JPS619091A - Still picture transmission system - Google Patents

Abstract

PURPOSE:To eliminate an error by variable sampling density from an original picture restored at the reception side by including a compression process and an expansion process by means of the variable sampling system in a pre-value forecast loop and applying compression coding to the forecast residual for transmission at the compressing process. CONSTITUTION:A line buffer F is provided in a feedback loop at the inside of a forecast circuit A and the 1st-order forecast is applied. Further, a compression circuit B and an expansion circuit C by the variable sampling density system are provided in a feedback loop at the outside of the forecast circuit A. Further, a signal subject to compression coding in the direction of amplitude and time axis by the 2nd-order forecast in a line is a direction at a right angle to that of the 1st-order forecast is transmitted through a telephone line, the signal received by the reception side is expanded by a variable sampling density expanding circuit D to restore the 1st-order residual. Further, the sampling is restored by a decording loop comprising the forecast circuit E and the line buffer G.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a still image transmission system for transmitting grayscale images using public telephone lines or the like.

[Background technology] Character code transmission paths are generally constructed in units of 8 bits, but if the control hood is excluded, the number becomes 7 bits, so when transmitting image information, one pixel of data (6 to 6 bits) is used.
If data of 2 pixels per character can be compressed from 7 bits to 3 bits, data of 2 pixels per character can be transmitted.
Since the prediction residuals non-linearly quantized in M) are required to obtain a practical reconstructed image, more than 4 pinots are required, so only one pixel of data can be placed on one character, which reduces the compression effect. The problem was that it was low. Furthermore, a method in which the previous prediction residual is further compressed in the time axis direction using a variable sampling density encoding method is extremely effective in increasing compression efficiency; There is a problem in that the quality of the image deteriorates due to such errors.

[Object of the Invention] The present invention has been made in view of the above problems, and provides a still image transmission method with high compression efficiency by combining prior value prediction and a variable sample density method. The purpose is to remove errors associated with the method and improve the quality of images.

[Disclosure of the Invention] The method of the present invention includes a compression process and an expansion process using a variable sample density method in the previous value prediction loop, and compresses and encodes the previous value prediction residual through the compression process and transmits it.
By performing compression and expansion within the prediction loop, the error caused by the compression and expansion of the variable sample density is included in the prediction residual and transmitted, thereby eliminating the error caused by the variable sample density from the original image restored on the receiving side. This is what I did.

FIG. 1 shows an example of a device implementing the method of the present invention. In the figure, a composite video signal output from a monochrome camera 1 is separated into synchronization signals by a synchronization separation circuit 2, digitized by an A/D converter 3, and then digitized by a data selector 4.
is stored in the frame memory 5. This data is automatically compressed and encoded by the microcombi 6 and sent to the public telephone line via the modem 7. This device is used, for example, in a security system that mutually monitors abnormalities between a store and a residence.On the receiving side, a device similar to that shown in the figure is used to connect a D/A converter 8 and a synthesis circuit 9. 1) Restore the image and display it on the monitor TV 10. 11 is a mode switching circuit. frame memory 5
consists of one screen, that is, 256 x 256 pixels, and 64 bytes in the case of 8-bit grayscale, A, /D, D/A
Reading and writing is performed at 200 nSec per pixel including conversion. Intel 8086 or Zilog 28 for CPU
000 is used.

FIG. 2 is a block diagram showing the main parts of one embodiment of the system of the present invention. In the same figure (,), the previous value prediction circuit (
A) is, for example, a previous value prediction circuit using the DPCM method,
In the feedback loop of this previous value prediction circuit (a), there is a compression circuit (b) using a variable sampling density method. 1,)ゎh(l(+
bh(yl, ., iii) A signal compressed and encoded in the amplitude and time axis direction by one circuit (b) is transmitted through a telephone line, and the receiving side in the same figure (b) processes the received signal. The sample is expanded by a variable sample density expansion circuit (d), and then restored by a decoding loop using a surface position prediction circuit (e).

Compression and expansion using the variable sampling density method are performed in units of one line or 17 frames, and the compression circuit (b) and expansion circuit (c) each include a line buffer or 7 frames 77. Figure 3 illustrates an example of a variable sampling density encoding method, in which the relationship between the sampling period and the sample value is defined by a triangle, and by moving this triangle as shown in the figure, the difference is shown by the arrow. By transmitting the waveform, the sampling interval is determined from the difference value and the triangle on the receiving side, and the original waveform is restored. The smaller the variation in sample values, the longer the sampling interval becomes and the more compressed the data becomes.

