# Patent

## Title
Decoding apparatus and decoding method in an order opposite to the encoding order

## Abstract

There is provided a coding apparatus in which an input image signal is divided into blocks, the block data is compression coded by using an orthogonal transformation, and (n) sync blocks are produced from the (m) compression coded block data, wherein each sync block has a first area in which important data in the orthogonal transformation coded block data of a specific number of blocks is arranged and a second area in which non-important data in the orthogonal transformaton coded block data of an unspecific number of blocks is arranged. There is also provided a decoding apparatus in which an image signal is divided into blocks, the block formed block data is compression coded, and the compression coded block data is decoded on an (m) unit basis (m is a natural number), wherein the apparatus comprises a first decoding unit for decoding the coding data of the inputted (m) blocks in accordance with the inputting order on a block unit basis, a second decoding unit for decoding the coding data of the inputted (m) blocks in accordance with the order opposite to the inputting order on a block unit basis, and an output unit for integrating the data decoded by the first and second decoding units and for outputting decoding data of the (m) blocks.

## Background
RELATED APPLICATION
This application is a divisional of application Ser. No.10/215,017, filed Aug 9, 2002 now U.S. Pat. No. 7,035,336, which is a divisional of application Ser. No. 08/944,955, filed Oct 7, 1997, now U.S. Pat. No. 6,539,057, which is a continuation of application Ser. No. 08/168,996, filed Dec. 20, 1993, now abandoned, the entire contents of all of which are incorporated herein by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a coding/decoding apparatus and, more particularly, to an apparatus for variable length coding image data after it was orthogonally transformed on a block unit basis comprising a predetermined number of pixels and to a decoding apparatus for decoding the coding data which was coded by the coding apparatus.
2. Related Background Art
Generally, since an information amount of an image signal is very large, in case of recording the image signal by a digital recording and reproducing apparatus such as a digital VTR or the like, the information amount is reduced by a high efficient compression coding and the reduced image signal is recorded.
An orthogonal transformation coding using a DCT (Discrete Cosine Transform) is known as an example of the high efficient compression coding techniques.
According to the orthogonal transformation coding, an input image signal is separated into blocks and each of the frequency components obtained by frequency dividing the image signal on such a block unit basis is coded. By using a method such that a data amount which is allocated is reduced or the like with respect to the high frequency component in which an influence by the deterioration on the eyesight characteristics is small, the information amount of the input image signal can be reduced.
The case where the signal which was compression coded by the above method is recorded and reproduced by the digital VTR will now be described.
When the coded data is recorded onto a tape, it is separated into sync blocks of a predetermined data amount unit as a minimum synchronous unit in the reproducing mode and the data is recorded.
FIG. 1 shows a construction of a sync block.
In FIG. 1, SYNC 1 denotes a synchronous pattern; and ID 2 indicates identification information comprising address information or the like to indicate the position on the screen of the data recorded; and DATA 3 denotes image data which was compression coded.
FIG. 2 shows an arrangement on the tape of the sync blocks recorded by a conventional VTR.
Reference numerals 2a, 2b, and 2c in FIG. 2 denote tracks. The sync blocks are arranged in those tracks.
Each track is a locus of a recording head in the recording mode. In the normal reproducing mode, a reproducing head scans on the same locus as the locus which was scanned by the recording head in the recording mode, so that the image data in each sync block can be reproduced.
A method of reproducing the recording data in a special reproducing mode will now be described.
In FIG. 2, reference numeral 10 denotes a locus of the reproducing head in a high speed searching mode as one of special reproducing modes.
Since a tape travelling speed in the high speed searching mode is faster than that in the normal reproducing mode, the locus 10 of the reproducing head is a locus such that the reproducing head scans a plurality of tracks.
Therefore, the data of only the sync blocks shown by hatched regions in FIG. 2 can be extracted from the tape by the reproducing head.
In the above conventional recording/reproducing method of image data mentioned above, however, a sync block in which only a part can be scanned exists in the reproducing head locus 10.
For example, there is a sync block like a sync block 11 in FIG. 2 such that the whole portion cannot be scanned although only the front portion of the sync block can be scanned. Therefore, since the whole DATA arranged in the rear portion in the sync block 11 cannot be fetched, there is a problem such that the data which is necessary for the expanding process cannot be prepared and the whole image data existing in the sync block 11 cannot be reproduced.
