JPH02214280A - Picture coding transmitter - Google Patents

Abstract

PURPOSE:To eliminate the need for making a reception buffer of large capacity and a decoding circuit of high speed by controlling a condition not overflowing the reception buffer at a sender side. CONSTITUTION:A timing comparison section 5 is provided, which compares an output of a reference timing generating section 4 and a timing monitored with a transmission buffer 3. Then a timing (c) when a prescribed period of a picture is coded and sent to a transmission line is monitored, and the timing (c) is compared with a reference timing (b) and when the transmission timing (c) is retarded, the reference timing (b) is reset when the transmission of the code word corresponding to the period is finished, and a time difference is obtained when the transmission timing (c) is faster, and only when the same time difference is larger than a predetermined threshold level, a dummy is added after the end of transmission of a code word corresponding to the period to absorb the time difference. Thus, the condition enabling reception and decoding at the receiver side is guaranteed at the sender side and the equipment constitution at the receiver side is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image encoding and transmitting apparatus that encodes and transmits an image signal, and receives and decodes an image signal.

[Conventional technology]

Figure 4 shows, for example, the Institute of Electronics and Communication Engineers technical report IE84-4゜(
19B4) l'-Interframe coding device for video conference"
In FIG. 0, which is a block diagram showing a simplified configuration of the conventional image encoding and transmitting device shown in FIG.
2) is a variable length encoding unit that performs variable length encoding on the code word encoded in the encoding unit (1); (3) is a transmission buffer that performs speed smoothing; (6) is a frame encoding unit; (7
) is the deframing section, (8) is the reception buffer, (9)
is a variable length decoding section, (II is a decoding section.

Further, (101) is a digitized image signal sequence, (102) is a code word sequence encoded in the encoding section (1), and (103) is the variable length encoding section (2).
), a sequence of codewords variable-length encoded in (1c8
) is a feedback control signal, (109) is a sequence of code words velocity smoothed by the transmission buffer (3),
(110) is a sequence of received code words, (ill) is an output read from the reception buffer (8), and (112) is a sequence of nine code words converted into a fixed length in the variable length decoding section (9). , (113) are the digital image signal sequences decoded by the decoding section Ql. Further, FIG. 5 is an explanatory diagram showing the operation of the transmission buffer (3), and FIG. 6 is an explanatory diagram showing the operation of the reception buffer (8).

Next, the operation will be explained. The digitized image signal sequence (101) is converted into a sequence of code words (102) in the encoding section (1). At this stage, each code word has a fixed length. Next, a variable length encoding unit (2) performs variable length encoding using the bias in the probability of occurrence of each code word. That is, the codeword sequence (102) is converted into a variable-length codeword sequence (103). As a result, the sum of the lengths of the variable-length codeword sequence (103) becomes smaller than the code amount, which is the sum of the lengths of the codeword sequence (102), and transmission efficiency is improved. Since the amount of code is variable, speed smoothing is performed in the transmission buffer (3) before rounding to send it to the transmission path at a constant transmission speed. The output (109) of the transmission buffer (3) has a constant rate (code amount per unit time) corresponding to the transmission rate. The operation of the transmission buffer (3) will be explained with reference to FIG. In FIG. 5(a), the horizontal axis represents time and the vertical axis represents the buffer storage amount. The sequence input to the transmission buffer (3) has a variable length and the output is at a constant speed, so the accumulated amount is as shown in Fig. 5 (
It changes as shown in a). FIG. 5(b) shows the output of the buffer corresponding to FIG. 5(,)K. The buffer storage amount decreases when more data is read from the buffer than is written to the buffer, and if the buffer storage amount becomes 0,
Since there is nothing left in the buffer to read, a dummy is output. Conversely, if more data is written to the buffer than read from the buffer, the amount of buffer storage increases.

Since the buffer capacity is finite, if the buffer storage continues to increase, it will eventually overflow (overload). To prevent overflow, when the buffer storage amount is large, a feedback control signal (10B) is used to control the operation of the encoder (2) to suppress the generation of code words. Output read from buffer (109) /I'
The 0-framing section (6), which has a constant speed, frames the above-mentioned transmission buffer output (109) at constant intervals and sends it out to the transmission path. On the receiving side, the received signal sequence is deframed by the deframing section (7), and the received signal sequence is stored in the receiving buffer (8).
Save up. The output of the receiving buffer (8) is a variable length code sequence (111), which is converted into a fixed length code sequence (112) in a variable length decoding section (9). Further, the decoding unit (11) decodes the fixed length code sequence (112) to generate a digital image signal sequence (
113) is obtained. In the above reception and decoding process, the decoding unit (11) decodes a certain section of the image signal sequence (for example, a continuous fixed length image signal sequence such as one image frame or one line) at a constant speed. Therefore, at least the fixed machine code series (112)
is not allowed to exceed the decoding speed of the decoding unit ω. Similarly, the variable length decoding section (9) also has a limit to its operating speed. Corresponding to the fact that the transmission buffer (3) near the exit on the transmission side performs speed smoothing, the reception buffer (8) on the reception side performs velocity smoothing.
The operation of the receiving buffer (8) which adjusts the speed will be explained with reference to FIG. Assume that the input signal sequence (110) of the receiving buffer (8) is given as shown in FIG. 6(a). Since the signal sequence is a sequence of variable-length code words, the intervals are not constant when divided into image frames, for example.

