Interpolation circuit for variable speed reproduction in a video tape recorder

Abstract: A picture enhancing circuit including reproducing means, a field memory 14 and writing means. The reproducing means reproduces a field signal comprising fields each containing a plurality of sync blocks each constituted by sync data and picture data. The writing means writes the output of the reproducing means to the field memory 14 in units of sync blocks, the picture data being written to the memory 14 along with the sync data whose contents are reset. When sync blocks are read from the field memory 14 the contents of the sync data are updated. The contents of the sync data indicate the number of times that data has been read and thus its age and the data can be used or interpolated depending on its age.

Description: The present invention relates to a picture enhancing circuit for use with digital video tape recorders (VTR's). Editing on digital VTR's often involves varying the playback speed and can involve playing back the tape at a speed higher than normal reproduction speed. In such a variable speed reproduction mode, the magnetic head of the machine does not follow the path of the originally recorded diagonal tracks on the tape but, as shown by the broken line in Fig 8 of the accompanying drawings, runs across the tracks (shown in solid line). Thus the variable speed reproduction mode, recorded data on the tape is reproduced from a plurality of tracks thereof depending on the actual speed. Suppose that a magnetic head 3 attached to a rotating drum 2 is used to record and reproduce signals as shown in Fig. 9 and that a plurality of sync blocks constitute a one-track field signal as depicted in Fig. 10. During playback the reproduced field signal is written to a field memory or the like in units of sync blocks and a single picture is produced by reading one sync block from the field memory. The data written to the field memory is held unchanged unless and until new data is written thereto. If the field signal reproduced by the magnetic head 3 has a corresponding reproduced sync block, the whole corresponding sync block.is replaced by the new sync block. However where the playback speed is varied from the normal speed, not all of the recorded data is reproduced and so some data in the field memory will not be updated. It follows that where the data of the same sync block in successive pictures is not encountered for a certain period of time because of the varying speed of reproduction, the picture data of the old sync block is used as the reproduced picture signal. This means that mutually uncorrelated items of data will be utilized to construct the reproduced picture. This can result in reproduced pictures being poorly animated or appearing dragged across the screen, thereby drastically deteriorating the quality and degree of recognition of reproduced pictures. The degraded correlation between data items may be somewhat alleviated by using interpolation depending on whether the sync block data about to be used is new or old as proposed by the present applicants in US-A-4,799,113. The alleviated correlation enhances the degree of reproduced picture quality. Fig. 11 is a block diagram of the prior art picture enhancing circuit. The enhancing circuit of Fig. 11 comprises a single reproduction system that uses a pair of reproducing magnetic heads shown in Fig. 9. In Fig. 11, a reproduced field signal input through a terminal 11 is sent to a sync detection circuit 12 and an error correction circuit 13 (e.g. an inner code corrector). The sync detection circuit 12 detects sync data inserted in each sync block. The detected sync data is used by the error detection circuit 13 to correct the reproduced field signal. If the sync data has no error or if the error found therein is of a correctable nature, ID information inserted in the sync block is relied on to write to a field memory 14 the picture data from that sync block. The picture data read from the field memory 14 is fed to an interpolation circuit 15. Interpolation is carried out only when the interpolation conditions, to be described later, are met where the picture data of an old sync block is used. Otherwise the picture data is allowed to pass through the field interpolation circuit 15 unprocessed. The reproduced output interpolated or passed on unprocessed appears at a terminal 16. A sync flag memory 17 has as many memory areas as the sync blocks of a field. When picture data is written to the field memory 14, a sync flag, e.g. of eight bits, is written to the memory area corresponding to the sync block of the picture data or more specifically the contents of the sync flag in the applicable area are reset e.g. to zero. When the picture data of the corresponding sync block is read from the field memory 14, the sync flag is also read from the sync flag memory 17 in synchronism with the picture data read operation. The flag is incremented by 1 by an incrementer 18, and then the flag is rewritten to the same sync block memory area. For example, if the picture data of a sync block i is read from the field memory 14, the corresponding sync flag (see Fig. 12) is