JPH0226912B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention is directed to a high-efficiency coding and transmission device for image signals that prevents image quality from deteriorating when sub-sampling or sub-line coding is performed to achieve high compression. This relates to an encoding method for encoding.

Prior Art and Problems In high-compression coding of image signals, high-efficiency coding and transmission apparatuses that perform composite differential predictive coding and the like are used. FIG. 1 is a block diagram of the main parts of a conventional high-efficiency encoding and transmitting device, in which 1 is an input terminal for a digitized image signal, 2 is an encoding circuit, 3 is a frame memory, 4 is a pre-prediction circuit, 5 is a quantization circuit, 6 is a code conversion circuit for converting into a transmission path code such as a variable length code, 7 is a buffer memory, and 8 is a sending circuit. The image signal is converted into, for example, an 8-bit digital image signal and applied to the input terminal 1.
In the case of a color image signal, for example, a luminance signal and a chromaticity signal are separated, time-division multiplexed, and applied to the input terminal 1. The digital image signal applied from the input terminal 1 to the encoding circuit 2 is calculated by calculating the difference between it and the output of the frame memory 3.
An inter-frame difference value is determined and applied to the pre-prediction circuit 4. The pre-prediction circuit 4 has a configuration that further calculates the difference between the inter-frame difference values, for example, 1
It is possible to perform subsample encoding in which encoding is performed for every other pixel, or subline encoding in which encoding is performed for every other scanning line, for example. Whether or not this subsample encoding or subline encoding is performed is controlled by a control signal a from the buffer memory 7. The output of the pre-prediction circuit 4 is applied to a quantization circuit 5, where it is quantized by a predetermined quantization step and applied to a code conversion circuit 6.

The code conversion circuit 6 performs coding such as block coding and variable length coding to obtain a transmission path code, adds the transmission path code to a buffer memory 7, and transmits the transmission path code sequentially read out from the buffer memory 7 in accordance with the transmission speed. The transmission line code is sent from the sending circuit 8 to the transmission line.
The buffer memory 7 has a function of detecting the amount of accumulated information, and when the amount of accumulated information reaches a predetermined amount before overflowing, that is, the amount of information read out corresponding to the transmission speed is input from the code conversion circuit 6. When the amount of stored information reaches a predetermined amount before the amount of input information exceeds the storage capacity due to the amount of information input,
When a control signal a is applied to the code conversion circuit 6 and the encoding circuit 2, and subsample encoding or subline encoding is performed in the pre-prediction circuit 4 described above so as to reduce the amount of information input to the buffer memory 7. or by changing the quantization step of the quantization circuit 5,
Alternatively, control is performed to shorten the code length in the case of variable length encoding in the code conversion circuit 6.

When high compression encoding is performed using the control signal a mentioned above, the information is sent to the receiving side.If subsample encoding or subline encoding is performed on the transmitting side, the receiving side Based on the information, decoding is performed by sub-sample decoding or sub-line decoding, and the decoded digital image signal is converted into an analog image signal and displayed on a cathode ray tube display device or the like.

As mentioned above, if high compression is achieved by performing composite difference using subsample coding or subline coding, aliasing components will occur as a frequency characteristic of the transmitted signal, and the image quality of the received and reproduced image will deteriorate. become.

OBJECTS OF THE INVENTION An object of the present invention is to reduce aliasing components when sub-sample or sub-line encoding is performed, thereby preventing deterioration in the image quality of received and reproduced images. Examples will be described in detail below.

Embodiment of the Invention FIG. 2 is a block diagram of an embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate the same parts, 9 is a filter circuit, 10 is a low-pass filter, and 11 is a selector. The selector 11 selects whether to input the digital image signal applied to the input terminal 1 directly to the encoding circuit 2 or to input it to the encoding circuit 2 via the low-pass filter 10. The selector 11 is controlled by the control signal a when the signal a becomes greater than or equal to a predetermined value, and the output of the low-pass filter 10 is selected and input to the encoding circuit 2. That is, when sub-sample encoding or sub-line encoding is performed in the encoding circuit 2, the output of the low-pass filter 10 is selected by the selector 11 and input to the encoding circuit 2, and the output is inputted to the encoding circuit 2 to perform sub-sample encoding or sub-line encoding. If encoding is not performed, the digital image signal applied to the input terminal 1 by the selector 11 is directly input to the encoding circuit 2.

When the image moves rapidly, the amount of information added to the buffer memory 7 due to inter-frame differences increases. is input to the encoding circuit 2, and after a period of time determined by the responsiveness of the encoding circuit 2, the aliasing component that occurs in the inter-frame difference value is reduced, and sub-sample encoding or sub-line encoding is performed. It is possible to reduce aliasing components due to encoding. In this case, the image signal will have a narrow band, causing blurring in the received and reproduced image, but distortion will be reduced by removing the aliasing component. In addition, when the image changes from a rapidly moving image to a still image, the image quickly returns to its normal state, so that the overall image quality can be improved.