In the case where a transmission error exceeding an error correction ability occurs on a transmission path, there is also a problem such that the data after the position at which the transmission error occurred cannot be reproduced and the data of a fixed length unit disappears in the worst case.
SUMMARY OF THE INVENTION
Under such circumstances, it is an object of the invention to provide a coding/decoding apparatus which can reproduce a wider region on a screen than that of a conventional apparatus in case of the occurrence of a transmission error or in a special reproducing mode and can minimize the deterioration of a picture quality.
According to one preferred embodiment, the above object is accomplished by a coding apparatus comprising: block forming means for dividing an input image signal into blocks; coding means for compression coding the block data obtained by dividing by the block forming means by using an orthogonal transformation; and generating means for generating (n) sync blocks from the coding data of the (m) blocks, wherein each sync block has a first area in which important data in the orthogonal transformation coded block data of the number as many as a special number of blocks is arranged and a second area in which non-important data in the orthogonal transformation coded block data of the number of an unspecific number of blocks is arranged.
According to another preferred embodiment, there is provided a decoding apparatus in which an image signal is divided into blocks and the block-formed block data is compression coded and the compression coded block data is decoded on an (m) unit basis (m is a natural number), wherein the decoding apparatus comprises: first decoding means for decoding the coding data of the (m) inputted blocks on a block unit basis in accordance with the inputting order; second decoding means for decoding the coding data of the (m) inputted blocks on a block unit basis in accordance with the reversed inputting order; and output means for integrating the data decoded by the first and second decoding means and for outputting the decoding data of the (m) blocks.
The above and other object and features of the invention will become apparent from the following detailed description taken in conjunction with the appended claims with reference to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory diagram showing a construction of sync blocks;
FIG. 2 is an explanatory diagram showing an arrangement of sync blocks on a tape;
FIG. 3 is a block diagram of a digital recording apparatus of an embodiment according to the invention;
FIG. 4 is a diagram for explaining DCT transformed block data;
FIG. 5 is a diagram showing a construction of sync blocks in the embodiment;
FIG. 6 is a block diagram of a digital reproducing apparatus of the embodiment according to the invention; and
FIG. 7 is a diagram showing schematically an internal structure of a sync block memory 204.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A digital recording/reproducing apparatus according to an embodiment of the invention will now be described hereinbelow.
FIG. 3 is a block diagram of a digital recording apparatus of the embodiment.
An image signal inputted from an input terminal 101 is converted into a digital image signal by an A/D converting circuit 102.
The converted digital image signal is divided into blocks on a DCT processing unit basis by a block forming circuit 103. In the embodiment, a 2-dimensional block (hereinbelow, referred to as a DCT block) of total 64 pixels (8 pixels in the lateral direction ×8 pixels in the vertical direction) is used.
The DCT block formed image signal is converted into the DCT component by a DCT circuit 104. The block data which was converted into the DCT component is supplied to a delay circuit 105 and a code amount control circuit 106.
The DCT converted block data will now be described with reference to FIG. 4. In the embodiment, total 64 pixels (8 pixels in each of the vertical and lateral directions) are set to one block. FIG. 4 shows the correspondence relation of 64 DCT coefficients obtained by DCT arithmetic operating the block data. The left upper DC component indicates the mean value of 64 pixels in the block and is called a direct current (DC) coefficient. The remaining 63 DC components are called alternating current (AC) coefficients and indicate magnitudes of AC component electric powers in the block.
Returning to the description of FIG. 3, the code amount control circuit 106 controls quantization steps of a quantization circuit 107 in a manner such that a data amount when a predetermined number of DCT blocks are collected and coded is set to an almost constant value. In the embodiment, 30 DCT blocks are set to a fixed length unit for simplicity of explanation.
The delay circuit 105 delays 30 DCT block data by a time which is expended to execute the processes in the code amount control circuit 106.
Each of the DCT block data outputted from the delay circuit 105 is quantized by the quantization circuit 107.
The quantized DCT block data is zigzag scanned as shown in FIG. 4 and is converted into a one-dimensional data train from a low frequency component of the DCT transformation coefficients to a high frequency component and is coded every DCT block by the variable length coding circuit 108.
The variable length coded data is supplied to a sync block generation circuit 109, by which sync blocks are generated.
A construction of the sync block in the embodiment will now be described.
FIG. 5 is a diagram showing a construction of the sync block in the embodiment.
In FIG. 5, each sync block has synchronous information (SYNC) 50, identification information (ID) 51, and coding data 52 and 53 from the head.
