Cryptography – Video cryptography – Video electric signal modification
Reexamination Certificate
1998-12-15
2002-07-23
Barron, Gilberto (Department: 2132)
Cryptography
Video cryptography
Video electric signal modification
C380S224000
Reexamination Certificate
active
06424716
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to processes for scrambling television signals transmitted over the air or via a cable environment, and in particular to a scrambling technique which generates non-interlaced horizontal sync modulation as well as a double horizontal pulse in selected horizontal blanking intervals, to enhance horizontal tearing and vertical instabilities in a program video picture. The invention is particularly effective over prior art scrambling systems which use typical horizontal and vertical overlay signals, when applied to modern television set scanning systems using count down circuits with ceramic resonator voltage controlled oscillators. The invention's effectiveness is not limited to television sets and monitors using cathode ray tube displays. It is effective in other display systems such as LCD, plasma display and other solid state display systems.
In typical prior art scrambling systems, the horizontal and/or vertical sync modification techniques are ineffective on more modern television sets. With their scanning systems containing digital circuits, such modern sets can lock to a modified television signal with or without vertical sync pulses. As a result, a scrambled television signal containing prior art time position varying vertical sync signals has no effect on such modern television sets, even though such prior art signals will induce good concealment for scrambling purposes on older sets using conventional horizontal oscillators.
The prior art horizontal overlay sync modifications of previous mention use an interleaved pattern. This interleaved (interlaced) pattern in a field-to-field basis was thought to achieve maximum concealment, however such an interleaved (interlaced) pattern is found to impart less concealment because the tearing is distributed over two fields. As a result, the tearing appears to be diluted.
In contrast, in the present invention, more scrambling concealment is achieved since the horizontal sync is position modulated at a non-interleaved frequency that is a multiple of the field frequency. This consistently causes a tearing pattern which is generally the same in every field and that is less revealing of picture content.
It should be noted that in some horizontal sync width modulation schemes (i.e. the horizontal sync is pulse width modulated roughly 3:1 for 2.4 microseconds (&mgr;s) to 7 &mgr;s), decoding artifacts arise because the television or cable tuner detects the varying horizontal sync pulse width for its automatic RF and/or IF gain control (AGC). As a result, a narrowed horizontal sync width delivers a different AGC voltage than a wider horizontal sync width. The video gain of the tuner is then modulated according to the horizontal sync width and thus, causes undesirable AGC artifacts.
OBJECTS OF THE INVENTION
Exemplary objects and advantages of the invention are:
a) To generate unique preferably non-interlaced horizontal sync modulation for a scrambling process, that can be descrambled, which causes more effective horizontal concealment to an unauthorized viewer:
b) To generate unique multiple horizontal sync modulation which is combinable with position varying vertical sync pulses in a scrambling process, that can be descrambled, which causes more horizontal and vertical concealment when viewed by an unauthorized viewer. This increased concealment occurs especially when viewed on a more modern television set such as those sets using ceramic resonators and digital count down circuits in their scanning system; and
c) To provide a new scrambling method as described in “a” or “b” above with reduced or no AGC artifacts in a television or cable tuner.
SUMMARY OF THE INVENTION
The present invention overcomes the shortcomings and problems of the aforementioned prior art while providing a method and apparatus which achieves the objects and advantages of previous mention.
To this end, a first embodiment of the present invention comprises a method and apparatus for modifying, i.e. scrambling, the horizontal sync and burst within a standard horizontal blanking interval of, for example, about 11 microseconds (&mgr;s). If a subsequent descrambler system replaces such a scrambled sync and burst beyond the standard horizontal blanking interval (i.e. greater than 11 &mgr;s; for example, 14 &mgr;s), the modified or scrambled sync and burst occur over an extended horizontal interval and thus yield greater horizontal concealment.
In accordance with a first embodiment of the invention, horizontal sync and/or burst envelope signals preferably are narrowed by about half within the horizontal blanking interval. In one situation, the narrowed sync and/or burst are located at a position just after the end of an active program video line. This may allow for a breezeway of approximately 400 nanoseconds (ns) if desired, which is not required in the present invention (200 ns to 500 ns will also work for the breezeway period). In another location, the narrowed sync and/or burst are positioned closest to the beginning of the following program video line. The net positional displacement of these two narrowed sync and burst locations is a “gap” of about 6 &mgr;s (even more displacement exists in the situation where the horizontal blanking interval, and thus the gap, is enlarged).
The scrambling method of the invention includes position modulating or switching between the two locations (inclusive) at a rate of N * Field Frequency where N is a positive whole number. For example, in NTSC, the field frequency is 59.94 Hertz (Hz). It has been found with many television sets, the maximum concealment (is at N=11) and the rate of modulation is a non-interleaved frequency of about 660 Hz. In this embodiment, it has been found that field-to-field horizontal overlay patterns with an interleaved frequency such as 690 Hz do not provide as much concealment as the pattern with a non-interleaved frequency of 660 Hz. The invention is equally useful in other scanning standards including PAL, SECAM and higher line and field rates used in higher definition television systems.
For slight rolling effects (up or down the screen) that can cause even more concealment, a modified rate of sync modulation for the 660 Hz example is from 654 Hz to 666 Hz. Thus, the following range of frequencies based on N=8, N=9, N=10, N=13, will also provide concealment: 474 Hz to 486 Hz, 534 Hz to 546 Hz, 594 Hz to 606 Hz, 714 Hz to 726 Hz, 774 Hz to 786 Hz, respectively, and the like. These different rate frequencies may be used in any combination in position modulating the modified horizontal sync pulse throughout the field. For example, the top and bottom third of the television field may have the modified horizontal sync pulse modulated at 714 Hz while the middle portion of the field may have the modified horizontal sync pulse modulated at 665 Hz.
Accordingly, to provide optimum horizontal concealment with a slight rolling effect vertically, the rate of sync modulation is for example made equal to N * Field Frequency plus or minus K * 10% of field frequency, where K generally is between 0 and 1 inclusive. For example, K can be larger than 1.
The preferably narrowed horizontal sync widths are about the same for each television line, regardless of location or position, therefore tuner AGC artifacts are reduced or eliminated.
In a second (alternative) embodiment, fake vertical sync (V sync) pulses are inserted before and/or after the normal vertical sync pulse's location (for example, in NTSC, lines 1-3 and lines 18-20) and the normal vertical sync pulses (broad sync pulses) are taken out. These fake pre-vertical and post-vertical sync pulses are for example, alternately switched from one location (pre-V sync) to another (post-V sync) at a selected frequency, such as for example, field rate or at selected random rates. Normally these fake vertical pulses will cause jumping up and down (vertical jumping) of the picture in many television sets, but not in the more modern sets which use ceramic resonator oscillators an
Almeida George
Barron Gilberto
Macrovision Corp.
Meislahn Douglas J.
LandOfFree
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