JP2586299B2 - Television telephone equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video telephone, and more particularly to a video telephone having improved quantization characteristics.

[0002]

2. Description of the Related Art Recent video telephones (including video conferencing devices) attempt to digitize video signals and transmit the digitalized video signals using, for example, a digital line having a communication speed of 64 kb / s. When a video signal is digitized and encoded, it is considered to be effective because the differential pulse code modulation method (hereinafter referred to as DPCM) is simple and the device can be downsized.

[0003] The basic configuration of a television telephone device will be described. A video signal and an audio signal are digitized by an A / D conversion circuit, quantized, DPCM encoded, and the encoded video signal and audio signal are converted, for example. Time-division multiplexing and sending to a receiving side via a digital transmission path, where the receiving side separates and decodes the video signal and the audio signal, converts them to analog by a D / A conversion circuit, and supplies them to a TV receiver and a speaker. I have to.

[0004]

When DPCM coding is applied to a television telephone as described above, considering the use thereof, the receiving side looks at the image of a person sent from the transmitting side while watching the image. There is a method of making a call and a method of using it for remote monitoring.

As a transmission method, a video signal is transmitted in a few seconds.
A high-definition image transmission mode for transmitting a high-definition still image for transmitting a single image and a simple moving image transmission mode for transmitting a video signal at about 5 to 10 frames per second are conceivable.

When the DPCM encoding method is used to encode a frame having a different number of pixels according to the type of video signal information transmitted in this manner, the distance between pixels is small in the high-definition image transmission mode, The correlation between the sample points in the case of the conversion becomes strong, and the difference becomes small even when DPCM is performed between adjacent pixels.

On the other hand, in the simple moving image transmission mode, the number of pixels per image is reduced, so that the correlation between each sample point is weakened.
Even if DPCM is performed between adjacent pixels, the difference is large.

[0008] For this reason, there is a disadvantage that the degree of image quality deterioration changes in accordance with the number of frame pixels of transmission information of a video signal in which the quantization characteristic is kept constant.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described drawbacks, and has as its object to obtain a television telephone apparatus which does not deteriorate in image quality even when transmitted video information changes.

[0010]

According to the present invention, an A / D converter 4a for converting an input video signal 2 into a digital video signal as shown in FIG. Quantizer 4d for quantizing the difference value between pixels
4i, and a coding circuit 4f for coding the output signals of the quantizers 4d and 4i, wherein the video signal transmitted from the coding circuit 4f is transmitted via a transmission line. The quantizers 4d and 4i switch the quantization characteristics according to the number of pixels in the frame of the video signal 2, and when the number of pixels in the frame is large, narrow the quantization width and reduce the number of pixels in the frame. In such a case, the videophone device is characterized in that the quantization width is made coarse.

[0011]

In the video telephone apparatus of the present invention, the quantization characteristic at the time of encoding a video signal is switched according to the number of pixels, thereby compensating for the deterioration of the image quality due to the difference in the number of frame pixels. High quality images can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a television telephone according to the present invention will be described in detail with reference to FIGS. FIG. 1 is a system diagram of the video telephone apparatus of the present invention, and FIGS. 2 and 3 are quantization characteristic diagrams for explaining the present invention.

FIG. 1 shows a television telephone set 12 according to the present invention.
Shows the overall configuration of one embodiment. The video telephone 12 has an image transmitting device and a video receiving device. However, for convenience of explanation, the video telephone 12 has its own video transmitting device (prediction coding circuit 4) and a partner connected thereto. The image receiving device (prediction signal decoding circuit 9) of the television telephone device on the side will be described.

First, the predictive coding circuit 4 will be described with reference to FIG. For example, an NTSC video signal 2 is supplied from an input terminal 1 to an A / D conversion circuit 4a and digitized. This digital video signal is supplied to the first subtraction circuit 4b.

The output of the one-line delay circuit 4m is supplied to the first subtraction circuit 4b, which is subtracted from the digital video signal from the A / D conversion circuit 4a to obtain a difference signal between lines.

The output of the first subtraction circuit 4b is supplied to a second subtraction circuit 4c constituting a difference PCM circuit 4n between adjacent pixels. The output of the second subtraction circuit 4c is a plurality, here a pair of quantization circuits, ie, the first and second quantization circuits 4c.
d, 4i and quantized.

FIG. 1 shows a pair of quantizing circuits 4d and 4i, but three or more quantizing circuits can be juxtaposed as required.

The outputs of the first and second quantization circuits 4d and 4i are connected to the first and second switches S of the switching means 4e.
W ₁ , SW ₂ and the first and second switches SW
_1, the output terminal of the SW ₂ is supplied to the commonly connected by the encoding circuit 4f a first adding circuit 4g.

The first adder circuit 4g includes a one-pixel delay circuit 4
The outputs of h are added, and this output is also supplied to the second subtraction circuit 4c. The output of the first addition circuit 4g is supplied to a one-pixel delay circuit 4h and a second addition circuit 4k, and the output of the second addition circuit 4k is supplied to a one-line delay circuit 4m.
The output of the line delay circuit 4m is also supplied to the second addition circuit 4k and the above-described first subtraction circuit 4b.