The coding data is divided into two regions 52 and 53 and inserted into the sync block.
The region 52 is used for the coding data of the low frequency component of the DCT transformation coefficient. The region 53 is used for the coding data of the high frequency component of the DCT transformation coefficient.
In the embodiment, the data of a predetermined code amount is sequentially written into the region 52 of each sync block every block in accordance with the order from the coding data of the low frequency components of the DCT transformation coefficients of six blocks. The coding data of the high frequency components of the DCT transformation coefficients which could not be written into the region 52 is written into the regions 53 of five sync blocks after an ID code (EOB) of each DCT block unit was added to such coding data. Further specifically speaking, Ln and Hn shown in FIG. 5 are multiplied and the coding data of one DCT block is enclosed (n is an integer of 1 to 30). Each Ln has a predetermined code amount and a code amount of each Hn differs.
The EOB is written in a hatched region 53a of shown in FIG. 5. A hatched region 53b shown in the region 53 of the sync block #5 in FIG. 5 denotes a space region which is not yet used.
In the embodiment, 30 blocks are set to one unit and quantizing characteristics (for instance, quantization steps) are controlled so that the coding data of 30 DCT blocks is enclosed in five such blocks.
Returning to the explanation of FIG. 3, an error detection correction code is added to each sync block data with the above construction by an error detection correction coding circuit (ECC) 110.
The data which is outputted from the ECC circuit 110 is subjected to a predetermined modulating process by a modulation circuit 111 and is recorded onto a magnetic tape 113 by a recording head 112.
FIG. 6 is a block diagram of a digital reproducing apparatus of the embodiment. In FIG. 6, the portions corresponding to those shown in FIG. 3 are designated by the same reference numerals and their descriptions are omitted here.
In FIG. 6, the data recorded on the magnetic tape 113 is read out by the reproducing head 112. The read-out data is subjected to a predetermined demodulating process by a demodulation circuit 202 and is supplied to an error correction circuit 203.
The error correction circuit 203 corrects erroneous data by the error detection correction code which was added in the recording mode. With respect to the sync block in which uncorrectable data occurs, an error flag is outputted to a sync block memory 204.
The sync block memory 204 stores the error corrected coding data on a sync block unit basis.
The error correction circuit 203 outputs an error flag to the sync block in which the error uncorrectable data exists.
That is, the error correction circuit 203 generates “1” in the case where the sync block has error uncorrectable data and generates “0” when no error uncorrectable data exists on a sync block unit basis. The value “1” or “0” is written into a predetermined region in the sync block memory 204.
FIG. 7 schematically shows an internal structure of the sync block memory 204.
The error flag outputted from the error correction circuit 203 is written into a region 71.
The coding data of the low frequency component of the DCT transformation coefficient in the region 52 (refer to FIG. 5) of the sync block is written into a region 72. The coding data of the high frequency component of the DCT transformation coefficient in the region 53 (refer to FIG. 5) of the sync block is written into a region 73.
L1 to L30 in the region 72 indicate cod data of the low frequency components of the DCT blocks #1 to #30. H1 to H30 denote code data of the high frequency components of the DCT blocks #1 to #30. A hatched portion indicates a delimiter code EOB.
In case of reading out the coding data every block from the memory 204, since the coding data of the low frequency component of the DCT transformation coefficient of each DCT block has been stored at a predetermined memory location in the region 72 in the memory 204, it can be sequentially read out. However, although the memory location of the coding data of the high frequency component of each DCT block has been stored in the region 73 in the memory 204, since the position in the region 73 is unspecified, the coding data of the high frequency component is sequentially read out on the basis of the EOB.
A forward direction low frequency data read-out circuit 205 sequentially reads out the coding data L1 to L30 of the low frequency components in accordance with the order from the head, address, in the region 72 in the sync block memory 204 (forward direction decoding mode).
A forward direction high frequency data read-out circuit 206 sequentially reads out the coding data H1 to H30 of the high frequency components in accordance with the order from the head address in the region 73 in the sync block memory 204 on the basis of the EOB.
The coding data L1 to L30 of low frequencies and coding data H1 to H30 of high frequencies which were read out by the forward direction low frequency read-out circuit 205 and the forward direction high frequency read-out circuit 206 are supplied to contacts (a) and (b) of a switch 207.
The switch 207 is controlled by a switch control circuit 208 so that the coding data of low frequency continues after the coding data of the high frequencies of each DCT block.
