SU965016A1 - Television signal filtering device - Google Patents

Description

Image is a communication technique and is intended to reduce the level of noise in a video signal of a rasterized image.

A video filtering device is known, comprising a filtering unit, the input of which is input by the device and combined with the inputs of the duration selector and the edge selector, the inputs of which are combined and connected to the control input of the filtration unit 1.

The disadvantage of this device. There is a low noise immunity of the control pulse selection circuit arriving at the key / included in the filtering unit.

It is also known to have a television signal filtering system comprising an adaptive filtering unit consisting of a low-pass filter, a subtracting element, a key and an adder, a differentiating circuit, an inverter, two threshold elements, and a pulse width selector 2.

A disadvantage of the known device is the low noise immunity of the formation of control caching pulses applied to the control input of the key in the adaptive filtering unit.

which reduces the filtration accuracy due to the filtering off during the passage of noise emissions exceeding the trigger level of the threshold element.

The purpose of the invention is to improve the accuracy of filtering television signal.

The goal is achieved by those; that a television signal filtering device containing an adaptive filtering unit, the information input of which is the device input, a differentiating circuit and two threshold elements, whose outputs are combined and connected to the control input of the adaptive filtering unit, is introduced an additional differentiating circuit; and low-pass filters, the first shaper module of the derivative and the first low-pass filter are connected in series and connected between the output of the differential chaining

25 and the input of the first threshold element, and the second low-pass filter, whose input is combined with the input of the differentiating circuit and connected to the input of the device, an additional differential circuit and the second driver of the derived module are connected sequentially and connected to the input of the second threshold element. Fig. 1 shows a structural electric circuit of a television signal filtering device; figure 2 - timing charts of the device. ". The device contains a block; adaptive filtering 1 (Fig. 1), differentiating circuit 2, additional differentiating circuit 3, modifiers of the derivative module 4 and 5, low-pass filters 6 and 7, threshold elements 8 and 9, and the adaptive fi unit of section 1 can, for example, consist of low pass filter 10, delay 11 and switch 12., Figure 2 shows the time diagram of the device where a) A (t) is a fragment of the original television signal; b) A (t) signal at the output of the low pass filter 7; c) AMt) derivative of the signal at the output of the first differentiating circuit 2; F) ACt) is the derivative of the filtered signal on you. during the second differential. run chain 3; d) D (I) - the module of the derivative signal at the output of the imaging device 4; e) A (t) is the modulus of the derivative of the filtered signal at the output of the driver 5; g) A (t) the filtered signal at the input of the first threshold element 8; h) (l (t)) - control signal at the control input of adaptive filtering block 1 ;. and) A (t) is the television output of the device. . The device works as follows. The input television signal (Fig. 2 &) is fed to the information entry of the adaptive filtering unit 1 and the outputs of the differentiating circuit 2 and the second low-pass filter 7 (LPF). The output signals of the low-pass filter 7 (Fig. 26) and the differential circuit 2 (Fig. 2c) are fed to an additional differentiating circuit 3, respectively, and the first, the former of the module of the derivative 4. The output signals of an additional differentiating circuit 3 (Fig. 2 g) and the first generator of the module of the derivative 4 (Fig. 23) receives, respectively, the second module of the derivative 5 and the first LPF output signals of which (Fig. 2e and.) arrive at the threshold elements 9 and 8, respectively. Threshold elements 8 and 9 form a control signals during periods of excess input signal element of the threshold level, which is shown in Fig. 2e by the dotted line. The output signals of the threshold elements 8 and 9 are combined (phi 2z) and are fed to the control input of the adaptive filtering unit 1. Unit 1 adaptive filtering works as follows. The input signal through the low-pass filter 10 and the delay element 11 is fed to the switch 12. The control input of the switch 12- (control input of the unit 1) receives the output signals of the threshold elements 8- and 9 (fig.2z). In the interval where the control signal Q has a low level, switch 12 provides a signal from the low-pass filter 10 to the device’s output, and in the interval where the control signal Q has a high level, switch 12 sends a signal from the delay element 11 to the output of the device, which takes into account Due to the TV signal in the low-pass filter 10. Thus, the output signal of the filtering device (Fig. 2i) is not filtered only on the interval of the fronts (decays), single pulses and groups of pulses. Optimum operation is ensured at the same output or close parameters of the LPF 6, 7 and 10i Constantly, the time of the differentiating circuit 3 is chosen longer (approximately 2-3 times) of the constant time of the differentiating circuit 2. 1 The detection of groups of pulses is performed in the first channel consisting of elements 2, 4 , b and 8. In the second channel, consisting of elements 7.3, 5 and 9, there are fronts (decays) and single pulses. The groups of pulses in the second channel cannot be detected, since the low-pass filter 7 attenuates the high-frequency spectrum of the signal together with the noise of the former 4. Low-pass filters 6 and 7 attenuate the level of high-frequency noise in front of threshold elements 8 and 9 and thereby increase the noise immunity of the formation of control pulses. An improvement in the quality of the color television image is observed due to the fact that the energy spectrum of the high-frequency noise when decoding color-difference signals is transported to the low-frequency region and becomes well noticeable. Therefore, the application of the proposed image-most appropriate in color television. Thus, the feasibility of the proposed device is to improve the quality of the reproduced television image, especially color, to reduce the required nominal level of illumination on the object.

Claims (2)

1. Authors certificate of the USSR 439942, cl. H 04 N 5/14, 1972. 2. USSR author's certificate  614552, class H 04 H 5/14, 1976 (prototype). fug. g