How to recognize advertising in a television signal. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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The proposed article touches on a sore subject - annoying advertisements on the TV screen that irritate many viewers. We present it to the readers without commenting on the legal and economic aspects of the problem, the possibility of technical implementation, and most importantly, the effectiveness of the proposed technical solution.

The whole problem of automatic recognition of advertising in a television signal is the correct choice of the sign of its presence. I suggest taking the most obvious one. In one of the corners of the frame on the screen of the TV receiver there is always an emblem (logo) of the broadcasting company. Almost always... During the demonstration of advertising, it is not. This is the rule we use. However, from it, as from any other, there are exceptions: sometimes the emblem remains on the screen during the advertising of feature films, sometimes it disappears when the ads are transmitted by a "creeping line". Alas, all exceptions will have to be taken into account when developing and improving the algorithm of the device. Algorithms for recognizing emblems of various types will also have their own characteristics: opaque white (as, for example, with Vostok-TV), translucent white (as with Channel One), opaque white with black edging (as with Ren-TV "), multicolor (like NTV). There are emblems with other important features for recognition.

The algorithm is based on the observation of the color of several characteristic points of the image inside the emblem and outside it. The term "color" is used here in a broad sense. In the simplest case, it is sufficient to analyze only the brightness of selected points. It is very important to choose the right number and location in the frame. The more points, the more reliable the recognition, but the higher the computational costs.

To recognize an opaque emblem, it is enough to make sure that the color of only a few dots inside it matches the standard. In this regard, emblems with black edging are very "convenient", the signal level of which coincides with the black level, which is almost never found in artistic shots. To detect a translucent logo that can be considered part of the main image with reduced contrast and increased brightness, you will have to monitor the color of the dots lying both inside and outside it.

It is possible to ensure high reliability of recognition, including in the presence of noise, using statistical methods. To do this, it is necessary to analyze the signals in several adjacent lines or consecutive image frames with subsequent averaging of the results.

Let pij be a feature of detecting an emblem in a television frame i based on the analysis result of point j. Its value 1 corresponds to the absence, and 0 - the presence of advertising. The decision is made by comparing the instantaneous value of the video signal Yij at a given point in a given frame with an exemplary Y0j corresponding to a "clean" emblem. If |Yij-Y0j|<Δj, pij=1, otherwise рij = 0. The larger Δj, (permissible deviation from the sample at a given point), the more likely the logo on the screen will not be missed, however, the more likely and erroneous detection of a missing emblem. After analyzing n points in each of the k frames, the average value of the sign P is calculated by the formula

The coefficients Wij take into account the comparative "weight" of the contribution of each analyzed point to the final result. The final decision is made by comparing the obtained value of P with the threshold P0.

As you can see, the proposed procedure has a large number of parameters, varying which, you can achieve the desired result. Optimal values ​​are chosen both on the basis of theoretical calculations and experimentally, providing for all kinds of adjustments in the recognition device. Some of them are performed manually, others - automatically, compensating, for example, for changes in the average brightness or color tone of the television image.

In the most general form, the block diagram of the ad detector is shown in the figure. Counters of rows and image elements in a row allow you to determine the time points corresponding to the analyzed points. The oscillator pulses with a frequency of 6,5 MHz, which are counted by the element counter, simultaneously serve as triggers for the ADC, which converts the analog television signal into digital form. In fact, there can be several converters - for each of the color components of the video signal. Vertical and horizontal sync reset the corresponding counters.

If the current line and element numbers match the given ones (received from the controller), the comparison node generates a pulse to write the current ADC reading to the storage register. The same pulse serves as an interrupt request, upon receiving which, the controller sends the coordinates of the next control point to the comparison node, then reads the code from the register and analyzes it. The speed of the controller should be sufficient to process all control points according to the algorithm in 20 ms - the duration of a television half-frame.

If the advertisement is recognized (there is no logo), the controller instructs the channel selector of the TV receiver to switch to another program, supposedly free of advertisements. If it is present here too, the next program will be included and so on until the last one received. The enumeration sequence must be included in the algorithm. The return to the original program, the viewing of which was interrupted by advertising, will occur after a user-specified time, sufficient, in his opinion, to complete the "advertising break".

The latter is the greatest drawback of the considered device, which cannot be eliminated without a second TV receiver. It can only consist of a channel selector and a signal processing unit, there is no need for scanning nodes and a kinescope, but it must be equipped with a set of advertising recognition tools similar to those discussed above. With a sufficient supply of computing power, the controller of the two recognition channels can be shared.

The second receiver solves two problems. As long as the program viewed by the first receiver is not interrupted by advertisements, the second periodically analyzes the others, choosing the one suitable for viewing after switching. After the transition of the first receiver to the backup program, the second one analyzes the original one, determining the moment of the end of the ad block, and then issues a return command.

I really hope that the development of such a device will be of interest to radio amateurs.

Author: V.Pelis, Khabarovsk

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