JP2936627B2 - Image decoding method with compensation for abandonment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to an image data transmission system, and more specifically, to a packet discarded at the time of discarding a packet in a receiver of the image data transmission system which transmits a plurality of pixels in a packet unit by performing DPCM encoding. For image decoding systems with a function to compensate for video signals, we aim to provide an image decoding system with a discard compensation function that suppresses image quality degradation when discarding packets. In a receiver of an image data transmission system that encodes and transmits in packet units, a packet decomposition processing unit that decomposes a received packet to extract image data, and a discard that detects discard of a packet and outputs a discard detection signal Detecting means for receiving the image data extracted from the packet decomposing means, and When there is packet discard in the data, discard compensating means for replacing the image data of the group received this time with the image data of the group received last time on a group basis is provided. When the discard detection signal is not received by the middle group, the image data of the group received this time is decoded, and when the discard detection signal is received by the group currently being received from the discard detection means, the image data of the previously received group is decoded. It is configured to decrypt.

[Industrial applications]

The present invention relates to a receiving device of an image data transmission system,
More specifically, the present invention relates to an image decoding system having a function of compensating for a packet discarded at the time of discarding a packet in an image data transmission system that transmits a plurality of pixels in a packet unit by DPCM encoding.

2. Description of the Related Art Recently, digitization of image equipment and transmission methods of pixel digital signals have been widely developed and studied in many application fields such as videophones. Generally, image data has a very large amount of information. For example, if a current television video signal is directly digitized, a transmission capacity of 100 Mb / s is required, and the image data has 1500 times the information amount of the audio.
On a TV, the screen switches 30 times per second,
Frames are switched in seconds. Pixels are generally arranged two-dimensionally on one screen for one frame, and even if the level of one pixel is represented by, for example, 8 bits,
The image data for one frame has a very large amount of information.

Some of the statistical properties of this image data are:
This is the correlation between adjacent pixels. That is, pixel levels that are close to each other on one frame often take similar values. For example, in the case of a human figure, it can be easily imagined that the face portion will have a similar flesh color, and if there is a sky in the background, it will also have a similar blue or gray color. For this reason, the difference distribution of the levels of the adjacent pixels is biased near zero.
By using this property, differential data with a high frequency of occurrence is encoded with short bits and differential data with a low frequency of occurrence is encoded with long bits, and as a result, the amount of information can be reduced. Therefore, when transmitting such a screen, an intra-frame difference encoding method (hereinafter referred to as an intra-frame DPCM method) that encodes, for example, the difference between adjacent pixel levels is used rather than the pixel level itself. ing.

[Conventional technology]

FIG. 6 is a block diagram of an image data transmitting / receiving apparatus using the intra-frame DPCM method. In the figure, an encoding unit 60 and a packet assembling unit 61 are provided on the transmission device side. The encoding unit 60 includes an A / D converter 601, a quantizer 602, a prediction circuit 603,
It comprises an adder 604, a subtractor 605, a variable length encoder 606, a buffer memory 607, and a control unit 608. The packet assembler 61 divides the coded image data so as to have a certain length or less, attaches a header including a destination address to each of the divided image data, and packetizes the data and sends it out to the line.

The receiving device includes a packet decomposing unit 62 and a decoding unit 63. The packet decomposing unit 62 extracts the sent image data by decomposing the packet. Decoding section 63
Comprises a D / A converter 614, a prediction circuit 613, an adder 612, a variable length decoder 611, a buffer memory 609, and a control unit 610.

The input video signal is converted by the A / D converter 601 into a code of, for example, 8 bits per pixel (hereinafter, described assuming 8 bits). Next, the converted pixel data is sent to the prediction circuit
The difference from the value predicted by 603 (previous pixel data value) is calculated by the subtractor 605. The pixel data having the difference from the predicted value is quantized by the quantizer 602. The quantized output signal (the difference between the previous pixel data value and the current pixel data value) and the output signal (previous pixel data value) of the prediction circuit 603 are added by the adder 604, and the output signal (current pixel data value) is obtained. Prediction circuit 60 as an input signal when performing prediction
Entered in 3.

On the other hand, the quantized image data is
According to 6, variable length coding is performed by assigning a short code to a value having a high frequency of occurrence. When variable length coding is performed,
Since the amount of output data generated varies irregularly according to the input image information, the information is temporarily stored in the buffer memory 607.
If the buffer memory 607 having a finite capacity overflows (overflows) or becomes empty (underflows) due to an increase in input information, the information is destroyed. For this reason, the “coarse” and “fine” of the quantizer 602 are controlled in accordance with the amount of information stored in the buffer memory 607 by the control unit 608.
, And the generated information is controlled. The output of the buffer memory 607 is assembled by the packet assembling unit 61 in packet units.

