZERO as "0" from the terminal 20.

On the other hand, the DCT coefficient restoration unit 28 multiplies the held decoded data (D1) by the quantization threshold held at the DC component address (ADR = 0) of the quantization threshold holding unit 27, and divides the result by Output from terminal 29. Then, the image signal is converted into an image signal by the two-dimensional inverse DCT conversion unit 16, and the image signals of all the pixels of the block are restored.

In the case of a block in which the coefficients of the DC component and the AC component exist (FIG. 4 (b)), first, the decoded data (D
2) is selected by the demultiplexer 21 and output to the DCT coefficient restoration unit 28. Then, according to the number count signal (ICN) from the timing control unit 25, the significant coefficient number calculation unit 2
3 counts the number of significant coefficients “1” in the target block. Further, the significant coefficient selection unit 26 holds the address (ADR = 0) where the decoded data (D1) exists. Next, the demultiplexer 21 selects the run (R0) and outputs it to the block end detection unit 22. Since the input value of the run (RUN) is R0, the block end detection unit 22 determines that the coefficients in the block have not ended. The significant coefficient selection unit 26 determines the address (A) of the next significant coefficient from the input run value.
DR) is calculated and retained. On the other hand, since the demultiplexer 21 selects the index (I1) this time, the input index (I1) is held in the DCT coefficient restoration unit 28. Also, the count signal from the timing control unit 25 (IC
According to N), the number of significant coefficients “+1” in the target block is added to the significant coefficient number calculation unit 23, and “2” is counted. Next, the demultiplexer 21 selects the run (R0) and outputs it to the block end detection unit 22. Since the input run value is R0, the block end detection unit 22
Determines that the coefficients in the block have not been completed. Therefore, the significant coefficient selection unit 26 calculates and holds the address (ADR) of the next significant coefficient from the input value of the run (RUN).

On the other hand, the demultiplexer 21 selects the index (I2) this time. The index (I2) input by this selection is held in the DCT coefficient restoration unit 28. Also, the count signal from the timing control unit 25 (IC
According to N), the number of significant coefficients in the target block is added to the significant coefficient number calculation unit 23 by “+1”, and “3” is counted. Next, the demultiplexer 21 selects a run (Reob) and outputs it to the block end detection unit 22. Since the input signal is a run (Reob), the block end detection unit 22
Determines that the coefficients of the remaining pixels in the block are all invalid coefficients and the coefficients in the block have been completed.
Signal indicating the end of the significant coefficient in the block to 25 (BE
N) is output. Then, the timing control unit 25 instructs the significant coefficient number determination unit 24 to determine the number of significant coefficients in the block (BCN). Since the number of significant coefficients in the block is three, the significant coefficient number determination unit 24 determines that the target block has a significant coefficient, and outputs the invalid block signal ZERO as "0" from the terminal 20. Also, the DCT coefficient restoration unit 28 multiplies the held decoded data (D1, I1, I2) by the quantization threshold held at the corresponding address (ADR) of the quantization threshold holding unit 27, and as a result Is output from the terminal 29. Then, the image signal is converted into an image signal by the two-dimensional inverse DCT conversion unit 16, and the image signals of all the pixels of the block are restored.

On the other hand, in the second and subsequent stages of hierarchical restoration, the demultiplexer 21 first selects a run. If there is no significant coefficient (FIG. 4C), the selected run (Reob) is output to the block end detection unit 22. Since the input value of the run (RUN) is Reob, the block end detection unit 22 determines that all the coefficients of the remaining pixels of the block are invalid coefficients and the coefficients in the block have been completed, and the timing control unit 25 Outputs a signal (BEN) indicating the end of the significant coefficient in the block. And the timing control unit 2
5 instructs the significant coefficient number determination unit 24 to determine the number of significant coefficients in the block (BCN). Significant coefficient number judgment unit 24
Since the number of significant coefficients in the block is 0, it is determined that the target block has no significant coefficient, the invalid block signal ZERO is output from the terminal 20 as "1", and all the processing of the block is performed. finish.

