JP2544349B2 - Narrow band transmission equipment - Google Patents

Description

The present invention relates to a narrow band transmission device for transmitting a video signal using, for example, a telephone line.

[Outline of Invention]

The present invention provides a narrow band transmission apparatus for band-compressing a digital image signal and transmitting the band by using, for example, a telephone line.
By changing a predetermined section for each predetermined pixel in the horizontal direction to a constant level, for example, a substantially black level, the block-shaped pixels appearing on the display are made almost inconspicuous and the image quality is improved.

[Conventional technology]

Delay the frame period of the video signal of a black and white video,
A transmission device has been proposed in which bandwidth is compressed by reducing the number of pixels to be transmitted and transmission is performed using, for example, a 64 kbit / sec telephone line. By using this transmission device, for example, two digital telephone lines can be used to enable bidirectional communication of video and audio.

By the way, when the band-compressed video signal is reproduced, the number of pixels is small, so that the boundaries between the pixels are conspicuous and the pixels appear in blocks. Therefore, conventionally, for the image signal in the horizontal direction, a high-pass component is cut by a low-pass filter to make the boundary between the pixels inconspicuous.

However, if the high frequency components are cut using a low pass filter, the entire screen will be blurred.

Therefore, as shown in FIG.
It has been proposed to dispose a mesh shadow mask 102 on the surface 1 so that the boundary 103 of pixels is visually inconspicuous.

[Problems to be solved by the invention]

When the mesh shadow mask 102 is used as described above,
Due to the visual low-pass filter effect, pixel boundaries are hardly recognized. But this shadow mask
The mesh size of 102 is constant. Therefore, when the image signal is transmitted in a mode in which the number of pixels is four times, for example, the shadow mask 102 becomes an obstacle as shown in FIG.
Although the number of pixels is increased and a fine image is sent, there is a problem that the image cannot be reproduced in detail.

Therefore, an object of the present invention is to provide a shadow mask according to the transmission mode on the display,
An object of the present invention is to provide a narrow band transmission device with improved image quality.

[Means for solving problems]

According to the present invention, in a narrow band transmission apparatus for band-compressing and transmitting a digital image signal, a predetermined data section for each predetermined pixel in the horizontal direction of the transmitted digital image signal is changed to a constant level. Is a narrow band transmission device.

[Action]

By changing a predetermined data section for each predetermined pixel in the horizontal direction of the transmitted digital image signal to a substantially black level, black lines are projected in a stripe shape on the display. Due to the stripe-shaped black line, the boundaries of pixels are hardly recognized visually.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a transmission device to which the present invention is applied. As shown in FIG. 1, this transmission device is composed of a transmission circuit 1 and a reception circuit 2. A black-and-white image signal of 30 frames per second is supplied from the video camera to the input terminal 3 of the transmission circuit 1. This black-and-white image signal is digitized by the transmission circuit 1 and band-compressed. This band-compressed image signal is output from the output terminal 4 and, for example, 64
It is transmitted over a digital telephone line of kilobits / second. As the mode of the image signal which is band-compressed and transmitted, for example, in addition to the mode of transmitting an image of 64 pixels in the horizontal direction and 48 lines in the vertical direction for one frame in 0.2 seconds, 128 pixels in the horizontal direction and in the vertical direction There are modes such as transmitting 96 frames of image in 1 frame in 0.8 seconds. These modes are set by the keyboard 20 connected to the microprocessor 12.

The band-compressed image signal transmitted via the digital telephone line is supplied to the input terminal 5 of the receiving circuit 2. Pixels are interpolated in the receiving circuit 2 according to the mode, and every second
It is returned to the analog black and white image signal of 30 frames. This monochrome image signal is taken out from the output terminal 6, and an image is displayed on the display by this monochrome image signal.

That is, the black and white image signal supplied to the input terminal 3 of the transmission circuit 1 is supplied to the A / D converter 7, and the frequency of
It is digitized with a sampling lock of c / 5 (fsc: color subcarrier frequency), and is converted into, for example, 6-bit digital data. The output of the A / D converter 7 is selectively supplied to the frame memories 10A and 10B via the switching circuit 8.

