JPS6249795B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a video reporting device using a baseband transmission method.

[Background Art] In a society where information has become increasingly diverse in recent years, the development of information systems in buildings, apartments, homes, etc. has been remarkable. In particular, CATV systems,
Security systems using video such as TV intercoms and monitor TVs are rapidly becoming widespread, and various video reporting devices have been provided for this purpose. That is, coaxial cable 2
The video reporting system that combines the TV camera 1 and monitor TV receiver 3 using
It is not suitable for complex systems that require multiple branches and distributions or for long-distance transmission because it does not have a distributor and the high frequency range of the transmitted signal decreases as the transmission distance increases, degrading the image quality. . However, CATV
It is often used for simple systems and short-distance transmission because it is inexpensive because it does not require a modulator/demodulator, and it saves wires by superimposing the power supply on the coaxial cable. .

In more detail, regarding the baseband transmission method, as mentioned above, in this baseband transmission method, as the transmission distance of the video signal increases, the high frequency components of the transmission signal decrease due to the influence of the distributed constant of the coaxial cable 2. However, there is a problem in that the sharpness of the image is substantially reduced. FIG. 2 shows the video signal frequency characteristics at this time. Video signals consist of frequency components from 60KHz to 4MHz, so they usually range from 60KHz to 3.5MHz as shown in a in the same figure.
However, as the transmission distance becomes longer, the high-frequency components deteriorate as shown in FIG. Therefore, in order to compensate for this, a method is generally used in which the level of the high frequency component is raised in advance and transmitted, as shown in d in the same figure. By doing this, specifically, preshoot and overshoot are added to the step response waveform of the video signal as shown in Fig. 3A.
The contours are emphasized and the sharpness is substantially increased.
However, it is believed that if the degree of edge enhancement is too large, the image will be too sharp and cause visual discomfort, so it is usually necessary to keep the preshoot and overshot below 10%. Note that in FIG. 3, B shows a normal waveform, and C shows a waveform with degraded high frequency components.
For this reason, conventional video reporting devices that fixed the degree of edge enhancement had the problem that depending on the transmission distance, the images could become blurry or too sharp, making it impossible to always obtain high-quality images. . In addition, even in a video reporting device with contour enhancement adjustment developed to compensate for this problem, depending on the transmission distance from the TV camera 1 to the monitor TV receiver 3 during construction,
There was a problem in that the degree of contour enhancement had to be set each time.

[Object of the Invention] The present invention was provided in order to solve the above-mentioned problems, and it is possible to automatically perform contour compensation according to the transmission distance, and to provide an inexpensive system using a baseband transmission method. The object of the present invention is to provide a video reporting device that can be configured as follows.

[Disclosure of the invention] In a normal video reporting device, the characteristic impedance of the video signal sending section is 75% of the coaxial cable 2.
Ω, but if the matching is shifted in a frequency band higher than the video signal frequency (for example, around 10 MHz), the image as shown in Figure 4a will appear due to reflections caused by this shift in impedance matching. Pulse noise occurs within the horizontal synchronization signal as shown in FIG. The time Δt until this pulse noise occurs is the coaxial cable 2
As the transmission distance increases,
In the present invention, by detecting the timing at which this pulse noise occurs, the transmission distance can be ascertained, and the degree of edge enhancement can be controlled. Note that matching is made to 75Ω in the frequency component band of the video signal, and since the pulse noise mentioned above is a frequency component in a higher range than the video signal component, it does not affect the video in any way.

An embodiment of the present invention will be described below. Fifth
The figure is a block diagram of one embodiment of the present invention, and 1 in the figure is
TV camera, 2 is coaxial cable, 3 is monitor TV
In the image receiver, numeral 4 indicates an edge enhancement adjustment circuit, and numeral 5 indicates a pulse noise detection circuit. Further, FIG. 6 shows a specific circuit example of the above-mentioned contour emphasis adjustment circuit 4 and pulse noise detection circuit 5. 4 in the figure is an outline enhancement adjustment circuit, which obtains the second-order differential waveform of the TV camera 1 output by the inductance Lo connected to the collector of the transistor Tr and the capacitor Co, which is connected to the resistor R. ₁ , _R2
Divide the pressure at and obtain the output of ~. At this position, a step response waveform with large preshoot and overshoot levels is obtained, at the position, a similar waveform with a lower level than in the above case is obtained, and at another position, a response waveform with no waveform distortion is obtained. It is designed so that you can get Therefore, by controlling the output waveforms from these positions with analog switches SW ₁ , SW ₂ , and SW ₃ , the transmission distances are divided into long, medium, and short distances and are output. Next, 5 in the figure is a pulse noise detection circuit, which sets the reference voltage V _th slightly above the horizontal synchronizing signal level as shown in Figure 7, and uses it as the reference voltage input to the two comparators 6 and 7. As a result, the falling edge of the horizontal synchronizing signal and the rising edge due to the pulse noise are respectively detected and inputted to the flip-flop 8 to obtain a Q output corresponding to the pulse noise generation time Δt. Therefore, this Q output is further passed through an operational amplifier 9, and then the capacitor _C1 is charged with the output of this operational amplifier 9. Therefore, the input voltages to the comparators 10, 11, and 12 to which the reference voltages V ₁ , V ₂ , and V ₃ are respectively set in advance increase linearly. Therefore, these comparators 10, 11, 12 are
The final voltage Vc of this linearly changing input voltage is compared with the respective reference voltages V ₁ , V ₂ , V ₃ , and the inverters 13 and 14 and the AND gates 15 and 16
The combinational circuit turns on analog switch SW ₁ when Vc > V ₁ , and when V ₁ Vc > V ₂ , V ₂
For VcV ₃ , each analog switch
SW ₂ and SW ₃ are turned on, and the contour enhancement adjustment circuit 4 is controlled.

[Effects of the Invention] Since the present invention is configured as described above, the degree of contour enhancement can be automatically adjusted according to the transmission distance of the video signal by the coaxial cable, and adjustment at the time of construction is facilitated. This has the effect of allowing you to always see a clear image despite the fact that it is

[Brief explanation of the drawing]

Fig. 1 is a basic system configuration diagram of a conventional example, Fig. 2 is a video signal frequency characteristic diagram, and Fig. 3 A to C are waveform diagrams during high frequency component compensation, normal operation, and high frequency component degradation, respectively. , Figures 4a and 4b are enlarged waveform diagrams of the video signal and its horizontal synchronizing signal portion, respectively, Figure 5 is a block diagram of an embodiment of the present invention, and Figure 6 is the same contour enhancement adjustment circuit and pulse noise detection as above. 7 is an explanatory diagram of the same operation as above, 1 is a TV camera, 2 is a coaxial cable, 3 is a monitor TV receiver, 4 is an outline enhancement adjustment circuit, and 5 is a diagram of a specific circuit example of the circuit section.
is a pulse noise detection circuit.

Claims (1)

[Claims] 1. In a video reporting device that transmits a video signal from a TV camera to a monitor TV receiver via a coaxial cable using a baseband transmission method, by shifting the impedance matching of the video signal transmitter to the above coaxial cable at high frequencies. , a pulse noise detection circuit that detects pulse noise that occurs in the horizontal synchronization signal, and a contour that uses this pulse noise detection circuit to grasp the transmission distance by the coaxial cable and automatically adjust and compensate the clarity according to the transmission distance. A video reporting device comprising: an emphasis adjustment circuit.