CA2234971C

CA2234971C - Method and apparatus for removing or defeating effects of copy protection signals from a video signal

Info

Publication number: CA2234971C
Application number: CA002234971A
Authority: CA
Inventors: Ronald Quan
Original assignee: Macrovision Corp
Current assignee: Rovi Corp
Priority date: 1995-10-17
Filing date: 1996-10-17
Publication date: 2001-08-07
Anticipated expiration: 2016-10-17
Also published as: CN1200219A; US6421497B1; KR19990064292A; AU7718396A; JPH11513861A; ATE312475T1; EP0856224A4; JP4355819B2; AU7458096A; US6002830A; DE69638231D1; DE69635555D1; US6173109B1; CN1118192C; AU715473B2; DE69635555T2; JPH11513872A; KR100489145B1; EP1416730A2; CA2234971A1

Abstract

In a known copy protection process for preventing recording of video signals, pseudo sync and AGC pulses (Fig. 2) are present on predetermined lines within the blanking intervals of the video signal so that any subsequent video tape recording of the video signal shows a picture of very low entertainment quality. This copy protection process is defeated first by determining the location of the video lines containing the copy protection using the color burst signal or chroma in the horizontal blanking interval to determine online detection (Fig. 4). Then some or all of the lines including copy protection signals are modified so as to render the overall video signal recordable. The modification is accomplished in a number of ways, including gain shifting portions of the video signal, level shifting portions of the video signal, bandwidth limiting certain portions of the video signal or replacing certain portions of the video signal with other video elements (Fig. 5).

