JPS6384282A - Video scrambling system - Google Patents

Abstract

PURPOSE:To contrive to prevent the degradation in quality of descrambled pictures by setting a cut point to be the reference time of time base processing in a feedback period in case of the time base processing of a video signal to be scrambled. CONSTITUTION:The video signal to be scrambled is inputted to a synchronizing signal separating circuit 20 for the purpose of performing the time base processing and has horizontal and vertical synchronizing signals separated and is applied to a timing signal generator 21, and a timing signal is outputted from the generator 21. The video signal which is inputted to an A/D converter 10 and is converted to a digital quantity is written in a picture memory 30 for the purpose of performing video scrambling based on the time base processing. In case the read address of the memory 30 is controlled to perform video scrambling based on the time base processing, the cut point is provided in the feedback period to reduce the influence of nonlinear distortion, thus preventing the degradation in quality of descrambled pictures. a: video signal, b: audio signal, 22: W address counter, 31,32: 1H memory, 51: sample number latch circuit, 52: initial data, c: latch circuit, 26: decoder, 63: transmission data processing, 64: interleaving, 42: preemphasis, 44: FM modulation.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a video scrambling method, and in particular to a video scrambling method that divides a video signal into a plurality of parts within a scanning line and performs time axis processing. The present invention relates to a video scrambling method that causes less image deterioration when the processed data is descrambled.

(Prior Art) In paid broadcasting, program images are provided only to subscribers who have subscribed, and processing such as video scrambling is applied to subscribers who have not subscribed. For this reason, paid broadcasting is required to satisfy both portability for non-subscribers and image reproducibility to prevent deterioration of descrambled images for subscribers.

As an example of time axis processing in video scrambling, there is a so-called line rotation method in which a video signal is A/D converted, divided into a plurality of parts, and the divided pixels are temporally replaced and D/A converted.

The video scramble signal generated by this line rotation is susceptible to non-linear distortion caused by amplifiers, RF frequency converters, etc., and when descrambled by time-axis processing, the image appears at the cut point (image dividing point for one horizontal scanning period). Deterioration is noticeable.

FIG. 4 is a waveform diagram showing signal processing in a conventional video scrambling method using line rotation.

In the figure, (a) shows the original video signal. The cut point CP for performing line rotation on this original signal is set at time t2.

Time t1-t2. The picture signals from t2 to t3 are subjected to time-axis processing on the encoder side, and the original signals are converted into scrambled signals shown in (b).

In the scrambled signal shown in FIG. 4(b), distortion occurs in the signal near the cut point due to nonlinear distortion of the amplifier itself and distortion of the transmission system. These distortions are called line tilts and are mainly caused by deterioration of DC (differential gain) characteristics.

FIG. 4(C) shows a video signal waveform obtained by descrambling the scrambled image signal shown in FIG. 4(b). As can be seen from the figure, the video signal gain characteristics deteriorate near the cut point due to the influence of line tilt. This deterioration in the gain characteristics for the descrambled signal affects all horizontal scanning lines that have been scrambled by line rotation.

As a result, in the reproduced image obtained by performing descrambling processing on a video signal that has been subjected to video scrambling processing using line rotation processing, a brightness level change occurs at the cut point of the relevant line, and noise occurs in the entire image. .

As described above, in the conventional pay broadcasting system based on time axis processing, the descrambled image deteriorates, causing problems in terms of system operation.

(Problems to be Solved by the Invention) This invention has been made in view of the above points, and in a video scrambling method that involves time axis processing, the deterioration of the descrambled image is caused by waveform distortion etc. An object of the present invention is to provide a video scrambling method that can prevent deterioration.

[Structure of the Invention] (Means for Solving the Problems) In the video scrambling method according to the present invention, when performing time axis processing on a video signal to be scrambled,
A cut point, which is the base time for time axis processing, is set within the retrace period.

Further, in order to enhance the confidentiality of the video, substantial reverse scanning processing is performed on the signal during the picture period as necessary.

(Function) In the present invention, by setting the base point of time axis processing for the video signal within the retrace period, image deterioration of the descrambled image is prevented and the influence of nonlinear distortion is prevented.

FIG. 1 is a circuit diagram showing the encoder side of the video scrambling method according to the present invention, in which a reverse scanning method is adopted as video scrambling processing, and if necessary, cut points are used to prevent deterioration of the video signal for the picture. In order to do this, a cut point is set in the retrace period to prevent deterioration of the descrambled image.

Furthermore, the configuration is such that scrambling effects and the like can be controlled by setting multiple modes of address random number control for the image memory during time axis processing.

