JPH0378383A - High efficiency encoding device for television signal - Google Patents

Abstract

PURPOSE:To suppress error rate below a definite value independently of a communication state by constituting a normal mode and a fall back mode so as to be capable of being switched, and changing the length of picture data by a prescribed means according to these modes. CONSTITUTION:The output of a variable length encoding circuit 6 is inputted to an error correction encoding circuit 7, and the error correction encoding circuit 7 adds an error correction code to the variable length encoded picture data. Error correction code length is changed by a normal/fall back mode selection signal, and it is constituted so as to be short at the time of the normal mode and to be long at the time of the fall back mode. Then, when the communication state is aggravated, the mode is changed into the fall back mode. In the fall back mode, the picture data is shorter compared with the normal mode, and the error correction code can be made longer by this portion. Thus, the error rate can be suppressed low.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-efficiency encoding device for television signals that encodes and digitally transmits television signals.

[Summary of the Invention] The present invention provides a high-efficiency encoding device for a television signal that encodes a television signal and adds an error correction code to the encoded image data, which switches between a normal mode and a fallback mode. By changing the length of the image data according to these modes, the fallback mode can be switched to when the communication condition deteriorates, and the image data is shorter in the fallback mode than in the normal mode. Since the error correction code can be made longer, the error rate can be kept below a certain level regardless of the communication state.

[Prior Art] For example, in satellite broadcasting, television signals are encoded and transmitted in order to reduce the amount of data to be transmitted as much as possible.

If this encoded image data is not received as proper data, the playback screen will be very distorted.
Error correction codes and the like are added to image data, and television signals are composed of image data and error correction codes. In such a high-efficiency image encoding apparatus, the bit rate of the television signal is usually determined, and the encoding method, various parameters, etc. are set accordingly.

[Problems to be Solved by the Invention] However, in conventional devices, the length of the error correction code is constant, so when the communication condition deteriorates, the error rate increases and the reproduced image deteriorates significantly. .

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a highly efficient encoding device for television signals that is capable of keeping the error rate below a certain level even when communication conditions deteriorate.

[Means for Solving the Problems] A high-efficiency encoding device for television signals according to the present invention to achieve the above object includes a low-pass filter that limits the passband of the television signal, and a digital signal that has passed through the low-pass filter. A predictive encoding circuit that encodes a television signal at a lower bit rate than the input signal using the correlation, and a predictive encoding circuit that detects the output amount of this predictive encoding circuit and performs the prediction in order to keep the output amount below a reference amount. a flow rate control circuit that controls quantization characteristics in encoding of the encoding circuit; a variable length encoding circuit that converts the output of the predictive encoding circuit; and variable length encoded image data output from the variable length encoding circuit. and an error correction encoding circuit that adds an error correction code to the image data, and is configured to be switchable between a normal mode and a fallback mode, and the length of output image data is varied according to these modes.

In the above configuration, the image data length can be varied according to the mode by varying the passband characteristics of the low-pass filter, or the image data length can be varied according to the mode by the quantum The image data length can be varied according to the mode, or the image data length can be varied according to the mode, or the image data length can be varied according to the mode. In order to vary the variable length coding allocation of the variable length coding circuit, or to vary the image data length according to the mode, it is possible to vary the passband characteristics of the low-pass filter, or to quantize the predictive coding circuit. To vary the characteristics, to vary the reference amount of the flow control circuit,
varying the variable length coding allocation of the variable length coding circuit;
This is a combination of two or more of the following.

[Operation] When the communication condition is good, transmission is performed in the normal mode with a predetermined image data length and error correction code length, and when the communication condition deteriorates, it is switched to the fallback mode. In the fallback mode F, the image data is shorter than in the normal mode, and the error correction code can be lengthened accordingly, so the error rate can be kept low.

[Example〕 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit block diagram of a high efficiency encoding device. In FIG. 1, an NTSC television signal is converted into an 8-bit digital signal, and this digital television signal is input to a low-pass filter 1. This low-pass filter 1 cuts the high-frequency components of the television signal and limits the passband, and this filter characteristic is determined by the normal/fallback mode selection signal as shown in Fig. 2(b).
and (a). The output of the low-pass filter 1 is input to a sub-sampling circuit 2. This subsampling circuit 2 thins out the television signal every other pixel, and offsets the signal by one pixel between the first and second fields. This thinned-out television signal is input to a predictive encoding circuit 3, and the predictive encoding circuit 3 performs predictive encoding using the correlation between image data. For predictive coding, the optimal prediction is selected from intra-field prediction, inter-frame prediction, motion-compensated inter-frame prediction, inter-field prediction, etc., and the difference value between the actual value and predicted value is output as 5-bit data. Data conversion of this difference value is performed by a quantizer, and the quantization characteristic indicating data allocation to the difference value is varied by the normal/fallback mode selection signal as shown in FIGS. 3(b) and 3(a). The output of this predictive encoding circuit 3 is sequentially stored in a buffer memory 4. The buffer memory 4 is configured as a FIFO (first in, first out), and the write address and read address are sent to the flow rate control circuit 5. The flow rate control circuit 5 determines the memory amount from the difference between the write address and the read address, and detects the output amount of the predictive encoding circuit 3 from this memory amount. In order to suppress this output amount to a reference amount or less, eight levels (Q, to QS) of control signals are output to the predictive encoding circuit 3. The predictive encoding circuit 3 converts the quantization characteristics according to this control signal. Further, the reference amount of the flow rate control circuit 5 is varied by the normal/fallback mode selection signal.

