JPH09149259A - Picture communicating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently transmit a picture in short time by adding an error detection code to a DC component and adding an error correction code to an AC component so as to transmit them and interpolating the DC component and correcting an error on the AC component when the error is detected on a reception side. SOLUTION: When picture data is inputted a discrete cosine converter 1 discretely cosine-converts data in an encoding block unit, a quantizer 2 quantizes it and a Huffman encoder 3 entropy-encodes it. Then, data is divided into the DC component and the AC component. The DC component is outputted to a detection encoder 3 and the AC component to an error correction encoder 11. Error block information is outputted to an interpolation unit 13 on a frame where the error is detected and the DC component is interpolated. The error correction code is added to the AC component in the error correction encoder 11. The AC component passes through a modulator 5 and it is demodulated in a demodulator 6. Then, it is error-corrected/decoded in an error correction decoder 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image communication method for compressing and transmitting an image, and in particular, an image communication capable of efficiently transmitting an image while maintaining a certain degree of accuracy even in a communication path with poor line quality. Regarding the method.

[0002]

2. Description of the Related Art First, a conventional image communication apparatus is shown in FIG.
I will explain using. FIG. 5 is a configuration block diagram of a conventional image communication apparatus. As shown in FIG. 5, the conventional image communication device has a discrete cosine transformer 1 and a quantizer 2 on the transmitting side.
, Huffman encoder 3 ', and error detection encoder 4'
And a modulator 5, and the receiving side has a demodulator 6 ',
An error detection decoder 7 ', a Huffman decoder 8', an inverse quantizer 9, and an inverse discrete cosine transformer 10 are provided, and the transmission side and the reception side are connected via a communication path. There is.

Next, each section of the conventional image communication apparatus will be described. The discrete cosine transformer 1 transforms the input image data, which has been digitally converted, into discrete cosine (Discrete Cosine Transform: DCT) transforms in units of coding blocks (for example, 8 × 8 pixels, which will be simply referred to as blocks hereinafter) and performs DC
The transform coding is performed to output the T coefficient. The quantizer 2 is the DC coded by the discrete cosine transformer 1
The T coefficient is quantized and the quantized coefficient in which the number of effective coefficients is reduced is output. The Huffman encoder 3'entropy-encodes the quantized coefficients quantized by the quantizer 2 and outputs information source encoded data (encoded data). As an example of entropy encoding, a Huffman code is used. Is known.

The error detection encoder 4'adds an error detection code for detecting a transmission error to the encoded data output from the Huffman encoder 3 ', and forms a transmission frame according to the transmission control procedure. It is created and output to the modulator 5. Note that one or more blocks of information source encoded data are incorporated in one transmission frame.

Here, as an example of the error detection code, it is known that C can detect both an independent error in which an error independently occurs and a burst error in which an error continuously occurs.
There is RC (Cyclic Redundancy Checks) code, and the details are described in "Computer Communication and Network" by Kunio Fukunaga, Kyoritsu Shuppan Co., Ltd. p78-p82. In addition, as an example of the transmission control procedure, it is possible to transmit variable-length data in bit units, and by transmitting a retransmission request at the time of error detection, HDLC (High level Data Link Control) procedure is common.

As shown in FIG. 6, a transmission frame, which is a transmission unit in the HDLC procedure, has a flag for detecting the start of the frame, a destination address, and a control for setting a command or response according to the procedure. , Variable length data to be transmitted, that is, image data (source coded data) here, and error correction code (here C
(RC code) and a flag for detecting the end of the frame. FIG. 6 is an explanatory diagram showing the transmission frame format of the HDLC procedure. HDLC
Details of the procedure are described in “Computer Communication and Network”, Kunio Fukunaga, Kyoritsu Shuppan Co., Ltd., p113-p130.

In the HDLC procedure, when an error or loss in frame units is detected on the receiving side, a retransmission request is transmitted. Therefore, the error detection encoder 4'corresponds to the retransmission request from the receiving side. Then, the frame retransmitting operation is also performed.