In order to explain the operation of the circuit shown in FIG. 2, a reference example is shown in FIG. In Fig. 5, as shown in Fig. 5(a), a prediction loop (H) performs previous value prediction, and the residual is compressed and encoded in a variable sample density compression circuit (W) and transmitted.
b) Since the receiving side in the figure performs decompression using variable sampling density, there is no opportunity to correct the error introduced during the encoding and decoding process using the variable sampling density method, and therefore this error increases line by line. There is a risk that the second
If the compression and expansion processes of variable sample density are included in the prediction loop as shown in the figure, the error caused by the compression and expansion of the variable sample density method will be included in the prediction residual and transmitted. Therefore, when the receiving side uses this residual to restore the sample, the error caused by the variable sample density method is automatically corrected.

FIG. 4 shows another embodiment. Figure (a) shows the transmitting side, horizontally (or vertically)
In a configuration that includes a compression circuit (b) and an expansion circuit (c) using a variable sampling density method in the outer feedback loop of the previous value prediction circuit (a) by scanning, the inner feedback loop of the prediction circuit (a) An in-buffer 7 (for one line) is provided in , and the sample values of this line buffer and the next line are used to predict the previous value in the vertical direction (or horizontal direction). , (b) On the receiving side, a line buffer (g) is provided in the prediction loop for restoring the sample.

In general, the planar pattern of the previous prediction residuals has a strong correlation in the axis direction orthogonal to the spatial axis direction in which the prediction was made, and this may appear as vertical stripes in the restored image, or
Alternatively, it is a cause of reducing the efficiency of compression encoding. However, with the configuration shown in Figure 4, if the compression direction using the variable sample density method, that is, the scanning direction of the original image and the prediction direction are made orthogonal, some correlation will still remain in the residual pattern after the previous value prediction. By performing compression in the vertical direction, data compression efficiency can be increased.

[Effect 1 of the Invention As described above, in the present invention, the feedback loop outside the previous value prediction circuit includes a compression process and an expansion process using a variable sample density method, and the previous value prediction residual is added to the compression process by the city. Because it is compressed and encoded for transmission, it is possible to combine prior value prediction and the variable sampling density method for efficient data compression, and by using this combination, it is possible to reduce the errors associated with the 1ζ variable sampling density method. In addition, by inserting a line buffer in the inner prediction loop, the correlation in the direction perpendicular to the scanning direction, which remains strongly in the first-order residual pattern, can be removed. It has the advantage of being able to extract and improve compression efficiency and significantly reduce transmission costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
a) (b) are block diagrams of the main parts of the same as above, FIG. 3 is an explanatory diagram showing the operation of the same as above, FIGS. 4(a) and (b) are block diagrams of main parts of the embodiment of the pond, and FIG. (aHb) is a professional drawing showing a reference example. 1 is a monochrome camera, 2 is a synchronization separation circuit, 3 is an A/D converter, 4 is a data selector, 5 is a frame memory,
6 is a microprocessor, 7 is a modem, 8 is a D/A converter, 9 is a synthesis circuit, 101, 1V, 111, 1, 1, 1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 7, 8, 7, 8, 9, 9, 101, 1V, 111, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 2, 2, 3, 3, 6, 7, 7, 8, and a compression circuit, respectively. , C is an expansion circuit, 2 is an expansion circuit on the receiving side, E is a previous value prediction circuit on the receiving side, 3 is a line buffer, and 3 is a line buffer on the receiving side. -7. Figure 2 (b) Non-No. 5 WA Hand (b) Procedural amendment (voluntary) October 8, 1980 Patent Application No. 130583 2, Title of invention Still image transmission system 3, Amendment Relationship with the case of the person who filed the patent application Patent applicant Location 1048 Kadoma, Kadoma City, Osaka Name (583) Matsushita Electric Works Co., Ltd. Representative Iku Kobayashi 4, Agent 5 Date of amendment order In the drawings attached to the specification of this application , Figure 4 is corrected as shown in the attached sheet. Procedural Amendments (issued by Qian) June 6, 1985

Claims (2)

[Claims] (1) A still image characterized in that a feedback loop outside the previous value prediction circuit includes a compression process and an expansion process using a variable sample density method, and the previous value prediction residual is compressed and encoded by the compression process and transmitted. Transmission method. (2) A line buffer for one line is provided in the feedback loop inside the previous value prediction circuit, and the previous value is predicted in the vertical direction (or horizontal direction) using the sample values of this line buffer and the next line. A still image transmission system according to claim 1, characterized in that the still image transmission system performs the following.