In Fig. 1, the input terminal IN to be scrambled is
The video signal applied to the
The converter 10 converts it into a digital value. This A/D
The conversion timing of the converter is determined in consideration of the image quality of the descrambled image. Usually, the frequency satisfies the Nyquist interval, and for example, the frequency of 4f (f: color subcarrier frequency) sc sc is selected. A synchronization separation circuit 20 separates a horizontal synchronization signal f and a vertical synchronization signal f, and applies the signals to a timing generation circuit 21 that generates various predetermined timing signals. Here, various timing signals necessary for scrambling the A/D converted original video signal are generated.

The video signal, which is converted into a digital signal by the A/D converter 10 according to the timing of the timing generator 21, is written into the image memory 30 for video scrambling by time axis processing. This image memory 30
consists of line memories 31 and 32 for storing and processing video sample signals for one horizontal period, and the addresses and the like of both line memories are controlled so that writing and reading operations are performed in a complementary manner.

Video scrambling by time axis processing is essentially performed by address control of the write address or read address of the video data to the image memory. In this embodiment, an example will be described in which video scrambling is performed by time axis processing by controlling the read address.

In video scrambling using line rotation, which is a form of time axis processing, if a cut point (video division point) is set within the scanning period, the descrambled image will deteriorate due to line tilt, etc., as described above. be.

In order to deal with this problem, the present invention sets a cut point during the flyback period and performs video scrambling to prevent deterioration of the reproduced image after descrambling.

FIG. 2 is a waveform diagram showing signal processing for video scrambling in an embodiment of the video scrambling method according to the present invention, and FIG. 2(a) shows an original video signal to be scrambled. The cut point for this original video signal is set at the position of time t of the front porch portion during the horizontal retrace period.

(CP) That is, the original video signal data shown in FIG. 2(a) is once stored in the line memory 31 of the image memory 30, and when reading the written data, it is read out in the order shown in FIG. 2(b). Performs read address control. Therefore, the video scrambled signal becomes the signal shown in FIG. 2(b), and this signal is sent to the decoder side via the D/A converter 40. In this case, line tilt due to encoder/decoder amplifier distortion, transmission system distortion, etc.
The video scramble signal will receive G distortion. The effect of this distortion is shown by the broken line in FIG.

In fact, even if the transmitted video scramble signal is distorted as shown by the broken line in FIG. When descrambling is performed under the reverse control, the descrambled signal shown in FIG. 2(C) is obtained. As can be seen from the figure, the portions that are subject to distortion due to line tilt are only the portions near the cut point, and the descrambled video signal for the transmitted image has no distortion due to the scrambling process. Further, in FIG. 2, the signal portion indicated by diagonal lines is the horizontal retrace period, and is not used as a descrambled image. In addition, non-contractors are shown in Figure 2 (b) (t(H
A signal whose time axis has been processed by pt+) is received, and as will be described later, the cut point cannot be deciphered and the descrambling operation is prohibited, making it impossible to obtain a normal reproduced image. In this case, the movability with respect to the image is enhanced by randomly changing the positions of the cut points.

Furthermore, in the pay broadcasting system, it is necessary to satisfy both of the requirements of portability due to video scrambling and prevention of image quality deterioration of descrambled images. In the present invention, in order to prevent image quality deterioration of the descrambled image, the cut point is set in the horizontal retrace period to improve the playback image quality, and furthermore, the position of the cut point is randomly controlled within the retrace period. This increases portability.

The movement of the cut point can be controlled by, for example, once writing image data corresponding to the original signal into the image memory 30, reading it out at the time of reading, and controlling the address. Further, write address control may be performed when writing to the image memory 30, and sequential reading may be performed when reading image data. In this embodiment, an example will be shown in which address control is performed when reading image data and cut points are randomly controlled.

In FIG. 1, a timing signal generator 21 generates a timing signal such as 4f (f, color subcarrier sc sc transmission frequency) necessary for processing image data using a synchronization signal separated by a synchronization separation circuit 20. do. Above A/
The image data converted into digital quantity by the D converter 10 is
The data is written into the image memory 30 in response to the output value of the write address counter 22, which is driven by a clock corresponding to the data sampling frequency and continues to sequentially count up up to the maximum sample value.

The image memory 30 is composed of line counters of line memories 31 and 32, and when image data is written in one line memory, the changeover switch SW is set so that data can be read out from the other line memory.
I, SW2 are provided. Therefore, the line memories 31 and 32 write and read data in a complementary manner. This complementary operation of data is switched by the CPU.
According to the control of 50.

Next, the operation when reading out the image data written in the image memory 30 will be described.