The modulator 5 modulates transmission data into a signal suitable for a communication path and sends it out to the communication path. The demodulator 6'demodulates the transmission data received from the communication path and outputs it to the error detection decoder 7 '. The error detection decoder 7'performs error detection on the demodulated received data,
H if an error is detected or a frame is missing
According to the DLC procedure, a retransmission request is transmitted and exchanges are performed until error-free data can be received.
Then, for the error-free data, the information source coded data portion is taken out and output to the Huffman decoder 8 '.

The Huffman decoder 8'entropy-decodes the error-free coded data received from the error detection decoder 7'and outputs the quantized coefficient. The inverse quantizer 9 outputs the Huffman decoder. The quantized coefficient from the decoder 8'is inversely quantized and a DCT coefficient is output, and the inverse discrete cosine transformer 10 inversely discrete cosine transforms the DCT coefficient from the inverse quantizer 9 to obtain an information source. It is for outputting the decoded image data.

Next, the operation of the conventional image communication apparatus will be described with reference to FIG. In a conventional image communication device, when image data of an image to be transmitted is input to a transmission side, the discrete cosine transformer 1 performs discrete cosine transform, the quantizer 2 quantizes, and the Huffman encoder 3'entropy. The data is encoded and information source coded, and further, an error detection code is added by an error detection encoder 4 ', incorporated into an HDLC frame, modulated by a modulator 5 and transmitted to a communication path.

On the receiving side, the data received from the communication path is demodulated by the demodulator 6 ', the error is detected by the error detection decoder 7', and a resend request is issued to the frame in which the error is detected. The error detection encoder 4'transmitted to the transmitting side via 6 ', and receiving the retransmission request via the modulator 5, retransmits the frame requested to be retransmitted. For the frame in which no error is detected by the error detection decoder 7 ', the source coded data portion is extracted, entropy-decoded by the Huffman decoder 8', and dequantized by the dequantizer 9. Then, the inverse discrete cosine transformer 10 performs the inverse discrete cosine transform, the information source decoding is performed, and the image data is output.

[0012]

However, in the above-mentioned conventional image communication apparatus, when an image is transmitted through a communication path having a large error rate such as wireless communication, the frequency of retransmission is high and the communication time becomes very long, which is not practical. There was a problem.

The present invention has been made in view of the above circumstances, and provides an image communication method capable of efficiently transmitting an image in a short time while maintaining a certain degree of accuracy even in a communication path having a large error rate. The purpose is to

[0014]

The invention according to claim 1 for solving the above-mentioned problems of the prior art is an information source coding obtained by discrete cosine transform, quantization and entropy coding of an original image. In an image communication method for transmitting data, the information source coded data is divided into a direct current component and an alternating current component, an error detection code is added to the direct current component, and the data is transmitted. It is characterized in that the component is interpolated, the AC component is added with an error correction code and transmitted, and the error is corrected on the receiving side. By performing error correction, an image can be efficiently transmitted in a short time while maintaining a certain degree of accuracy even in a communication path with a large error rate.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the claimed invention will be described with reference to the drawings. The image communication method according to the present invention divides the information source coded data of an image into a direct current (DC) component and an alternating current (AC) component. For the DC component, error detection is performed using an error detection code, and an error is detected. If detected, interpolation is performed from the normally received DC component, and error correction is performed on the AC component using an error correction code, so the communication time of the DC component is greatly reduced, and even if an error occurs However, since almost perfect data can be obtained by interpolation and the AC component may contain some errors, it has little effect on the reproduced image. Therefore, even if the communication path has a large error rate, some accuracy is maintained. While
The image can be transmitted efficiently in a short time.

First, the configuration of an image communication apparatus for implementing the image communication method according to the present invention will be described with reference to FIG.
FIG. 1 is a block diagram showing a configuration of an image communication apparatus for realizing an image communication method according to the present invention. It should be noted that parts having the same configuration as in FIG.

The image communication apparatus (present apparatus) of the present invention is shown in FIG.
As a part basically similar to the conventional image communication device shown in FIG. 1, the transmitting side has a discrete cosine transformer 1, a quantizer 2, and
It is composed of a Huffman encoder 3, an error detection encoder 4, and a modulator 5, and the receiving side includes a demodulator 6, an error detection decoder 7, a Huffman decoder 8, and an inverse quantizer 9. And an inverse discrete cosine transformer 10, and an error correction encoder 11, an error correction decoder 12, and an interpolator 13 are provided as a characteristic part of the present invention.