A switching signal is supplied from the timing signal generating circuit 9 to the switching circuit 8. This switching signal is formed based on the synchronizing signal in the video signal supplied from the input terminal 3 to the timing signal generating circuit 9.

The output data of the A / D converter 7 is thinned out by the switching circuit 8 every predetermined sample, and the frame memories 10A and 1
In 0B, for example, 128 pixels in the horizontal direction and 120 lines of image data in the vertical direction are alternately written for each frame.

The frame memories 10A and 10B are controlled so that one of them is in a writing state and the other is in a reading state. While the data is read from one frame memory at a low speed according to the mode, the data of the next frame is written to the other frame memory. By controlling the frame memories 10A and 10B in this manner, image data of one frame in 0.2 seconds or one frame in 0.8 seconds is alternately read from the frame memories 10A and 10B, depending on the mode.

This image data is thinned out by the switching circuit 11 according to the mode, for example, image data of 64 pixels in the horizontal direction, 48 lines in the vertical direction or 128 pixels in the horizontal direction, and 96 lines in the vertical direction is output to the microprocessor 12. Supplied.

This 6-bit image data is
4 bits are encoded by DPCM processing (intra-frame differential encoding). The image signal and mode information are output as serial data from the output terminal 4 and transmitted via the digital telephone line.

The microprocessor 13 of the receiving circuit 2 and the microprocessor 12 of the transmitting circuit 1 are connected via a signal line 19. Keyboard 20 connected to microprocessor 12
By the operation of, the mode of the transmission circuit 1 and the reception circuit 2 is set.

Input terminal 5 of receiving circuit 2 via digital telephone line
The image signal supplied to is supplied to the microprocessor 13.

The serial data transmitted from the transmission circuit 1 by the microprocessor 13 is separated into 4-bit DPCM code,
It is decoded into bit pixel data. Further, processing based on the mode information received by the microprocessor 13 is performed, interpolation data is inserted into data of 64 pixels in one line, and data of 128 pixels in one line is formed.

The output of the microprocessor 13 is selectively supplied to the frame memories 15A and 15B via the switching circuit 14.

The frame memories 15A and 15B are controlled so that when one is in a writing state, the other is in a reading state. While one frame of data is being written into one frame memory at a low speed according to the mode, image data is read from the other frame memory at a speed of 30 frames per second according to the mode.

The image data selectively read from the frame memories 15A and 15B is sent to the D / A converter 17 via the switching circuit 16.
To be converted into an analog signal. A timing signal is supplied from the timing signal generation circuit 18 to the switching circuit 16 and the D / A converter 17. The output of the D / A converter 17 is taken out from the output terminal 6, and an image is displayed on the display by this output.

The data output from the switching circuit 16, for example, the data in the section of 2/5 of each pixel in the horizontal direction is converted into the data of 0 and supplied to the D / A converter 17. As a result, black lines are projected in stripes on the display.

That is, as shown in FIG. 2, the output of the switching circuit 16 (FIG. 3A) is supplied to the D flip-flop 21, and the output of the D flip-flop 21 is supplied to the D flip-flop 22. A clock having the sampling frequency fs shown in FIG. 3B is supplied to the D flip-flop 21 from the terminal 23. D
Flip-flop 22 and D / A converter 17 have terminals 24
The clock having the frequency of 5fs shown in FIG. A clear pulse is supplied from the terminal 25 to the D flip-flop 22 at the timing shown in FIG. 3D.

The data supplied to the D flip-flop 22 is shown in FIG. 3D.
The output data of the D flip-flop 22 is shown in FIG. 3E with respect to the data (FIG. 3A) supplied to the D flip-flop 21 by being cleared by the clear pulse supplied at the timing shown in FIG. As described above, the hatched section is converted into data of 0. In this way, the output of the D flip-flop 22, which has been converted into data of which the predetermined section is 0, is supplied to the D / A converter 17 and converted into an analog signal. As a result, a black signal BL appears as shown in FIG. 4 in, for example, a 2/5 section of each pixel in the horizontal section of the video signal. As shown in FIG. 5, a plurality of stripe-shaped black lines 32 lined up in the vertical direction are displayed on the display 31 by the black signal BL appearing in the predetermined section for each pixel.

