Abstract:
This invention provides a recording and/or reproducing apparatus having a reproducing circuit for reproducing coded main information, and historical information, with respect to signal processing which was performed on the main information. An error correcting circuit corrects a code error in the main information. The reproducing circuit provides error correcting information with respect to the error correcting processing. A first constructing circuit constructs coded data based on the correcting information by concealing an error which cannot be corrected by said error correcting circuit. A decoding circuit decodes the main information provided by the first constructing circuit, and a second constructing circuit constructs decoded data by concealing the error, which cannot be corrected by the error correcting circuit, in the main data which has been decoded by the decoding circuit. The decoded data is constructed based on the historical information and the correcting information, thus preventing degradation of the signal and allowing a high quality image to be obtained.

Description:
This application is a continuation of application Ser. No. 08/681,496 filed Jul. 23, 1996, now abandoned, which is a continuation of application Ser. No. 08/174,441, filed Dec. 28, 1993, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a recording and/or reproducing apparatus, and more particularly to a recording and/or reproducing apparatus for digitally recording and/or reproducing information such as images and voices on/from a recording medium. 
     2. Description of the Related Art 
     Traditional apparatuses of this type include a digital video tape recorder (VTR) or digital video cassette recorder (VCR). In the digital VTR, there are two known digital recording methods: one is to record base band digital data associated with images or voices on a recording medium without data compression, and the other method records data, after reducing the amount of data, by performing data compression such as discrete cosine transformation (DCT) or variable length coding (VLC). 
     In the former method, or base band recording method, signals can be transmitted without degradation in the signal-to-noise ratio. In addition, in the base band recording method, it is possible to connect different types of apparatus to each other, and a digital switch is available. However, because the base band recording method does not involve performing data-compression, there are disadvantages in that a large amount of data must be recorded and that long recording on a recording medium is impossible. 
     In the latter method, on the other hand, signals (video or voice signals) to be recorded are subjected to high efficiency coding and further to error correction coding. The signals are then modulated and recorded on a recording medium. When the signals are reproduced, inverse processing is carried out. This method has the advantage that the amount of recording data can be greatly reduced. However, this method also has the disadvantage that distortion of data occurs due to the high efficiency coding and decoding, i.e., noise is generated and a slight degradation of picture quality occurs. 
     For example, when compression coding is carried out by means of orthogonal transformation such as DCT, data is rounded off after orthogonal transformation. Thus, the data digits cannot be perfectly preserved during calculation. These errors cause distortion of data after inverse orthogonal transformation. If editing or dubbing is repeatedly carried out, the degradation in picture quality will gradually increase. 
     To overcome this problem, a method has been proposed in which dubbing is carried out with coded signals before decoding. For example, in a reproducing apparatus, error correction is performed on reproducing data and if there is coded data having an error which cannot be corrected, interpolation is performed on the data using data corresponding to the same pixel location of preceding and succeeding frames. Then, the data is sent to an error correction coding circuit in the recording apparatus. 
     However, in the conventional recording and reproducing apparatus described above, the recording apparatus treats all data in the same way, without distinction between the data which has been interpolated in the reproducing apparatus and the data which has been reproduced correctly. The recording apparatus therefore records the data on a recording medium without distinguishing between the data which has been interpolated in the reproducing apparatus and the correct data which has not been interpolated. 
     As a result, when data which has been dubbed in this way is reproduced, the reproduction is performed without distinguishing between the data which has been interpolated and the data which has been reproduced correctly. If failure occurs in correction for some data, there is a possibility that the interpolation circuit will perform interpolation on this uncorrectable data by using the data which has already been interpolated by the reproducing apparatus during the dubbing operation. If such an interpolation occurs, the desired quality of pictures and sounds cannot be maintained and degradation will occur in the reproduced pictures. 
     In addition, the characteristic features of pictures do not contribute to interpolation for high-efficiency-coded data. This causes such a problem in that it is impossible to perform adaptive processing, such as switching between intra-frame interpolation (or intra-field interpolation) and inter-frame interpolation (or inter-field interpolation) depending on motion detection. As a result, in some cases, distortion occurs in a region corresponding to interpolated data. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to solve the problems described above. 