Next, each part of the present apparatus will be specifically described. The discrete cosine transformer 1, the quantizer 2, the dequantizer 9, and the inverse discrete cosine transformer 10 are completely different from the conventional ones. Since it is the same, the description is omitted here.

The Huffman encoder 3 entropy-encodes (here, Huffman-encodes) the quantized coefficients quantized by the quantizer 2 in units of coding blocks (simply referred to as blocks), and entropy-codes. The encoded data (encoded data) is divided into a DC component and an AC component, and D
The C component is output to the error detection encoder 4, and the AC component is output to the error correction encoder 11. As a feature of the Huffman coding, the DC component and the AC component are separately coded, and in particular, for the DC component, the difference value with the DC coefficient of the immediately preceding block is coded.

The error detection encoder 4 encodes the DC component encoded data (DC encoded data) from the Huffman encoder 3.
Error detection coding is performed internally, and DC for one screen is internally
It has a memory for storing encoded data.

Specifically, when the error detection encoder 4 receives the DC coded data in block units from the Huffman encoder 3, the error detection encoder 4 stores one screen worth in the internal memory. Since the DC encoded data has one value in one block, for example, when the original image has 640 × 480 pixels and the block has 8 × 8 pixels, the DC component for one screen is 80 × 60. It becomes a value.

When the storage of the DC coded data for one screen is completed, an error detection code is added by using one block or a plurality of blocks (for example, 8 × 8 blocks) of DC coded data as one transmission frame, and then transmitted. The transmission frame is created according to the control procedure and is output to the modulator 5. Incidentally, as the transmission frame format, the same HDLC frame as the conventional one is used, however, unlike the HDLC as a transmission control procedure, retransmission is not performed when an error occurs.

DC to be incorporated in one transmission frame
In order to reduce the probability that the DC coded data of the adjacent blocks will be erroneous at the same time, the coded data may have
The C encoded data may be sent in the same frame. Incidentally, if it is prepared that the transmission efficiency is deteriorated, the influence of the error becomes smaller when the DC encoded data of one block is transmitted by one transmission frame.

The error correction coder 11 performs error correction coding on the AC component coded data (AC coded data) from the Huffman coder 3, and internally stores one screen of AC coded data. Has a memory for storing. Specifically, the block unit AC from the Huffman encoder 3
When the encoded data is received, one screen worth is stored in the internal memory. Then, the AC coded data for one block or a plurality of blocks (for example, 8 × 8 blocks) is subjected to error correction coding as one transmission frame, and here, a BCH (Bose Chaudhuri Hocquenghem) code is used as the error correction code. As an example, when encoding with BCH (16,8), 8 bits of error correction code are added to 8 bits of data, and the transmission frame of the AC component becomes as shown in FIG. FIG. 2 shows an AC in the image communication apparatus of the present invention.
It is explanatory drawing which shows the transmission frame format of a component.
If the AC encoded data to be incorporated in one transmission frame is expected to have a poor transmission efficiency, the AC component of one block may be transmitted in one frame to reduce the influence of errors.

The modulator 5 receives the D signal from the error detection encoder 4.
The transmission frame of the C component and the transmission frame of the AC component from the error correction encoder 11 are respectively modulated according to the communication path and sent out to the communication path. The demodulator 6 demodulates the data received from the communication path and outputs it to the error detection decoder 7 in the case of the DC component and outputs it to the error correction decoder 12 in the case of the AC component. The error correction decoder 12 performs error correction on the demodulated AC component transmission frame. When the demodulated data of the AC component is received from the demodulator 6, the error correction decoder 12 performs error correction to Huffman-decode the AC encoded data. It is output to the container 8.

The error detection decoder 7 detects an error in the demodulated DC component transmission frame, and has an internal memory for storing the DC component for one screen. Specifically, when the demodulator 6 receives a demodulated DC component transmission frame, error detection is performed, and if no error is detected, the DC encoded data included in the transmission frame is stored in each block position of the internal memory. Remember. On the other hand, when an error is detected, an alternative value (for example, 0) is stored in each block position of the DC component included in the transmission frame (error detection frame), and block information indicating the block position of the DC component is stored. (Error block information)
Is output to the interpolator 13.