The number of pixels transmitted from the transmission circuit 1 is as described above.
In one mode, for example, 64 pixels horizontally and vertically
There are 48 lines. Since the number of pixels is small in this way, the pixels look like a grid on the display 31 when reproduced as it is.

However, the display 31 has black stripes
Since 32 is displayed, pixel boundaries are hardly recognized due to a visual low-pass filter effect. Since the stripe-shaped black lines 32 are formed by the black level signal inserted in the video signal, the optimum line widths and line intervals can be appropriately set according to the mode and the image quality. This setting can be done by the microprocessor 13 based on the received mode information. Therefore, even when the mode is changed, the image can be reproduced in detail according to the change.

Such a stripe-shaped black line 32 may be formed by switching the output of the D / A converter 17 and inserting an analog black level signal at predetermined intervals.

In addition, instead of the black line 32 having a stripe shape, a gray line or a white line having a stripe shape may be displayed on the display 31 to obtain the same effect of improving the image quality. For example, when displaying a gray line, the D flip-flop 22 may not clear only the MSB data. In this way, the predetermined data section for each predetermined pixel in the horizontal direction includes "1000000" data,
Gray lines can be displayed on the display 31.

Also, if the black line 32 is oscillated left and right for each frame by, for example, 1/2 pixel, the black line 32 becomes almost invisible, and the pixel boundaries are not conspicuous, and the image quality is further improved. it can.

In addition, add a horizontal black line for each predetermined line,
The black lines may be projected in a grid pattern.

〔The invention's effect〕

According to the present invention, the predetermined data section for each predetermined pixel in the horizontal direction of the transmitted digital image signal is changed to a substantially black level, whereby a stripe-shaped black line is displayed on the display. This stripe-shaped black line makes it possible to make the boundaries of pixels virtually inconspicuous. This striped black line is
It can be set appropriately according to the mode and image quality. Therefore, even if the mode changes and the number of pixels changes, the image quality does not deteriorate.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of a transmission device to which the present invention is applied, FIG. 2 is a block diagram used to explain one embodiment of the present invention, and FIG. 3 is a waveform used to explain one embodiment of the present invention. FIG. 4 is a waveform diagram of a video signal in one embodiment of the present invention, FIG. 5 is a schematic diagram used for explaining one embodiment of the present invention, and FIGS. 6 and 7 are conventional narrow band transmissions. It is a schematic diagram used for description of an apparatus. Description of main symbols in the drawings 1: Transmitter circuit, 2: Receiver circuit, 7: A / D converter, 17: D / A converter, 21, 22: D flip-flop.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Hashimoto 1-2356 Takeshi, Yokosuka City, Kanagawa Nihon Telegraph and Telephone Corporation, Communication Research Laboratory (72) Inventor Hideo Morita 6-7 Kita-Shinagawa, Shinagawa-ku, Tokyo No. 35, Sony Corporation (72) Inventor, Motoaki Hayakawa 6-7, Kita-Shinagawa, Shinagawa-ku, Tokyo No. 35, Sony Corporation

Claims (1)

(57) [Claims] 1. A transmitting means for band-compressing a digital image signal and transmitting the band-compressed digital image signal through a public line, and a band-compressed digital image signal transmitted through the public line for receiving the band-compressed digital image signal. In a narrow band transmission device comprising a receiving means for performing decompression processing, the receiving means sets the level of the image signal to black, white, or black in order to form a mask of a predetermined width of black, white, or gray on the screen. Alternatively, it is provided with a level setting means for setting a gray level and a timing signal generating means for forming a timing signal of a predetermined timing according to the transmission mode and giving the timing signal to the level setting means, depending on the transmission mode. A narrow band transmission device characterized in that a plurality of black, white, or gray masks are displayed on the screen at different intervals.