JPS59224934A - Signal processing circuit - Google Patents

Abstract

PURPOSE:To improve the quality of a reproduced picture by converting time series of a PCM code before an error correction code is added to the PCM code to apply inverse time series conversion to a interleaved code signal thereby eliminating error correction. CONSTITUTION:The time series of an input signal (a) PCM-coded is converted by a time series converting circuit 1, an error correction code is added to the converted code by a coder 2 and plural error correction codes (c) in the unit of block are applied to an interleave processing circuit 3. The circuit 3 converts the codes (c) into time series codes (d) and records the codes in a VTR. Further, the reproduced code is converted into the original time series signal by a deinterleave processing circuit 4 and a decoder 5 performs error correction. This corrected code is processed by a delay circuit 6, a time series inverting circuit 8 and a delay circuit 10 and the result is added to a selecting circuit 12. Further, a control signal processed by a correction disable detecting circuit 7, a time series inverting circuit 9, and a counter circuit 11 is applied to the circuit 12 to eliminate miscorrection due to erroneous correction thereby improving the quality of reproduced picture.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is a signal processing circuit, and more specifically, a signal processing circuit that can correct errors that occur when converting image signals into digital signals and transmitting, recording and reproducing them. The present invention relates to a signal processing circuit that decodes and reproduces transmitted or recorded data by converting it into an error correction code.

[Background of the invention]

2. Description of the Related Art Digital magnetic recording devices such as digital VTRs that record and reproduce television signals by PCM encoding use error correction codes to correct code errors that occur during reproduction. However, with error correcting codes, there is a limit to the number of code errors that can be corrected, and for errors that exceed this limit, no correction is performed during error correction (hereinafter referred to as uncorrectable) or no correction is performed. An operation occurs in which an operation is performed but is incorrectly corrected (hereinafter referred to as an incorrect correction). If it is uncorrectable, it is possible to determine whether it is uncorrectable, for example, by dividing by the generator polynomial of the error correction code and checking the remainder.

Therefore, a so-called modification operation is performed in which the code corresponding to the code word that cannot be corrected is replaced with a signal from, for example, one scanning line earlier by utilizing the redundancy of the television signal. On the other hand, when an error correction operation is performed, even if the correction is performed by mistake, it is zero, and it is impossible to determine this based on the code after the correction. Therefore, if a code is incorrectly corrected during the correction operation due to an error that exceeds the scope of error correction, there is an error in this code, and correction is not performed. As a result, there is a problem in that incorrect corrections occur and image quality deteriorates.

Furthermore, in order to deal with burst errors in which errors are concentrated in one place due to dropouts caused by scratches on the tape, etc., it is possible to temporally interleave the code between multiple code words of the error correction code. As is known, burst errors that occur in VTRs can have burst lengths exceeding several hundred bits in some cases. In order to make it possible to correct even these long burst errors, it is necessary to interleave codes corresponding to multiple scanning lines. When performing interleaving on codes equivalent to multiple scanning lines in this way, if a longer burst error that exceeds the error correction range occurs, it is not possible to correct all the codes equivalent to multiple scanning lines, which may result in poor image quality. Since the deterioration of the signal is large, it is necessary to correct only the vicinity of the part with the code error using a correction code having a strong correlation, such as a TV signal before the -scanning line.

In this case, when the range of errors that can be corrected is exceeded, several lines are corrected by the same correction code (image) as will be explained in detail later, resulting in deterioration of image quality.

[Purpose of the invention]

Therefore, it is an object of the present invention to convert an image signal into a digital signal, add an error correction code to it, transmit or record it, and eliminate erroneous corrections caused by erroneous corrections in a circuit that decodes and reproduces the signal, thereby improving the reproduced image quality. It is to realize the means to improve.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that the digital signal of the image signal is subjected to code conversion before an error correction code is added to the digital signal. More specifically, temporal interleaving is performed in which an error correction code is added after time-series conversion of the code of a PCM encoded image signal, and a plurality of error correction codes are made into one block. After processing and transmitting or recording, during playback, dinterleave processing is performed in block units, and after conversion to the original time-series error correction code, error correction operation is performed. When the code is further time-series converted to return it to the original PCM code, the erroneous correction codeword that has become uncorrectable is corrected. This modification can take various forms, as explained in the examples below.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a block diagram showing the configuration of an embodiment of a signal processing circuit according to the present invention, and FIG. 2 is a time chart for explaining the operation of the embodiment.

A PCM encoded television signal (input code) shown in FIG. 2(a) is applied to the PCM code time series conversion circuit 1. Here, PWr, PW2, ... song/PWa
is the sample (pixel) signal, Wth ~ W1 s, W 21
~W26. ...Wl s - Wl a is PCM
It is a sign.