When the DC coded data or the alternative value for one screen is stored, the DC coded data or the alternative value is read from the internal memory in the order of performing the information source decoding, that is, in the order of the information source coding. It is read and output to the Huffman decoder 8.

The Huffman decoder 8 performs entropy decoding of the received information source coded data, and includes an AC memory for storing one screen of decoded AC components (AC quantized coefficients), and the decoding. It has a DC memory that stores the generated DC component (DC quantization coefficient) for one screen.

Specifically, the Huffman decoder 8 receives the AC coded data from the error correction decoder 12 and performs entropy decoding (here, Huffman decoding) to obtain AC quantized coefficients for one screen. Store in AC memory.

On the other hand, when the Huffman decoder 8 receives the DC coded data or the substitute value from the error detection decoder 7, the Huffman decoder 8 performs entropy decoding (here, Huffman decoding) to 1
The DC quantized coefficients for the screen are stored in the DC memory, and when the decoding for one screen is completed, the interpolation instruction is output to the interpolator 13. When the end notification indicating the end of the interpolation processing in the interpolator 13 is received, the AC quantized coefficient stored in the AC memory and the interpolated DC quantized coefficient stored in the DC memory are combined, The data is output to the inverse quantizer 9 in units of coding blocks.

The interpolator 13 interpolates the DC quantized coefficient of the DC component included in the error detection frame, and has an internal memory for storing error block information. The interpolator 13 is, specifically, the error detection decoder 7
When the error block information output from is stored in the internal memory and the interpolation instruction is received from the Huffman decoder 8,
According to the stored error block information, the DC memory of the Huffman decoder 8 is referred to, the DC quantized coefficient at the error location is calculated from the normally received DC quantized coefficients, and the interpolation processing is performed. Upon completion, the end notification is output to the Huffman decoder 8.

Here, an example of the interpolation processing will be described with reference to FIG. FIG. 3 is an explanatory diagram showing an example of an interpolation processing method in the image communication apparatus of the present invention. An example of the interpolation processing method is that the DC quantized coefficients x of a plurality of blocks (8.times.8 blocks in the gray portion in FIG. 3) included in the error detection frame are the DC quantized coefficients a of the four normally received surrounding blocks, It is calculated by the mathematical expression [Equation 1] using b, c, and d.

[0033]

(Equation 1)

Incidentally, the interpolation method is not limited to this example, and from a simple method of copying the DC quantized coefficient of the adjacent block to a curve interpolation in which the interpolation calculation is performed using a curve formula, there is a trade-off between processing speed and interpolation accuracy. Any method may be used as long as the interpolation method is selected.

Next, the operation of the image communication apparatus of the present invention will be described with reference to FIG. In the image communication device of the present invention, when image data of an image (original image) to be transmitted to the transmission side is input, the discrete cosine transformer 1 performs discrete cosine transform for each coding block, and the quantizer 2 quantizes it. And is entropy coded by the Huffman encoder 3 to obtain D
It is divided into a C component (DC encoded data) and an AC component (AC encoded data), the DC encoded data is output to the error detection encoder 4, and the AC encoded data is output to the error correction encoder 11. It

Hereinafter, the operation will be described separately for the DC component and the AC component. The DC encoded data of the DC component is temporarily stored in the error detection encoder 4 for one screen, added with an error detection code in transmission frame units, incorporated into an HDLC frame, modulated by the modulator 5, and transmitted through the communication path. Sent to.

Then, with respect to the frame which is demodulated by the demodulator 6 on the receiving side and error-detected by the error-detection decoder 7, the DC coded data contained therein is included in the error-detection decoder. Stored in the internal memory of 7.
On the other hand, for a frame in which an error has been detected, a substitute value is stored in the block position of the internal memory corresponding to the DC component included in the frame, and the error detection decoder 7 outputs the error block information to the interpolator 13. Remembered.

If one screen of DC coded data or alternative value is stored in the error detection decoder 7,
The DC encoded data or alternative values are output to the Huffman decoder 8 in the order in which the information source decoding is performed, and the Huffman decoder 8
Is entropy-decoded and the DC quantized coefficient is the internal D
Stored in C memory.