Description

METHOD AND APPARATUS FOR REMOVING OR DEFEATING EFFECTS OF
COPY PROTECTION SIGNALS FROM A VIDEO SIGNAL
BACKGROUND OF THE INVENTION
Field of the Invention The present invention pertains to a method and apparatus for processing a video signal, and more particularly to removing (defeating) effect; of copy protection signals from a video signal.
Description of the Prior Art United States patent Nunber 4,631,603 ('603) by Ryan, issued on Dec. 23, 1986 entitled METHOD AND APPARATUS FOR PROCESSING A
VIDEO SIGNAL SO AS TO PROHIBIT THE MAKING OF ACCEPTABLE VIDEO
TAPE RECORDINGS THEREOF describes a video signal that is modified so that a television receiver will still provide a normal color picture from the modified video signal while a videotape recording of the modified video signal produces generally unacceptable pictures.
The '603 invention relies on the fact that typical videocassette recorder's automatic gain control systems cannot distinguish between the normal sync pulses (including equalizing or broad pulses) of a conventional video signal and added pseudo-sync pulses. Pseudo-sync pulses are defined here as pulses which extend down t:o a normal sync tip level and which have a duration of a least 0.5 microseconds. A plurality of such pseudo-sync pulses :is added to the conventional video during the vertical lanking in.terva7_, and each of such pseudo-sync pulses is followed by a posi.t:ive pulse of suitable amplitude and duration. As a result, t:he automatic gain control system in a videotape recorder will make a fake measurement of video level which causes an improper recording of the video signal. The ' CA 02234971 2000-06-23 result is unaccept~.ble picture quality during playback.
United States 1?atent Number 4, 819, 098 (' 098) by Ryan, issued on Apr. 4, 1989 entitled METHOD AND APPARATUS FOR CLUSTERING
MODIFICATIONS MADE TO A VIDEO SIGNAL TO INHIBIT THE MAKING OF
ACCEPTABLE VIDEOTAPE RECORDING describes a signal modification so that a television monitor receiver still produces a normal picture from the modified signal, whereas a videotape recording of this signal produces generally unacceptable pictures.
Videotape recorders have an automatic gain control circuit which measures the sync ~_evel. in a video signal and develops a gain correction for keeping the=_ video level applied to an FM modulator in the videotape r~ecord:ing system at a fixed, predetermined value. A plurality of positive pulses are added to a video signal with each immediately following a respective trailing edge of a normally occurring sync pulse. These added pulses are clustered at the vertical blanking interval of each field to minimize the affect of the same on the viewability of the picture defined by the signal while ;~til= causing the automatic level control circuit in a recorder to assess the video level at many times its actual value. The sync pulses themselves can also be at a reduced level, in order to enhance the effectiveness of the process.
United States Patent Number 4, 695, 901 (' 901) by Ryan, issued on Oct. 2, 1990 entitled METHOD AND APPARATUS FOR REMOVING
PSEUDO-SYNC AND/OR AN AGC". PULSES FROM A VIDEO SIGNAL describes removing pseudo-sync pu=Lses and AGC pulses that have been added to a video signal to enable acceptable video recording thereof.
The added signals previously interfered with acceptable video recording of the video signal because the automatic gain control of videotape recor~3ers :sensed false recording levels, while conventional t:elev_~siori receivers were unaffected by those modifications t=o the video signal. Removal of the added pulses ' CA 02234971 2000-06-23 permits accept=able video recording of the previously modified video signal. A sel~=ctively-operable clipping circuit is used to remove selected negative-value components (i.e. pseudo-sync pulses)from the video signal, while added AGC pulses are effectively blanked f=rom the video signal with an electrically-operated switch. Both the blanking and clipping functions are selec=tively achieved by sensing both the normal sync pulses of the video signal and the added pseudo-sync pulses .
Method and apparatus are disclosed for "cleaning up" video signals modified by either the pseudo-sync pulses alone, the AGC
pulses alone, or ccmbinat:ions thereof.
United States Patent Number 4,336,554 ('554) by Okada et al., issued on January 21, 1992 entitled CODE SIGNAL BLANKING
APPARATUS describes a code signal blanking apparatus comprising a switching means operative during a given period of a vertical blanking period of a te7_evision signal and a reference level setting means for producing an output of the reference level during said given period when the switching circuit is operative.
United States Patent Number 5, 194, 965 (' 965) by Quan et al. , issued on Mar. 16, 1993 entitled METHOD AND APPARATUS FOR
DISABLING ANTI--COPY PROTECTION SYSTEM IN VIDEO SIGNALS describes a method and a~~paratus for disabling the effect of copy-protection signals placed in a recording video signals which is based on differences in the characteristics of television and VCR circuitry. Copy-protect signals include pseudo-sync pulses and/or added AGC pulses in the blanking interval of a video signal. The specific' method described includes altering the level of the video signal during the vertical blanking interval, e.g.
level-shifting, so as to render the copy-protect signals ineffective to prevE~nt unauthorized copying by a VCR. A circuit for achieving the mE~thod includes a sync separator for detecting the vertical blanking interval, pulse generating circuits for producing pulses of predetermined widths during the interval, and a summing circuit for w~umming the predetermined pulses with copy-protect signals thereby to shift their level. An alternative method includes ir..creasing the effective frequency and / or narrowing of the copy-protect signals during the vertical blanking interval :~o as to achieve attenuation and/or low-pass filtering in the VCR circuitry to thereby render the signals ineffective in preventing copying. A circuit for achieving this method includes pulse narrowing and/or pulse multiplication circuitry which effectively increases the high-frequency content of the pseudo-sync and/or AGC pulses.
United States 1?atent Number 5, 157, 510 (' 510) by Quan et al . , issued on Oct. 20, 1992 entitled METHOD AND APPARATUS FOR
DISABLING ANTI-COP'C PROTECTION SYSTEM IN VIDEO SIGNALS USING
PULSE NARROWING des~~ribes method and apparatus for disabling the effects of copy-protect: signals added to a video signal using differences in the characteristics of television and VCR
circuitry. Copy-protect signals as described include pseudo-sync pulses and/or added AGC pulses in the vertical blanking intervals of a video signal. The specific method described includes increasing the effective frequency of the copy-protect signals during the vertical blanking intervals so as to achieve attenuation and/or low p<~ss filtering in the VCR circuitry to thereby render the signals ineffective in preventing copying. A
circuit for achieving this method comprises pulse narrowing and/or pulse multiplication circuitry which effectively increases the high-frequency content of the pseudo-sync and/or AGC pulses.
United States Patent Number 5,625,691 ('691), issued April 29, 1997, entitled "METHOD AND APPARATUS TO DEFEAT CERTAIN COPY
PROTECTION PULSES WITHIN P, VIDEO SIGNAL, " discloses defeating the affects of the signal generated by the '603 patent by modifying the relative amplitudes of the pseudo sync pulses to the normal sync pulse so that synchronizing pulse detection system within a recorder will onl~r detect the normal synchronizing pulses, thus permitting normal recordung of said copy protection signal.
U.S. Patent I~~o. 5,633,927 ('927), issued May 27, 1997, entitled "VIDEO COPY PROTECTION PROCESS ENHANCEMENT AND VERTICAL
PICTURE DISTORTION:3," discloses various defeat mechanisms the affects of the signal generated by the '603 patent to permit normal recording of said copy protection signal.
U.S. Patent Number. 4,907,093 ('093) entitled "Method and Apparatus for Pre~,renting The Copying of a Video Program,"
discloses a method ;end apparatus for detecting the ordered pairs of pseudo-sync pulsE=_s and AGC pulses described in the ' 603 patent and disabling the recording function of a video cassette recorder. The '093 patens= discloses several detection methods.
Additionally, U.S. Patent Number 4,571,615 ('615) entitled "TIMING GENERATOR I~OR SYNC SUPPRESSED TELEVISION SIGNALS," by Robbins et al. issued on F'eb. 18, 1986, discloses a timing signal generator for recovering timing signals in scrambled video signals in which the ~~ynchronizing signals are suppressed including a detector responsive to the color burst or chroma in the horizontal blanking interval signal contained on the back porch of a suppressed horizontal blanking interval. The vertical interval is detected as the absence of color burst or chroma in the horizontal blanking interval for a specified time interval, and horizontal sync information is obtained by the detection of the first color burst or chroma in the horizontal blanking interval after an absen~~e of color burst or chroma in the horizontal blanking interval.
All of the defeat methods described in the referenced defeat ' CA 02234971 2000-06-23 patents use th.e vertical and horizontal synchronizing pulses to determine the location of the copy protection signals within a copy protected video signal. There is a need for copy protection defeat mechanisms that do not rely on the horizontal and vertical synchronizing pulses to determine the location of the copy protection signals within a copy protected video signal.
SUMMARY
The present invention is directed to a method and apparatus that use the color burst or chroma in the horizontal blanking interval signal to ~3eteimine the location of the copy protection signals within a cc~py protected video signal.
The invention contains two basic elements: a method and apparatus for :locating the copy protection signals using a color burst or chroma in the :horizontal blanking interval signal; and a generic method and apparatus for modifying the copy protection signals in at :Least some of those lines and / or copy protection pulses whereby an a~Jceptable video recording of the video signal can be made.
The "generic" way o:E defeating or effectively eliminating the effects of the copy protection pulses is called "Circuit ACP". "Circuit ACP" is controlled by the pseudo sync AGC pulse pixel location circuit that uses the color burst or chroma on the horizontal blanking interval signal as a trigger element as described above.
This "Circuit ACP" eliminates or reduces the effectiveness of the copy protection signals while in the digital domain by:
a) Level shifting and/or pulse narrowing and/or pulse attenuation as described in 4,695,901 ('901) Ryan, 5,194,965 ('965) and 5,157,510 ('510) Quan et al.; b) Normal composite sync replacement; c') In~~reased normal composite sync size that is larger in amplitude than the pseudo sync such that sync separators will not detect. pseudo syncs (as disclosed in the ' 965 patent and the '691 patent discussed above); d) Replacement of at least part of pseudo AGC locations with a signal (i.e. flat field) such that a reco:rd.able copy is possible.

