JP2006277842A - Reproducing device, reproducing method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reproducing device, a reproducing method and a program for increasing a correction distance while reducing a miscorrection probability. <P>SOLUTION: An error correction processing circuit 3 applies C1-correction to data read at reproduction in real time, and only when no error is present in a C1 direction or error correction is possible, utilizes already corrected OWP and calculates the appearing frequency (histogram) of the OWP for each sector. Also, when there is an error in the C1 direction, the appearing frequency of the OWP is not calculated. A system control circuit 6 judges the probable value of the OWP from the appearing frequency of the OWP, and performs error control corresponding to correction conditions after product code correction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a playback apparatus, a playback method, and a program for playing back recorded digital data from a recording medium on which information data is recorded as digital data.

  A digital VTR is known as a recording / reproducing apparatus that records information data as digital data on a magnetic recording medium and reproduces the recorded digital data. In a digital VTR, due to the momentary clogging of the magnetic recording head or dust on the magnetic tape, an unrecorded area is generated on the magnetic tape even though the magnetic recording head scans the magnetic tape. The recorded data may not be normally recorded on the magnetic tape.

  In particular, when information data is newly overwritten and recorded on a magnetic tape on which information data has already been recorded, if an unrecorded area is generated on the magnetic tape due to clogging of the magnetic recording head, the underlying information data is not reproduced during playback. Will be played.

  In general, digital VTR records information data by performing error correction coding processing using a Reed-Solomon product code or the like for error correction at the time of reproduction. When the data is reproduced as it is, no error can be detected with the correction code in the same direction as the recording direction (for example, the C1 direction in the product code configuration), but in a direction orthogonal to the correction code (for example, the C2 direction in the product code configuration). It needs to be corrected.

In addition to the error correction code, a technique for performing error correction processing using an identification flag added at the time of recording and having a different value for each scene is known. An erasure flag for correcting an error in the C2 direction is set according to the value of an identification flag in which a different value is set between the data and the underlying information data to be overwritten, thereby improving the error correction capability in the C2 direction. A method has been proposed (see, for example, Patent Document 1).
JP 2004-55091 A

  However, in the above-described conventional method, the correctable limit distance of erasure correction matches the minimum code distance, and therefore, when there is an error in the corresponding sync block, random correction (correction without specifying an error position) is performed. While it has a correction capability that is twice as large as the comparison, if there is no error in the corresponding sync block, performing erasure correction at the correction distance limit (minimum code distance) dramatically increases the error correction probability. There is a problem of making it.

  Also, random correction and erasure correction effective for burst correction are in a trade-off relationship, and increasing the correction distance used for erasure correction, that is, increasing the erasure correction flag decreases the random correction capability. There's a problem.

  The present invention has been made paying attention to these problems, and an object of the present invention is to provide a playback device, a playback method, and a program capable of increasing the correction distance while reducing the error correction probability. .

  In order to achieve the above object, the playback apparatus according to claim 1 records and records information data including identification data in which a different value is set for each scene by performing an error correction encoding process of a product code configuration. Reproducing means for reproducing the information data from the recording medium, and error correction processing means for performing error correction decoding processing on the information data reproduced by the reproducing means, wherein the error correction processing means is in the C1 direction. An error position in the C2 direction is detected based on identification data included in information data having no error.

  In order to achieve the above object, the reproduction method according to claim 5 records the information data including identification data in which a different value is set for each scene by performing an error correction encoding process of a product code configuration. A reproduction step for reproducing the information data from the recording medium; and an error correction processing step for performing an error correction decoding process on the information data reproduced by the reproduction step. An error position in the C2 direction is detected based on identification data included in information data having no error.

  According to the present invention, the probability of erroneous correction is reduced while dealing with a case where an unrecorded area occurs even though the magnetic recording head scans the magnetic recording medium and the recorded data is not normally recorded on the magnetic recording medium. Thus, error correction substantially close to the correction limit of the Reed-Solomon product code can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a digital VTR 1 to which a playback apparatus according to an embodiment of the present invention is applied.

  In the figure, a digital VTR 1 mainly includes a reproduction circuit 2 that reproduces image data by scanning a number of helical tracks formed on the magnetic tape 100 with a rotating head (not shown), and reproduced image data. In contrast, an error correction processing circuit 3 that performs error correction processing, which will be described later, a decoding circuit 4 that decodes image data that has been subjected to error correction processing, and an output circuit 5 that outputs the decoded image data to an external monitor or the like The system control circuit 6 controls each unit and the operation unit 7 having various switches.

