JPH0869671A - Video recording and reproducing device - Google Patents

Abstract

PURPOSE: To obtain a video recording and reproducing device in which degradation of the picture quality is reduced. CONSTITUTION: A detection correction decoding of the reproduced data from a magnetic tape 1 is performed by an inner encoder and decoder 4 and an outer encoder and decoder 9 and the corrected data and the flag information, that indicates the data are impossible to be corrected, are stored in a memory 8. A DOS threshold value controller 13 counts the number of the flag information stored, discriminates the condition of errors by the counted value and appropriately controls the threshold value of a DOS generator 5 in accordance with the result of the discrimination. A reading controller 14 controls the reading of the memory 8 by an appropriately generated drop out signals DOS and the data and the flag information are handed over to a high efficiency decoder 10 and an interpolation memory 11. Thus, only the reproduced data, which greatly exceed the correction capability, are surely handed over to an interpolation process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording / reproducing apparatus such as a digital VTR.

[0002]

2. Description of the Related Art In recent years, a consumer VTR has been proposed which encodes an image signal with high efficiency and records and reproduces it on a recording medium such as a magnetic tape. In this method, an image signal is grouped into blocks each having a predetermined number of pixels, orthogonal transform such as discrete cosine transform is performed, and the transformed coefficients are quantized / entropy coded and recorded.

By the way, when a VTR is constructed using a variable length code, considering special reproduction and error propagation,
It is desirable to make the code amount constant in predetermined block units. Therefore, there is known a method of adjusting the code amount by adjusting the quantization parameter of the image data to be subjected to the variable length coding.

FIG. 4 shows an example of a format in which the code amount is adjusted by the above method using discrete cosine transform.
Here, it is assumed that the code amount is fixed length in units of M (three in FIG. 4) sync blocks, and a sync signal (SYNC) and additional information (at the beginning of each sync block 1, 2, 3). ID) is recorded.

Then, as shown in FIG. 5, the sync-blocked data is added with an error correction code such as a product code RS code and recorded on a magnetic tape.

Next, referring to the block diagram of FIG.
The decoding operation when reproducing from a magnetic tape will be described. In the figure, 1 is a magnetic tape, 2 is a reproducing head,
Reference numeral 3 is a demodulator, and the demodulator 3 is for demodulating the reproduction data detected by the reproduction head 2.

Reference numeral 4 denotes an inner code decoder, which performs inner code error correction on demodulated data, and judges judgment of data Data and error correction (hereinafter referred to as flag information) Flag.
Is for outputting. A dropout signal generator (hereinafter referred to as DOS generator) 5 determines amplitude (hereinafter referred to as envelope) information Env of reproduction data detected by the reproduction head 2 and generates a dropout signal DOS. It is for.

Reference numeral 7 is a write controller for controlling the output of the data Data and the flag information Flag which are the output of the inner code decoder 4 according to the state of the dropout signal DOS which is the output of the DOS generator 5. Is. 8
Is a memory for storing the data Data output-controlled by the write controller 7 and the flag information Flag. An outer code decoder 9 is for performing outer code error correction on the data stored in the memory 8.

Reference numeral 10 is a high-efficiency decoder for performing high-efficiency decoding on the outer-code error-corrected data output from the memory 8. Reference numeral 11 denotes an interpolation memory, which is for performing an interpolation process on the block data that cannot be error-corrected by the flag information Flag. Next, 12 is an output terminal.

In the magnetic recording / reproducing apparatus having such a structure, during normal reproduction, the reproduction data detected by the reproducing head 2 is demodulated by the demodulator 3. Also, DO
The S generator 5 detects the dropout signal DOS from the envelope information Env of the reproduction data detected by the reproduction head 2.
Generate. FIG. 7A shows the envelope of the reproduction data detected by the reproduction head 2.

The DOS generator 5 judges the envelope by a certain threshold value and generates a dropout signal DOS showing the reliability of the data as shown in FIG. 7 (c). The dropout signal DOS is a signal for executing write inhibition to the memory 8 in correspondence with the lower portion of the envelope in FIG. 7A. In the demodulator 3, at the time of demodulation, the low envelope portion of FIG. 7A is amplified by increasing the gain as shown in FIG. 7B, and the inner code decoder 4 performs inner code error correction. The data in the lower part of the envelope is likely to contain an error that exceeds the error correction capability.