PFA/US6 2 ~ 6 ~ ~~7 Several different circuits that. cal be used within "Circuit ACP" are described.
The methods and apparatusses for removing or defeating effects of copy prctection signals include modifying less than all of the lines in which the copy protection signals are present, but sufficient of the lines so that the acceptable video recording can be made.
BRIEF DESCRIPTION OF TFiE DRAWINGS
With reference to the accompanying drawings:
1o Figures lA, 1B and 1C show the vertic:a:L interval of standard NTSC video signal;
Figure 2 shows a copy protected signal v~ncluding pseudo sync pulses and AGC pulses as described in the '603 patent;
Figure 3 shows a copy protection signal as described in the '098 patent:
Figure 4 shaws a general block diagram of a first embodiment of the inver.,tion;
Figure 5 shows a voltage controlled amplifier or modulator embodiment of "Circuit ACP" depicted in Figure 4;
2o Figure 6 shows a switch to modify copy protection pulses as another embodiment cf "Circuit ACP" depicted in Figure 4;
Figure 7 shows a :gumming amplifier embodiment of "Circuit ACP" depicted in Figure 4;
Figure 8 shows a combination of circuits as shown in Figures 5, 6, and 7; and "~ Figure 9 shows a :~loc:k diagram of a second embodiment of the invention.
DETAILED DESCRIPTION
The principal object of the invention i~; to locate and 3o defeat or reduce the effectiveness of copy protection signals.
Figures lA,lB and C shows the vertical interval of standard NTSC video signal. Note that the color burst or chroma in the horizontal blanking interval signal is not present during the first nine lines of each field.
m a-us As discussed above there are two basic type of copy protection signals that are commonly present in video signals.
The first includes signals in the Vertical Blanking portion of the video signal. The second which will be discussed below -includes copy protection signals in the Back Porch portion of the video signal.
Figure 2 shows a one horizontal line within a vertical blanking interval of the copy protection signal including pseudo sync pulses and AGC pulses as described in the '603 1o patent. The key element of this signal as described in the '603 patent is the relationship of the pseudo sync pulse with the AGC Pulse. This relationship is the cause of the AGC
disturbance in a recorder recording the copy protected signal.
The elements of these copy protection signals are the combination of either a pseudo sync or a regular sync pulse with an AGC pulse. These pairs sync and AGC pulses are designed to cause the AGC circuitry in a recorder to miscalculate the proper gain setting and thus make an inferior recording. The primary object of the embodiments discussed 2o below is to locate the copy protection signal using the Color Burst Signal and to modify a copy protected signal to reduce or eliminate the effects of the copy protection signals.
Figure 3 shows a commercial embodiment of the copy protection signal as described in the '098 patent. This signal is placed on several horizontal lines prior to the pre equalizing pulses of the vertical interval in each field. The combination of these pulses with the pulses in Figure 2 increases the effectiveness of the copy protection without reducing the playability of the signal on a display device.
3o Figure 4 is an over all block diagram of an embodiment of the invention. This embodiment comprises two primary elements. , The first of these is a novel pseudo sync AGC pulse location circuit that unlike that of the '901, '965, '510 patents. The second is a-"generic" Circuit ACP" that modifies the copy pro-SUBSTITUTE SHEET (RULE 26) CA 02234971 1998-04-16 PCTIUS 6 ~ 16 7 2 2 AFR 19~~
tection signal under the control of a control pulses generated by the location circuitry.
As discussed above, the referenced patents use the verti cal and horizontal s~~nchronizing signals within the video sig nal to detect the loc~ati.on of the copy prote{~tion pulses. The present invention senses color burst or chro~a in the horizon-tal blanking interva~_ to detect the copy protection pulses. As noted above, the color burst or c:hroma in the horizontal blanking interval s__gna.l is not present i.n the first nine lines of each field. The copy protection p,alses are in known locations relativa_ to the period con?=aining no color burst or chroma in the hor:.~zontal blanking interval signals.
Each of the embodiments in the '901, 51~:a and '965 patents use sync separatars, one shot timing circuit;a, logic, counters and digital line location. An embodiment as described in Fig ure 4 shows a novel pseudo sync AGC pulse location circuit that unlike '901, '9E>5, and '501 patents, does not sense sync pulses to locate the copy protection pulses. Instead the em bodiment of Figure 4 relies on colon- burst or chroma in the 2o horizontal blanking interval.
Device 10 has an Copy Protected Input Video Signal 12 which is inputted to a "Circuit ACP" 14 and to a Chroma Band Pass Amplifier 16. Chroma Band Pass Amplifier 16 separates the chroma signal from the luminance :>ignal. The Band Passed Chroma Signal 18 is coupled to Envelope Detector Amplifier 20.
"' As shown in Figures lA, 1B, and 1C, t:he color burst or chroma in the horizontal blanking interval signal is missing for about 9 lines in the vertical blanking interva:~. The circuitry of Figure 4 takes advantage of this. The output of Chroma 3o Envelope Detector Amplifier 20 is coupled to Non-retriggerable One Shot 22 (timing circuit) of about 52 m~.croseconds to 54 microseconds (less than one TV line). This insures that the output of this circuit triggers off only burst and not chroma in the active TV line and field. The output of the Chroma 35 Envelope Detector Amplifier 20 goes also to a Retriggerable m a-us AMENDED SHEE~1 WO 97lI5142 1'CT/US96/16783 One Shot 24 (timing circuit) of about 70 microseconds (greater than one line). an interval that must be greater than 1 TV
line but preferably less than 2 TV lines (less than 126 micro-seconds). The output of this 70 microsecond one shot is a pulse high from about line 10 to the end of the TV field (and possible high for 1 line into the next TV field) . Since the AGC pulses and Pseudo sync pulses are known to be for lines 10 through 16 or 20, a 6-10 TV Line One Shot 26 triggers of the low to high transition of the 70 microsecond one shot into 1o Logical 'AND' Circuit 28 with the 52-54 microsecond one shot output (active pixel location) that produces Pseudo sync AGC
Pulse pixel and line location pulses suitable to control 'Circuit ACP' as to attenuate, clip, blank, level shift, en-large normal sync pulses relative pseudo sync pulses, narrow and modify the copy protection pulses sufficiently as to allow a recordable copy into a video tape recorder.
Note the concepts of Figure 4, while in the analog do-main, also apply in the digital domain.
The second portion of. Figure 4 is the use of Control 2o Pulse 30 to control the modification of the copy protection signals within Circuit ACP 14. In each of the embodiments below, the Copy Protected Video 12 is inputted to a first in put of Circuit ACP as signal to be modifi2d by Circuit ACP 14.
A second input of Circuit ACP is the above mention Control Signal 30.
A first embodiment of Circuit ACP 14 uses a voltage con-trolled amplifier or modulator to for instance, increase the gain during the normal composite sync pulses and video outside the VBI but excluding the pseudo syncs. During the pseudo sync 3o and/or AGC pulses the gain can be turned down. This is done via Control Signal 30. Figure 5 shows Circuit ACP 14 with , such a voltage controlled amplifier. Copy Protection Video 12 is inputted to an input of Voltage Controlled Amplifier 32. _ Control Signal 30 is inputted to the control element of Volt-age Controlled Amplifier 34. This produces a voltage con-ZO
SUBSTITUTE SHEET (RULE 26) ' CA 02234971 2000-06-23 trolled output that. will perform the various function described above. The use of the voltage controlled amplifier is used to change the relative po:~ition of the pseudo sync pulses to the normal sync pulses (for Example) as shown in Figure 3(e) of the '965 patent. The changing of the relative position of the normal sync pulses to the pseudo sync pulses will cause a recorder to not respond to the ~~seudo sync pulses. This is discussed further at Column 4, lines 22-29 of the '965 patent.
Another embod:iment~ ( figure 6 ) of Circuit ACP 14 uses a switch and a signal generator to modify the copy protected added pulses. For instance if, the signal generator produces a signal representing a blanking level, the control signal can be used to replace the added pulses with a signal that allows a recordable copy. The signal gf:nerator may be used to generate any signal including random noise or a test signal, or some variations of the input signal may include a modified version (i.e. narrowed pseudo sync pulses or AGC pulses, level shifted copy protected pulses, enlarged sync pulses and / or a filtered version of the copy protection pul;~es mar be used ( i . a . bandpass, low pass, high pass) so as to pro~~uce distorted copy protection pulses. This signal would replace or modify the copy protection signals so as to allow a recordable copy.
Figure 6 shows Circuit ACP 14 with such a switch generator combination. Video Copy Signal 12 containing copy protection pulses is inputted to an input of Switch 38. Control Signal 30 is inputted to the coat=rol element of Switch 38. The second signal input to Switch 38 is a Video Signal 40 which is generated by Generator 42. The us~~ of the Switch 38 and Generator 42 replaces the Copy Protection pulses within Video Input 12 with a blanking level si~~nal or some other signal i.e. modified part or all of copy protection signals or test signal, thus permitting a normal recording of the Video Input Signal 12 by a recorder.