On the other hand, the output of the buffer memory 4 is input to the variable length encoding circuit 6. The variable length encoding circuit 6 performs variable length encoding in which the shortest codes are assigned in the order of the highest ratio, taking advantage of the fact that the data ratio of predictive encoding exhibits Yamabushi characteristics. and,
The assignment characteristics of variable length encoding to predictively encoded data are varied by the normal/fallback mode selection signal.

The output of this variable length encoding circuit 6 is the error correction encoding circuit 7.
is input. This error correction encoding circuit 7 adds an error correction code to the variable length encoded image data. The error correction code length is varied by a normal/fallback mode selection signal, and is short in normal mode and long in fallback mode. That is, in the normal mode, the image data length is longer and the error correction code is shorter, and in the fallback mode, the image data length is shorter and the error correction code is longer, so that a transmission signal with the same overall bit rate is output. .

In the above configuration, the digital TV signal is low-pass filtered! The high frequency components are removed and the data is converted into highly correlated data, and the data is compressed in half by the subsampling circuit 2. Thereafter, the data is further compressed by a predictive encoding circuit 3 and a variable length encoding circuit 4, respectively. The filter characteristics of the low-pass filter 1 are different in the fallback mode compared to the normal mode, as shown in Fig. 2(b) and Fig. 2(a), and the data is converted into highly correlated data, making predictions difficult. It becomes easier to hit.

Furthermore, the quantizer characteristics of the predictive encoding circuit 3 are also shown in FIG. 3(b).
As shown in FIG. 3(a), the data is converted to a small value. Further, the reference value of the flow rate control circuit 5 is set low, and the variable length coding allocation of the variable length code ossification circuit 6 is changed to shorten the variable length coded data. Since the variable-length encoded data is short, the error correction code in the error correction encoding circuit 7 is long.

Therefore, if the fallback mode is selected when communication conditions are poor, the error rate can be kept below a certain level, although the image quality will deteriorate to some extent.

In this embodiment, the passband characteristics of the low-pass filter 1, the quantization characteristics of the predictive coding circuit 3, the reference amount of the flow rate control circuit 5, and the variable length coding allocation of the variable length coding circuit 6 are all variable. Although the image data length is configured to be varied by the following, it is also possible to configure one of them or a combination of two or more of them. However, in order to prevent image quality deterioration, it is preferable to vary as many circuit characteristics as possible.

It is further preferable that the low-pass filter 1 is configured as a temporal filter and applied to a moving region as a motion-compensated temporal filter in the fallback mode.

[Effects of the Invention] As described above, according to the present invention, in a high-efficiency encoding device for television signals that encodes television signals and adds error correction codes to the encoded image data, normal mode and fall mode are possible. The configuration is configured to be switchable between the back mode and the length of the image data using a predetermined means according to these modes, so if the communication condition deteriorates, the fallback mode is switched to, and the fallback mode is set to the normal mode. Since the image data is shorter than the mode, the error correction code can be made longer, so the error rate can be kept below a certain level regardless of the communication state.

[Brief explanation of drawings]

1 to 3(b) show embodiments of the present invention, and the first
The figure is a circuit block diagram of a high-efficiency encoding device, Figure 2 (a)
is a filter characteristic diagram in fallback mode, Figure 2(b) is a filter characteristic diagram in normal mode, Figure 3(a) is a quantization characteristic diagram in fallback mode, and Figure 3(b) is a filter characteristic diagram in fallback mode. ) is a quantization characteristic diagram in normal mode. ■...Low pass filter, 3...Predictive coding circuit,
5...Flow rate control circuit, 6...Variable length encoding circuit. Figure 2 (Q) Diagram of the filter well and pressure line at one time with a fall bag of two people Figure 2 (b) A diagram of the filter pressure at one time with a fall lever' and one spider Figure 8 (Q) Non-Less Mode Call J1 Dry Is Dried Hours Figure 3 (1))

Claims (6)

[Claims] (1) a low-pass filter that limits the passband of a television signal; a predictive encoding circuit that encodes the digital television signal that has passed through the low-pass filter at a lower bit rate than the input signal using its correlation; a flow rate control circuit that detects the output amount of the predictive encoding circuit and controls a quantization characteristic in encoding of the predictive encoding circuit to keep the output amount below a reference amount; and a flow rate control circuit that varies the output of the predictive encoding circuit. It has a variable length encoding circuit that performs long encoding, and an error correction encoding circuit that adds an error correction code to the variable length encoded image data output by this variable length encoding circuit, and has a normal mode and a fall pack. 1. A high-efficiency encoding device for a television signal, characterized in that it is configured to be switchable between modes, and the length of output image data is varied according to these modes. (2) The high-efficiency encoding apparatus for television signals according to claim (1), wherein the image data length is varied according to the mode by varying the passband characteristics of a low-pass filter. (3) The high-efficiency encoding apparatus for television signals according to claim (1), wherein the image data length is varied according to the mode by varying the quantization characteristics of the predictive encoding circuit. (4) The high-efficiency encoding apparatus for television signals according to claim (1), wherein the image data length is varied according to the mode by varying the reference amount of the flow rate control circuit. (5) The high-efficiency code for television signals according to claim (1), wherein the image data length is varied according to the mode by varying the variable length coding allocation of the variable length coding circuit. conversion device. (6) The image data length can be varied according to the mode by varying the passband characteristics of the low-pass filter, by varying the quantization characteristics of the predictive coding circuit, by varying the reference amount of the flow rate control circuit, and by varying the standard amount of the flow rate control circuit. 2. The high-efficiency encoding apparatus for television signals according to claim 1, characterized in that a combination of two or more of the following is performed: varying the variable length encoding allocation of the long encoding circuit.