Since a decoding circuit 209 restores the image data by executing the processes opposite to the processes upon coding, their detailed descriptions are omitted here. The decoding circuit 209 restores the image data by executing a variable length decoding, a reverse quantization, and reverse DCT transformation to the coding data of each DCT block which is supplied from the switch 207. The restored image data is inputted to a frame memory 210.
On the other hand, a reverse direction low frequency data read-out circuit 211 sequentially reads out the coding data L1 to L30 in the region 72 in the sync block memory 204 in accordance with the order opposite to that in case of the low frequency read-out circuit 205, namely, in accordance with the order from L30 to L1.
A reverse direction high frequency data read-out circuit 212 reads out the coding data H1 to H30 of the high frequencies in the region 73 in the sync block memory 204 in accordance with the order opposite to that in case of the forward direction high frequency read-out circuit 206, namely, in accordance with the order from H30 to H1 (reverse direction decoding mode).
In case of reading out on a bit unit basis, it is convenient that the EOB is set to the same bit train even in case of reading in the direction from any of the LSB or MSB.
The coding data L30 to L1 of the low frequencies and the coding data H30 to H1 of the high frequencies which were read out by the reverse direction low frequency read-out circuit 211 and reverse direction high frequency read-out circuit 212 are supplied to contacts (a) and (b) of a switch 213.
The switch 213 is controlled by the switch control circuit 208 in a manner such that the coding data of the high frequency continues after the coding data of the low frequencies of each DCT block.
A decoding circuit 214 restores the image data by executing the variable length decoding, reverse quantization, and reverse DCT transformation to the coding data of each DCT block which is supplied from the switch 213 in a manner similar to the decoding circuit 209. The restored image data is inputted to the frame memory 210.
As shown in FIG. 7, it is now assumed that an error occurs in the sync block #3 and the error flag has been set to “1” in the sync block memory 204.
The switch control circuit 208 refers to the error flag region 71 in the sync block memory 204 and controls the switches 207 and 213 as mentioned above and restores the image data so long as the error flag is not set to “1”.
That is, since the image data is restored in both of the forward direction decoding mode and the reverse direction decoding mode, the block is restored in two decoding modes. However, it is sufficient that the image data restored by either one of the decoding modes is read out from the frame memory 210. For example, in the embodiment, the image data restored in the forward direction decoding mode is outputted to the post stage.
On the other hand, in the case where the error flag has been set to “1”, with respect to the sync block with such an error flag, the switches 207 and 213 are held in a state in which they are connected to the contact (a).
That is, in the example of FIG. 7, a part of H13 and parts of H14 to H17 and H18 are ignored. With respect to those DCT blocks #13 to #18, they are decoded by only the low frequency components.
A circuit comprising the circuits 205 to 209 sequentially reads out the coding data from the head address and restores the image data of each DCT block by the coding data of the low and high frequencies. However, as for the sync block having the error flag, the image data of the DCT block is restored by only the coding data of low frequency. The restored image data is stored into the frame memory 210.
On the other hand, the circuit comprising the circuits 208 and 211 to 214 reads out the coding data in accordance with the order opposite to that mentioned above and restores the image data of each DCT block by the coding data of the low and high frequencies and writes the restored image data into the frame memory 210. However, as for the sync blocks after the sync block having the error flag, the reading operation from the memory 204 is stopped and the writing operation into the frame memory 210 is also stopped.
As mentioned above, in the sync blocks, the circuits 205 to 207 and 209 properly restores the image data by using the coding data of low and high frequencies from the first sync block to the sync block just before the sync block having errors in the forward direction. The circuits 211 to 214 properly restores the image data by using the coding data of low and high frequencies from the last sync block to the sync block just before the sync block having errors in the reverse direction.
With respect to the DCT blocks included in the sync block with errors, the circuits 205 to 207 and 209 reproduces the image data by only the low frequency component.
As mentioned above, when the image data is stored into the frame memory 210, it is read out and supplied to a D/A converting circuit 215 in accordance with the raster scanning order and is converted into the analog signal. The analog signal is outputted to the outside from an output terminal 216.
In the embodiment, with regard to the DCT blocks included in the sync block having errors, the circuits 205 to 207 and 209 reproduces the image data by only the low frequency component. However, the circuits 211 to 214 can also reproduce the image data by only the low frequency component.
For the errors of the sync block unit, a deterioration of the picture quality can be minimized by the construction of sync block and decoding method mentioned above. Even in a special reproducing mode, the reproduced image of a good picture quality can be obtained.