  In the present embodiment, an error correction encoding process using a Reed-Solomon product code is performed for each predetermined amount of encoded image data, and sync data and various additional data are added to the C1 direction. A sync block is formed and recorded on the magnetic tape 100 for each sync block. Also, flag data called an OWP (Over Write Protection) flag having different values for each scene of image data and different values between adjacent scenes is recorded together with the image data.

  FIG. 2 shows a state in which new image data is overwritten on the image data recorded on the magnetic tape 100. In FIG. 2, OWP = 1, OWP = 2 and OWP = 3 on the magnetic tape 100. A state is described in which each piece of image data is recorded and image data with OWP = 4 is about to be overwritten. When overwriting is prohibited for each image data with OWP = 1 and OWP = 2, image data with OWP = 4, that is, new image data at the recording position of the image data with OWP = 3. Will be overwritten.

  As shown in FIG. 2, when the image data with OWP = 4 is overwritten and recorded at the recording position of the image data with OWP = 3 as shown in FIG. This shows a state in which an unrecorded area 100a is generated without being recorded. In this unrecorded area 100a, the background data with OWP of 3 remains as it is, and as shown in FIG. 3, the background image data (OWP = 3) is mixed in the image data with OWP = 4. .

  FIG. 4 is a diagram showing an image on the sector when an unrecorded area enters as shown in FIG.

  As shown in FIG. 4, the sync block with OWP = 3 is mixed in on the sector, and the data of the sync block with OWP = 3, which is the background data, should be detected as an error originally. However, since all the data of the sync block remains as it is as the background data of OWP3, it is determined that there is no error even if error correction decoding processing using C1 parity that is the scanning direction (recording direction) of the head is performed. Therefore, this background data error can only be detected by error correction decoding processing using C2 parity in a direction perpendicular to the head scanning direction.

  Therefore, in this embodiment, as will be described later, a histogram is formed only with OWP having no error in the C1 direction during real-time C1 correction, and error detection is performed using this histogram.

  FIG. 5 is a diagram illustrating an example of the data structure of the sync block.

  As shown in the figure, the sync block data is composed of flag data including a track number (TrkN), a sync block number (SyncN) and an OWP flag, main data such as image data and audio data, and a C1 parity portion. Has been.

  If C1 correction is possible during C1 real-time correction, the corrected sync block data is transferred to the address on the memory calculated by the corrected track number and sync block number. On the other hand, when C1 correction is impossible, the track number and sync block number of the current sync block data are inferred from the track number and sync block number of the previously transferred sync block data using continuity. . Then, the sync block data is transferred to the address on the memory calculated based on the analogized value.

  FIG. 6 is a diagram illustrating an example of a data structure of a sector.

  As shown in the figure, one sector is composed of a plurality of sync blocks. A C1 parity is added in the head scanning direction (recording direction), and a C2 parity is added in a direction orthogonal to the C1 direction.

  FIG. 7 is a diagram showing the data structure of the sync block after the real-time C1 correction.

  As shown in the figure, the C1 update flag (C1Up) indicating that the sync block data has been written on the memory at the time of C1 correction, and the C1 correction flag (C1Flg) indicating that the C1 correction has been performed are the sync block flags. It is added as data. The C1 update flag and the C1 correction flag are used as erasure flags in the first C2 correction when correcting the product code following the real-time C1 correction. Further, instead of the C1 parity part, the C1 syndrome coefficient data calculated at the time of real-time C1 correction constitutes a part of the sync block data. The C1 syndrome data is set to “0” when real-time C1 correction is performed.

  FIG. 8 is a diagram showing the data structure of the sync block after product code correction.

  When product code correction is performed, as shown in the figure, as sync block flag data, a C2 update flag (C2Up) indicating that the product code correction has been completed, and a product code indicating that the product code has been corrected. A correction flag (C2Flg) and an error correction existence probability flag (Sys) indicating the presence or absence of the error correction existence probability are added. In the subsequent processing, it is recognized that the product code correction is completed based on the C2 update flag, and error processing is performed based on the error correction existence probability flag, the product code correction flag, the C1 correction flag, and the OWP.

  FIG. 9 is a functional block diagram for explaining error correction processing executed by the error correction processing circuit 3 and the system control circuit 6.

  As shown in the figure, the error correction processing circuit 3 includes a real-time C1 correction processing unit 3a, a memory 3b, and a product code correction unit 3c.

  The sync block data having the data structure shown in FIGS. 5 and 6 is input to the real-time C1 correction processing unit 3a, and C1 correction processing is performed in real time. If C1 correction is possible, the corrected sync block data is transferred to the address on the memory 3b calculated based on the corrected track number and sync block number. On the other hand, if C1 correction is impossible, the track number and sync block number of the current sync block data are calculated using continuity based on the track number and sync block number of the sync block data transferred previously. By analogy, the sync block data is transferred to the address on the memory 3b calculated based on the analogized value. FIG. 7 shows a data structure on the memory 3b.