     More specifically, it is an object of the present invention to provide a recording and/or reproducing apparatus which can provide a high quality picture without degradation of signals. 
     To achieve the objects described above, the present invention provides a reproducing apparatus, having means for reproducing coded main information and also historical information with respect to signal processing which was performed on the main information at a past time, means for correcting a code error in the main information reproduced by the reproducing means, the error correcting means providing error correcting information with respect to the error correcting processing; first constructing means for constructing coded data for error data which cannot be corrected by the error correcting means, the coded data being constructed based on the error correcting information; decoding means for decoding the main information provided via the first constructing means; and second constructing means for constructing decoded data which has been decoded by the decoding means, or the error data which cannot be corrected by the error correcting means, the decoded data being constructed based on the historical information and on the correcting information. 
     Additional objects and features of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a configuration of a digital VTR embodying the present invention; 
     FIG. 2 is a block diagram showing a configuration of the high efficiency coding circuit of the apparatus shown in FIG. 1; and 
     FIGS. 3 a ,  3   b , and  3   c  are schematic diagrams illustrating digital formats used in the embodiments of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the figures, embodiments of the present invention will be described below. 
     FIG. 1 is a block diagram illustrating configurations of two digital VTRs in accordance with a first embodiment of the present invention, wherein the digital VTRs are connected to each other for digital dubbing operation, and only major elements are shown. 
     General recording and reproducing operations will be described first for a digital VTR  100 . In the following description of this embodiment, only recording and reproducing operations for video signals will be described; no description will be given for voice signals. An analog-to-digital converter  112  converts an analog video signal, applied to an input terminal  110 , into a digital signal. A block-dividing circuit  114  divides the signal provided by the analog-to-digital converter  112  into blocks (hereafter referred to as DCT blocks), each of which consists of 8×8 pixels, and provides the signal to a high efficiency coding circuit  116 . The high efficiency coding circuit  116  performs discrete cosine transformation (hereafter referred to as DCT), performs quantization of the transformation coefficients, and, performs variable length coding so as to perform high efficiency compression. In this compression operation, thirty DCT blocks are divided into five synchronous blocks, from the viewpoints of error propagation and special reproduction. 
     Referring to FIG. 2, the operation of the high efficiency coding circuit  116  will be described below. 
     The video signal, which has been divided into DCT blocks by the block-dividing circuit  114 , is converted by a DCT circuit  301  from a space domain signal to a frequency domain signal, and the signal is then provided to a delay circuit  302  and also to a code amount estimation circuit  303 . The code amount estimation circuit  303  performs quantization and DCT on the applied signal for each of thirty DCT blocks and determines the amount of codes for thirty DCT blocks. Based on the amount of codes, quantization coefficients for quantization processing are determined. A signal (quantizing number) representing the determined quantization coefficient is provided to a quantization circuit  304 . 
     The delay circuit  302  provides a delay corresponding to the time required for estimation of the amount of data (determination of the quantizing number). The quantization circuit  304  has a table associated with quantization coefficients corresponding to a plurality of quantizing numbers, and it quantizes the video signal, which has been already subjected to DCT, by using a quantization coefficient corresponding to the quantizing number provided by the code amount estimation circuit  303 . The quantized video signal is then coded by a VLC circuit  305  by means of coding, such as 2-dimensional Huffman coding, and the resulting signal is provided to a switch  120  shown in FIG.  1 . As a result of the successive processing in the high efficiency coding circuit  116 , the amount of video data is reduced and DCT blocks with a certain amount of data are compressed into a predetermined size of synchronization blocks. 
     The video signal, which has been reduced as to the amount of data by the high efficiency coding circuit  116 , is applied via the switch  120  to an error correction coding circuit  122 . The error correction coding circuit  122  produces parity bits for error correction by means of an error correction coding scheme, such as double Reed-Solomon coding, and adds the produced parity bits to the video data. The video data with parity bits is applied to a modulator  124 . The modulator  124  adds sync codes and ID codes to a series of data, consisting of high-efficiency-coded data and parity bits for error correction, so as to form synchronous blocks. The data is then modulated and applied to a recording equalizer  126 . The output data of the modulator  124  is equalized by the recording equalizer  126  and is then amplified to a predetermined level by a recording amplifier  128 . The data is then recorded on a recording tape  132  via a recording head  130 . 