The above-described difference PCM circuit 4n between adjacent pixels
Are the second subtraction circuit 4c, the first and second quantization circuits 4
d, 4i, switching means 4e, first adding circuit 4g
In addition, a one-pixel delay circuit 4h is configured to calculate a difference value between adjacent pixels.

The difference between the lines is calculated by the second adder 4k, the one-line delay 4m, and the first subtractor 4b.

That is, first, a difference value between lines is calculated, and a difference value between adjacent pixels is calculated from the obtained difference value between lines, and is encoded by the encoding circuit 4f. Such predictive coding results in the predictive coding circuit 4 having a considerably high prediction efficiency among fixed prediction methods.

The encoded output of the encoding circuit 4f is supplied to a third adding circuit 3, and a flag is added from the flag generating circuit 7 to the encoded output. The flag generation circuit 7 is controlled by the quantization characteristic changeover switch 8 for the video signal.
The output of the quantization characteristic switching switch means 8 turns on one of the _first and _second switches SW ₁ and SW ₂ of the switching means 4e and turns off the other.

The quantization characteristic changeover switch means 8 switches between the high-definition image transmission mode and the simple moving image transmission mode and outputs them.
, An identification flag is generated corresponding to each of them, and the switches SW ₁ and SW ₂ of the switching means 4e are switched.

The first and second quantization circuits 4d and 4i have quantization ROM tables for quantizing digitized digital signals, and the first and second quantization circuits
The ROM tables in d and 4i are, for example, non-linear quantizations in which normal gradations are compressed from 64 gradations to 8 gradations (quantization width) as shown by characteristic curves 13 and 14 in FIG. 2 and FIG. The quantization width of the high-definition image transmission mode and the quantization width of the simple moving image transmission mode are made finer in the high-definition image transmission mode, so that a fine range of the difference input can be encoded. The third addition circuit 3 adds a characteristic switching flag that differs according to the quantization characteristic curves 13 and 14 to the encoded data. The data is transmitted to the transmission line 5.

Next, the prediction signal decoding circuit 9 will be described with reference to FIG. The encoded data from the transmission line 5 is the first
And second decoding circuits 9g and 9h and a flag separating circuit 11
Supplied to

The first and second decoding circuits 9g and 9h have decoding ROMs corresponding to the quantization characteristics of the first and second quantization circuits 4d and 4i. Is carried out and supplied to the third and fourth switches SW ₂ and SW ₃ of the switch means 9f.

The outputs of the third and fourth switches SW ₃ and SW ₄ are shared, and the output of the flag separating circuit 11 is the third or fourth switch SW ₃ and SW of the switching means 9f.
₄ is turned on and the other is turned off.

The outputs of the third and fourth switches SW ₃ and SW ₄ are supplied to a fourth adder 9e, a one-pixel delay circuit 9d, a fifth
The processing opposite to the processing of the predictive encoding circuit 4 is performed through the addition circuit 9c, the one-line delay circuit 9b, and the D / A conversion circuit 9a, and the video signal 2 is output to the output terminal 6.

The outputs of the one-pixel delay circuit 9d and the one-line delay circuit 9b are supplied to fourth and fifth adders 9e and 9c.

The video signal extracted from the output terminal 6 is T
The image is supplied to the V receiver and displayed on the cathode ray tube surface. The description of the audio signal has been omitted,
The audio PCM signal that has been M-encoded and time-division multiplexed together with the video signal on the transmission line 5 is separated from the video signal on the receiving side by PCM.
After decoding, D / A conversion is performed and sound is emitted from a speaker or the like, whereby a videophone device is configured.

[0032]

[0033]

According to the present invention described above, it is possible to obtain a high-quality image with less distortion as compared with the conventional one simply by switching the quantization characteristics according to the image state of the video signal. Further, since the amount of quantization is switched for each frame in accordance with the number of pixels in the frame, there is an effect that the quantization characteristics can be made the same in the frame.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a television telephone apparatus of the present invention.

FIG. 2 is an explanatory diagram of a high-definition quantization characteristic used in FIG. 1 of the present invention.

FIG. 3 is an explanatory diagram of a simplified moving image quantization characteristic used in FIG. 1 of the present invention.

[Explanation of symbols]

 Reference Signs List 4 prediction encoding circuit 7 flag generation circuit 9 prediction signal decoding circuit 11 flag separation circuit 12 video telephone

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-47-30210 (JP, A) JP-A-47-24717 (JP, A) JP-A-60-54581 (JP, A) 25372 (JP, B2)

Claims (1)

(57) [Claims] An A / D converter for converting an input video signal into a digital video signal; a quantizer for quantizing a difference value between adjacent pixels of the digital video signal; An encoding circuit for encoding the output signal, wherein the video signal is transmitted through a transmission path via the transmission line . The number of pixels
The quantization characteristics are switched according to the number of pixels in the frame.
If the number of pixels in the frame is smaller,
The video telephone apparatus is characterized in that when the number is small, the quantization width is made coarse .