incremented by 1. The updated sync flag is written to the same sync block memory area i, as shown in Fig. 13. As mentioned when new picture data is written to the field memory 14, the corresponding sync flag is reset accordingly which causes the whole contents of the sync flag to be reset to 0, as depicted in Fig. 12. The sync flag read from the memory 17 is passed on to a flag decoder 19 for determination of the flag value. If the flag value is found to exceed a predetermined reference value (e.g., 30 - 50), indicated that it is very old data which has been used several times and not overwritten by new data, a "1" is output by the flag decoder 19, which triggers interpolation. This is because picture data which is too old, if used unchecked, loses its correlation to other picture data and hence lowers the degree of recognition of reproduced pictures. The foregoing description applies to digital VTR's having a single reproduction system. If two reproduction systems are incorporated as shown in Fig. 14, the newer of the two streams of picture data reproduced therefrom may be selected for picture reproduction. This scheme enhances the degree of reproduced picture recognition appreciably. As shown in Fig. 14 this magnetic head device has four recording magnetic heads 3 and also two independently provided reproduction systems. That is, four magnetic heads make up a first reproduction system 4, close to which is located a separate second reproduction system 5. Fig. 15 is a block diagram of a prior art picture enhancing circuit 10 that utilizes the rotating magnetic head device of Fig. 14. As shown in Fig. 15, the picture recognition enhancing circuit 10 comprises first and second enhancing circuits 10A and 10B each of which has a basic construction the same as that in Fig. 11. In this example, the reproduced outputs from the first and second reproduction systems 4 and 5 enter terminals 11 and 21, respectively. From the terminals, the reproduced outputs are written to field memories 14 and 24 in units of sync blocks, the picture data in the outputs being later read therefrom in the same units. When read from the field memories 14, 24, the picture data is supplied to a changeover switch 31 for selection of the most recent picture data within the same sync block. The picture data thus selected serves as the data for picture reproduction. The changeover switch 31 works as follows: The sync flag of the same sync block from the sync flag memories 17 and 27 are fed to a flag comparator 32 and a flag decoder 33. The flag comparator detects the sync flag having the smaller of the two values (the detected flag indicates the sync block containing the most recent picture data). The detected flag activates the changeover switch 31 so as to select the most recent picture data from among the picture data coming from the field memories 14 and 24. The flag decoder 33 compares the sync flag value selected on the basis of the detected flag with the above-mentioned reference value. If the detected flag is found to exceed the reference value, the interpolation circuit 15 is activated to interpolate the picture data. The system of Fig. 15, which reproduces pictures always on the basis of the most recent picture data, provides a more enhanced degree of reproduced picture recognition than the constitution of Fig. 11. However, these prior art setups have a major disadvantage. The system of Fig. 11 requires the memory 17 in which to retain sync flags, while that of Fig. 11 needs two such memories. Although these memories 17 and 27 are required to have only limited amounts of memory capacity, the comparable small-capacity memories are difficult to procure on today's memory market. Manufacturers are thus forced to utilize commercially available memories that have a far greater capacity than is actually needed which is a significant waste of resources. It is therefore an object of the present invention to provide a picture recognition enhancing circuit that eliminates the need for sync flag memories while still providing processing capabilities comparable to those offered by systems with such memories. According to the present invention, there is provided an apparatus for processing digital data comprising: input means for providing an input digital signal including block data and address data, the address data being associated with said block data, said block data comprising sync data and word data; storing means connected to said input means for storing in a field memory said block data, comprising the word data and associated sync data, from said input means according to said address data associated with said block data, and for resetting said sync data of said block data to form a flag on storage of the data, means for reading the data from the field memory; rewrite means for rewriting, in response to a reading operation by said read means of said word data, said sync data stored in said field memory associated with the word data whereby the stored sync data is indicative of the number of times the associated word data has been read; processing means connected to said field memory for processing said read word data and outputting