     FIG. 3 shows a recording format for one synchronous block in accordance with the present embodiment. An inner parity bit and an outer parity bit are produced by means of double Reed-Solomon coding for the information data (the video data in this case). A sync code and an ID code (identification information) are also added so as to construct the data in the form of synchronous blocks. At this time, 0&#39;s are commonly written in a flag data area denoted by slanted lines. In this area, error flag information provided by a reproducing apparatus will be written at a time when dubbing is carried out, as will be described later. 
     The data, which has been recorded as described above, may be reproduced in the following way. Output data reproduced by a reproducing head  134  (shown in FIG. 1) is applied to a demodulator  140 , via a reproducing amplifier  136  and reproducing equalizer  138 . The data is demodulated by the demodulator  140  and the data is then stored in a memory  142  according to a reproduced ID code. An error correction circuit  144  decodes the inner parity then the outer parity, so as to correct errors of the reproduced data stored in the memory  142 , within its correction ability. An error flag is set for uncorrectable data for each set of constant-sized blocks (five blocks). The error flag is provided to a code concealment circuit  146 , the output terminal  148 , and an image concealment circuit  154 . 
     If the error flag is set, the code concealment circuit  146  replaces the data with that of preceding frame for each of the constant-sized blocks (five blocks) to which the error flag is set, rather than rewriting the data in the memory  142 . That is, the code concealment circuit  146  performs code-based inter-frame interpolation on uncorrectable coded data. The output data of the code concealment circuit  146  is provided to the output terminal  148  and to a high efficiency decoding circuit  150 . 
     The high efficiency decoding circuit  150  performs processing which is inverse to the processing performed by the high efficiency coding circuit  116 . The variable length data is subjected to decoding, inverse quantization, and inverse DCT. Therefore, the output data of the code concealment circuit  146  is decoded and the reproduced video data is provided to a motion detection circuit  152 . The motion detection circuit  152  determines, by means of inter-field calculation, whether motion exists between fields of the reproduced pictures, and the motion detection circuit  152  provides, in synchronization with the output data of the high efficiency decoding circuit  150 , a motion flag which indicates existence of motion. As a matter of course, the motion detection may be performed for each area having a small size. 
     As described above, the image concealment circuit  154  performs interpolation on the output data (reproduced image) of the high efficiency decoding circuit  150  or  250 , based on the error flag provided by the error correction circuit  144  or  244  and also according to the motion flag provided by the motion detection circuit  152  or  252 . More specifically, intra-field interpolation, using adjacent pixels within a field, is carried out on a DCT block having motion to which the error flag is set. The intra-field interpolation is also performed for a DCT block if the error flag is set to both of two successive fields. 
     If the error flag is set to certain data and if motion is not detected in that data, the inter-frame interpolation has been carried out on the data by the code concealment circuit  146 , and the video signal which has been subjected to inter-frame interpolation is directly output. On the other hand, for the data to which motion has been detected, interpolation can be performed by using data within a field, which has better correlation with respect to time. Thus, optimized interpolation can be performed corresponding to the detected motion of the image. 
     The reproduced image data, which has been subjected to interpolation by the image concealment circuit  154 , is further converted to analog data by a digital-to-analog converter  156  and then is output to the outside via an output terminal  158 . 
     The digital dubbing operation will now be described in which the output terminal  148 , of the recording and reproducing apparatus  100 , is connected via a coaxial cable  300  to an input terminal  218  of a digital VTR  200 . In this dubbing operation, a switch  220  of the digital VTR  200  is switched to select a contact (a). 
     In the digital VTR  100 , recording signal recorded on a magnetic tape  132  is reproduced in a manner described above, and thus errors in the reproduced data are corrected by the error correction circuit  144 , within its correction ability, and data having uncorrectable errors are subjected to code-based interpolation at the code concealment circuit  146 . The data which has been interpolated by the code concealment circuit  146 , together with an error flag provided by the error correction circuit  144 , is applied via the output terminal  148  and via the cable  300  to an input terminal  218  and further to an error correction coding circuit  222  via a switch  220 . In this operation, the error flag is inserted into the flag data area, which is denoted by slanted lines in FIG. 3, and it is then provided to the error correction coding circuit  222 . 
