JP2827317B2 - Image transmission device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image transmission apparatus that efficiently encodes an image signal and transmits the image signal efficiently.

[Conventional technology]

FIG. 4 is, for example, No. 275 of “Multidimensional Signal Processing of TV Images” by Norihiko Fukinuki (Nikkan Kogyo Shimbun, published on November 15, 1988).
It is a block diagram of a conventional image encoding apparatus as shown from page to page 277, in which (1) is an A / D converter for A / D converting an input image signal, and (2) is an A / D converter. A transmission frame memory for storing digital data output from the A / D converter (1) for each frame, and (3) a quantization code for quantizing and encoding data output from the transmission frame memory (2). An encoding unit (4) for encoding data; a decoding unit (5) for decoding encoded data output from the encoding unit (4); and a decoding unit (5). ), The in-loop frame memory (6) for storing the decoded data, the decoded data output from the in-loop frame memory (6), and the frame data output from the transmission frame memory (2). And an operation unit (7) that performs the operation of (8) is a variable length coding unit for entropy coding and compressing the quantized coded data output from the quantization coding unit (3), and (9) is an output from the variable length coding unit (8). A transmission buffer for temporarily storing encoded data to be output and outputting the read data with a clock corresponding to the transmission speed of the transmission line at the time of readout;
Is a buffer remaining amount detection unit that detects the remaining buffer amount from the amount of data stored in the transmission buffer (9);
6) changes the encoding characteristics of the quantization encoding unit (3), for example, the threshold value and quantization step size in the quantization, based on the remaining buffer amount detected by the remaining buffer detection unit (10). In addition, it is an encoding control unit that stops data output to the transmission frame memory (2) and stops encoding so that the transmission buffer (9) does not overflow.

 Next, the operation will be described.

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

Here, the writing and reading of data to and from the transmission buffer (9) are completely asynchronous, but the buffer remaining amount of the transmission buffer (9) is constantly monitored by the buffer remaining amount detection unit (10). Controls the threshold value and quantization step size in quantization.

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

As an example of such control, the remaining buffer capacity is 800 k
When the bit size is less than or equal to 8 bits, the step size is 8, and the remaining buffer is 600.
When the bit size is less than kbit, the step size is 6, and the remaining buffer capacity is 40.
When the bit size is 0 kbit or less, the step size is set to 4, and the remaining buffer and the step size are always synchronized. On the other hand, the remaining amount of the buffer when stopping the encoding for the transmission frame memory (2) changes depending on the rate.

[Problems to be solved by the invention]

In the conventional image transmission apparatus as described above, when the remaining amount of the transmission buffer exceeds a predetermined threshold, the control of stopping the encoding is performed on the transmission frame memory. Depending on the method, the amount of data generated varies widely from 100 to 200 bits per frame to several tens of times depending on the input image.
For example, when the data of 30 frames is accumulated in the buffer, and immediately after that, the movement of the input image becomes large and data suddenly occurs, the delay of the movement becomes large on the receiving side, resulting in an awkward image. For this reason, the transmission buffer threshold value for stopping the encoding has to be set relatively low, but as a result, the encoding is liable to occur frequently.

On the other hand, since the quantization step size control is also based on the remaining amount of the buffer, if the encoding is stopped as described above, the writing side of the buffer continues, so the remaining buffer amount is equal to the threshold value. There is a problem that the motion is only performed in the vicinity, and therefore the step size does not change, and the magnitude of the data generation lengthens the encoding stop time, so that it is not directly reflected in the remaining amount of the buffer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has as its object to make the amount of generated information uniform and reduce image delay.

[Means for solving the problem]

An image transmission device according to the present invention, encoding means for performing variable-length encoding of an image signal based on a predetermined quantization characteristic value,
A data generation amount counting means for counting the data amount output from the encoding means, and a data amount for calculating a result obtained by accumulating the data amount counted by the data generation amount counting means in a short cycle and a long cycle in time Arithmetic means, and coding control means for changing a quantization characteristic value of the coding means based on the short-cycle cumulative result and the long-cycle cumulative result calculated by the data amount calculating means. It is.

[Action]

According to the present invention, since the quantization characteristic value of the encoding is changed according to the result of accumulating the data amount output from the encoding means in a short period and a long period in time, the data output from the encoding unit is changed. The amount is controlled reliably,
The output data amount is made uniform.

〔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, wherein (1) to (10) are the same as those in the above-mentioned conventional example. (11) data generation amount counting means for counting the amount of data generated in the variable length coding unit (8); (1)
2) is a data amount calculation means for calculating the history of the data generation amount by accumulating the data counted by the data generation amount counting means (11) every predetermined period, and (13) is a data amount calculation means (12) Is a coding control unit that controls the coding characteristics of the quantization coding unit (3), that is, the quantization characteristic values such as the quantization step size, based on the calculation result. An encoding unit is formed by the quantization encoding unit (3) and the variable length encoding unit (8).