The reason why such a good image is obtained will now be described with reference to FIG. 2. In a high speed reproducing mode, as for the sync block 11 in which only a part could be scanned by the reproducing head, the whole DATA arranged in the rear portion in the sync block 11 cannot be taken out in the conventional apparatus, so that there are problems such that the data necessary for the expanding process cannot be fully prepared and the whole image data existing in the sync block 11 cannot be reproduced. However, by constructing the sync block as in the embodiment, since the data of the low frequency portion of the data which was DCT transformed and coded is arranged in the front portion of the sync block, the image signal can be restored even from the sync block in which only a part of the image data can be taken out. Therefore, many newer picture plane regions can be reproduced on the screen.
The present invention can be embodied by many other forms without departing from the spirit and main features of the invention.
For example, in the description of the above embodiment, two reading and decoding circuit systems such as circuits 205, 206, 207, and 209 and circuits 211, 212, 213, and 214 have been provided. However, as already described with respect to one of those circuits, it is also possible to construct in a manner such that the reading and decoding operations are first executed from the head address and the decoding is executed by only the low frequency component for the sync block having the error flag and, after that, the reading and decoding operations are executed in accordance with the opposite order from the last address.
In the embodiment, only an example has been shown and described with respect to the number of sync blocks corresponding to the DCT blocks or their relations and the number of sync blocks and their relations can be arbitrarily set. The fixed length unit of the code amount and the size of DCT block can be also similarly arbitrarily set.
In other words, the foregoing description of embodiment has been given for illustrative purposes only and not to be construed as imposing any limitation in every respect.
The scope of the invention is, therefore, to be determined solely by the following claims and not limited by the text of the specifications and alterations made within a scope equivalent to the scope of the claims fall within the true spirit and scope of the invention.

## Claims

1. A decoding apparatus for decoding, on a block basis, input coded data of a plurality of blocks which are provided by dividing an image signal into blocks, by performing a compression coding on the blocks in a predetermined order, and by adding sync information to the coded data on an m blocks basis, m being a natural number, comprising:
storing means for storing the coded data on the m blocks basis;
detecting means for detecting erroneous data included in the input coded data, on the m blocks basis, wherein said storing means stores a detecting result with respect to the sync information;
decoding means having a first decoding mode for decoding the coded data in the predetermined order and a second decoding mode for decoding the coded data in an order opposite to the predetermined order, on the block basis, and selecting the first decoding mode and the second decoding mode in accordance with the detecting result of said detecting means so that the second decoding mode is selected on the m blocks basis when said detecting means detects the erroneous data and the first decoding mode is selected on the m blocks basis when said detecting means does not detect the erroneous data; and
output means for outputting the data decoded by said decoding means, in the predetermined order regardless of the result of the detection by said detecting means and the decoding mode selected by said decoding means,
wherein said storing means stores a flag for the detecting result, and
wherein said decoding means decodes the coded data in the m blocks basis in the predetermined order from a first sync block to the sync block just before the sync block having errors, and in the order opposite to the predetermined order from the last sync block to the sync block just before the sync block having errors.

2. A decoding method of decoding, on a block basis, input coded data of a plurality of blocks which are provided by dividing an image signal into blocks, by performing a compression coding on each block in a predetermined order, and by adding sync information to the coded data on an m blocks basis, m being a natural number, said decoding method comprising:
a storing step, of storing the coded data on the m blocks basis;
a detecting step, of detecting erroneous data included in the input coded data, on the m blocks basis, wherein said storing step includes storing a detecting result with respect to the sync information;
a decoding step, of effecting a first decoding mode for decoding the coded data in the predetermined order and a second decoding mode for decoding the coded data in an order opposite to the predetermined order on the block basis so that the first decoding mode and the second decoding mode are selected in accordance with a detecting result of said detecting step in such a manner that the second decoding mode is selected on the m blocks basis when said detecting step detects the erroneous data and the first decoding mode is selected on the m blocks basis when said detecting step does not detect the erroneous data; and
an output step, of outputting the data decoded in said decoding step, in the predetermined order regardless of the result of the detection in said detecting step and the decoding mode selected in said decoding step,
wherein said storing step stores a flag for the detecting result, and
wherein said decoding step decodes the coded data in the m blocks basis in the predetermined order from a first sync block to the sync block just before the sync block having errors, and in the order opposite to the predetermined order from the last sync block to the sync block just before the sync block having errors.