FIG. 5 is a block diagram of a second embodiment of the present invention in a case where image updating is included. The first-stage code data D1 (X01... Xn1: n1 <64) divided in advance from the terminal 61 is decoded by the variable-length decoding unit 62 using the decoding table 63, and is input to the inverse quantization unit 64. In the first stage, since the DC component is included, the invalid block signal is set to “0”, and the inverse quantization unit 64 performs a normal inverse quantization process using the quantization matrix 65. Here, the inversely quantized DCT coefficients are output to the two-dimensional DCT transform unit 66, and are restored to image data by the two-dimensional inverse DCT transform unit 66. The selector 69 is instructed by the signal FIRST indicating the first stage, and selects the restored divided image data. At this time, the image memory 68 stores the output of the two-dimensional inverse DCT transform unit 66 selected by the selector 69 according to the write signal WRITE output from the image memory control unit 67. This storage address is the address MADR output from the address generator 71. By repeating the above processing for all the blocks, the image restoration of the first stage for one screen is completed.

Next, the second stage code data D2 (Xn1 + 1... Xn2: n
1 <n2 <64) is restored to image data in the same process as above. However, when there is no significant coefficient as shown in FIG. 4 (c), the invalid block signal ZERO is output as "1" as described above. At this time, the image memory controller 67
Does not access the image memory 68, and only increases the value of the block address generation counter 74 by 1 via the OR circuit 72 as shown in FIG. finish. If there is a significant coefficient, the image data restored as usual is added by the adding unit 70 to the image data of the previous stage. The selector 69 selects this addition result, and writes the write signal WR output from the image memory control unit 67.
In accordance with the ITE, the data is written to the image memory 68, and the 6-bit counter 73 for generating the address in the block by the address update request signal REQ is increased by one. Then, the write address MADR to the image memory is updated. When all pixels in the block have been updated, the carry signal CARR
Y is output from the 6-bit counter 73, the value of the block address generation counter 74 is increased by 1 via the OR circuit 72, and the processing of the block ends. By repeating the above processing for all blocks, the second screen for one screen
The image restoration of the stage ends.

By performing the same processing as the processing of the second stage up to the code data Di (Xni + 1... X64: ni <64) of the i-th stage, the hierarchical restoration for one screen is completed.

〔The invention's effect〕

As described above, according to the present invention, when no significant coefficient exists in a block, inverse quantization, inverse DCT transform,
By not updating the image memory, it is possible to realize high-speed image restoration at the time of hierarchical restoration.

[Brief description of the drawings]

1 is a block diagram of the principle of the present invention, FIG. 2 (A) is a block diagram of a first embodiment of the present invention, FIG. 2 (B) is an operation flowchart of the present invention, and FIG. FIG. 4 is a block diagram of a decoded data sequence, FIG. 5 is a block diagram of a second embodiment of the present invention, and FIG. 6 is a block diagram of an ADCT-type encoding circuit. FIG. 7 is a block diagram of a two-dimensional DCT converter, FIG. 8 is a block diagram of an ADCT type restoration circuit, FIG. 9 is an example of a circuit block diagram of a two-dimensional inverse DCT converter, FIG. Is a diagram showing an original image signal, FIG. 11 is a diagram showing DCT coefficients, FIG. 12 is a diagram showing threshold values for DCT coefficients, FIG. 13 is a diagram showing quantization coefficients, and FIG. 14 is a scan of quantization coefficients. FIG. 15 is a block diagram of a conventional ADCT hierarchy restoration unit, and FIG. 16 (A) is an example of dividing DCT coefficients (first stage). FIG. 16B shows an example of dividing the DCT coefficient (second stage). 1 ... Decoding means, 2 ... Inverse quantization means, 3 ... Inverse DCT conversion means, 4 ... Significant coefficient detection means, 5 ... Addition means, 6 ...
... Selection means, 7... Image memory means.

Claims (5)