Next, the operation will be described. As in the conventional example, the input image signal is digitized by the A / D converter (1), stored in the transmission frame memory (2), and then encoded by the quantization encoding unit (3). The data is encoded by the variable length encoding unit (8), output to the transmission buffer (9), and transmitted to the transmission path.

Here, the amount of data output by the variable length coding unit (8) is counted by the data generation amount counting means (11), and the result is sent to the data amount calculation means (12). The data amount calculation means (12) performs the accumulation of the data amount generated in the past as follows. FIG. 2 shows the structure of the data amount calculating means (12), which is a short cycle accumulator (14) for accumulating generated data for a fixed image unit.
And a long-period cumulative average unit (15) for accumulating the data generation amount of the immediately preceding predetermined number of image units from the accumulation result by the short-period accumulator (14) and calculating the average value.

For example, as shown in FIG. 3, the short-cycle accumulator (14) divides the entire image (one video frame) into several units, each of which is an image unit. Is output, and the long cycle accumulator (15) accumulates the data generation amount of a predetermined number of image units up to immediately before and calculates the average value. These cumulative operation results are sent to the encoding control unit (13), and the encoding control unit (13) determines the contents of the current quantization characteristic of the quantization encoding unit (3) based on both results. And perform control. For example, since the accumulation result of the short cycle accumulator (14) means the data generation amount of one image unit controlled last time, by using this, it is possible to correspond to the magnitude of the local motion of the image. Since fine control for equalizing the data generation amount can be realized, and the output of the long-period cumulative averaging unit (15) indicates the generation history of the data generation amount over a plurality of image units,
When a large amount of data is generated, it is possible to suppress the amount of data generation not only by the local amount of data generation but also by considering a long cycle.

As a result, the capacity of the transmission buffer (9) can be reduced by the amount by which the threshold value of the coding stop can be reduced.

When the remaining buffer capacity of the transmission buffer (9) exceeds the threshold value, as in the conventional example, the transmission frame memory (2)
To control the coding stop.

Further, when the read clock of the transmission buffer is constant, the transmission speed of the transmission path is, for example, 64 kb / s, 384 kb / s, 1.536 Mb.
In the case of a system that changes to / s, the data comes out in a burst, and the data accumulation in the transmission buffer becomes irregular, but in the present invention, encoding is performed by such irregular data accumulation amount. Since the encoding is performed without affecting the characteristics, there is an advantage that the information generation amount can be made uniform to some extent even if the transmission rate changes.

〔The invention's effect〕

As described above, according to the present invention, the amount of data output from the encoding unit is counted, and the quantization of the encoding unit is performed according to the result of accumulating the data generation amount in a short period and a long period in time. Since the characteristic value is changed, the amount of data generation is adjusted appropriately, such as making the amount of data generation uniform for the magnitude of local movement of the screen and adjusting the data generation amount corresponding to the data generation amount for multiple screen units The effect that the quantization characteristic value is appropriately determined even if the transmission stop is controlled for the transmission frame memory, the data generation amount is made uniform, and high quality image transmission can be performed. There is.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image transmission apparatus according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a data amount calculation unit, and FIG. 3 is an explanatory diagram showing a state where one screen is divided into a plurality of image units. ,
FIG. 4 is a configuration diagram of a conventional image transmission device. In the figure, (3) is a quantization coding unit, (8) is a variable length coding unit, (11) is a data generation amount counting unit, (12)
Is a data amount calculating means, and (13) is an encoding control unit. In the drawings, the same reference numerals indicate the same or corresponding parts.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-61387 (JP, A) JP-A-62-272790 (JP, A) JP-A-52-44512 (JP, A) JP-A-63-1987 180282 (JP, A) JP-A-61-196687 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 7/24-7/68 H04N 1/41-1/419

Claims (1)

(57) [Claims] An encoding means for encoding an image signal based on a predetermined quantization characteristic value; a data generation amount counting means for counting an amount of data output from the encoding means; A data amount calculating means for calculating a result obtained by accumulating the data amount counted by the means in a short period and a long period in time, and a screen localization based on the accumulation result in the short period calculated by the data amount calculating unit. The quantization characteristic value of the encoding means is changed so as to equalize the data generation amount corresponding to the magnitude of the motion, and based on the long period cumulative result calculated by the data amount calculation means. Encoding control means for changing the quantization characteristic value of the encoding means so as to equalize the data generation amount over a long period. Apparatus.