When one screen of DC quantized coefficients is stored in the Huffman decoder 8, an interpolation instruction is output from the Huffman decoder 8 to the interpolator 13 and stored in the interpolator 13. Interpolation processing is performed according to the error block information from the error detection decoder 7.

On the other hand, the AC encoded data of the AC component is added with an error correction code by the error correction encoder 11, modulated by the modulator 5 and sent to the communication path, and the demodulator 6 on the receiving side.
Is demodulated by, the error correction decoder 12 performs the error correction decoding, and the Huffman decoder 8 performs the entropy decoding.
The AC quantized coefficients for the screen are stored in the internal AC memory.

Then, the interpolation processing in the interpolator 13 is completed, and the end notification from the interpolator 13 is sent to the Huffman decoder 8
Received by the Huffman decoder 8, the DC of the DC memory
The quantized coefficient and the AC quantized coefficient of the AC memory are combined to create a quantized coefficient for each coding block, which is inversely quantized by the inverse quantizer 9 and inverse discrete cosine transform by the inverse discrete cosine transformer 10. The image data is decoded by the information source and output.

Comparing the case of transmitting an image using the image communication method of the present invention with the conventional method in terms of the relationship between the error rate of the communication path and the communication time, as shown in FIG. It can be seen that in the case of the image communication method of the invention, the communication time is constant regardless of the error rate of the communication path, and the communication time is considerably shorter than that of the conventional method especially in the case where the error rate is large.
FIG. 4 is an explanatory diagram showing the relationship between the error rate of the communication path and the communication time.

According to the image communication apparatus for realizing the image communication method of the present invention, the Huffman encoder 3 on the transmission side divides the information source coded data of the image into the DC component and the AC component, and D
When an error is detected by the error detection encoder 4 and the error detection decoder 7 with respect to the C component, the interpolator 13 interpolates from the normally received DC component, and the AC component is corrected with the error correction encoder 11 and Since the error correction decoder 12 transmits by a method of correcting some errors, the communication time is constant regardless of the error rate, and the AC component may include an error, but the DC component can be transmitted almost completely. Therefore, there is an effect that an image can be efficiently transmitted in a short time while maintaining a certain degree of accuracy even on a communication path having a large error rate.

[0044]

According to the invention described in claim 1, the information source coded data is divided into a direct current (DC) component and an alternating current (AC) component, and an error detection code is added to the DC component for transmission and reception. When an error is detected on the side, the DC component is interpolated, the AC component is added with an error correction code and transmitted, and the receiving side corrects the error. Therefore, the DC component retransmits the error. Instead, it can be restored by interpolation and the error can be corrected by the AC component, and there is an effect that an image can be efficiently transmitted in a short time while maintaining a certain degree of accuracy even in a communication path with a large error rate.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image communication apparatus that realizes an image communication method according to the present invention.

FIG. 2 is an explanatory diagram showing a transmission frame format of an AC component in the image communication device of the present invention.

FIG. 3 is an explanatory diagram showing an example of an interpolation processing method in the image communication apparatus of the present invention.

FIG. 4 is an explanatory diagram showing a relationship between an error rate of a communication path and communication time.

FIG. 5 is a configuration block diagram of a conventional image communication device.

FIG. 6 is an explanatory diagram showing a transmission frame format of an HDLC procedure.

[Explanation of symbols]

1 ... Discrete cosine transformer, 2 ... Quantizer, 3, 3 '
... Huffman encoder, 4, 4 '... Error detection encoder,
5 ... Modulator, 6, 6 '... Demodulator, 7, 7' ... Error detection decoder, 8, 8 '... Huffman decoder, 9 ... Inverse quantizer, 10 ... Inverse discrete cosine transform, 11 ... Error Correction encoder, 12 ... Error correction decoder, 13 ... Interpolator

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Claims (1)

[Claims] 1. An image communication method for transmitting information source coded data obtained by subjecting an original image to discrete cosine transform, quantization and entropy coding, and dividing the information source coded data into a DC component and an AC component. , An error detection code is added to the DC component and transmitted, and when an error is detected on the receiving side, the DC component is interpolated, and an error correction code is added to the AC component and transmitted, and the receiving side An image communication method, characterized in that error correction is performed by.