JPS5950682A - Video signal discriminator - Google Patents

Abstract

PURPOSE:To discriminate effectively a video signal, by comparing sequentially a digital video data at a sampling point, obtaining a digital difference signal and generating a discriminating signal when a value adding sequentially this signal exceeds a set value. CONSTITUTION:A video signal SV is transmitted to a clamp circuit 5 through a buffer amplifier 2 and led to a timing circuit 4 after synchronizing separation 3 and its output CP clamps the circuit 5. The output is A/D-converted 6 to obtain a digital video signal SD, and a data of the present field and that at preceding field are compared 9 to obtain a level difference signal, which is integrated 11 into a value SD0 and compared 12 with an output value of a set value generator 13. As a result, when the signal SD0 exceeds an output value of the generator 13, the signal SC is outputted to detect the change in the screen at an interval detecting circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image signal identification device, and particularly provides such a device suitable for use in detecting changes in a screen.

BACKGROUND TECHNOLOGY AND PROBLEMS Recently, scrambled broadcasting has been developed, in which a broadcasting station scrambles a television signal of a specific program and sends it out, allowing viewers who have a contract with the broadcasting station and have a decoder to view the specific program. system (or reservation television system) is being developed. In this system,
A signal obtained by scrambling a television signal of a specific program by, for example, inverting the polarity or changing the level in a predetermined period, or by changing the order of the signals in a predetermined period, and a key signal for decoding this scrambled signal. is transmitted from the broadcasting station. Therefore, even if this scrambled signal is received by a normal television receiver, the correct image and sound cannot be viewed. Then, only viewers who have signed a contract with the broadcasting station can use a decoder to restore (unscramble) the scrambled signal to its original form based on the above key signal and watch the correct image and sound of the program. I have to.

In such a scrambled broadcasting system, when the scrambled signal is received by normal reception (inlay), it is important to make the contents as hidden as possible.
Various scrambling methods have been proposed in addition to the methods described above.

In the above-described scrambling method of inverting the polarity or changing the level of a signal, specifically, the polarity of the video signal is inverted or the level is changed in a predetermined field period. However, with this method, if the scrambled signal is affected by distortion in the transmission system, it will not correctly return to its original waveform when unscrambled on the receiving side. For example, if a signal whose polarity has been inverted is inverted again by a decoder, a level difference will occur from the original waveform, or the waveform will be distorted. When this signal is applied to a receiver, flicker occurs at the polarity reversal portion. This flicker is particularly noticeable when the screen is close to a still image. Furthermore, when a scrambled broadcast program is recorded on a VTR, flicker is particularly likely to occur because the VTR has nonlinearity in both direct current and alternating current.

In order to solve this problem, the present applicant, for example,
According to No. 7-67809, when the contents of the screen change,
In other words, we proposed a method of scrambling when there is a scene change. According to this method, even if a signal unscrambled by a receiving side decoder is applied to a receiver, flicker occurs at the same time as a scene change, so flicker is not substantially felt.

Therefore, conventional scene change detection methods detect the average level of a video signal field by field, and recognize a scene change when this average level exceeds a predetermined threshold level. . Therefore, when the screen changes slightly or gradually, the average level of both does not change, so it is not detected as a scene change. On an actual television screen, such subtle changes or gradual changes often occur continuously, and for this reason, in the case of the scrambled broadcast described above, there is a long period during which scrambling cannot be performed. Therefore, if such a scrambled program is received by a normal television receiver, its contents will be distorted to some extent.

In the above-described scrambling method of inverting the polarity or changing the level of a signal, a pattern is formed by arbitrarily combining field periods to be scrambled and field periods not to be scrambled, and scrambling is performed using a crumple pattern. Therefore, in order to prevent anyone other than the subscriber from deciphering the scramble pattern, it is necessary to make the scramble pattern as complex as possible. However, the scene change described above is simpler and easier to decipher.

OBJECTS OF THE INVENTION The present invention provides a video signal identification device capable of identifying slight changes in a screen.

SUMMARY OF THE INVENTION The present invention involves sampling a video signal by a predetermined number of fields to form a plurality of digital video data, and sequentially comparing the digital video data at corresponding sampling points every n fields to generate a digital signal that shows a level difference. This video signal identification device sequentially adds the digital difference signals and generates a discrimination signal indicating a change in the screen of the video signal when the added output exceeds a set value.