' CA 02234971 2000-06-23 A fourth a_mbodiment of Circuit ACP 14 uses a summing circuit to level shift the pseudo syncs such that the VCR' s circuitry does not sense the 7_evel. :shifted pseudo syncs. Thus, a recordable copy can be made. Prefe:ra.bly there is no or little effect during the normal composite syn~~ pulses and video outside the VBI but excluding the pseu~~o syn.cs . During the pseudo sync and/or AGC
pulses the level ca.n be turned varied. This is done via Control Signal 30. Figure 7 shows Circuit ACP 14 with such a summing circuit. Copy Protection. Video 12 is inputted to an input of Voltage Controlled Ampli:Eier 32. Control Signal 30 is inputted to the contro7_ element of Summing Circuit 44. This produces a level shifted output that will perform the various function described above. The use of the level shifting signal is used to change the relative position of the pseudo sync pulses to the normal sync pulses as shown in FIG. 3(e) of the '965 patent. The changing of the relative position of the normal sync pulses to the pseudo sync pulses will cause the AGC system within a recorder to not respond sufficiently to the pseudo sync pulses.
This is discussed further at Column 4, lines 22-29 of the '965 patent.
Figure 8 show; a combination of the various Circuit ACP
embodiments describ~=d above in one package . These include Summing Circuit 44, Voltage Controlled Amplifier 34 and a combination of Switch 38 and Voltage Genc=_rator 42 and narrowing via the Control Alt signal into SW9~3 and n.ulling (attenuation via SW9 and Sum 9) .
The control signal is a logic high representing at least a portion of the time when AGC and or portion of the time when AGC
and / or pseudo sync pul~~es are on.
Other "Circuit ACF"' variations can be circuits that turn logic high by sensing the copy protected video's AGC and pseudo sync pulses. Then using timing generators to output pulses shorter in duration of the AGC and pseudo syncs, which in turn is used to narrow the video's AGC pulses and pseudo sync pulses.