When reading image data, the cut points are randomly controlled, and confidentiality effect control is performed to reverse the increase/decrease in address values in order to perform reverse scanning as necessary.

First, to describe the operation of randomly controlling the movement of a cut point set during the horizontal retrace period, for example, the random control for the cut point is performed by controlling the read address by a read address control section according to a random number generated by the random number generator 24. This is done by

The random number generator 24 determines the position of the cut point during the horizontal retrace period shown in FIG. 2 at the beginning of the rung (tcp-
Reading of image data from the image memory 30 is stopped for a time of t+), and the start of reading of picture data is substantially delayed by (tcp-tl). Furthermore, this amount of delay changes depending on the random number value generated by the random number generator 24.

The random number generator 24 is configured, for example, by a cyclic shift register so as to generate random numbers based on M-sequence codes. The maximum value of the delay time is set to R, for example.

In this case, the random number generator 24 generates random numbers at R clock cycles. Therefore, the cut point is randomly changed and controlled every horizontal period.

The random number generation sequence of the random number generator 24 may be based on, for example, an M-sequence code, or the secrecy may be compromised if the sequence is known. To counter this, the initial value data for the random number generator 24 may be changed to initial value data. Generator 5
Occurs in 2. At this time, the initial data is used as key data and transmitted to the decoder side, but in order to increase confidentiality, the key data is transmitted in a concealed state using a layered configuration by the CPU 50.

The image data read out from the image memory 30 can be processed by the device by performing so-called reverse scanning in which the order of image reading is reversed, in addition to the pattern data readout start delay control corresponding to the cut point set within the horizontal period. can be carried out.

The video scrambling process based on the read address control by the read address control section 23 will be explained with reference to the timing chart shown in the third screen.

First, the CPU 50 in FIG. 1 sets the sampling rate for the video signal, and sets the driving frequencies for the A/D converter 10, the D/A converter 40, the write address counter 22, and the read address control section. be done. When this driving frequency is set, the number of samples P for the picture period is inevitably determined. Then, this sample number P is latched by the sample number latch circuit 51.

Further, the read address control section 23 is composed of an up/down counter 25, a decoder 26, and an inverter 27, and the up/down counter 25 has a U/D terminal for controlling up-counting or down-counting, and a clock to be counted. The clock terminal is input manually, the R terminal is used to reset the count value, the Ps terminal is input with the preset value, the LD terminal is applied with the timing pulse to load the preset value, and the Q terminal is used to output the count value. do.

The picture period sample number P latched by the sample number latch circuit 51 is loaded into the PS terminal of this up/down counter. Before this loading operation, the up/down counter 25 is reset at the rising edge of the f11 pulse (FIG. 3(b)) near the trailing edge of the horizontal retrace signal (HBI) (FIG. 3(a)), and the inverter 27 is At the falling edge of the same pulse, the preset value is loaded into the up/down counter 23. Thereafter, the up/down counter 25 sequentially counts up the clock pulse (4f) applied to the clock terminal CK by the C order, with P as the initial value.

This up-counting operation converts the clock pulse to a random number R
Continue until the count is reached. Here, the above counter 2
The decoder 26 detects whether clock pulses have been counted for R clocks from the initial value P. The decoder 26 has a function of determining whether the random number generated by the random number generator 24 and the count value of the counter are equal. If it is determined that they are equal, the counter 25 is cleared ( time ts).

Here, the initial value is P, and the time required to count clock pulses by R clocks is as follows.
It is not read out from 0, and as a result, the picture data readout start time is delayed by the time (ts-to) as shown in FIG.

The counter 25, which has been cleared by the signal from the decoder 26, continues counting again, and the output is "
Continue counting from 0'' to rPJ.

The decoder 26 detects that the counter 25 mentioned above has reached the random value R, and also detects that the counter 25 has reached the random value R.
It has a function of detecting that the output value of becomes P, and once clears the counter 25. After this second clearing operation, the cut point address value (P+R) is loaded into the counter 25 from the adder 28 by a clock pulse immediately after time tcP. This clearing operation and loading operation are performed by controlling the switch SWO under the control of the CPU 50.

Then, address value (P+R
) is loaded with a count value of N.
The counting operation continues until . When the count value reaches N, the counter 25 is cleared.

As a result, when reading image data from the image memory 30, the read address control unit 23 sets a cut point during the horizontal retrace period, and the delay time corresponds to the random number generated by the random number generator 24. This makes it possible to read out picture data.

In this way, the image memory 3 follows the read address controlled by the read address control section 23.
Image data is read from 0. At this time, the picture period of the image data read from the image memory 30 is delayed and changed, and the amount of delay is controlled randomly for each horizontal line by the operation of the random number generator 24, thereby improving device performance.