it; control means for controlling the output operation so that word data processed by said processing means is selectively provided as an output data instead of said word data read from said field memory according to said flag associated with said read word data. The apparatus is particularly suitable as a picture enhancing circuit for improving the quality of reproduced pictures by enhancing the degree of recognition of the pictures acquired in variable speed reproduction. It may comprise reproducing means for reproducing a field signal made of a field containing a plurality of the sync blocks each constituted by the sync data and picture data as the word data. In accordance with invention the image data including the sync data is written in the field memory and the sync data is reset, e.g. to zero, on storage, i.e. either before, at or just after storage. When the image data is read the associated sync data is rewritten, e.g. incremented, so as to be indicative of the number of times that data has been read. If the data has been used before too often, it can be replaced, e.g. by interpolation from newer data, to avoid including uncorrelated picture data in the output. The sync data can be rewritten, e.g. incremented, before, during or after reading of the associated data and is reset only when new data is written to the memory. Thus according to the invention, the sync data in the sync block double as a sync flag because after the sync detection circuit has detected the sync data inserted in the sync block, the sync data becomes unnecessary. Thus the invention makes a positive use of the sync data as the sync flag when that data is no longer needed. Illustrative embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which:- Fig. 1 is a block diagram of a picture enhancing circuit of a first embodiment of the invention; Fig. 2 is a view showing the construction of a typical sync block; Fig. 3 is a set of views depicting a field memory used both as a picture data memory and as a sync flag memory according to the invention; Fig. 4 is a set of views illustrating another field memory used both as a picture data memory and as a sync flag memory according to the invention; Fig. 5 is a block diagram of a picture enhancing circuit of a second embodiment of the invention; Fig. 6 is a view showing a circuit arrangement according to the invention; Fig. 7 is a block diagram of a picture enhancing circuit of a third embodiment of the invention; Fig. 8 is a view of track patterns in connection with the digital VTR; Fig. 9 is a view of a typical magnetic head device of the digital VTR; Fig. 10 is a view showing the structure of a field signal used by the digital VTR; Fig. 11 is a block diagram of a typical prior art picture enhancing circuit; Fig. 12 is a view of a sync flag memory for use with the prior art picture enhancing circuit; Fig. 13 is a view of another sync flag memory for use with the prior art picture enhancing circuit; Fig. 14 is a view of another typical magnetic head device of the digital VTR; and Fig. 15 is a block diagram of another prior art picture enhancing circuit that utilizes the rotating magnetic head device of Fig. 14. Fig. 1 is a block diagram of a first embodiment of a picture enhancing circuit 10 of the invention which uses a single reproduction system rotating magnetic head device of Fig. 9. As mentioned above the field signal recorded on each track contains a plurality of sync blocks and as shown in Figure 2 each sync block includes sync data SYNC, picture data DATA that contains an ID code, and a parity code PARITY. With one inner code block (ID, DATA, PARITY) constituting one sync block, error correction is accomplished using the data within each block. The construction of Fig. 1 is similar to that of Fig. 11, except that the data within the sync block corrected for error is placed in the corresponding area in the field memory 14. Conventionally, the picture data alone is stored in the memory as shown in Fig. 3A. With the first embodiment of the invention, by contrast, not only the picture data in the sync block but also the sync data and ID data attached thereto are stored in the same sync block memory area, as illustrated in Fig. 3B. Alternatively, only the sync data and picture data may be stored in the memory area as shown in Fig 3C. This requires using a field memory 14 whose capacity is slightly larger than the comparable prior art memory. With the present invention the sync data written to the field memory 14 is used as the sync flag because the sync data after detection by the sync detection circuit 12 from the sync block becomes unnecessary. Thus with the present invention that data is utilized productively as the sync flag. Thus sync detection is followed by the setting of all bits in the sync data (8-bit data) to 0. The preset sync data is written to the field memory 14 as the sync flag alone with the picture data, as depicted in Fig. 4A. Meanwhile, when picture data is read from the field memory 14, the sync flag stored in the same sync block memory area as the picture data is also read therefrom. After readout, the picture data is fed to the interpolation circuit 15 and