Embodiment This embodiment is based on the above-mentioned television scramble system l.
In this case, a scene change signal SC is obtained by detecting a change in the screen. In this case, detection of screen changes is performed as follows.

Screen changes are detected field by field, and for this reason, 1
Set many sampling points on the field screen, and
The video signal of the field is sampled according to the sampling points, and this is A/D converted to obtain digital and video data.

First, the data of the current field and the data of the previous field are compared for each sampling point, and the level difference between them is determined. When the sum of the level differences exceeds the first set value, the signal SC is output.

Therefore, if the first set value is set to a small value, even a minute change in the screen, such as a slight movement of an object on the screen, can be detected as a scene change.

If the signal SC is not obtained for several field periods while the above comparison is being performed, a second set value smaller than the first set value is set. Then, when the sum of the level differences of each data exceeds the second set value, the signal S
Output C. Therefore, in this case, a screen change is detected whose degree of change is even smaller than when the comparison is performed using the first set value.

If the signal 80 is still not obtained for several field periods even after the comparison using the second set value, the sixth set value is still smaller.
The setting value is set, and the comparison is made in the same manner as described above, so that the signal 80 is obtained.

The above setting values may be set in several stages as necessary.

Even with the above third setting value, the signal SC still increases by several feet.
If there is no gain during the field period, switch the signal to be compared from the previous field to the signal several fields before (for example, four fields before), and compare the data of this few fields before with the data of the current field. to be accomplished. This comparison is performed based on the sixth set value. Therefore, in this case, it is detected that there has been a gradual screen change over several fields.

If the signal SC is still not heard for a long time even with the above method, for example, if the signal SO is not obtained for 8 seconds, the pseudo signal SO is forcibly output. In addition, if the signal SC is output frequently in the above-mentioned detection stage, for example, if the signal SC is output 5 times or more in 8 fields, the first stage, that is, the current field and the previous field, is immediately performed. The process returns to the step of comparing based on the first set value.

According to the above, the scene change signal SC can be obtained by automatically following a sudden screen change or a gradual screen change. Therefore, the scramble pattern described above can be made complex, and the secrecy of the transmitted scramble program can be increased. Also, for example, when a static screen continues for a long time, a pseudo signal S
Since o is obtained, it becomes possible to perform scrambling. Note that the detection method described above is merely an example, and the comparison method at each detection stage may be modified in various ways. For example, when comparing the current field with the previous field several fields, the set values may be changed sequentially.

Figure 1 shows an example of a video signal sampling method and a data comparison method.
The illustration corresponds to No. 11.

The screen (11 is divided into blocks of ■(. Therefore, 1
The number of lines in the block is 64. Sampling is 1
This is done using one line of the block as one sample point. For example, regarding blocks, the current field is IH in block ■.

3H, 5H......Each average value of the 65H line is sampled, and in the previous field (or several fields before), 2H and 4H in block ■.

6H......64 Each average value of the H line is sampled. These sampled values are converted into digital data. Sampling is similarly performed for blocks 1 to 0, and data is obtained.

When comparing each data, 1■ (and 2H, 3H and 4H
Each piece of data is compared,
Different levels are required for each. In this case, the comparison operation may be stopped and data processing may be performed during the 5H period. Similarly, data comparison is performed for blocks ① to 0, and differences are determined for each block. The total sum of the differences between the respective comparison data obtained in the following manner is determined, and this total sum is first compared with each of the first setting values. And the value of the above sum is the first
If the set value is exceeded, the signal SO is output. The sum total is also compared with the second and sixth set values according to the detection step described above. Note that the signal SC is output during the vertical blanking period between the current field and the next field.

FIG. 2 shows an embodiment of a video signal identification device according to the present invention based on the detection method described above.

In Figure 2, the normal video signal SV before being scrambled is sent to the buffer amplifier (2) and the sync separation circuit (3).
). The horizontal and vertical synchronization signals HD and VD separated by the synchronization separation circuit (3) drive the timing circuit (4). The timing circuit (4) receives the above signals HD and VD.
Various pulses, which will be described later, are formed and output at predetermined timings. On the other hand, the signal SV amplified to a predetermined level by the buffer amplifier (2) is sent to the clamp circuit (5).
In addition to this, the pedestal level is clamped to, for example, ground potential by a clamp pulse CP applied from a timing circuit (4). The level-clamped signal SV is converted into a digital signal by an A/D conversion circuit 161.