FIG. 3 is a block diagram of an example of the low-pass filter 10, in which 21 and 22 are delay circuits having a delay time of Z ^-1 corresponding to one sampling time, 24 is a summation circuit, and 25 is a division circuit to halve. The circuit 11 is the aforementioned selector. The division circuit 25 has a simple configuration that shifts the output of the summation circuit 24 by one bit.
Note that it is also possible to employ low-pass filters with other configurations.

FIG. 4 is a block diagram of main parts of another embodiment of the present invention, in which the same reference numerals as in FIGS. 1 and 2 indicate the same parts, 12 is a low-pass filter, and 13 is a selector. The control signal a generated when the amount of information stored in the buffer memory 7 reaches a predetermined value causes the selector 1 of the filter circuit 9 to
1 selects the output of the low-pass filter 10 and adds it to the encoding circuit 2, and in the encoding circuit 2, the selector 13
selects the output of the low-pass filter 12 and applies it to the pre-prediction circuit 4, the pre-prediction circuit 4 performs sub-sample encoding or sub-line encoding, and adds the encoded output to the quantization circuit 5, The quantized output is applied to the next code conversion circuit 6.

The low pass filter 10 of the filter circuit 9 is inserted by the control signal a from the buffer memory 7, and the low pass filter 12 of the encoding circuit 2 is inserted.
By inserting , it is possible to smoothly transition to subsample encoding or subline encoding. That is, at the same time as transitioning to subsample encoding or subline encoding, the band for interframe difference values can be narrowed by the low-pass filter 12, and aliasing components generated due to high compression can be suppressed at the same time as switching the encoding means. be able to.

On the receiving side, by receiving control information indicating that the code is a highly compressed code that has undergone subsample encoding or subline encoding, the filter corresponding to the low-pass filter 12 is changed to an interframe difference decoding circuit. This method performs decoding that corresponds to high-compression encoding on the transmitting side, thereby improving the quality of received and reproduced images.

Effects of the Invention As explained above, the present invention inputs an input digital image signal to the encoding circuit 2 via the low-pass filter 10, and inputs the input digital image signal to the encoding circuit 2 through the low-pass filter 10, and performs high compression encoding using sub-samples or sub-line encoding. When subline encoding is not performed, the input digital image signal is directly input to the encoding circuit 2 without passing through the low-pass filter 10.
This is a type of input that can suppress aliasing components caused by high-compression encoding, and although the received and reproduced image will be blurred due to band limitations, distortion due to aliasing components can be removed, so high-compression encoding can suppress aliasing components. It is possible to prevent the deterioration of image quality when the image quality changes. Furthermore, since the image quality is quickly restored when the image changes from moving to static, the overall image quality can be improved. Also, when the low-pass filter 12 is inserted for the frame difference value of the encoding circuit 2 during high compression encoding,
Since the transition to high compression encoding is performed smoothly, it is possible to further prevent deterioration of image quality.

[Brief explanation of drawings]

Figure 1 is a block diagram of the conventional encoding method, Figure 2
3 is a block diagram of an example of a low-pass filter, and FIG. 4 is a block diagram of a main part of another embodiment of the present invention. 1 is an input terminal for a digital image signal, 2 is an encoding circuit, 3 is a frame memory, 4 is a pre-prediction circuit, 5 is a quantization circuit, 6 is a code conversion circuit, 7 is a buffer memory, 8 is a sending circuit, and 9 is a A filter circuit, 10 is a low-pass filter, 11 is a selector,
12 is a low-pass filter, and 13 is a selector.

Claims (1)

[Claims] 1. An input digital image signal is compressed and encoded by an encoding circuit, and the encoding circuit performs sub-sample or sub-line encoding according to a control signal outputted in accordance with the amount of information stored in the buffer memory. In an encoding method that performs high compression encoding, a low-pass filter for removing aliasing distortion corresponding to the sampling frequency when performing the sub-sample or sub-line encoding; and an output of the low-pass filter and the input digital image. and a selector for selecting a signal and inputting the signal to the encoding circuit, and controlling the selector according to the control signal outputted in accordance with the amount of information stored in the buffer memory to perform the sub-sample or sub-line encoding. When performing the sub-sample or sub-line encoding, the input digital image signal is input to the encoding circuit via the low-pass filter, and when the sub-sample or sub-line encoding is not performed, the input digital image signal is directly input to the encoding circuit. An encoding method that is characterized by