The above-mentioned signal (a) is time-series converted by the conversion circuit 1 according to a certain rule as indicated by the symbol 6) in FIG. The above-mentioned converted codes) are sent to the encoder 2 as an error correction code P! as shown in FIG. 2(C). ...Pg is added. One block is composed of four error correcting codes: Wl + Wz g Ws HWl. The interleave processing circuit 3 converts the plurality of error correction codes (C) into the code sequence shown in FIG. 2(d). Signal (d) is recorded on the VTR.

On the other hand, during playback, the reproduced code from the VTR is converted by the dinterleave processing circuit 4 into a time-series signal that is the same as the original time-series error correction code (C) as shown in FIG. 2(e). , error correction is performed by the decoder 5. The error-corrected code is delayed by one code word of the error-corrected code in the delay circuit 6, and then converted into the original time series PCM in the PCM time series conversion circuit 8 as shown in FIG. 2(g). converted to code. However, if a so-called burst error occurs in which errors are concentrated in one place due to scratches on the tape, etc., as shown by the arrow in (d), the same problem occurs when dinterleave processing is performed. In the code series e), each code word has a code error (shaded area) that exceeds the correctable range. Therefore, the code after error correction is uncorrectable,
This results in a mixture of codes that have been incorrectly corrected and codes that have been incorrectly corrected. For example, as shown in the same figure (f), WI HW
I HW4 cannot be corrected, Wt results in an incorrect correction. This corrected code is converted into a PCM code shown in FIG.

Therefore, in the uncorrectable detection circuit 7, the code word that has become uncorrectable is determined, and the PCM time series conversion circuit 9, which has the same configuration as the PCM time series conversion circuit 8, converts the code word into a PCM
A sequence of uncorrectable code words corresponding to the code is given. The delay circuit 10 provides a delay equal to the number of PCM quantization bits, while the counting circuit 11 counts the number of codes of uncorrectable code words included in the corresponding PCM code. A control signal of 1'' is generated if the signal is 0, and a control signal of 0 is generated otherwise.

Then, the selection circuit 12 selects the modified code when the control signal is 1, and selects the output of the delay circuit 10 when the control signal is 0. Therefore, as the output code of the selection circuit 12, a code sequence from which erroneous modification has been removed can be obtained.

The effects of the signal processing circuit according to the present invention will be explained in more detail below using the above embodiments.

In conventional methods that do not perform time series conversion, even if uncorrectable code words are corrected, the influence of erroneous correction becomes large. For example, in a conventional system that does not perform time series conversion, PWl shown in FIG.

Error correction codes are added to the PCM codes of PWl, PWs, and PW4, respectively, and Wl + Wt + Ws
+ W4 will be created. And when playing, W
It is assumed that t + Wa + W4 is uncorrectable, and Wt is equivalent to an incorrect correction. In this case, PW+, PWs of the PCM code included in Wt+Ws+W4.

Since PW4 is an uncorrected code error, it is corrected when it is decoded into a PCM code, but the PCM code PW2, which is in charge of Wt, is an error without being corrected because Wt incorrectly corrected it. It includes.

That is, in a code structure in which conventional time series conversion is not performed for the same erroneous code, the influence of erroneous correction occurs.

However, by performing time-series conversion as in the present invention, even if there is an erroneously corrected code word, the PCM
Upon decoding to the code, this effect is almost eliminated.

Now, let the number of error correction codes included in a block be N, PC
If the probability that the error correction code corrects an error in which the number of quantized bits in M encoding exceeds the M1 correction range is pe, then when a code error exceeding the correction range occurs, the time is In the conventional method that does not involve sequence conversion, the probability P of incorrect correction in a block that still contains an incorrect correction is P
=1-(1-Pe) medium NPe. On the other hand, according to the present invention, the probability P of incorrect modification in a block is given by P=Pe' α=MIN(N, M). For calls, N=4. If M = 6 and Pe is approximately 0.1 to 0.2 depending on the type of error correction code, then in the conventional system P- = 0.4 to 0.8, whereas in the present invention, P Medium 10-4 to 1.6X10-s and potash,
According to the present invention, the rate of erroneous corrections due to erroneous corrections can be reduced by several orders of magnitude compared to conventional methods that do not perform time series conversion.

FIG. 3 is a block diagram showing the configuration of another embodiment of the signal processing circuit according to the present invention, and FIG. 4 is a time chart for explaining its operation. This is effective when performing interleave processing.

PCM encoded image signal (a) is used as an input code,
It is added to the time series conversion circuit 1. The input code (a) is a three-scan line code. In the time series conversion circuit, this sign (a
) is time-series transformed into the signal shown in (b).

The encoder 2 adds error correction codes (P11P21...Ps) to each fixed interval of the code sequence (b),
Multiple error correction codewords (WI, Wz,...W
A) is converted into a code sequence (C) with one block, interleaved by the interjeep processing circuit 3, converted into a code sequence (d), and then recorded on a VTR.

During playback, the playback code from the VTR and the dropout information corresponding to long burst errors exceeding the correctable range are passed through the dinterleave processing circuits 4 and 13 to the code shown in FIG. 4(e). sequence and code error information corresponding to this code sequence. Here, the signal (
The shaded area in e) indicates code errors due to burst errors shown in signal (d) above, and it is assumed that all of these errors are beyond the range of errors that can be corrected. The error correction circuit 5 controls error correction using code error information caused by dropouts that is separately detected by a dropout sensor, etc., and corrects errors within the range of correctable code errors. Correct actions are performed for those. Therefore, for errors that exceed the scope of correction, the correction operation (11) will not be performed.

In the case of FIG. 4, all errors are beyond the correctable range, so no correction is performed.

Therefore, after decoding, the code sequence shown in FIG. 4(f) is obtained, and the time series is further converted by the time-series inverse conversion circuit 7 to obtain the input code shown in FIG. 4(g). Convert to the same time series code. This conversion causes code errors to be concentrated.

On the other hand, the time series conversion circuit 8 generates a control signal H1l+ if there is a code error that is not corrected as shown in FIG. 4 Φ), and 0'' otherwise.

Then, the selection circuit 9 selects and outputs the modified code when the control signal is 1'', and selects and outputs the output of the time series conversion circuit 7 when the control signal is 0''.

Therefore, W23 to W210 of line 2 are line 1
With Wz3~W■o, Ws t + Wa of line 3
2 is modified by replacing it using W21 and Wl2 of line 2. That is, the incorrect sign of each line is
Each is modified with a different modification code. In order to further clarify the effects of this embodiment, the case of the conventional method in which the input PCM code (12) is not time-series transformed will be explained.

FIG. 5 is a time chart diagram explaining the operation of the circuit according to the conventional method, in which each symbol <aL (c) (f
) and (+1) correspond to those with the same symbols in FIG. Signal (+)) by time series conversion in Fig. 4,
Since there is nothing corresponding to (g), it is necessary to modify the shaded portion of the decoded signal (f) by replacing it with a modified code before scanning, for example.

That is, Wt s + Wt 41 Wt of line 1
s r Wl 9 is Wz 3 of the previous line
', Wth', Wt s', Wt s'. Next, on line 2, W23 * W24 +w
2. , w2. Wt s v Wt 4 of line 1
1 Wt s +Wle or WIs', WI
4' + Wts', replace with Wts'. Also, Ws s and W3 g of line 3 are W2 of line 2
3. Replace with Wa8, ie, Wts '1w1g'.

Therefore, the part with the code error is on the line 1°2.3
Since both images are modified using the same modification code, deterioration of image quality becomes a problem. However, in the embodiment shown in FIG. 3 above, by performing time series conversion, multiple lines of incorrect (13) codes are not corrected with the same correction code as in the conventional method described above. , an attempt is made to improve image quality.

Note that in the explanation of the example shown in FIG. 4, the case was about a time-series transformation in which code errors that were not corrected are concentrated in one place in the code sequence after decoding, but in the code sequence after decoding, A similar effect can be obtained by performing time-series transformation such that uncorrected code errors are placed at different positions in two consecutive scanning lines of a plurality of scanning lines included in a block. For example, FIG. 6(a),
When the time series transformation shown in (b) is performed, in the finally decoded code sequence (g), in line 1, WI4
゜Wls + Wt s + Wt 7% In line 2, Wz t and Wz 2 .

At WH, W29, and line 3, Ws a and Ws 7 will be corrected. However, the portions to be corrected on each line are at different positions on two consecutive lines. Therefore, the time-series conversion according to the present invention causes much less deterioration in image quality during retouching than the conventional method that does not perform time-series conversion.

(14)

[Brief explanation of the drawing]

1 and 3 are block diagrams showing the configuration of an embodiment of the circuit according to the present invention, FIG. 2 is a time chart diagram for explaining the operation of the embodiment shown in FIG. 1, and FIGS.
This figure is a time chart for explaining the operation of the embodiment shown in FIG. 3, and FIG. 5 is a time chart for explaining the operation of the conventional circuit. DESCRIPTION OF SYMBOLS 1... Time series conversion circuit, 2... Encoder, 3... Interleave processing circuit, 4.13... Dinterleave processing circuit, 5... Decoder, 6.10... Delay Circuit, 7... Uncorrectable detection circuit, 8, 9... Time series inversion circuit, (15)

Claims (1)

[Claims] 1. means for adding an error correction code to a PCM code; means for interleaving and recording/reproducing the code signal to which the error correction code has been added; In a signal processing circuit having means for releaving and means for error correction and modification of the dinterleaved code signal, the time series of the PCM code is processed before the means for adding an error correction code to the PCM code. 1. A signal processing circuit comprising: a circuit for performing conversion; and a circuit for performing inverse time-series conversion of the above-described time-series conversion on the dinterleaved code signal. 2. In the signal processing circuit described in item 1, the modifying means detects an error correction code in which error correction is not performed and a code error is present in the PCM signal obtained by the inverse transformation, and converts the PCM code to the error correction code. A signal processing circuit that consists of a circuit that replaces with modified codes that have a strong correlation.