SU788442A1 - Television signal coding device - Google Patents

Description

The invention relates to radio engineering and can be used for masked transmission of television images over open communication channels or in subscriber television.

A device for encoding television signals containing a polarity switch of the image signal, the control input of which is connected to the output of the code line generator, and the input of the code line generator is connected to the first output of the clock [1].

However, the known device has ^J 'a low degree of masking of transmitted image signals.

; The purpose of the invention is to increase (Degree #, masking the transmitted image signals.

To achieve this goal, a television signal coding device containing a polarity switch for the image signal, the control input of which is connected to the output of the code line generator, and the input of the code line generator is connected to the first output of the sync generator, is connected to it in series with 2 connected sampling devices, a sample polarity inverter and a low-pass filter, and also introduced a code generator of readings, and the second output of the synchro-generator of the torus is connected to the gating input of the sampler, a. the third output of the clock is connected to the input of the code sample generator, the output of which is connected to the control input of the inverter of the polarity of the samples, and the output of the polarity switch of the image signal is connected to the second input of the sampler.

The drawing shows a structural electrical diagram of the proposed device.

The television signal encoding device comprises a polarity switch 1 for the image signal, a sampler 2, an inverter 3 for polarity counts, a low pass filter 4, a code generator 5 lines, a clock 6, a code generator 7 samples.

The essence of the invention is that, in order to increase the degree of masking of transmitted images ·., Encoding blocks of the image in the direction of lines are introduced into the known device. In contrast to the known device 788442 country, in which one-dimensional encoding of the image across the lines is carried out, the proposed device performs two-dimensional encoding of the image along the lines and across the lines.

. The device operates as follows.

The original video signal is fed to the input of the image signal polarity switch 1, controlled by a 5-line code generator connected to the sync generator 6. In the image signal polarity switch 1, the polarity of a certain number of lines is changed in accordance with the code · generated by the 5-line code generator. From the output of the switch 4, the video signal is fed to the input of sampler 2, in which the samples of the video signal are taken with a frequency equal to or greater than twice the upper cutoff frequency of the spectrum of the source signal. From the output of sampler 2, the samples are sent to the input of the inverter 3 of the polarity of samples, controlled by a code generator of 7 samples connected to the clock 6. In the inverter 3 counts polarity

The coefficients of the series S (pbb) are equal to the value of the signal at the moments of sampling η l.

Physically members of the series

Sin 237 F e> (t - nat)

2. JTF (t - nat) are the responses of the low-pass filter with a cutoff frequency equal to F _B to the samples of the signal. The shape of the responses is described by the function to / Sin 2ίΓ Ρ - and d-t) n ^v 'TtfF ₆ (t - hat)' the amplitude of the responses is S (pdb).

Due to the fact that the response of the low-pass filter U to any sample of the signal is equal to the value of the signal at the moment of taking this sample and is equal to zero at time instants corresponding to other samples, the samples of the signal by changing the polarity of the transmitting side of the television system can be inverted according to the pseudo-random law for purposes. Masking transmitted images without loss of source information. Passing the inverted samples through a low-pass filter with a cutoff frequency of F _ft , we obtain a coded video signal from that video signal in accordance with the code generated by the code generator of 7 samples. From the inverter output 3 sample polarity samples of the video signal are fed to the input of the low pass filter> 4 with a cutoff frequency equal to the upper cutoff frequency of the video signal spectrum. In the low-pass filter 4, the analog form of the video signal is restored. From the output of the low-pass filter 4, the encoded analog video signal is output to the device. Sync generator b provides synchronous operation of a 5-line code generator, .2 sampler and 7 samples code generator.

The introduction to the known device of a discretizer, an inverter of polarity of samples, a low-pass filter for encoding a video signal inside the lines is based on the following. According to the Kotelnikov theorem, any analog signal S (t) / limited in spectrum by the highest frequency F _& can be represented as a series equal to the sum of linearly independent terms

Sln2Jt ~ ηδ-l)

ZiT-F _e (-t -nat) where ^x s

- signal duration;

- the interval between samples ^β signal.

View function

Sin 2.JT -ΠΔΦ)

7GSh (-t -Πd-t)

0 at the point t = nat is 1, and at the points c = K & t, where K is any positive or negative integer other than n, it is O '.

same spectral width as the original video signal. On the receiving side of the television system, samples of the encoded 3Q video signal are taken at the same instants of time as on the transmitting one, which will be identical to the inverted samples of the signal on the transmitting side. To restore the original video signal, the polarity of the samples is inverted according to the law opposite to the inversion (coding) law on the transmitting side, and a sequence of samples corresponding to the original video signal is passed through a low-pass filter with a cutoff frequency equal to F _g .

Since sampling results in the loss of most of the energy of the video signal after passing the samples through a low-pass filter, the resulting 'analog signal must be amplified' to the required amplitude.

Thus, the introduction of new elements (a sampler, an inverter of polarity of samples, a code generator of samples, a low-pass filter) distinguishes the proposed device from the known one because it increases the degree of maximized image because the number of elements of the code generated by the code generator of samples significantly more than the number of code elements generated by the code line generator in an equal time interval of 40 seconds.

Claims (1)

1. US patent 3,610,828, cl. 179-15, published. 05.10.71, (prototype),. - L / I