JPH0389688A - Picture transmitter - Google Patents

Abstract

PURPOSE:To uniformize data generation quantity by counting data generation quantity outputted from a coding means, varying the characteristic of the coding means in response to the data generation quantity and controlling the data generation quantity properly. CONSTITUTION:A data quantity inputted by a variable length coder section 8 is counted by a data generation quantity count means 11 and the result is fed to a data quantity arithmetic means 12. The data quantity arithmetic means 12 accumulates the data quantity generated in the past. The accumulation calculation result is sent to a coding control section 13, which decides the content of current coding characteristic by a quantizing coding section 3 based on the both results to apply control. For example, since the accumulation result of a short period accumulation section 14 means a data generation quantity of one picture unit controlled precedingly, fine control for uniformizing the data generation quantity for the local movement of the pattern is realized by using the result.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image transmission device that encodes an image signal in variable length and efficiently transmits the encoded image signal.

[Conventional technology]

Figure 4 shows, for example, a conventional image encoding device as shown in pages 275 to 277 of "Multidimensional Signal Processing of TV Images" by Takahiko Fukinuki (published by Nikkan Kogyo Shimbun, November 15, 1988). In the figure, (1) is an A/D converter that A/D converts the input image signal, and (2) is a block diagram that converts the digital data output from the A/D converter (1) into various types. Transmission frame memory that stores each frame (3)
is a quantization encoding unit that quantizes and encodes the data output from this transmission frame memory (2), and an encoding unit (4) that encodes the data and a a decoding unit (5) that decodes the encoded data;
An in-loop frame memory (6) that stores the decoded data output from this decoding section (5), and a loop frame memory (6) that stores the decoded data output from this in-loop frame memory (6) and the above-mentioned transmission frame memory (2). It consists of an arithmetic unit (7) that performs arithmetic operations on the output frame data. (8) is a variable length encoding unit that entropy encodes and compresses the quantization encoded data output from this quantization encoding unit (3), and (9) is output from this variable length encoding unit (8). A transmission buffer that temporarily stores encoded data and outputs it at a clock according to the transmission speed of the transmission line when reading. αQ is calculated from the amount of data stored in this transmission buffer (9) to the remaining buffer amount. Based on the remaining buffer amount detected by the buffer remaining amount detection section αQ, the buffer remaining amount detection section αQ determines the encoding characteristics of the quantization encoding section (3), such as the threshold value in quantization, etc. In addition to changing the quantization step size, the transmission frame memory (2) is changed to prevent the transmission buffer (9) from overflowing.
) is an encoding control unit that stops data output and stops encoding.

Next, the operation will be explained.

First, an analog image signal is converted into digital data by an A/D converter (1) and stored in a transmission frame memory (2). The data thus output from the transmission frame memory is quantized and encoded in a quantization encoder (3) based on a predetermined encoding characteristic value. Further, the output data is entropy encoded and compressed in a variable length encoder (8) and stored in a transmission buffer (9). Then, data is read out from the transmission buffer (9) at a clock according to the transmission speed of the transmission line.

Here, writing and reading data to and from the transmission buffer (9) are completely asynchronous, but the remaining buffer amount of the transmission buffer (9) is constantly monitored by the buffer remaining amount detection unit αQ, and the quantization is performed based on the buffer remaining amount. Control the threshold and quantization step size in .

For the transmission frame memory (2), data output is still limited and encoding is stopped so that the transmission buffer (9) does not overflow.

An example of such control is that the remaining buffer capacity Boo
When kb i is below, the step size is 8, when the remaining buffer amount is 600 kb i or less, the step size is 6, when the remaining buffer amount is 400 kbit or less, the step size is 4, and the step size is always the same as the remaining buffer amount. Synchronize sizes. On the other hand, the remaining buffer capacity when encoding is stopped for the transmission frame memory (2>) changes depending on the rate.

[Problem to be solved by the invention]

In the conventional image transmission device as described above, when the remaining amount of the transmission buffer exceeds a predetermined threshold, the transmission frame memory is controlled to stop encoding. Depending on the method, the amount of data generated varies greatly depending on the input image, ranging from 100 to 200 bits per frame to several tens of times that amount, and when the input image has small motion, it may take a long time to exceed the buffer threshold. If 20 to 30 frames worth of data accumulates in the buffer, and immediately after that the input image movement increases and data is suddenly generated, there will be a large movement delay on the receiving side, resulting in an awkward image. I end up.

For this reason, the transmission buffer threshold for stopping coding must be set relatively low, but as a result, coding stops tend to occur frequently.

On the other hand, since the step size control for quantization is also controlled based on the remaining amount of the buffer, if the encoding stops as described above, the writing side of the buffer will continue, so the remaining amount of the buffer will be below the threshold value. It will only move in the vicinity, so the step size will not change, and the amount of data generated will be
There is a problem in that the encoding stop time becomes longer or shorter and is not directly reflected in the remaining amount of the buffer.