(57) [Claims] An original image is divided into blocks each including a plurality of N × N pixels, and for each of the blocks, tone values of the plurality of N × N pixels are subjected to a two-dimensional discrete cosine transform to obtain a plurality of spatial frequency distributions. In a device for obtaining a transform coefficient represented by, quantizing the transform coefficient with a coefficient corresponding to the spatial frequency distribution, and restoring an image from code data obtained by coding the quantized coefficient obtained by the quantization, Decoding means (1) for decoding code data into quantized coefficients; dequantizing means (2) for dequantizing the quantized coefficients decoded by the decoding means (1) to obtain DCT coefficients; An inverse DCT transforming means (3) for performing an inverse DCT transform on the DCT coefficient inversely quantized by the transforming means (2); and that the quantized coefficient in the block decoded by the decoding means (1) is not zero. The number of significant coefficients representing When There does not exist, the inverse D inverse quantization and the inverse DCT unit of the inverse quantization means (2) (3)
An image data restoration apparatus comprising: a significant coefficient detection unit (4) for performing control for outputting as restored image data without performing CT conversion. 2. The method according to claim 1, wherein the original image is divided into blocks each including a plurality of N × N pixels, and a gradation value of each of the plurality of N × N pixels is subjected to a two-dimensional discrete cosine transform to obtain a plurality of spatial frequency distributions. In a device for obtaining a transform coefficient represented by, quantizing a coefficient corresponding to the spatial frequency distribution of the transform coefficient, and restoring an image from code data obtained by coding the quantized coefficient obtained by the quantization, Decoding means (1) for decoding code data into quantized coefficients; dequantizing means (2) for dequantizing the quantized coefficients decoded by the decoding means (1) to obtain DCT coefficients; Inverse DCT transforming means (3) for inversely DCT transforming the DCT coefficients inversely quantized by the transforming means (2); and image memory means for storing the image data inversely transformed by the inverse DCT transforming means (3). 7) and an image stored in the image memory means (7). When the data is stored, the image data stored in the image memory means (7) and the image data subjected to the inverse DCT transformation by the inverse DCT transformation means (3) are added, and the image memory means (7) is added. ), And the output of the adding means (5) and the output of the inverse DCT transforming means (3) are added, and the inverse DCT transforming means ( Selecting the output of 3), selecting the output of the adding means (5) after the second stage, which is the frequency component area next to the first stage, and storing it in the image memory means (7); ), And detecting the number of non-zero significant coefficients present in the quantized coefficients in the block decoded by the decoding means (1), and when no significant coefficients exist, the dequantizing means (2)
The inverse quantization and inverse DCT of the inverse DCT transforming means (3) are not performed, and the quantized coefficients in the block decoded by the decoding means (1) as restored image data are added to the adding means (5).
And a significant coefficient detecting means (4) for performing control for outputting to the selecting means (6). 3. The image memory means (7) has an image memory and an address generating means for advancing a block address. The address generating means generates a block address and an intra-block address, and the decoding means (1). Means for detecting the significant coefficient in the quantized coefficient in the block decoded by
3. The image data restoring apparatus according to claim 2, wherein the block address is advanced when the significant coefficient detected in step (a) does not exist. 4. An original image is divided into blocks each including a plurality of N × N pixels, and for each of the blocks, a gradation value of the plurality of N × N pixels is subjected to a two-dimensional discrete cosine transform to obtain a plurality of spatial frequency distributions. In a device for obtaining a transform coefficient represented by, quantizing the transform coefficient with a coefficient corresponding to the spatial frequency distribution, and restoring an image from code data obtained by coding the quantized coefficient obtained by the quantization, Decoding means for decoding the code data into quantized coefficients; block end detection means for detecting the end of the coefficient of the block from the signal decoded by the decoding means; and end of the coefficient of the block by the block end detection means Until the detection, a significant coefficient number calculating means for counting the number of significant coefficients present in the block which is not 0, and counting by the significant coefficient number calculating means A significant coefficient number determining means for determining the number of significant coefficients in the block, and an invalid block if the number of significant coefficients in the block is determined to be 0 by the significant coefficient number determining means. An image data restoration apparatus for outputting a signal. 5. An original image is divided into blocks each including a plurality of N × N pixels, and tone values of the plurality of N × N pixels are subjected to a two-dimensional discrete cosine transform for each of the blocks to obtain a plurality of spatial frequency distributions. In a method of obtaining a transform coefficient represented by, quantizing the transform coefficient by a coefficient corresponding to the spatial frequency distribution, and restoring an image from encoded data obtained by encoding the quantized coefficient obtained by the quantization, Decodes the code data into quantized coefficients, detects the presence or absence of a significant coefficient indicating that it is not 0 existing in the block from the decoded signal, and outputs an invalid block signal when the detection result is absent. Output zero data, and when the detection result is positive, the quantization coefficient is
An image data restoration method, comprising: performing inverse quantization for converting into coefficients, and subsequently performing inverse DCT on the obtained DCT coefficients to restore an image signal.