JPH0497683A - Picture transmitter - Google Patents

Abstract

PURPOSE:To improve the utilizing efficiency of a communication line by setting a CODEC to the expansion mode when a reception data is in existence, selecting the compression mode, and repeating the operation of the compression mode when no reception data exists. CONSTITUTION:A couple of picture transmitters A, B are connected via a communication line L, and when the one is in the transmission state, the other is in the reception state to repeat the transmission and reception alternately. An arithmetic control section 8 expands a reception data while bringing a CODEC 5 into the expansion mode when the reception data is in existence and the compression mode is set to compress the picture data and when no reception data exists, the operation of the compression mode is repeated. Thus, the utilizing efficiency of the communication line is enhanced.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image transmission device that compresses and transmits image data to be transmitted, receives the compressed image data, decompresses it, and restores the compressed image data.

[Conventional technology]

BACKGROUND ART Conventionally, in systems for crime prevention, equipment monitoring, videophone calls, video conferences, etc., image transmission devices have been provided that transmit images captured by an image input device such as a television camera to a long distance via a communication line. ing. Since the amount of image data is large, a broadband (high speed) communication line is required to transmit the image data of moving images. Broadband communication lines are generally expensive, so in order to use inexpensive low-speed (for example, 64 kbps) communication lines, the transmitting side compresses the image data and sends it to the communication line, and the receiving side compresses the image data and sends it to the communication line. It has been considered to reduce the amount of data transmitted over communication lines by decompressing and restoring compressed image data. In this case, the image data to be transmitted is usually a quasi-moving image or a still image. By the way, if bidirectional communication is to be performed, a codec that can compress and expand image data at the same time is required, but since processing to separate the transmitted signal and received signal is required, the configuration of the codec is The problem arises that it becomes complicated and expensive. Therefore, relatively inexpensive image transmission apparatuses adopt a method of transmitting image data in both directions while performing unidirectional communication at each point in time by alternately switching between the transmitting side and the receiving side. In this method, each image transmission device performs processing in the order of compression of image data, transmission, reception, and decompression of received data, but after one image transmission device decompresses received data, Until the next image data to be transmitted is compressed, the communication line remains unused, resulting in a problem in that the communication line is not used efficiently, resulting in a slow transmission speed. Therefore, it has been considered that while one image transmission apparatus is decompressing the received data, the other image transmission apparatus compresses the image data.

[Problem to be solved by the invention]

However, in the above-mentioned image transmission device, if the redundancy level and number of pixels of the image data are different between the two image transmission devices transmitting the image data, the time required to compress, expand, send, and receive the image data is This will be different for both image transmission devices. As a result, even though one image transmission device has finished compressing the image data and is ready to receive it, or has finished decompressing it and is ready to send it, the other image transmission device is unable to decompress the image data. In some cases, the communication line may be in the process of being compressed or compressed, resulting in a problem that the communication line usage efficiency decreases by the amount of waiting time. The present invention aims to solve the above-mentioned problems.The present invention aims to reduce the waiting time between compressing image data and decompressing received data and starting transmission/reception, thereby improving the utilization of communication lines. The present invention aims to provide an image transmission device that increases efficiency and suppresses a decrease in overall transmission speed.

[Means to solve the problem]

In the structure of claim 1, in order to achieve the above object, the image data is compressed and sent as transmission data, and the transmission data from the other party is received as reception data and expanded to restore the original image data. In a transmission device, a codec that can select a compression mode that compresses image data by a predetermined amount and an expansion mode that expands received data, and arithmetic control that selectively switches the operating state of the codec between compression mode and expansion mode. The arithmetic control section includes:
When there is received data, the codec is put into decompression mode to decompress the received data, then switched to compression mode to compress the image data, and then, if there is no received data, the operation in compression mode is repeated. In the structure of claim 2, an upper limit value is set for the number of repetitions of the operation in the compression mode during a period from the end of the expansion mode until the next reception data is received, and when the number of repetitions in the compression mode reaches the upper limit value, the reception is started. It is set to be in a standby state.

[Effect]

According to the structure of claim 1, when there is received data, the codec is put into the decompression mode and then switched to the W compression mode, and thereafter, if there is no received data, the operation in the compression mode is repeated, so that the codec is Even though it is a relatively inexpensive device with only one device, it can perform efficient transmission without wasting idle time even if there is a difference in the amount of data sent and received. As a result, the total time required for transmission can be shortened and relatively high-speed transmission can be performed. According to the configuration of claim 2, since an upper limit is set for the number of repetitions of the compression mode, it is possible to prevent a situation where only image data is compressed and the communication becomes essentially one-way. be.