  At the same time, a histogram is formed by OWP having no error in C1 at the time of real-time C1 correction, and the formed histogram is transferred to the system control circuit 6. The C1 corrected data stored in the memory 3b is read and input to the product code correction unit 3c. The C1 update flag and the C1 correction flag are used as erasure flags in the first C2 correction. After product code correction, the data is written into the memory 3b. FIG. 8 shows a data structure written in the memory 3b after the product code correction process. Note that the memory 3b has a data storage area that has been subjected to the C1 correction process and a data storage area that has been subjected to product code correction. The data subjected to the product code correction process is identified by the system control circuit 6 as to whether it is valid data, and the process proceeds to the next process.

  FIG. 10 is a flowchart showing a procedure of error correction processing.

  In the figure, first, in step S1, reproduction data in the format shown in FIGS. 5 and 6 is read out.

  Next, in step S2, real-time C1 correction is performed on the read data, and in step S3, it is determined whether or not C1 correction is possible.

  If it is determined in step S3 that C1 correction is possible, the process proceeds to step S4, and a histogram is calculated based on the corrected OWP value. On the other hand, if it is determined that C1 correction is impossible, In step S5, the track number and the sync block number are inferred using continuity.

  In the following step S6, an address on the memory 3b to which data is written is calculated from the track number and the sync block number, and in step S7, data is written in the format shown in FIG.

  In step S8, data in the format shown in FIG. 7 is read from the memory 3b in order to perform product code correction. In step S9, product code correction is performed.

  In subsequent step S10, the product code corrected data is written in the memory 3b in the format shown in FIG. 8, and in step S11, it is determined whether or not there is an error in the C2 direction. If it is determined in step S11 that there is no error, the process proceeds to step S12, and it is determined whether there is an error in the C1 direction and an error correction probability. If it is determined in step S12 that there is an error in the C1 direction and there is an error correction probability, the process proceeds to step S13, and processing is performed according to the contents of this data, while there is no error in the C1 direction or an error occurs. If it is determined that there is no correction probability, the process proceeds to step S14 and normal processing is performed.

  On the other hand, if it is determined in step S11 that there is an error in the C2 direction, the process proceeds to step S15 to determine whether there is an error in the C1 direction. If it is determined in step S15 that there is no error in the C1 direction, the process proceeds to step S16, and the OWP is determined based on the OWP value determined to be probable by the system control circuit 6. If the OWP values match in step S16, the process proceeds to step S14 and normal processing is performed. If the OWP values are different, the process proceeds to step S17 and error processing is performed.

  On the other hand, if it is determined in step S15 that there is an error in the C1 direction, the process proceeds to step S19 to perform error processing, and then this error correction processing is terminated.

  The above error correction processing is summarized as follows.

  (1) The error correction processing circuit 3 performs C1 correction on the data read at the time of reproduction in real time, and uses the corrected OWP only when there is no error in the C1 direction or error correction is possible. The appearance frequency (histogram) of OWP is calculated. When there is an error in the C1 direction, the appearance frequency of OWP is not calculated. The system control circuit 6 determines a probable OWP value from the appearance frequency of the OWP, and performs error control according to the correction status after product code correction.

  (2) After C1 correction in real time for each sync block, this data, OWP, C2 parity, and C1 syndrome polynomial coefficients are temporarily stored in the memory 3b for decoding the product code. If the C1 correction is possible, the address on the memory 3b is calculated from the track number and the sync block number, which are the sync block flag data, and the data is stored at the address, while the C1 correction is impossible. Uses the continuity to estimate the current track number and sync block number from the track number and sync block number of the previous sync block, calculates the address on the memory 3b based on the estimated value, and stores data in that address. Save. Then, a new C1 correction flag is added as flag data of the sync block, and when the C1 correction becomes impossible, or when the C1 correction becomes possible because the background data exists, the discontinuous sync block number When this occurs, a new C1 update flag is added as flag data of the sync block so that it can be identified on the memory 3b.