the sync flag is supplied to both the incrementer 10 and the flag decoder 19. The incrementer 18 increments the value of the sync flag by 1. The updated sync data is again written to the same memory area (see Fig. 4B). The flag decoder 19 compares the sync flag with the reference value in the same manner as with the prior art system. If the flag value is found to be below the reference value, the interpolation circuit 15 is disabled so as to let the picture data pass therethrough unprocessed. If the flag value is found to exceed the reference value, the picture data is interpolated by the same interpolation process as in the prior art before output. As described, a somewhat expanded memory area arrangement is provided in the field memory 14 to accommodate picture data along with sync data, the latter being reset and used after its primary use of detection as sync flags. This arrangement eliminates the need for a separate sync flag memory while still preserving the sync flags which can indicate how old given items of picture data are. Fig. 5 is a block diagram of a second embodiment of a picture recognition of the invention. This embodiment comprises a dual reproduction system whose basic construction is the same as that of Fig. 15. The field memories 14 and 24 provided respectively in the first and second enhancing circuits 10A and 10B double as sync flag memories as in the first embodiment above. The two sets of picture data output by the two enhancing circuits eventually reach the changeover switch 31. Based on the output from the flag comparator 32, the changeover switch 31 selects the more recent of the two sets of picture data. The changeover switch 31 then controls the operating status of the interpolation circuit 15 in accordance with the output from the flag decoder 33. The embodiments of Figs. 1 and 5 use the field signal in which error correction is accomplished within each sync block, as shown in Fig. 2. The invention may also be applied to digital VTR's wherein the shuffling of data or of error-corrected blocks extends over a plurality of fields. One such digital VTR records and reproduces the field signal containing an error correction code of, say a product code structure. The reproduction system in such a case contains field memories 44 and 54 generally having a total of two fields each, as depicted in Fig. 6. The writing to and reading from the field memories 44 and 54 are switched according to the type of reproduction mode for the shuffling of data or for outer code-based error correction. In the normal reproduction mode, a pair of changeover switches 35 and 36 in Fig. 6 are switched in an alternating manner. If the same write operation for the normal reproduction mode were performed in a variable speed reproduction mode such as a shuttle mode, 50 percent of the total data reproduced by the magnetic head would be stored in the field memories 44 and 54. During the read operation, the field memories would be read alternately in units of fields for the alternate output of half the total data amount. This would deteriorate the correlation among the picture data and would lower the degree of reproduced picture quality. This is circumvented by a third embodiment of the invention which will be described below. Fig. 7 is a block diagram of a third embodiment of a picture enhancing circuit of the invention. In this embodiment, the changeover switch 36 is identical in structure to the changeover switch 31 of Fig. 5. The constitution of the third embodiment is similar to that of Fig. 5 in that the embodiment comprises the first and second enhancing circuits 10A and 10B. Error-corrected field signals are switched in units of fields both in the normal reproduction mode and in the variable speed reproduction mode. Because the changeover switch 36 selects the most recent picture data, all data picked up by the magnetic head may be used for picture reproduction in units of fields. Since pictures are reproduced in units of fields using the continuously updated data, the degree of reproduction picture recognition is enhanced significantly. (In the example of Fig. 6, pictures are reproduced in units of frames.) The changeover switch 35 is controlled in the same manner with respect to the field memories 44 and 54 regardless of the type of reproduction mode in effect. This eliminates the possibility of reproduced pictures getting disrupted upon mode changeover. As described, the picture recognition enhancing circuit according to the invention first checks to see if a given sync block read from the field memory is updated by the data of a newly reproduced sync block, the data in the field memory being read therefrom in units of sync blocks. If the sync block is found yet to be updated, the contents of the sync data alone are updated every time picture data is read from the field memory. The updated sync data is again written to the field memory. This allows the field memory to be used both as the picture data memory and as the sync flag memory. This means there is no need for a separate sync flag memory required of the prior art picture recognition enhancing circuit significantly reducing manufacturing cost.