The digital signal that has reached the receiving unit via the transmission path is returned to the original video signal through a process reverse to that of the transmitting unit. At this time, the output signal decoded by the variable length decoding unit 611 and the output signal of the prediction circuit 613 are added by the adder 612, and the D / A converter 6
Enters 14 and is output as a video signal.

The number of TV screen lines varies depending on the type, but a normal television (TV: Television) has 525 lines, and a high-definition television (HDTV: High Definition Television) has about 1125 lines. When several lines of video signals are subjected to intra-frame DPCM encoding and transmitted as a group, the frames are transmitted in a number of groups per frame. Then, a true value is sent to only one pixel at the head of each group, and information of a difference from the head pixel is sent to other pixels.

As shown in FIG. 7A, the image data is transmitted in a fixed-length packet format (= cell) of several bytes (data 1 to data 3) to which a header indicating a destination address is added, for example, as shown in FIG. And FIG. 7 (b)
As shown in (1), for example, the data is transmitted in a variable length packet format of several bytes (data 1 to data n) to which a header indicating the destination address is added.

[Issues to be solved]

In the above coded transmission system, bit errors in the header of the packet Network congestion (when the number of cells on the transmission line increases rapidly and exceeds the processing capability of the network) Over-delay between the transmission timing and the reception timing (predetermined time) If the above-described delayed video signal is discarded, etc., packets may be discarded in the network.

When a packet is discarded, the necessary image data is not sent to the receiving side, so the image is damaged, the image is not synchronized, and the image is displaced. There was a problem of deterioration.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image decoding system having a discard compensation function for suppressing image quality degradation when a packet is discarded.

[Means for solving the problem]

FIG. 1 is a diagram for explaining the principle of the present invention, and FIG. 1A is a block diagram showing the principle configuration of a receiving apparatus according to the present invention. In the figure, reference numeral 10 denotes a packet disassembly processing means for disassembling a packet received via a transmission line to extract image data. Numeral 11 denotes a discard detecting means for recognizing normal reception of a putt and outputting a discard detection signal when a packet is discarded. Numeral 12 denotes a discard compensation unit which receives image data from the packet disassembly processing unit and, when receiving a discard detection signal, replaces the image data of the group in which the packet was discarded with the image data of the previously received group.

FIG. 1B shows a flowchart of the discard compensation means. When the discard detection signal is not received from the discard detection means 11 (YES in step 13), the image data received this time is decoded (step 14). On the other hand, when the discard detection signal is received (NO in step 13), the previously received image data is decoded (step 15).

(Operation)

In the present invention, when a packet is discarded, the discard is detected by the discard detection unit 11 and transmitted to the discard compensation unit 12 by a discard detection signal. Upon receiving this signal, the discard compensation unit 12 decodes the previously received image data and replaces it with the currently received image data.

〔Example〕

FIG. 2 shows an embodiment of the present invention. As shown in the figure, the discard identifier of the packet assembler 61 on the transmitting device side
When the image data is assembled as a packet in 26,
A discard identifier is provided. For example, in the case of a packet consisting of 46 bytes, one byte is assigned to this discard identifier. That is, a series of numbers “00000000” to “1111111” are sequentially assigned to the packets of each group.

The packet composed of a plurality of image data enters the packet decomposing unit 62 on the receiving device side via the transmission path. Packet disassembly unit 62
The discard detection unit 21 receives a series of numbers "00000000" to "1111111" assigned to each packet in order for each group, detects the discard of the packet by missing the number,
Outputs discard detection signal.

On the other hand, the image data subjected to the packet decomposition processing is stored in the first memory 22 as needed. The first memory 22 outputs the temporarily stored image data for each group under the control of the control unit 25. The signal read from the first memory 22 enters the second memory 23 and the selector 24. That is, the first
The image data output from the memory 22 is written into the second memory 23 and enters the selector 24 at the same time. Second memory 23
Is instructed to output the stored contents only when the control unit 25 receives the discard detection signal from the packet disassembly unit 21. The selector 24 selects the output signal from the second memory 23 containing the information of the previously received group only when there is discarding, and contains the information of the group received this time if no discarding has occurred. An output signal from the first memory 22 is selected and output.