【Example】

As shown in FIG. 1, the image transmission device includes a television camera 1 as an image input device and a display device 2 as an image output device.The video signal obtained as the output of the television camera 1 is After being converted into image data, which is a digital signal, by a video signal input section 3 that performs analog-to-digital conversion, etc., it is stored in a frame memory 4. The image data stored in the frame memory 4 is compressed by the codec 5 to create transmission data, and then sent to the communication line via the communication control unit 6. On the other hand, received data inputted to the communication control unit 6 through the communication line is decompressed by the codec 5 and restored as image data.One image data is stored in the frame memory 4 and converted into a video signal that undergoes digital-to-analog conversion, etc. A video signal is reproduced through the signal output section 7. This video signal is input to the display device 2 and a reproduced image is displayed. The codec 5 can select a compression mode in which the image data read from the frame memory 4 is compressed by a predetermined amount, and an expansion mode in which the image data obtained by decompressing the received data is written into the frame memory 4. The compression mode and the expansion mode are selected by an arithmetic control unit 8 equipped with a microprocessor. A pair of image transmission devices A and B having the above configuration are connected via a communication line, and when one is in a transmitting state, the other is in a receiving state, so that they are alternately connected. It operates by repeating sending and receiving. The operation will be explained below based on FIG. However, in Figure 2, the variable is the number of times compressed mode operation was performed during the period from one receiving state to the next receiving state, and the variable N is the upper limit value that can be used for compressed mode operation during that period. . As a variable, N is stored in the calculation control unit 8. When the operation starts, initialization is performed first, and variables are set to O.
Next, the presence or absence of received data to the communication control unit 6 is determined, and if there is received data, the received data is decompressed by the codec 5 and transferred to the frame memory 4.
, the image is displayed on the display device 2 via the image output section 7. When the display of the image is finished, the variable is set to 0. Next, an image is captured from the television camera 1, and the image data is compressed by the codec 5. After compressing the image data, the variable k is increased by 1. In other words, the variable indicates the number of times compression has been performed. The data compressed in this manner is sent to the communication line via communication system fl1M6. Thereafter, if there is received data, the same operation as above is performed, and if there is no received data and the variable k is smaller than the upper limit N, the next image data is compressed. When the variable k becomes equal to or greater than the upper limit value N, the device enters a reception standby state. Since the compression and decompression processes are performed using these steps, if the amount of image data in image transmission device A is considerably smaller than the amount of image data in image transmission device B, , in image processing device A,
If there is no received data after image data is compressed, the next image data is compressed, and as long as the number of times of compression does not exceed the upper limit N, a reception waiting state does not occur. That is, since the image data is compressed while minimizing idle time, the efficiency of using the communication line increases and the total time required for transmission can be shortened. Furthermore, by setting an upper limit value N to regulate the number of consecutive compression operations, only one of the image transmission devices A and B performs compression, effectively reducing the communication to one-way communication. This is to prevent this from happening. The upper limit value N of the number of times compression is performed consecutively is set as a value unique to each image transmission apparatus A, B according to the type and compression method of image data input to each image transmission apparatus A, B. For example, if there is a difference of about 3 times the amount of image data between image transmission devices A and B, if you set N=3, the image data will be compressed by the one image transmission device that has the larger amount of data. and transmission once, while the other image transmission device can perform compression and transmission three times, making it possible to perform two-way transmission with almost no idle time waiting for reception. .

【Effect of the invention】

As described above, according to the configuration of claim 1, when there is received data, after setting the codec to decompression mode,
It switches to compression mode and then repeats the compression mode operation if there is no received data, so even though it is an inexpensive device with only one codec, there is no difference in the amount of data sent and received. The advantage is that efficient transmission can be performed without wasting idle time. As a result, the total time required for transmission can be shortened and relatively high-speed transmission can be performed.6 According to the structure of claim 2, an upper limit is set for the number of repetitions of the compression mode. Therefore, there is an advantage that it is possible to prevent a situation in which only compressing image data results in essentially one-way communication.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the same operation. 1...TV camera, 2...Display device, 3
...Video signal input section, 4...Frame memory, 5
... Codec, 6... Communication control section, 7... Video signal output section, 8... Arithmetic control section, A, B... Image transmission device. Agent Patent Attorney Ishi 1) Choshichi

Claims (2)

[Claims] (1) Compress the image data and send it as transmission data,
In an image transmission device that receives transmitted data from the other party as received data and decompresses it to restore the original image data,
a codec that allows selection of a compression mode that compresses image data by a predetermined amount and an expansion mode that expands received data;
an arithmetic control unit that selectively switches the operating state of the codec between a compression mode and an expansion mode; the arithmetic control unit sets the codec to an expansion mode when there is received data; An image transmission device characterized by switching to a compression mode to compress image data, and then repeating the operation in the compression mode if there is no received data. (2) Set the upper limit for the number of repetitions of the compression mode operation during the period from the end of the decompression mode until the next reception data is received, and when the number of repetitions of the compression mode reaches the upper limit, the state enters the reception standby state. The image transmission device according to claim 1, characterized in that: