JPS6156530A - Differential pcm transmission system - Google Patents

Abstract

PURPOSE:To eliminate the delay of a rise part of a picture signal and to attain transmission of signals of high quality, by inserting a PCM signal of a prescribed bit which performs no DPCM coding directly to the rise part of each scan cycle of the picture signal when the picture signal undergoes the differential PCM coding at the transmission side and at the same time giving no DPCM decoding to the prescribed bit of the rise part of each scan cycle of the signal received and demodulated at the reception side and using a PCM signal as it is for reproduction. CONSTITUTION:When the transmission of picture signals is started, a switch circuit 17 is changed to the side of a frame memory 12 according to the output of a counter 18 just for a period equivalent to several bits from a rise time point of each scan line of the picture signal. Thus the PCM signal delivered from the memory 12 and underwent the DPCM coding is supplied as it is to a modulation circuit 14. For a receiver 20, the PCM signal underwent the DPCM decoding is supplied to a frame memory 23 since a switch circuit 29 is switched to the side of a modulation circuit 31 by a counter 30 just for a period of serveral bits from the rise time point of each scan line of the signal sent from a transmitter 10. Then said PCM signal is used for reproduction of picture signals through a D/A converter 24.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an improvement of a differential PCM transmission method for differentially PCM encoding and transmitting a wideband signal such as an image signal.

[Technical background of the invention]

Conventionally, there are the following systems that apply this type of transmission method, for example. FIG. 2 is a block diagram showing its configuration, in which 1 indicates a transmitting device, 2 a receiving device, and 3 a transmission path.

The transmitting device 1 converts the image signal VS into a digital signal using the A/D converter 11, stores it in the -H frame memory 12, reads it from the frame memory 12 at a speed compatible with the transmission path 3, and sends it to the encoding circuit 13. The encoded signal MS is encoded using differential pulse code modulation (DPCM).
is modulated by a modulation circuit (MOD) 14 and sent to the transmission line 3. The sampling timing of the A/D converter 11 is set by a clock pulse synchronized with a synchronization signal separated from the image signal S by the synchronization separation circuit 15.
Further, the write timing and read timing of the frame memory 12 are designated by a timing generation circuit 16 based on the clock pulse generated by the synchronization separation circuit 15 and the transmission clock pulse from the modulation circuit 14, respectively.

On the other hand, the receiving device first demodulates the signal/MS that has arrived via the transmission path 3 in a demodulation circuit (DMOD) 21, then performs DPCM decoding in a decoding circuit 22, and stores it in a frame memory 23. Then, the decoded signal is read out from the frame memory 23 and converted into an analog signal by the D/A converter 24, and the level of the reproduced image signal is controlled by the amplifier 25 and sent to the image monitor device 4 made of, for example, a CRT display. supply and display the image. Note that the write timing and read timing of the frame memory 23 are determined by a clock pulse generated from the clock generation circuit 26, and in synchronization with this clock pulse, the synchronization signal generation circuit 2
The timing is specified by the timing generation circuit 28 based on the synchronization signal generated from the timing generator 7 and the received clock from the demodulation circuit 21.

3 and 4 respectively show the encoding circuit 13 of the transmitting device 1 and the receiving device 2. 2 is a schematic configuration diagram of a decoding circuit 22 of FIG. The encoding circuit 13 includes a frame memory 12
The digitized image signal, that is, the PCM signal read out from the subtracter 31 is introduced into the subtracter 31, and the subtracter 31 calculates the difference between the predicted value obtained one pixel before, and this difference value is sent to the non-linear quantization circuit 32. The signal is quantized, then DPCM encoded by the code conversion circuit 35, and sent out. Here, the above-mentioned quantization is performed in small steps when the difference value is at a low level, and in large steps when the difference value is at a high level in accordance with the number of bits of the DPCM. Also, the above non-direct IIs! Child circuit 3
The output of No. 2 is added to the previous pixel value output from the delay circuit 34 in the adder circuit 33, and the added value is supplied to the delay circuit 34 and becomes the predicted value used for encoding the next pixel. .

On the other hand, the decoding circuit 22 introduces the received demodulated signal from the demodulation circuit 21 into the code conversion circuit 41 to convert it into a quantized code before encoding, and uses the output to decode the previous pixel output from the delay circuit 43. The added value is added by an adder 42, and the added output is outputted to the frame memory 23 as a DPCM decoded signal (PCM signal). Further, this addition output is supplied to the M plate circuit 43 as a predicted value of the next pixel.

With such a configuration, when a still image signal input from, for example, a solid input device is introduced into the transmitting device 1, this still image signal is converted into, for example, an 8-bit digital M number by the A/D converter 11. Thereafter, the signal is converted into, for example, a 3-bit difference signal by the encoding circuit 13 and sent to the transmission line 3. When the receiving bag N2 is reached, the decoding port M is first accessed.
At step 22, the 3-bit differential signal is converted back to an 8-bit PCM signal, and then at the D/A converter 24, the original analog still image signal is reproduced and displayed on the image monitor device 4. Therefore, if such a transmission method is used, the image signal, which is a wideband signal, can be sufficiently transmitted over a narrowband transmission path, and since differential signals are transmitted, the amount of transmitted information is reduced, thereby shortening the transmission time. be able to.

[Problems with background technology]

However, in this conventional method, the difference between each pixel and the predicted value of the previous pixel is calculated, this difference signal is sent out, and the receiving side also performs the reverse calculation to reproduce the image signal. Therefore, when an image signal as shown in FIG. 5(a) is input to the transmitting device 1 and transmitted, the receiving device 2 receives the rising and falling portions of the reproduced image signal as shown in FIG. 5(b), for example. A rise delay and a fall delay occur. In this case, the rising portion and the falling portion refer to the starting portion and ending portion of the image signal for each scanning period. Of these delays, the delay in the falling part is determined by the number of effective pixels to be transmitted (Fig.
) or blanking signal, it is difficult to remove the deterioration of the rising portion by post-signal processing as described above. For this reason,
For example, when the above-mentioned reproduced image signal is displayed as an image on an image monitor device, the left end of the displayed image may be distorted and the image in that part may become unclear, or if the scenery is significant, the entire image may become unrecognizable. This results in a loss of information.

In particular, recently, one screen has been reduced by thinning out pixels and scanning lines, and multiple such reduced screens are transmitted as one screen and displayed simultaneously on an image monitor device. In such a case, for example, as shown in FIG. 6, the image becomes sloppy not only at the left end of the screen but also at the center, making the image very difficult to see, which is not desirable.

(Object of the Invention) The present invention provides a differential PCM that can transmit human-quality signals by eliminating the delay in the rising edge of an image signal.
The purpose is to provide a transmission method.

(Summary of the Invention) In order to achieve the above object, the present invention provides li!
When performing differential PCM encoding on an i-image signal, a predetermined bit of P that is not subjected to DPCM encoding on the rising edge of the image signal is
The CM signal is inserted as it is, and the signal is reproduced as a PCM signal without DPCM decoding the predetermined bits of the rising edge of the received and demodulated signal on the receiving side.

[Embodiments of the invention]

FIG. 1 is a block diagram of a system to which a differential PCM transmission method is applied in an embodiment of the present invention. In this figure, the same parts as in FIG. 2 are given the same reference numerals and detailed explanations will be omitted.

A switching circuit (SW) 17 is interposed between the encoding circuit 13 and the modulation circuit 14 of the transmitting device 10. This cut! 11 circuit 17 is composed of, for example, a multiplexer,
According to the output of the counter 18, the difference signal from the encoding circuit 14, that is, the DPCM encoded signal and the frame memory 12
The PCM signal from the PCM signal is alternatively selected and supplied to the modulation circuit 15. The counter 18 starts counting the transmission clock output from the modulation circuit 15 from the rising edge of each scanning line of the image signal, and switches the switching circuit 17 to the frame memory 23 side until the count value reaches, for example, several bits. After that, the switching setting is made to the encoding circuit 13 side.

On the other hand, a switching circuit 29 is inserted between the decoding circuit 22 and the frame memory 23 of the receiving device W120. This switching circuit 29 consists of a multiplexer similar to the switching circuit 17 of the transmitter 10, and selects between the DPCM decoded signal from the decoding circuit 21 and the received demodulated signal from the modulation circuit 21 according to the output of the counter 30. This is to uniformly select and supply it to the frame memory 23. The counter 30 starts counting the reception clock output from the modulation circuit 21 from the rising edge of each scanning line of the reception tali signal, and during a period when the count value is less than, for example, several bits, the switching circuit 29 is switched to the modulation circuit 21. At the same time, the switching setting is made to the decoding circuit 22 side for the subsequent period.