Therefore, the write controller 7 prohibits the writing of the low reliability data and the flag information Flag indicating the correction result to the memory 8 based on the dropout signal DOS described above. The data stored in the memory 8 under such write control is subjected to outer code error correction in the outer code decoder 9 after being aligned for the product code blocks.

The data resulting from the outer code error correction and its flag information Flag are written again in the memory 8, and the data and flag information Flag are output from the memory 8 to the high efficiency decoder 10. The high-efficiency decoder 10 expands the input data, adjusts the flag information Flag and the timing, and then outputs the data to the interpolation memory 11.

The interpolation memory 11 determines the data that could not be error-corrected based on the flag information Flag, replaces the data with the previous frame data, etc., and interpolates the data that cannot be error-corrected. The interpolated data is output via the output terminal 12.

[0015]

For example, in a system such as a VTR, the dropout signal DOS is generated at a constant threshold value. For this reason,
If the defined threshold value is lower than the proper value, the probability of error correction is high at the time of error correction, and the image quality is noticeable because the error corrected data is displayed on the screen without interpolation. Like In addition, if the determined threshold value is higher than the appropriate value, it is determined that the data is in a poor reproduction state even though the error correction is correctly performed, and the interpolation process is performed, which may deteriorate the image quality. There were some problems.

The present invention has been made in order to solve the above problems, and an object thereof is to obtain an image recording / reproducing apparatus in which interpolation processing can be surely performed on reproduction data that greatly exceeds the correction capability. I am trying.

[0017]

In the image recording / reproducing apparatus according to the present invention, coding means for performing error detection / correction coding of input digital image information, and error detection / correction coding by the coding means. Recording / reproducing means for recording data on the recording medium and reproducing it from the recording medium, and error detection / correction decoding of the reproduced data reproduced from the recording medium, and flag information indicating that correction is impossible By comparing the amplitude of the reproduced data with a threshold value, a decoding means for outputting together with the detection-correction-decoded data, a storage means for storing the data error-corrected and decoded by the decoding means and the flag information. Dropout signal generation means for generating a dropout signal of the reproduction data, and reading the flag information from the storage means, Threshold control means for controlling the threshold value used in the dropout signal generator according to the flag information, and reading the data and the flag information from the storage means based on the dropout signal. Read control means and interpolating means for interpolating the uncorrectable data using the data and the flag information read by the read control means.

[0018]

[Operation] The reproduced data is error-corrected and decoded,
It is stored in the storage means together with the flag information indicating that the correction is impossible. The threshold value control means determines the error state of the data based on the stored flag information, and controls the threshold value used in the dropout signal generation means according to the determination result.

The dropout signal generating means generates the dropout signal by comparing the envelope of the reproduction data with the threshold value. Therefore, when the threshold value changes, the period of the dropout signal changes, and the dropout signal period is changed. The threshold value is controlled so that the ratio of is substantially constant. The read control means reads data and flag information from the storage means based on the dropout signal generated by the threshold control, and the interpolation means interpolates uncorrectable data by the read data and flag information. .

Therefore, since the threshold value for generating the dropout signal is properly controlled, the erroneous correction at the time of error correction is reduced and the corrected data is erroneously interpolated. There is no end.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the image recording / reproducing apparatus of the present invention will be described below with reference to the drawings. The most characteristic point of the image recording / reproducing apparatus of the present embodiment is that the result of the inner code decoding and the outer code decoding is determined within the period determined by the dropout signal DOS, and the dropout signal DOS is generated according to the result. Is to converge the threshold value for a proper value. 1 is a block diagram showing a schematic configuration of an image recording / reproducing apparatus according to a first embodiment of the present invention.

In FIG. 1, 1 is a magnetic tape, 2 is a reproducing head, 3 is a demodulator, and this demodulator 3 is for demodulating the reproduced data detected by the reproducing head 2. An inner code decoder 4 is for performing inner code error correction on the demodulated data.

A DOS generator 5 determines the envelope information Env of the reproduction data detected by the reproduction head 2 and generates a dropout signal DOS. Reference numeral 8 is a memory for storing the inner code correction data output from the inner code decoder 5 and the flag information.

Reference numeral 9 reads the inner code correction data stored in the memory 8 in code units of the outer code, corrects the outer code,
The outer code decoder writes outer code correction data and flag information Flag in the memory 8. Reference numeral 13 denotes a DOS threshold controller, which is flag information Fla output from the memory 8.
g is compared with the dropout signal DOS output from the DOS generator 5 corresponding to the flag information Flag, and the threshold value of the DOS generator 5 is changed.

Reference numeral 14 is a read controller 14 which corrects the correction data output from the memory 8 by a dropout signal DO.
It is for controlling whether to read by S.
A high-efficiency decoder 10 receives the correction data and flag information limited by the dropout signal DOS from the read controller 14.

Reference numeral 11 is an interpolation memory, which performs interpolation using the decoded data and the corresponding flag information Flag. 12 is an output terminal.

Next, the operation will be described. During normal reproduction, the tracing of the reproducing head 2 is performed in substantially the same direction as the recording track of the magnetic tape 1. Data that has been converted into product code blocks is recorded on each storage track, and the error correction process is completed for each track unit.

When the magnetic tape 1 is damaged, the envelope En detected by the trace of the reproducing head 2 is detected.
v becomes like FIG.2 (b). The reproduced data in such a state of the envelope Env is demodulated by the demodulator 3 and subjected to error correction processing by the inner code decoder 4, the memory 8 and the outer code decoder 9, and the envelope En of FIG.
The flag information Flag corresponding to v becomes like the final flag in FIG.

In this case, when the flag information Flag is in the L state, it indicates that the corresponding inner code block does not include erroneous data, and in the H state, the erroneous data is included and interpolation processing is necessary. Is shown.

After the error correction processing is completed, the data is stored in the memory 8 again, and the memory 8 is sequentially read by the read controller 14. Read controller 14
Is a dropout signal DO generated by comparing the envelope Env of the reproduction data with the threshold value set by the DOS threshold value controller 13 in the DOS generator 5.
Read control is performed from the S input.

In the DOS generator 5, the error correction process for the envelope Env which is the input from the reproducing head 2 is completed,
The high efficiency decoder 10 includes a delay circuit for delaying the read time. Then, the DOS generator 5
Determines the envelope Env by a threshold value, and FIG.
(B) When the envelope is larger than the threshold value as in (d), the dropout signal DOS in the L state is generated because the reliability of the data is secured, and when the envelope is smaller than the threshold value, the reliability of the data is The dropout signal D in the H state is considered to be incorrect and may be erroneously corrected.
Generate OS.

That is, when the dropout signal DOS is in the L state, the read controller 13 reads the data and the flag information, and when in the H state, the data reading is prohibited and the flag information is set to the H state. High efficiency decoder 10
Give to.

The threshold value for generating the dropout signal DOS is variable, and its control is performed by the DOS threshold value controller 13. This control is performed so that the H state of the final flag is counted while the dropout signal DOS is in the H state and the ratio of the final flag converges to a constant value.

For example, initially, with respect to the envelope Env shown in FIG.
It is assumed that the dropout signal DOS shown in (3) of (d) has been generated. At this time, it is determined that the ratio of the final flag is small, and the level of the dropout signal DOS is lowered.
As a result, the normal data that has been prohibited from being read by the dropout signal DOS is not prohibited and is read by the read controller 14 and input to the high-efficiency decoder 10.

It is also assumed that the threshold value is lowered from the level (3) in FIG. 2B to the level (1). In this case, the dropout signal DOS becomes as shown in (1) of FIG. 2D, the ratio of the final flag (FIG. 2C) in the H state of the dropout signal DOS becomes high, and it is erroneously corrected. There is a risk that the read data will not be prohibited from being read and will be output.

For this reason, the DOS threshold controller 13 controls to raise the threshold to prevent the correction omission. Then, it converges to the threshold value of the level (2) in FIG. 2B, and the optimum dropout signal DOS is obtained.

When obtaining the ratio of the final flag, the period in which the dropout signal DOS is in the H state is set to several tracks or more to avoid small fluctuations in the threshold value. The amount of change when the threshold value is changed may be determined from the ratio of the target flag amount and the actual flag amount, or may be constantly changed at a constant level and converged.

Next, the high-efficiency decoder 10 expands the data and the flag, and the interpolation memory 11 interpolates the data according to the flag information.

