JPH0310487A - Decoder - Google Patents

Abstract

PURPOSE:To reduce the correction error by replacing a data with a just preceding value with highest correlation at correction disable state and applying succeeding decoding with the replaced decoding value. CONSTITUTION:The decoder consists of an input terminal 42 for transmission data, an error detection correction circuit 44, an inverse quantizer 46, an adder 48, a switch 50 switched by a correction disable error code, a D flip-flop 52 acting like a delay device for one sample interval, and an output terminal 54 for the decoded value. Then the decoded value corresponding to the coded code disabled of error correction is replaced with the decoding value at one preceding sample with the highest correlation and the succeeding sample is decoded according to the replaced decoding value. Then the correction error is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a decoding device in a predictive coding method.

[Prior Art] When digitally transmitting image information, a method for reducing the number of transmission bits per sample is differential encoding, which compresses adjacent sample values by taking advantage of the property that they have a high correlation with each other. (hereinafter abbreviated as DPCM) is known.

FIG. 4 shows a configuration block diagram of the most general prior value predictive DPCM encoding device. 10 is the sample value input terminal, 12
is a subtracter that subtracts the predicted value from the input sample value, 14 is a quantizer, 16 is an inverse quantizer, 18 is an adder, 20 is a D flip-flop for outputting the predicted value, and 22 is an error correction code. 24 is an output terminal of the encoded code.

The subtracter 12 subtracts the previous predicted value (8 bits) of the output of the D flip-flop 20 from the sample value (8 bits) of the input terminal 10, and the quantizer 14 subtracts the difference value of the output of the subtracter 12. is quantized and a DPCM code (4 bits) is output. The error correction encoding circuit 22 adds error correction parity to the output of the quantizer 14 and outputs it to the output terminal 24.

Further, the inverse quantizer 16 converts the output of the quantizer 14 into DPCM.
The code (4 bits) is dequantized and the representative difference value (8 bits) is output. The adder 18 adds the previous predicted value to the output of the inverse quantizer 16, and the D flip-flop 20 adds this to 1
It is delayed by the sampling interval and applied to the subtracter 12 and adder 18 as the previous predicted value.

Generally, the difference value from the previous predicted value is a very small value, so by encoding and transmitting the difference value, large compression becomes possible.

FIG. 5 shows a block diagram of the configuration of a decoding device corresponding to FIG. 4. 26 is an input terminal for the transmitted DPCM code; 2
8 is an error detection and correction circuit, 30 is an inverse quantizer, 32 is an adder, 34 is a D flip-flop, 36 is a switch, 38
is a one-line delay device, and 40 is an output terminal for the decoded value.

The input data at the input terminal 26 is subjected to error detection and correction circuit 28, which detects and corrects errors that occur during data transmission.

The error detection and correction circuit 28 converts the DPCM code into the inverse quantizer 3.
0, and if the error cannot be corrected, an error flag (see FIG. 6) that controls the switch 36 is output. The dequantizer 30 dequantizes the DPCM code and outputs a representative difference value, and the adder 32 adds the previous decoded value to the output of the dequantizer 30. The output of adder 32 becomes the decoded value. The output of the adder 32 is a D flip-flop 34.
is delayed by one sample interval and sent to adder 3 as the previous value decoded value.
2 will be returned.

The output of the adder 32 is directly applied to the contact a of the switch 36, and is applied to the contact a of the switch 36 via the one-line delay device 38. Generally, in the DPCM encoding method, when an error occurs in the transmission path, it is known that the error propagates to subsequent decoded values until the next decoded value of the PCM code, which is quantized from the sample value itself, is obtained. . Therefore, when the error detection and correction circuit 28 detects an uncorrectable error in the encoded code, as shown in FIG. 6, an error flag is set after the uncorrectable error is detected.

While the error flag is set, the switch 36 is switched to the contact side, and the sample value of the previous line is substituted, that is, corrected. FIG. 6 shows changes in decoded values at every other sample point due to this modification.

[Problems to be Solved by the Invention] However, in the conventional example described above, since the sample value of one line before is substituted, a one-line delay device is required, resulting in an increase in hardware. In addition, all decoded values after an uncorrectable encoded code is detected are replaced, so if there is no correlation between the sample value of the current line and the sample value of the previous line, the image quality will be improved. It has the disadvantage of deterioration.

In such a case, as shown in FIG. 6, the difference between the sample value of the previous line and the sample value when there is no transmission path error becomes large, and the image quality deteriorates significantly.