With such a configuration, when transmission of an image signal is started, the switching circuit 17 switches to the frame memory 12 side according to the output of the counter 18 for a period of several bits from the rising edge of each scanning line of the image signal. has been switched to. Therefore, during this period, the D output from the frame memory 12
The PCM signal that has not been PCM encoded is supplied as is to the modulation circuit 14, modulated, and sent out to the transmission path 3.

On the other hand, in the receiving device [20], the switching circuit 29 is switched to the modulating circuit 31 side by the counter 30 for a period of several bits from the rising edge of each scanning line of the signal arriving from the transmitting device 10. Therefore, during the above period, instead of the output of the decoding circuit 22, the output signal from the modulation circuit 21, that is, D
The PCM signal that has not been PCM decoded is supplied to the frame memory 23, and subjected to image signal reproduction processing by the D/A converter 24.

Therefore, the rising portion of each scanning line of the image signal is the difference PC
The M signal is not subjected to any signal processing and is transmitted as a PCM signal, and as a result, there is no delay in the rising edge of the signal at the rising edge of the multi-scanning line. Therefore, even when the reproduced image signal is displayed on the image monitor device 4, the image will not be blurred at the left end of the screen, and as a result, a clear and accurate image without missing information can be displayed. .

Therefore, even if a plurality of reduced images are transmitted and displayed as one image, no scenery occurs at the boundary between each image, so that easy-to-see and accurate recognition can be performed. Also,
Even when the reproduced image signal is used for signal processing such as pattern recognition in addition to displaying it, accurate processing can be performed over the entire screen. Furthermore, since the part where the PCM signal is inserted instead of the DPCM signal is only a few bits, which is very short, the increase in the number of bits to be transmitted is small.
This does not reduce the advantages of the differential PCM transmission method. Furthermore, this embodiment has the advantage that it can be implemented with an extremely simple circuit that only includes a switching circuit and a counter for its replacement.

Note that the present invention is not limited to the above embodiments.

For example, another switch circuit such as a semiconductor switch circuit may be used as the switching circuit, and a microprocessor other than a counter may be used as the control circuit for the switching circuit. In addition, the number of inserted bits of the PCM signal, etc. can be modified in various ways without departing from the gist of the present invention.

〔Effect of the invention〕

As described in detail above, according to the present invention, when an image signal is differentially PGM encoded on the transmitting side, a predetermined bit of the PCM signal without DPCM encoding is used as it is at the rising edge of each scanning period of the image signal. The predetermined bits at the rising edge of each scanning period of the signal inserted and received and demodulated on the receiving side are used for signal reproduction as PCM signals without being subjected to DPCM decoding. It is possible to provide a differential PCM transmission method that can transmit high-quality signals by eliminating rise delays.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a system to which a differential PCM transmission method is applied in an embodiment of the present invention, and FIGS.
The figures are for explaining the conventional differential PCM transmission method. Fig. 2 is a block diagram of a system applying the same method, and Figs. 3 and 4 show the DPCM encoding circuit and DPCM decoding circuit, respectively. Block diagram showing the configuration, No. 5
Figures (a) and (b) are diagrams showing an example of the transmission waveform and reception reproduction waveform of the image signal, respectively, and Fig. 6 is a schematic diagram showing an example of the display state of the image signal. 3... Transmission line, 4... Image monitor device, 10...
Transmitting device, 11... A/D converter, 12... Frame memory, 13... Encoding circuit, 14... Modulation circuit, 15... Synchronization separation circuit, 16... Timing generation circuit , 17... switching circuit, 18... counter, 20
...Receiving device, 21...Demodulation circuit, 22...Decoding circuit, 23...Frame memory, 24...D/A
Converter, 25...Amplifier, 26...Clock generation circuit, 27...Synchronization signal generation circuit, 28...Timing generation circuit, 29...Switching circuit, 30...Counter.

Claims (1)

[Claims] In a differential PCM transmission method in which an image signal is differentially PCM encoded and transmitted, a PCM signal without differential PCM encoding of predetermined bits is directly inserted into the rising edge of each scanning period of the image signal in the transmitting device. and transmitting the signal as a PCM signal without performing differential PCM decoding on the predetermined bits of the rising portion of the received and demodulated signal at each rising edge of each scanning period of the received and demodulated signal in the receiving side device. 1. A differential PCM transmission system, characterized in that a means is provided, whereby a predetermined bit of a rising portion of a transmission signal is transmitted as a PCM signal.