JPH04233387A - Image decoding device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the picture quality at the time of decoding an image. CONSTITUTION:In an encoding part ECC encoding is executed in 402 and 403 to each of an AC component and a DC component. In a decoding part 402, an error is detected and corrected in ECC decoding parts 103, 104, and in the case of an error which cannot be corrected completely, reproduction is executed by only the DC component in a DC converting part 108.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image decoding device, and more particularly to an image decoding device having a function of decompressing compressed image data.

0002

2. Description of the Related Art Conventionally, a technique is known in which image data is frequency-converted block by block, compressed, and then transmitted. In particular, image compression efficiency is improved by separating frequency components into high-frequency components and low-frequency components and encoding each separately.

0003

[Problem to be Solved by the Invention] However, in the above conventional example, if an error occurs during transmission of encoded data, an image signal containing incorrect pixel data is reproduced, resulting in a large deterioration in image quality. There was a drawback. Furthermore, when variable codes are used to encode the high frequency components mentioned above, even the number of data cannot be reproduced accurately.
Significant deterioration in image quality, such as loss of image data, may occur.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image decoding device that can reduce the above-mentioned image quality deterioration.

[0005]

[Means and operations for solving the problems] In order to solve the above problems, the image decoding device of the present invention frequency-converts image data for each block composed of a plurality of pixels, and converts low frequency components and high frequency components. An image decoding device that decodes data that has been encoded separately, comprising means for detecting an error in encoded data of at least one of the components, and means for correcting an error detected by the detection means. has
The present invention is characterized in that decoding is performed in accordance with the error data detected by the detection means.

[0006]

[Embodiment] A video decoding apparatus according to the present invention described below includes means for detecting and correcting errors occurring during transmission or reproduction from a recording medium, and based on error information generated by the detection and correction means. characterized by comprising means for replacing decoded data in the block with a predetermined setting value,
After detecting the error that occurred on the transmission path and performing correction processing, it is determined that there is no error in the DC component in the block and A
If an uncorrectable error remains on the C component, that information is used to replace all data in the block with the DC component value, changing each pixel value in the block to a value close to the true value. can be replaced with

FIG. 1 shows a block diagram of the configuration of an image decoding apparatus according to an embodiment of the present invention and a corresponding image encoding apparatus.

Reference numeral 401 denotes an encoding device, and 402 denotes a decoding device, both of which are connected via a transmission line 403. Here, the transmission line 403 is a transmission medium such as optical fiber, satellite, terrestrial radio waves such as microwave, optical space, etc. for instant transmission.
For storage and transmission, storage media include tape-shaped media such as digital VTRs and DATs, disk-shaped media such as floppy disks and optical disks, and solid media such as semiconductor memories.

[0009] First, a video signal is input to an input terminal 404 of an encoding device 401, and a block forming circuit 406 converts the video signal into a block consisting of, for example, 8×8 pixels.
It is divided into blocks consisting of multiple pieces of data. The blocked data is converted into frequency components for each block in an orthogonal transform circuit 407, for example, by DCT (discrete cosine transform). The converted data is divided into a low frequency component and a high frequency component, for example, a DC component (direct current component) and other AC components (alternating current component), and is outputted separately, and each is sent to an encoding circuit 40 in order to compress the amount of information.
8, 409 separately. Here, examples of encoding include methods such as PCM encoding the DC component and run-length Huffman encoding the AC component. Each of the encoded data output from the encoding circuits 408 and 409 is sent to the ECC encoding circuit 4 as a countermeasure against errors during transmission.
After being subjected to error detection and correction coding in steps 10 and 411, they are synthesized in time series in a synthesis circuit 412, and are further added with a synchronization signal for transmission or recording for each plurality of blocks in a synchronization addition circuit 413. will be sent to.

On the other hand, in the image decoding device 402, a synchronization signal is detected in the received transmission data by a synchronization detection circuit 101, and the following signal processing is performed using the detected synchronization signal as a reference.

First, transmission data is separated by a separation circuit 102 into coded data corresponding to a DC component and coded data corresponding to an AC component. At this time, the format of the encoded data is assumed to be such that, for example, as shown in FIG. 2, the DC component and AC component can be reliably separated in one synchronous block.

Each separated data is input to ECC decoding circuits 103 and 104, which are the above-mentioned error detection and correction means, and errors during transmission are corrected. Then, the ECC decoding circuits 103 and 104 transfer the corrected data to the decoding circuit 105.
, 106, and at the same time, the error information is sent to D, which is means for replacing the error information with a predetermined setting value, according to each correction result.
It is sent to the C replacement circuit 108.

[0013] The encoded data corresponding to the DC component and AC component after the correction processing are input to decoding circuits 105 and 106, respectively, where they are subjected to composite processing and restored to the information of the DC component and AC component. If errors remain in the converted data, the correct information will of course not be restored.