     The error correction coding circuit  222  produces an inner parity code and outer parity code for error correction, as in the case of recording described above. Succeeding operations are then carried out in the same way as that in the recording operations described above, and the data is recorded on a recording tape  232 . 
     When the image which has been recorded by a dubbing operation in this way is reproduced, the error correction circuit  244  provides an error flag (a current flag) to a code concealment circuit  246 . The error flag has been produced for an uncorrectable block on the basis of the parity for error correction which has been added to the data by the error correction coding circuit  222 . The error correction circuit  244  also provides an error flag recorded in the flag data area (a previous error flag), which has been produced for uncorrectable data during the reproducing operation in the digital VTR  100 , together with the current error flag, to an output terminal  248  and also to an image concealment circuit  254 . 
     The code concealment circuit  246  performs code interpolation based on the current error flag, and the image concealment circuit  254  performs image interpolation based on both the current and previous error flags. These interpolation operations are carried out in the same way as that of the reproducing operation. 
     As described above, in the arrangement of the present embodiment, there is provided an area in which a flag, indicating that the data is uncorrectable, is written for each information data. Thus, in a digital dubbing operation, reproduced data is output together with the flag indicating that the data is uncorrectable, whereby it becomes possible to prevent the dubbed data from being interpolated by using the uncorrectable data. As a result, the quality of pictures in digital dubbing is improved. 
     In the present embodiment, the flag data area is provided for each synchronous block, whereby it becomes possible to perform code-based interpolation for each synchronous block. 
     In this embodiment, the code concealment circuits  146  and  246  perform interpolation for each constant-sized block. However, the interpolation may also be performed for each synchronous block, taking into account the following matters. In the present embodiment, thirty DCT blocks are compressed into five constant-sized synchronous blocks. However, the data of each DCT block is not transferred to respective synchronous blocks in the order of frequency from low to high, i.e., the data is not recorded (output) in the order of occurrence of DCT processing. As a result, if code interpolation is carried out for each synchronous block, each of the blocks in five synchronous blocks will be broken up. More specifically, high frequency data are included in the synchronous blocks. It is possible that the data in a certain synchronous block will include the high frequency data of a DCT block in other synchronous blocks. Therefore, if code interpolation is carried out for each synchronous block, the high frequency data may be deleted and the entire coded data (from low frequency to high) of the five synchronous blocks may not be perfectly decoded. 
     To avoid the problem described above, the error flag may consist of data having a plurality of bits so that the flag may indicate whether the data is uncorrectable, whether the data has been interpolated, and what the unit of code interpolation is (or which synchronous block has been interpolated). Thus, it becomes possible to demodulate the data for each synchronous block. In this case, when error correction is carried out, the error flag which has been previously stored in the flag data area should be read out and, taking into account the contents of this flag data, a new error flag including should be produced so as to reflect both the result of error correction and the previous error flag. In this case, the image concealment circuit  254  also performs intra-field interpolation based on the error flag stored in the flag data area as in the case described above. 
     In this embodiment, inter-frame interpolation is carried out by the code concealment circuits  146  and  246 . However, the inter-frame interpolation may be carried out after decoding is carried out, by a succeeding stage, so that a suitable selection is made between intra-field interpolation data and inter-field interpolation data based on the result of the detection of motion. In this case, the image concealment circuits  154  and  254  become unnecessary, and, instead, a frame memory is added to a location after decoding. 
     In this embodiment, a tape is used as a recording medium. However, any recording media, including a magnetic disk, optical disk, magneto-optical disk, and hard disk may also be used. The present invention may be applied to recording and reproducing between different types of recording media, with the same effect as that in the previously-described example. 
     In this embodiment, outer parity is added to the error flag and to information data. However, outer parity may also be added to the ID code and to the sync code, as shown in FIGS. 3 b  and  3   c , depending on its importance. In this case, it is possible to obtain a correct ID code and sync code, and thereby to obtain better quality of pictures.