Note that the A/D conversion is performed using the sampling pulse SP from the timing circuit (4) based on the sampling method described in FIG. 1, and the valley sample values are digitized. Data for one field of this digital video signal SD is latched in a latch circuit +77. This latch circuit (7) is latched with a latch pulse LP obtained by delaying the pulse SP by a delay circuit (8). Data SD for one field obtained from the latch circuit (7) is applied to one terminal of the comparator (9) and
Written to QOI.

This R, A M QO) has a capacity of several fields,
Write clock pulse O from timing circuit (4)
It is written at a predetermined timing by KW, and read out at a predetermined timing by a read clock pulse OKR.

Data SD one field or several fields earlier read from this RAMQOI is applied to the other terminal of the comparator (9) and compared in level with the data SD. This comparison is made for each sample point according to the method described with respect to FIG. These comparison data ΔSD are integrated by the integration circuit -), and the total value SDo is calculated by the comparator G21.
is applied to one terminal of

A set value generation circuit (13) is connected to the other terminal of the comparator a21.
), the first set value S1 is first added and compared with the integrated value 8Do. Comparator u2 outputs a scene change signal SC when SDo>Sl.

Although not shown, this signal SC is applied to a subsequent scrambling device and used when scrambling the signal SV.

At the same time, the signal SO is added to the interval detection circuit 0,
The number of occurrences can be investigated.

That is, it is checked whether the signal SC was output during a period of several fields, whether it was detected five times in eight fields, whether it was detected for eight seconds, etc., and each detection signal ST1. ST
2. ST3 is output. These detection signals ST,5
T2ST3 controls the timing circuit (4) and the control circuit a9.

First, if the signal SO is not output for several field periods, the control circuit (15) controls the set value generating circuit (1 row) to change the set value to be applied to the comparator a2 from 81 to 82 (
However, it is changed to S2 (Sl). Furthermore, if the signal SC cannot be obtained for several fields, the set value is changed from 82 to 83 (however, Ss < 82). Furthermore, if the several field period signal SC is not obtained, the timing circuit (4) reads data SDn several fields before from the RAM port 0) and adds it to the comparator (9).

If the signal SC is detected five times in eight fields, the set value is returned to 81, and if and AMflol read the data SDn of one field before. If the signal So is not obtained even once in eight seconds, the comparator II2 outputs the pseudo signal SC. Incidentally, this pseudo signal SC is forced to be output by setting the set value to 0, for example.

Application Example The video signal identification device according to the present invention can be applied to, for example, a monitoring device using a television camera. In that case, the time interval detected by the interval detection circuit (I) will be, for example, several hours or longer.The set value etc. will be determined as appropriate depending on the situation.In addition, the sampling point may be changed, etc. This method can be applied to various uses.

Effects of the Invention Subtle changes and gradual changes in the video signal can be identified, and the degree of change to be identified can be freely set by changing the setting values as desired.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a television screen for explaining an example of the zumbling method, and FIG. 2 is a circuit block diagram showing an actual example of the present invention. In addition, in the numerals used in the drawings, (6)...
・・・・・・・・・・・・・・・A/D converter (9)・・
・・・・・・・・・・・・・・・Comparator (10)・・
・・・・・・・・・・・・・・・RAM0】)...
・・・・・・・・・・・・・・・・Integrator circuit 02)...
・・・・・・・・・・・・Comparator (13)・・・
・・・・・・・・・・・・・・・This is a set value generation circuit. Agent Masaru Doyo〃 Yoshio Tsunekako〃 Toshiki Sugiura 477-

Claims (1)

[Claims] The video signal is sampled a predetermined number of times in field units to form a plurality of digital video data, and the digital and video data at corresponding sampling points every n fields are sequentially compared to obtain a digital difference signal indicating a level difference. A video signal identification device that sequentially adds difference signals and generates a discrimination signal indicating a change in the screen of the video signal when the added output exceeds a set value.