This invention was made to solve the above problems, and aims to equalize the amount of information generated and reduce image delay.

Means for Solving the Problem] An image transmission apparatus according to the present invention includes an encoding means for variable-length encoding an image signal based on a predetermined characteristic value, and a method for counting the amount of data output from the encoding means. The encoder includes a data generation amount counting means, and an encoding control means for changing the characteristic value of the encoding means according to the data amount counted by the data generation amount counting means.

[For production]

In this invention, since the characteristic value of encoding is changed according to the amount of data output from the encoding means, the amount of data output from the encoding means is reliably controlled, and the amount of output data is uniform. transformation is done.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image transmission apparatus according to an embodiment of the present invention, and (1) to OQ are the same as those in the conventional example. αυ is a data generation amount counting means for counting the amount of data generated in the variable length encoder (8), and (6) is a data generation amount counting means for accumulating the data counted by this data generation amount counting means aυ every predetermined period. Data amount calculation means 03 calculates the history of the amount of generation, and 03 is an encoding device that controls the encoding characteristics of the quantization encoding unit (3), such as the quantization step size, based on the calculation result of the data amount calculation means 0. This is the control section.

A quantization encoder (3) and a variable length encoder (8) form an encoding means.

Next, the operation will be explained. Similar to the conventional example, the input image signal is digitized by the A/D converter (1), stored in the transmission frame memory (2), encoded by the quantization encoder (3), and further It is encoded by a variable length encoder (8), output to a transmission buffer (9), and sent to a transmission path.

Here, the amount of data outputted by the variable length encoder (8) is counted by the data generation amount counting means aυ,
The result is sent to data amount calculation means 0. This data amount calculating means (2) calculates the cumulative amount of data generated in the past as follows. FIG. 2 shows the configuration of this data amount calculation means O, which consists of a short-cycle accumulator 0 that accumulates generated data for a certain image unit, and the accumulation result by this short-cycle accumulator α◆. , and a long-period accumulation averaging section (b) that accumulates the amount of data generated for a predetermined number of immediately preceding image units and calculates the average value thereof.

For example, the short-cycle accumulation unit α◆ calculates the cumulative value of the amount of data generated for each image unit when the entire screen (one video frame) is divided into several parts as shown in FIG. Furthermore, the long-period accumulator (to) accumulates the amount of data generated for a predetermined number of image units up to the immediately preceding time and calculates the average value. These cumulative calculation results are sent to the encoding control unit 0, and the encoding control unit 0 determines the contents of the current encoding characteristics of the quantization encoding unit (3) based on both results, and performs control. conduct. For example, the accumulation result of the short-cycle accumulation part a◆ means the amount of data generated for one image unit that was previously controlled, so by using this, it is possible to calculate the amount of data generated for the size of local movement of the screen. In addition, since the output of the long-period cumulative averaging section (2) shows the history of the amount of data generated over multiple image units, a large amount of data can be generated. , regardless of the local amount of data generated.
It is possible to suppress the amount of data generated.

As a result, the capacity of the transmission buffer (9) can be reduced by the amount that can lower the threshold for stopping encoding.

Note that, as in the conventional example, when the remaining buffer capacity of the transmission buffer (9) exceeds a threshold value, encoding stop control is performed on the transmission frame memory (2).

Further, when the read clock of the transmission buffer is constant, the transmission speed of the transmission line is, for example, 64 kb/s.

In the case of a system where the speed changes from 384 kb/s to 1.536 Mb/s, data will go out in bursts, making the data accumulation in the transmission buffer irregular. Since encoding is performed without the encoding characteristics being affected by the amount, there is also the advantage that the rate can be made uniform to some extent.

〔Effect of the invention〕

As described above, according to the present invention, the amount of data generated output from the encoding means is counted and the characteristic value of the encoding means is changed according to the amount of data generated, so that the amount of data generated can be appropriately controlled. Even if the transmission frame memory is controlled to stop encoding, the encoding characteristics are determined appropriately, the amount of data generated is equalized, and high-quality image transmission is possible. be.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an image transmission device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of its data amount calculation means, and FIG. 3 is an explanatory diagram showing a state in which one screen is divided into a plurality of image units. ,
FIG. 4 is a block diagram of a conventional image transmission device. In the figure, (3) is a quantization encoding section, (8) is a variable length encoding section, (b) is a data generation amount counting means, 0 is a data amount calculation means, and 0 is an encoding control section. Note that the same symbols in each figure indicate the same or equivalent parts.

Claims (1)

[Claims] an encoding means for variable length encoding an image signal based on a predetermined characteristic value; a data generation amount counting means for counting the amount of data output from the encoding means; and a data generation amount counting means for counting the amount of data output from the encoding means. An image transmission device comprising: encoding control means for changing the characteristic value of the encoding means according to the amount of data.