FIG. 3 is a block diagram showing the features of the second embodiment of the present invention. The feature of this embodiment resides in that the outer code decoder 9 in FIG. 1 of the first embodiment is replaced with the iterative decoder 15, and the result of the iterative decoding of error correction is within a period determined by the dropout signal DOS. This is a point where the threshold value of the dropout signal DOS is converged to an appropriate value.

In FIG. 3, the same components as those in FIG. 1 are designated by the same reference numerals and detailed description thereof will be omitted. In FIG. 3, reference numeral 15 is an iterative decoder capable of executing error correction processing of an inner code and an outer code, and data input / output is connected to the memory 8.

Next, the operation will be described. The data subjected to the inner code decoding by the inner code decoder 4 is stored in the memory 8.
Then, the inner code decoded data in the memory 8 is outer code decoded by the iterative decoder 15, and the result is stored again in the memory 8.

Further, the iterative decoder 15 performs second inner code decoding on the product code decoded data in the memory 8. The result is stored in the memory 8 and the data and flag in the memory 8 are output to the read controller 9.

On the other hand, the DOS threshold controller 13 outputs the optimum threshold to the DOS generator 5 according to the final flag and the delayed dropout signal DOS.

According to the above-mentioned structure and operation, the dropout signal DO is used even if the result of iterative decoding is used.
The threshold value of S can be converged to an optimum value. For example, it is effective in the case where the state of the transmission path is bad and data cannot be obtained without iterative correction decoding.

The inner code decoder 4 and the outer code decoder 9 or the iterative decoder 15 constitute decoding means. Although FIG. 1 and FIG. 3 show the reproducing system, it is assumed that the recording system (not shown) is provided with encoding means for performing error detection correction encoding of image data.

[0046]

As described above, according to the present invention, the threshold value for generating the dropout signal is controlled based on the flag information obtained after performing the error detection correction decoding. Therefore, an appropriate dropout signal can be obtained, and thus only the reproduced data that greatly exceeds the error correction capability can be surely passed to the interpolation processing. For this reason, erroneously corrected data will not be displayed on the screen without being interpolated, or erroneously corrected data will not be erroneously interpolated and will not be displayed on the screen. There is an effect that can be greatly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image recording / reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing a relationship between an envelope of reproduced data, a dropout signal DOS, and a flag according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a schematic configuration of an image recording / reproducing apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a sync block format.

FIG. 5 is a diagram showing a block configuration of an error correction code.

FIG. 6 is a block diagram showing a schematic configuration of a conventional image recording / reproducing apparatus.

FIG. 7 is a diagram showing a relationship between a conventional envelope and DOS.

[Explanation of symbols]

 1 Magnetic Tape 2 Playback Head 4 Inner Code Decoder 5 DOS Generator 8 Memory 9 Outer Code Decoder 11 Interpolation Memory 13 DOS Threshold Controller 14 Readout Controller Flag Flag Information DOS Dropout Signal Env Envelope Information

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G11B 20/18 E 8940-5D C3 550 F 8940-5D Z 8940-5D 552 Z 8940-5D C3 560 J 8940-5D 576 F 8940-5D H04N 5/92 5/937 5/94 B

Claims (3)

[Claims] 1. Encoding means for performing error detection and correction encoding of input digital image information, and data for which error detection and correction encoding is performed by the encoding means are recorded on a recording medium and reproduced from the recording medium. A recording / reproducing unit for performing the error detection / correction decoding of the reproduction data reproduced from the recording medium, and outputting flag information indicating that the reproduction data cannot be corrected together with the error detection / correction decoded data; Dropout signal generation for generating a dropout signal of the reproduced data by comparing the amplitude of the reproduced data with a threshold value, and a storage means for storing the data decoded and error-corrected by the decoding means and the flag information. Means and the flag information from the storage means, and the dropout signal generating means according to the flag information. Threshold control means for controlling the threshold used, read control means for controlling the reading of the data and flag information from the storage means based on the dropout signal, and read by the read control means. An image recording / reproducing apparatus comprising: an interpolating unit that interpolates the uncorrectable data using the data and the flag information that have been corrected. 2. The threshold value control means is configured to control the threshold value so that a ratio of a period of the flag information to a period of the dropout signal is substantially constant. The described image recording / reproducing apparatus. 3. The image recording / reproducing apparatus according to claim 1, wherein the decoding means comprises an inner code decoder and an outer code decoder or an iterative decoder.