FIG. 3 is a processing flow of the control unit of the discard compensation unit. Hereinafter, the processing flow of the control unit 25 will be described. However, the first
It is assumed that the write command to the memory 22 is performed as needed. It is determined whether the writing and storing of one group in the first memory 22 has been completed (step 301). When writing of one group has not yet been completed (N in step 301
O), go back. When the writing of one group is completed (YES in step 301), an instruction to read the contents stored in the first memory 22 is given (step 302). Next, it is determined whether or not there is a discard detection signal in the group (step 303). If there is no discard detection signal (YE
S), the signal read from the first memory 22 is stored in the second memory 23 (Step 304). And selector 24
Is instructed to output the image data received from the first memory 22 (step 305). On the other hand, when there is a discard detection signal in the group (YES in step 303)
However, since some of the received image data could not be received, the video is broken. Therefore, the second memory 23
Instructing to read the previous stored contents (step 306)
This replaces the video of the current group with the video of the previous group. Then, it is determined whether a new group has been written to the second memory 23 (step 307). If a new group has been written (YES in step 307), the storage contents of the previous group are cleared (step 308). When a new group is not written (N in step 307)
O), proceed to the next step 309 as it is. Here, the selector 24 is instructed to output the image data received from the second memory 23 (step 309). Hereinafter, steps 301 to 309 described above are repeated.

FIG. 4 shows a first application example of the present invention, and the same components as those in FIG. 6 are denoted by the same reference numerals. Input data from the transmission path is subjected to a discard compensation process in a discard compensation unit 41 provided on the receiving device side. Then, the image data subjected to the discard compensation processing is decoded by the variable length decoding unit 611. The decoded output signal and the output signal of the prediction circuit 613 are added by an adder 612, and the resulting signal is input to a D / A converter 614 and output as a video signal.
At this time, the variable-length coded image data directly enters the discard compensation unit 41. Accordingly, since the length per group varies, the image data is read from the first memory 22 by controlling the output timing for each group.

FIG. 5 shows a second application example of the present invention, and the same components as those in FIG. 4 are denoted by the same reference numerals. Unlike the embodiment of FIG. 4, the discard compensation unit 41 is located after the variable length decoding unit 611. As a result, the image data of the variable-length code entering the discard compensation unit 41 has already been decoded by the variable-length decoding unit 611 in the preceding stage. Therefore, there is no variation in the length per group.

In the above-described embodiment, an example has been described in which the discard identifier is added by the packet assembling unit on the transmission side. However, this assignment position is not limited to this example. For example, the effect of the present invention does not change even if it is provided in the switching network on the transmission path side.

〔The invention's effect〕

As described above, according to the present invention, when the receiving side receives the image data, even if the packet of the current group information is discarded, the packet is replaced with the previous group information whose video content does not change much.

Therefore, it is possible to reduce the influence on the image quality due to the packet discard due to the transmission path failure.

[Brief description of the drawings]

1 is a diagram illustrating the principle of the present invention, (a) a block diagram of the principle of a receiving apparatus, (b) a flowchart of a discard compensating means, FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. FIG. 4 is a diagram showing a first example of adaptation of the present invention, FIG. 5 is a diagram showing a second example of adaptation of the present invention, and FIG. 6 is a diagram of an image data transmitting / receiving apparatus using an intra-frame DPCM system. FIG. 7 is a block diagram showing a transmission format of image data, (a) a fixed-length packet format (= cell), and (b) a variable-length packet format. In FIG. 1, the main parts in FIG. 1 are 10 packet decomposing processing means 11 discard detecting means 12 discard compensating means.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-86922 (JP, A) JP-A-2-30284 (JP, A) JP-A-2-58938 (JP, A) JP-A-2- 233082 (JP, A) JP-A-57-42252 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 7/24-7/68 H04L 11/20 H04B 14/04

Claims (1)

(57) [Claims] 1. A receiving device of an image data transmission system for encoding a video signal for each group consisting of a plurality of pixels and transmitting the packets in packet units, wherein the receiving device decomposes the received packets to extract image data. And discard detection means for detecting discard of the packet and outputting a discard detection signal; receiving the image data extracted from the packet disassembly processing means; and discarding the packet in the image data of the group currently being received. At this time, there is provided a discard compensating unit that replaces the image data of the group received this time with the image data of the group received last time on a group basis. If not, the image data of the group received this time is decoded, and the group currently being received from the discard detection means is decoded. An image decoding apparatus having a discard compensation function, which decodes image data of a previously received group when a discard detection signal is received in a loop.