[0014] If, for example, variable length coding is used as the encoding method for the AC component, not only the decoded value of the AC component may not be the true value, but also the number of data may not be restored. .

Now, each decoded data outputted by the restoration circuits 105 and 106 is restored by an orthogonal inverse transform circuit 107 from a value representing a frequency component to data representing a pixel value within a block. However, as mentioned above, EC
If the error correction cannot be completed in the C decoding circuits 103 and 104, the input value of the orthogonal inverse transform circuit 107 itself is not correct information, so the output value of the orthogonal inverse transform circuit 107 is correct pixel data. This results in completely different data.

Therefore, in the DC replacement circuit 108, E
The error information generated by the CC decoding circuit 103 indicates that there is no error in the DC component of the block, and the error information generated by the ECC decoding circuit 104 indicates that there is an uncorrectable error in the AC component of the block. If it indicates that there is, all pixel values in the block are replaced with DC component values.

[0017] Through this operation, even if there is an error that cannot be corrected as described above, the pixel value in the block can be taken as the DC component value which is the average value, and although it is not the true value, it is possible to This means that the value can be restored to a value close to the true value.

[0018]Then, the data is transferred to the time axis conversion circuit 10.
9, the video signals are rearranged on the same time axis as the video signals input to the encoding device and output from the output terminal 110.

With the above-described apparatus, even if an error that cannot be corrected occurs on the transmission path, image quality deterioration can be kept to a minimum.

(Other Embodiments) FIGS. 3 and 4 show other embodiments of the present invention.

FIG. 3 shows the DC replacement circuit 108 in FIG.
The function corresponding to 0 is realized by the 0 substitution circuit 308. Other circuit blocks are the same as those in FIG. 1, so they are given the same numbers.

The 0 substitution circuit 308 is the ECC decoding circuit 10
3. If the error information output from 104 indicates that there is no error in the DC component of the block, but that there is an uncorrectable error in the AC component, as in the previous embodiment; To do this, set all values of the AC component to 0. With this operation, the input data of the orthogonal inverse transform circuit 107 becomes
The AC component becomes 0, and therefore, in the output of the orthogonal inverse transform circuit 107, all values within the block become DC component values, resulting in the same effect as in the previous embodiment.

FIG. 4 is an example showing that the present invention can be applied even when the configuration methods of error detection and correction codes are different, and the ECC decoding circuit 104 in FIG.
The ECC encoding circuit 411 in the encoding device is located before the separating circuit 102 and after the combining circuit 412, and the former is used as the ECC decoding circuit 304 and the latter as the ECC decoding circuit 411.
The encoding circuit 311 shows a case where the error detection and correction code is encoded on data obtained by combining a DC component and an AC component.

[0024] Also in this case, the error information output from the ECC decoding circuit 304 indicates that an error exists, and the ECC decoding circuit 304
If the error information output from the CC decoding circuit 103 indicates no error, replacement with the DC component becomes effective.
The present invention can be implemented using a DC replacement circuit 108 similar to that shown in FIG.

As explained above, according to the embodiment of the present invention, there is provided means for detecting and correcting errors that occur during transmission or during reproduction from a recording medium, and error information generated by the detecting and correcting means. Basically, even if an error that cannot be corrected occurs, image quality deterioration can be kept to a minimum by replacing all the decoded data in the block with DC component values, or by using an equivalent method. It is possible to realize a decoding device that can perform this function and requires a small amount of hardware to be added for this purpose.

[0026]

As described above, according to the present invention, deterioration in image quality in an image decoding device can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a data transmission format.

FIG. 3 is a configuration block diagram of another embodiment of the present invention.

FIG. 4 is a configuration block diagram of another embodiment of the present invention.

[Explanation of symbols] 101 Synchronization detection circuit 102 Separation circuit 103, 104 ECC decoding circuit 105, 106 Decoding circuit 107 Orthogonal inverse transform circuit 108 DC replacement circuit 109 Time axis conversion circuit 308 0 replacement circuit

Claims (6)

[Claims] 1. An image decoding device that performs frequency conversion on image data for each block composed of a plurality of pixels, separates it into low frequency components and high frequency components, and decodes the encoded data, comprising: The method includes means for detecting an error in encoded data of at least one of the components, and means for correcting the error detected by the detecting means, and performs decoding according to the error data detected by the detecting means. An image decoding device characterized by: 2. The image decoding apparatus according to claim 1, further comprising means for performing a process of replacing the error data with a predetermined setting value in accordance with the error data. 3. The image decoding apparatus according to claim 1, wherein encoded data in a block in which an error is detected by the detection means is decoded based only on the low frequency component. 4. The image decoding apparatus according to claim 1, wherein the low frequency component includes a direct current component. 5. The image decoding apparatus according to claim 2, wherein the setting value is a DC component value. 6. The image decoding apparatus according to claim 2, wherein the setting value is 0.