CA 02234971 1998-04-16 PCTIUS 9 6 ~ 16 7 8 3 ~p~/~$ 2 2 APB 1991 Of course the cot:y~r protection pulses may als--~ be a combination of narrowing, attenuation, level shifting and or modifica-tion(i.e. replacement).
The embodiments discussed above have been to locate copy protection signa7_;~ w.ithi.n the vertical blar.:~ing interval and to modify the copy protection signal" as to e.Liminate them or make them less effective in copy protection.
The '098 and '603 patents also disclose copy protection techniques located on one or more lines within the back porch to of a video signal. The general concepts of ~ha instant inven tion can be used to eliminate or reduce the effectiveness of these signals.
Figure 9 shops an embodiment tc detect the position of the copy protection pulses as depicted in the '098 patent. A
very simple example would be to couple the chroma envelope pulse from the Chroma Pulse Detector directly to Circuit ACP.
However, a more reliable method is shown in Figure 9 in Device 50. As above, vhe present embodiment senses color burst 20 or chroma in the horizontal blanking interval to detect the copy protection pulses. As noted above, th~_ color burst or chroma in the horizont=al blanking interval signal is not pres ent in the first nine lines of each field. The copy protec tion pulses are in known locations relative t:~ the period con ta ming no color our:>t or chroma in the horizontal blanking "'' interval signals.
Device 50 has an Copy Protected Input Video Signal 12 which is inputted to a "Circuit ACP" 14 and to a Chroma Band Pass Amplifier 16.. Chroma Band Pass Amplifier 16 separates the 3o chroma signal from the luminance signal. The Band Passed Chroma Signal 18 is coupled to Envelope Dete_vtor Amplifier 20 to generate a Chroma hnvelope Pulse. As shown in Figures lA, 1B and 1C, the color burst or chroma in the horizontal blank-ing interval signa:L is. missing for about 9 lines in the verti-35 cal blanking inte:r_val. The circuitry of Figure 9 takes advan-AMEh~DED SHFFT