Furthermore, in order to increase the portability of the video scrambling operation, the counting operation of the up/down counter 25 is randomly switched between up counting and down counting for each predetermined line.

That is, the mode in which the up-down counter 25 performs an up-counting operation is equivalent to forward scanning, and as described above, the picture scanning period is delayed by the number of samples of the predetermined random value. On the other hand, the down-count operation mode is equivalent to reverse scanning, and the start point of picture scanning in this reverse scanning state is delayed and controlled in accordance with the random number generated by the random number generator 24.

Here, in order to randomly control whether the up/down counter 25 is made to count up or count down, U
The data to the /D terminal may be controlled, but either the MSB or LSB bit of the random number generated by the random number generator 24 is detected and applied to the Kouki U/D terminal according to this detected bit data. Data may be controlled.

Also, depending on the operating form of pay broadcasting, it may be necessary to ease the degree of video scrambling to encourage subscriptions, but in response to this request, for example, The pairing can be achieved by controlling the second CPU 50i to stop the clock to the up/down counter 25 and to set its output value to "0".

Furthermore, in order to control the movement of the above-mentioned cut points, in order not to damage the horizontal synchronization signal and burst signal, and to maintain device performance, the cut points should be set independently for the front porch, back porch, and back porch. Just set it up.

The video signal scrambled when reading the image data from the image memory 30 as described above is converted into an analog signal by the D/A converter 40.

After the scrambled baseband video signal passes through a low-pass filter 41, a pre-emphasis circuit 42 performs pre-emphasis processing for FM modulation. Then, the scrambled video signal subjected to time axis processing is subjected to FM modulation by an FM modulator 44 via an adder 43.

On the other hand, the audio signal is converted into a digital signal by an A/D converter 61 via a low-pass filter 60 and then applied to a multiplexer 62 . This multiplexer 62 supplies data corresponding to the initial value data generated by the initial value data generator 52 necessary for descrambling the video signal scrambled by the time axis processing from the transmission data processing circuit 63 to the subscriber who has the contract. Switching control is performed between the data necessary for controlling the above digital audio data and the like.

These data are interleaved by an interleave circuit 64 and then modulated by a QPSK modulator 65, for example. This modulated signal is then added to the adder 43 via the bandpass filter 66 and sent to the decoder side.

On the decoder side, only the contract subscriber can decode the initial value data for the random number generator 24 in FIG. By providing a random number generator with the same sequence as the random number generator, a random number value R, which is a parameter indicating a cut point, is decoded.

By adding this random value R to an address control section corresponding to the read address control section 23 provided on the encoder side, video descrambling can be achieved. This video descrambling operation based on address control is a descrambling process for video signals that have been scrambled according to time axis processing, regardless of whether image data is written to or read from the image memory provided on the decoder side. can be done.

(Effects of the Invention) As described above, in the video scrambling method according to the present invention, the cut point is set during the retrace period, so that the picture signal can reduce the influence of non-linear distortion due to line tilt, which is typified by transmission system distortion. , it is possible to prevent deterioration of the image quality of descrambled video.

Furthermore, video scrambling processing can be performed by substantial reverse scanning, and the degree of confidentiality of images can be improved as necessary without deteriorating the image quality of the descrambled images.

Note that when a cut point is provided, it may be provided not only during the horizontal retrace period but also during the vertical retrace period. In this case, a field memory is required as the image memory.

Furthermore, even when controlling the writing or reading address to the image memory to perform substantial reverse scanning,
Reverse scanning may be performed for one line, or may be performed for one field using a field memory.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the video scrambling method according to the present invention, FIG. 2 is a video signal waveform diagram for explaining the circuit shown in FIG. 1, and FIG. 3 is the circuit operation of FIG. 1. 4 is a timing chart for explaining the conventional video scrambling method. FIG. 4 is a video signal waveform diagram for explaining the conventional video scrambling method. 22... Write address counter, 23... Read address control unit, 24... Random number generator, 30... Image memory, 50... CPU0

Claims (2)

[Claims] (1) According to the random number period set corresponding to the scanning retrace period of the video signal to be scrambled, the start and end points of accessing the picture data are shifted by the predetermined random number period, and time axis processing is performed to scramble the video. A video scrambling method characterized by processing. (2) An image memory that converts the video signal to be scrambled into digital data and stores it, and a time axis that performs address value control that reverses the change in address value for the write address value and read address value for this image memory. A video scrambling method comprising: a processing means; and a means for transmitting a video signal scrambled by the time axis processing means.