T in FIG. 6(1,) is a time interval during which the variable length decoding unit (9) and the decoding unit (10) can process the code word corresponding to the block. If the amount of code words corresponding to a certain block is smaller than the time interval shown in FIG. ).If the accumulation continues for a long time, there is a risk of overflowing, so the capacity of the receiving buffer (8) is designed to be large.0 [Problem to be Solved by the Invention] Conventional image code Since the decoding device is configured as shown below, it is necessary to make the operating speed of the variable length decoding section and the decoding section as fast as possible, which necessitates making the device large and requiring a large reception buffer. This invention was made to solve the above-mentioned problems, and it transmits conditions that enable receiving and decoding operations on the receiving side. The purpose is to reduce the size of the device configuration on the receiving side.

[Means to solve the problem]

The image encoding and transmitting device according to the present invention monitors the timing at which a certain section of an image is encoded and sent to a transmission path,
The same timing is compared with the standard timing, and if the sending timing is delayed, the standard timing is reset when the sending of the code word corresponding to the section is completed, and if the sending timing is earlier, the time difference is calculated and the same time difference is determined. is larger than a predetermined threshold value, a dummy is added after the transmission of the code word corresponding to the section is completed to absorb the time difference.

[Effect]

The standard timing in this invention corresponds to the time interval required for decoding a certain section of the image on the receiving side, and is designed to prevent the standard timing from being sent to the transmission path at an extremely short time interval. to perform adaptive dummy insertion.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
FIG. 1 is a block diagram showing the configuration of an image encoding and transmitting apparatus according to an embodiment of the present invention. In the figure, (4) is a standard timing generating section that can generate a pulse signal at a constant cycle, and (5) is the standard timing generating section (4).
(104) is a standard timing (pulse train) output from the standard timing generator (4) described in III; Buffer (3
), (106) is a reset signal that resets the phase of the reference timing generating section (4), and (107) is the timing comparison section 114u (5).
), which is a control signal for controlling the operation of the transmission buffer (3), and other parts are the same or equivalent to those of the conventional example. FIG. 2 is an explanatory diagram showing the operation of the transmission buffer (3) according to an embodiment of the present invention;
FIG. 3 shows a receiving buffer (8) according to an embodiment of the present invention.
It is an explanatory diagram showing operation of.

Next, the operation will be explained. The digitized Ryotsu signal sequence (101) is converted into a code word sequence (102) in the encoding unit tl). At this stage each codeword has a fixed length. Next, the variable length encoding unit (2) performs variable length encoding using the bias of occurrence W1''4 of each codeword. That is, the sequence of codewords (102) is converted into the sequence of variable length codewords (103 ).As a result,
Compared to the code amount, which is the sum of the lengths of the codeword sequence (102), the sum of the lengths of the variable-length codeword sequence (103) is smaller, improving transmission efficiency. Since the amount of code is variable, speed smoothing is performed in the transmission buffer (3) in order to send it to the transmission path at a constant transmission speed. The operation of the transmission buffer (3) will be explained with reference to FIG. In FIG. 2(a), the horizontal axis represents time and the vertical axis represents the buffer storage amount.

The basic operation of the buffer (3) is that when more data is read from the buffer than is written into the buffer, the buffer storage amount decreases, and when more data is written to the buffer than it is read from the buffer, the buffer storage amount decreases. It becomes an increasing movement. Reading from the buffer (3) is at a constant rate (symbol t per unit time) corresponding to the transmission rate.

When data is not read from the buffer (3), the buffer (3) outputs a dummy signal. If data is not continuously output, there is a 2f1 type. First, there is a case where the buffer storage voltage is O and there is no data to be read. The second condition will be explained below.