Claims: An apparatus for processing digital data comprising: input means for providing an input digital signal including block data and address data, the address data being associated with said block data, said block data comprising sync data and word data; storing means connected to said input means for storing in a field memory said block data, comprising the word data and associated sync data, from said input means according to said address data associated with said block data, and for resetting said sync data of said block data to form a flag on storage of the data, means (15) for reading the data from the field memory (14,24); rewrite means (18) for rewriting, in response to a reading operation by said read means (15) of said word data, said sync data stored in said field memory associated with the word data whereby the stored sync data is indicative of the number of times the associated word data has been read; processing means (15) connected to said field memory (14) for processing said read word data and outputting it; control means (18) for controlling the output operation so that word data processed by said processing means (15) is selectively provided as an output data instead of said word data read from said field memory (14,24) according to said flag associated with said read word data. Apparatus according to claim 1, wherein said rewriting means (18,28) replaces said sync data associated with said read data in said field memory (14,24) with sync data which is incremented in response to said read operation. Apparatus according to claim 1 or 2, wherein said control means (19) includes comparing means for comparing said sync data associated with said read word data with a predetermined value and for controlling said output operation to selectively provide said processed word data as an output data according to the comparison. Apparatus according to claim 1, 2 or 3 wherein said processing means (19) comprises interpolating means for interpolating said word data read from said field memory (14,24). Apparatus according to any one of the preceding claims, wherein said input means (12,13,22,23) is adapted to receive a digital signal and include a sync detecting means (12,22) for detecting sync data inserted in said received signal. Apparatus according to claim 5, wherein said block data further comprises an error check data, and wherein said input means (12,13,22,23) include error correction means (13,23) for correcting said word data of said block data using said error check data. Apparatus according to any one of the preceding claims wherein said storing means stores said address data from said input means with said word data and said sync data in said field memory. Apparatus according to any one of the preceding claims wherein said rewrite means (18,28) comprises increment means connected to said field memory (14,24) to receive said sync data read out of said field memory (14,24) for incrementing said received sync data; and means for replacing said sync data stored in said field memory (14,24) which is associated with said read word data with said incremented sync data from said increment means. Apparatus according to any one of the preceding claims further comprising reproducing means having first and second reproducing heads (4,5) for reproducing said digital signal from a recording medium and providing it to the input means (12,13,22,23) and wherein respective first and second field memories (14,24) are provided for storing said block data comprising first and second sync data and first and second word data received respectively from said first and second reproducing heads (4,5), and said rewriting means comprises respective first and second rewrite means (18,28) for rewriting said first and second sync data stored in said first and second field memories in response to respective reading operations in said first and second field memories (14,24); and further comprising comparing means (32) for comparing together first and second sync data stored in first and second field memories (14,24) associated with data read out of said first and second field memories (14,24), and selecting means (31,36) for selectively providing said data read from one of said first and second field memories (14,24) in accordance with the result of the comparison provided from said comparing means (32). Apparatus according to claim 9 when dependent from claim 6 wherein said error correction means comprises first and second error correction means (13,23) for correcting using said error check data said block data detected by said detecting means (12,22) and providing said error-corrected data and sync data to said first and second field memories (14,24). Apparatus according to any one of claims 1 to 8 further comprising reproducing means for reproducing said digital signal from a recording medium and wherein first and second field memories (14,24) are provided, said storing means comprising a switch (35) for storing said block data alternately in said first and second field memories (14,24) and said rewriting means comprises respective first and second rewrite means (18,28) for rewriting said first and second-sync data stored in said first and second field memories in response to respective reading operations in said first and second field memories (14,24); and further comprising comparing means (32) for comparing together first and second sync data stored in first and second field memories (14,24) associated with data read out of said first and second field memories (14,24), and selecting means (31,36) for selectively providing said data read from one of said first and second field memories (14,24) in accordance with the result of the comparison provided from said comparing means (32). Apparatus according to claim 9 or 11 wherein said selecting means selects from said first and second field memories the data which has most recently been reproduced. Apparatus according to claim 12 when dependent from claim 9 or 11 with claim 6 wherein the sync detecting means (12) is connected between said reproducing means and said switch (35) for detecting sync data in said reproduced digital signal. Apparatus according to claim 13 further comprising error correcting means (12) connecting between said reproducing means and said switch (35) and receiving the output of said sync detection means (12) for correcting errors in the reproduced digital data to produce corrected digital data and supplying the corrected digital data to said switch (35).

Inventors: UEHARA KENJI, UEHARA, KENJI, Uehara, Kenji, c/o Sony Corporation
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: H04N5
IPC codes: H04N5