CA 02234971 1998-04-16 , y~!
PCTIUS 9 b l 1 E ;' ~ 3 $ 2 2 Ai~K 199 tage of this. The output of Chroma EnvelcpE:~ Detector Ampli-fier 20 is coupled to One Shot 54 ;:timing circuit; of about 200 to 250 TV lines. The One Shot 64 tri~,-gers off One Shot 54's output to generate a pulse coincident: with the pulses described in the '0~~8 patent. 'rhesF= lines are, for example, the last three lines of the field. ~nhi~; inures that the out-put of this circuit triggers off the area of the picture known to have copy prorect.ion signals within the Back Porch of the video signal. The width of these pulses c<~n be made adjust-l0 able to accommodate 'rari.ations of cony prote~~t:ion systems that may incorporate copy protection pul:~es over greater portions of the picture than. presently used. The output of Retrig-gerable One Shot 64 and the Chroma Envelope Detector Amplifier 20 are coupled into Logical 'AND' circuit 28 that produces Back Porch AGC Pulse pixel to contro_L 'c~ircuir_ ACP' as to at-tenuate, clip, blank, replace ar levE~l shift the copy protec-tion pulses as t:o al_low a recordablE=_ copy into a video tape recorder.
Circuit ACP can be used in this embodimtent to level shift 2o the copy protection pulse, limit thc~ bandwidth to pass only chroma or replac.:e the copy protection pulse with a normal color burst and banking level.
It should be noised that in each modifi~,_ation embodiment, only a sufficient part of the copy protection signal is needed to be modified tc:~ prcduce a defeat of the co~~y protection sig-nals. This means a portion of the pseudo sync and or AGC
pulses as described in Ryan '603 a::~d '098, combined with a sufficient number of added pulse pairs and lines of occur-rence.
30 This disclos~.~re is illustrative and nest limiting. All discussion in this specification have referenced the NTSC
format. However, the concepts are equally applicable to the PAL and SECAM fo.rmat:~. E'urther modifications will be apparent to one skilled in the art and are intended t ~ fall within the 35 scope of the appended claims.
ma-us 14 AMENDED SHEET