The present invention aims to present a decoding device that is free from such drawbacks.

[Means for Solving the Problems] A decoding device according to the present invention is a decoding device using a predictive coding method, and is a decoding device that uses a decoded value of one sample before a decoded value corresponding to an encoded code that cannot be error corrected. The present invention is characterized in that an alternative means is provided and the next sample is decoded in accordance with the decoded value output by the alternative means.

[Operation] With the above means, the decoded value corresponding to the erroneous encoded code is replaced with the immediately preceding decoded value with the highest correlation, so the modification error is extremely small, and this alternative decoded value is used for the next sample. Since decoding is performed, this correction error does not increase over time. Further, it is not necessary to use a one-line delay device, and the circuit configuration is simplified and the cost becomes low.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention. 4
2 is an input terminal for transmission data; 44 is an error detection and correction circuit;
46 is an inverse quantizer, 48 is an adder, 50 is a switch switched by an uncorrectable error code, and 52 is 1
a D flip-flop that acts as a sample interval delayer;
54 is a decoded value output terminal.

The error detection and correction circuit 44 receives the transmission data at the input terminal 42, detects and corrects errors during transmission, and supplies the DPCM code to the dequantizer 30. Error detection and correction circuit 44 also sets an error flag that controls switch 50 for one sample period, as shown in FIG. 2, for uncorrectable transmission errors.

The adder 48 adds D to the output (difference representative value) of the inverse quantizer 46.
The output of the flip-flop 52 (previous value decoded value) is added. The output of the adder 48 is connected to contact a of the switch 50,
The output of the D flip-flop 52 is connected to the contact point of the switch 50. The signal selected by switch 50 is supplied as a decoded value to output terminal 54 and is also applied to D flip-flop 52. That is, the switch 50 is normally connected to contact a to select the output of the adder 48, or
For uncorrectable errors, the contact is connected for one sample period according to the error flag from the error detection and correction circuit 44, and the previous decoded value is selected.

FIG. 2 shows an example of the operation of FIG. An uncorrectable transmission error occurs at the time of the fifth sample, and the erroneously decoded sample value at that time is replaced with the decoded value one sample before. Since the sample value one sample before has an extremely high correlation with the current sample value, the correction error in the decoded value is also extremely small. From then on,
Since decoding is performed using the transmitted DPCM code, the modification error remains within a certain value and does not become large. In particular, if an uncorrectable transmission error occurs in a sample of the same sample size as the sample value one sample before, the modification error is zero.

Inverse quantizer 46, adder 48 and switch 5 in FIG.
The 0 part can be formed by a ROM table. FIG. 3 shows its configuration block diagram. 56 is a ROM serving as the decoding table.

The ROM 56 receives as input 4 bits of DPCM code,
8 bits are allocated to the predicted value, 1 bit is allocated to the error flag output from the error detection and correction circuit 44, and it has an 8-bit output. The ROM 56 is written so that when the error flag is set, the previous decoded value, that is, the same code as the output of the D flip-flop, is output, and when the error flag is not set, the 4-bit DPC is output.
It may be written to output a value obtained by adding the previous decoded value from the D flip-flop to the representative difference value based on the M code.

Although the above embodiments have been described using the previous predictive coding method as an example, it goes without saying that the interframe pre-1 coding method and the interline predictive coding method can be similarly applied.

[Effects of the Invention] As can be easily understood from the above explanation, according to the present invention, since no one-line delay device is used, the circuit configuration is simplified and the cost is reduced. In addition, when correction is not possible, the immediately preceding value with the highest correlation is used as a substitute, so the correction error is extremely small.
Moreover, since subsequent decoding is performed using this alternative decoding value,
This modification error does not increase over time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, FIG. 3 is a configuration example in which a part of FIG. Fig. 5 is a block diagram of the configuration of the encoding device, and Fig. 6 is a block diagram of the configuration of the conventional decoding device.
The figure is an explanatory diagram of the operation of FIG. 5. 42; Input terminal 44: Error detection and correction circuit 46: Inverse quantizer 48: Adder 50: Switch 52: D flip-flop 54: Output terminal 23456 F 8. IjJ(,,'le2.
. Figure 2 Figure 5 Figure Time (Sanoble)

Claims (1)

[Claims] A decoding device in a predictive coding system, which has an alternative means for substituting a decoded value corresponding to an uncorrectable encoded code with a decoded value one sample before, and selects the next sample according to the decoded value output by the alternative means. A decoding device characterized by decoding.