T in M2 diagram (1)) is on the receiving side, which will be described later.
This is a time interval that allows decoding of a wide section of an image (a continuous fixed-length image signal sequence such as one picture frame or one line). Here, the period will be described as a frame. A pulse having a period of OT is generated as a reference timing (104) in a reference timing generating section (4). On the other hand, the transmission buffer (3) K j - then refines the timing (IQ5) of the beginning of the code word corresponding to each frame. (
(Fig. 2 (C)) Furthermore, the timing comparison adjustment unit (6) compares the reference timing (104) and the frame start timing (105). If the reference timing is earlier, ■ it is delayed. A reset signal (106) is generated at the frame head timing (105) to reset the reference timing. If the frame start timing (105) is earlier, the time difference d from the reference timing (104) is determined. d
is obtained by subtracting the elapsed time from the reference timing of the previous cycle from T. When the time difference d is larger than a preset threshold value, a control signal (107) is generated to stop reading from the transmission buffer (3). ■Furthermore, the reference timing (lO4) is delayed.
At the point in time, the control signal (107) is released to restart reading from the transmission buffer. If the time difference d is less than or equal to the threshold value, nothing is done. The above is the second case in which data is not read from the buffer. The purpose of this control is to ensure timing at which decoding is possible on the receiving side, which will be described later.

Output from the transmission buffer (3) (described in detail later) (
109) has a constant speed, including the dummy. The framing section (6) performs seven framings on the above-mentioned transmission buffer output (109) at regular intervals and sends it out to the transmission path. On the receiving side, the received signal sequence is deframed by a deframing section (7) and stored in a receiving buffer (8). The output of the receiving buffer (8) is a variable length code sequence (Ill), and the same sequence (Ill) is
111) is converted into a fixed length code sequence (112) in a variable length decoding unit (9). The fixed length code sequence (112) is roughly decoded in the decoding unit 4 to obtain a digital image signal sequence (113). In the process of receiving and decoding the L code, the decoding unit Ql requires a certain amount of time to decode the code word corresponding to a certain section of the image.

In accordance with the above-mentioned example, the operation of the receiving buffer (8) will be explained with the period as a frame and the minimum time required for decoding as T.The input signal sequence (110) of the receiving buffer (8) is the third 1' in FIG. 3(1)) is the minimum time in which the decoding section (II) can decode one frame's worth of code words, as described above. When the leading timing of each frame of the input signal series (110) precedes the timing of period T,
The code word corresponding to the time difference is stored in the receiving buffer (8).
Accumulate in. If the accumulated amount exceeds the capacity of the receiving buffer (8) (overflow) (because the decoding does not fit), decoding becomes impossible, but the upper limit of the accumulated amount is as stated in the explanation of the transmitting buffer (3) above. It never exceeds D. D may be determined in accordance with the capacity of the receiving buffer (8). Therefore, for the sender, T and D
If these two parameters are known as representing the decoding ability of the receiving side, there is no danger of the receiving buffer (8) overflowing.

In the first embodiment, the section of the image signal sequence is described as a frame, but the same effect can be obtained by using a line or other continuous section.

〔Effect of the invention〕

As described above, according to the present invention, since the transmitting side is configured to control the conditions that prevent the receive buffer from overflowing, it is no longer necessary to increase the capacity of the receive buffer or the speed of the decoding circuit, and the device can be improved. It can be done at low cost and also has the effect of proving operational stability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an image encoding and transmitting apparatus according to an embodiment of the invention, FIG. 2 is an explanatory diagram showing the operation of a transmission buffer according to an embodiment of the invention, and FIG. An explanatory diagram showing the operation of a reception buffer according to an embodiment of the invention, FIG. 4 is a block diagram showing the configuration of conventional image coding transmission & storage, and FIG. 5 shows a transmission buffer by a conventional image coding transmission device. FIG. 6 is an explanatory diagram showing the operation of a receiving buffer in a conventional image encoding and transmitting apparatus. In the figure, (1) is an encoding unit, (2) is a variable length encoding unit, (3) is a transmission buffer, (4) is a reference timing generation unit, (5) is a timing comparison adjustment unit, and (8) is a A reception buffer, (9) a variable length decoding section, and (4) a kyphosis conversion section 0. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] An image coding and transmitting device that converts continuous fixed-length sections of a digitized image signal sequence into a variable-length codeword sequence and then transmits the continuous variable-length codeword sequence. A transmission buffer that temporarily accumulates data and performs speed conversion in order to transmit at a constant transmission speed, a reference timing generator that can generate pulses with a settable constant period, and a pulse generator that corresponds to the fixed length section. When the reference timing is delayed based on the comparison result after detecting the variable cycle timing at which the beginning of the variable length code word sequence is about to be read from the transmission buffer and performing a phase comparison with the reference timing. In this step, the time difference with the read timing of the beginning of the variable-length code word sequence is determined, and when the time difference is larger than a preset threshold, reading from the transmission buffer is stopped, and the time corresponding to the time difference has elapsed. restarting the readout from the transmission buffer after the above-described comparison result, and resetting the reference timing generator at the readout timing of the beginning of the variable-length codeword sequence if the reference timing is ahead based on the comparison result. and a timing comparison adjustment section that adjusts the timing based on the reference timing, and adjusts the sequence of encoded data to be transmitted chronologically based on the reference timing given by the reference timing generation section. This is an image encoding and transmission device.