Claims

CLAIMS:

1. A method of removing the effects of pseudo sync and AGC pulse copy protection signals within respective video lines of a video signal having normal sync timing signals, the copy protection signals being for inhibiting the making of acceptable video recordings of the video signal after digital to analog conversion while still allowing the video signal to be viewed, the method comprising:
determining the presence of a color burst signal to determine which video lines contain said copy protection signals; and modifying the copy protection signals in response to the color burst signal presence in at least some of those lines whereby an acceptable video recording of the video signal can be made.

2. The method of Claim 1 wherein the copy protection signals are in the NTSC format.

3. The method of Claim 1 wherein the copy protection signals are in the PAL format.

4. The method of Claim 1 wherein the copy protection signals are in the SECAM format.

5. The method of Claim 1 wherein the step of determining comprises:
generating a control pulse representing a location in said lines of said copy protection signals;
inputting said copy protected video signal;
modifying said copy protected video signal using said control pulse; and outputting said modified signal having said modified video lines.

6. The method of Claim 1 wherein the step of modifying includes:
increasing an amplitude of all areas of said copy protected video signal except those areas defined by said control pulse.

7. The method of Claim 1 wherein the step of modifying includes:
modifying less than all of the lines in which the copy protection signals are present, but sufficient of the lines so that the acceptable video recording can be made.

8. The method of claim 1 wherein the step of modifying includes:
generating a control signal during the presence of said copy protection signals within said video signal; and controlling the gain of portions of said video signals.

9. The method of Claim 8 wherein the step of controlling comprises reducing the gain of a voltage controlled amplifier during said presence of said copy protection signals.

10. The method of Claim 8 wherein the step of controlling comprises increasing the gain of a voltage controlled amplifier during an absence of said copy protection signals within said video signal.