  (3) The C1 correction flag and the C1 update flag are used as the first C2 correction erasure flag at the time of repeated product code correction, and the data calculated at the time of real-time C1 correction is used as the C1 syndrome coefficient of the product code. There is a difference between the areas protected in the C1 direction and the C2 direction, and in addition to the erroneous correction, the C2 direction is all corrected, and there may be an error in the C1 direction. The product code is repeatedly corrected until the uncorrectable portion in the C1 direction becomes less than the correction distance limit in the C2 direction. If all the C2 directions are corrected and the uncorrectable part in the C1 direction exceeds the correction distance limit in the C2 direction, random correction in the C1 direction is performed, and all the C2 directions are corrected after the random correction in the C1 direction, and When the uncorrectable part in the C1 direction exceeds the correction distance limit in the C2 direction, the correction process is terminated because the C1 correction is impossible in principle and there is a high probability that this data is erroneously corrected. The system control circuit 6 is notified that there is an erroneous correction probability in the data. Then, a product code update flag for identifying whether or not product code correction is possible and completion of product code correction and an error correction probability presence flag are newly recorded as a sync block flag.

  (4) When the end of the product code correction is recognized by the product code update flag, all the C2 directions are corrected after the product code correction, and there is no error correction probability, it is determined that there is no error in this data. . If all the C2 directions are corrected and there is an erroneous correction probability, error processing corresponding to this data is performed on the sync block in which the C1 uncorrectable flag is set. Further, the C2 direction is not completely corrected and C1 correction is impossible, or the C2 direction is not completely corrected and C1 corrected, and the OWP that is determined by the system control circuit 6 in the above (1). If the value does not match, it is determined that an error exists only for the sync block.

  A program in which a storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus is stored in the storage medium. It goes without saying that the object of the present invention can also be achieved by reading and executing the code.

  In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, hard disk, magneto-optical disk, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD + RW, magnetic A tape, a non-volatile memory card, a ROM, or the like can be used. Further, the program code may be supplied from a server computer via a communication network.

  Further, by executing the program code read out by the computer, not only the functions of the above-described embodiments are realized, but also the OS running on the computer based on the instruction of the program code performs the actual processing. It goes without saying that a case where the functions of the above-described embodiment are realized by performing part or all of the above and the processing thereof is included.

  Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

It is a block diagram which shows schematic structure of digital VTR to which the recording / reproducing apparatus which concerns on one embodiment of this invention is applied. It is a figure which shows a mode that new image data is overwritten on the image data recorded on the magnetic tape. As shown in FIG. 2, when image data with OWP = 4 is overwritten and recorded at the recording position of image data with OWP = 3, an unrecorded area occurs, and new image data is not normally recorded on the magnetic tape. It is a figure which shows a mode. It is a figure which shows the image on the sector when an unrecorded area | region enters like FIG. It is a figure which shows an example of the data structure of the sync block of reproduction | regeneration data. It is a figure which shows an example of the data structure of the sector of reproduction | regeneration data. It is a figure which shows the data structure of the sync block after real-time C1 correction. It is a figure which shows the data structure of the sync block after product code correction. FIG. 2 is a functional block diagram for explaining error correction processing executed by an error correction processing circuit and a system control circuit in FIG. 1. It is a flowchart which shows the procedure of an error correction process.

Explanation of symbols

1 Digital VTR
2 reproduction circuit 3 error correction processing circuit 3a real-time C1 correction processing unit 3b memory 3c product code correction unit 4 decoding circuit 5 output circuit 6 system control circuit 7 operation unit 100 magnetic tape

Claims (6)

Reproduction means for reproducing the information data from a recording medium recorded by performing error correction coding processing of a product code configuration on information data including identification data in which a different value is set for each scene,
Error correction processing means for performing error correction decoding processing on the information data reproduced by the reproduction means,
The reproduction apparatus according to claim 1, wherein the error correction processing means detects an error position in the C2 direction based on identification data included in information data having no error in the C1 direction. The error correction processing means includes
Correction means for C1 correction of information data reproduced by the reproduction means in real time;
Calculating means for calculating the appearance frequency of the value of the identification data included in the information data that can be C1 corrected by the correcting means or information data that does not have an error in the C1 direction;
Determination means for determining the value of the probable identification data based on the appearance frequency of the value calculated by the calculation means,
2. The reproducing apparatus according to claim 1, wherein an error position in the C2 direction is detected based on the value of the identification data determined by the determination unit.   3. The reproducing apparatus according to claim 2, wherein the calculating unit does not calculate the appearance frequency of the value of the identification data included in the information data that cannot be C1 corrected by the correcting unit.   2. The reproducing apparatus according to claim 1, wherein the recording medium is a magnetic tape, and the reproducing means includes a rotating head that reads a plurality of oblique tracks on the magnetic tape and reads the information data. A reproduction step of reproducing the information data from a recording medium recorded by performing error correction coding processing of a product code structure on information data including identification data in which a different value is set for each scene;
An error correction processing step of performing error correction decoding processing on the information data reproduced by the reproduction step,
The error correction processing step detects an error position in the C2 direction based on identification data included in information data having no error in the C1 direction.   A program for causing a computer to execute the reproduction method according to claim 5.

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