11. The method of Claim 1 wherein the step of modifying includes:
generating a control signal during the presence of said copy protection signals within said video signal;
inputting a replacement signal; and replacing said copy protection signals with said replacement signal.

12. The method of Claim 11 wherein said replacement signal is a signal representing a blanking level of said video signal.

13. The method of Claim 11 wherein said replacement signal is a video signal.

14. The method of Claim 11 wherein said replacement signal is a test signal.

15. A method of removing the effects of pseudo sync and AGC pulse pair copy protection signals within selected video lines of a video signal having normal sync signals, the copy protection signals being for inhibiting the making of acceptable analog video recordings of the video signal after digital to analog conversion while still allowing the video signal to be viewed, the method comprising:
using a color burst for determining which video lines contain a location of normal sync pulses; and increasing the amplitude of said normal sync pulse relative to said pseudo sync pulses whereby an acceptable video recording of the video signal after digital to analog conversion can be made.

16. An apparatus for removing the effects of pseudo sync and AGC pulse copy protection signals within selected video lines of a video signal having normal sync timing signals, the copy protection signals being for inhibiting the making of acceptable video recordings of the video signal after digital to analog conversion while still allowing viewing of the video signal, the apparatus comprising:
a copy protection location circuit using a color burst signal for determining which lines of said video signal contain said copy protection signals; and a copy protection modification circuit for modifying the copy protection signals in at least some of those lines whereby an acceptable video recording of the video signal can be made.

17. The apparatus of Claim 16 wherein:
the copy protection location circuit includes means for providing a control pulse representing a location of said copy protection signals;
the copy protection modification circuit includes circuit means receiving the copy protected video signal for modifying the copy protection signals in response to said control pulse;
and an output terminal for providing a video signal with said copy protection signals modified or removed.

18. The apparatus of Claim 17 wherein the modification circuit comprises:

a voltage controlled amplifier responsive to said control pulse for increasing an amplitude of all areas of said copy protected video signal except those areas defined by said control pulse.

19. The apparatus of Claim 17 wherein the modification circuit comprises:
a voltage controlled amplifier responsive to said control pulse for decreasing an amplitude of the areas of said copy protected video signal defined by said control pulse.

20. The apparatus of Claim 17 wherein the modification circuit modifies less than all of the lines in which the copy protection signals are present, but sufficient of the lines so that an acceptable video recording can be made.

21. The apparatus of Claim 17 wherein the modification circuit includes:
a voltage controlled amplifier responsive to said control pulse for controlling the gain of portions of said video signal.

22. The apparatus of Claim 21 wherein said voltage controlled amplifier reduces the gain during said presence of said copy protection signals.

23. The apparatus of Claim 21 wherein said voltage controlled amplifier increases the gain during an absence of said copy protection signals within said video signal.

24. The apparatus of Claim 17 wherein the modification circuit comprises:
means for generating a replacement signal; and a switch responsive to said control pulse for replacing said copy protection signal with said replacement signal.

25. The apparatus of Claim 24 wherein said replacement signal is a signal representing a blanking level of said video signal.

26. The apparatus of Claim 24 wherein said replacement signal is a video signal.

27. The apparatus of Claim 24 wherein said replacement signal is a test signal.

28. An apparatus for removing the effects of pseudo sync and AGC pulse pair copy protection signals within selected video lines of a video signal having normal sync pulses and color burst signals, the copy protection signals being for inhibiting the making of acceptable analog video recordings of the video signal after digital to analog conversion while still allowing the video signal to be viewed, the apparatus comprising:
means for inputting said copy protected video signal;
a copy protection locating circuit using a color burst signal to generate a control signal indicative of a location of normal sync pulses on the selected lines; and a modification circuit responsive to said control signal for increasing the amplitude of said normal sync pulse relative to said pseudo sync pulses whereby an acceptable video recording of the video signal after digital to analog conversion can be made.

29. The apparatus of Claim 17 wherein the copy protection signals are in the NTSC format.

30. The apparatus of Claim 17 wherein the copy protection signals are in the PAL format.

31. The apparatus of Claim 17 wherein the copy protection signals are in the SECAM format.