Patent EA-001026-B1 (EA)
Title: Method and apparatus for treating a video signal, method for decoding a treated video signal and apparatus therfor
Inventor: FRANKLIN TREVOR
IPC: H04N5/76
Filed: 1996-04-04
Abstract: 1. A method for treating a video signal to mitigate the ability of a Video signal recording system having an automatic gain control for adjusting the video signal level, copying an acceptable video signal for displaying therefrom, including: inserting a pulse signal into the video signal during a horizontal blanking interval of a line of the video signal, said pulse signal having a magnitude sufficient to cause the treated video signal to overcompensate the automatic gain control of the video signal recording system; and biasing a portion of the video signal during said horizontal blanking interval to offset the direct current (dc) voltage shift caused in the video signal by said inserting; wherein said pulse signal is inserted into a sufficient number of lines of the video signal to cause visual impairment of the reproduced picture information contained in a copy made of the treated video signal by said video signal recording system. 2. A method as claimed in claim 1, including: inserting said pulse signal into the colour burst portion of the video signal during said horizontal blanking intervals, having a width sufficiently less than said colour burst portion to not affect the function of said colour burst portion during normal playing of the video signal; and said biasing comprising inserting an opposing pulse signal also into said colour burst portion of sufficient magnitude to achieve said offset and maintain the resultant (dc) voltage level of said colour burst portion of the treated video signal to the (dc) voltage level of said colour burst portion in the original video signal. 3. A method as claimed in claim 2, wherein said biasing comprises inserting said opposing pulse signal having a width commensurate to the remainder of the back porch of the horizontal synchronisation pulse from the commencement of said colour burst portion to the commencement of the picture information portion of the video signal. 4. A method as claimed in any one of the preceding claims including inserting a further pulse signal into lines of the video signal having said pulse signal, sometime after the completion of said colour burst portion and before the main displayable portion of the picture information portion of the video signal having a magnitude sufficient to cause the treated video signal to further overcompensate the automatic gain control of the video signal recording system or cause visual impairment of the reproduced picture information portion contained in a copy made of the treated video signal by said video signal recording system. 5. A method as claimed in claim 4, wherein said further pulse is from 1 to 4 microseconds in width. 6. A method as claimed in claim 4 or 5, including inserting said further pulse after at least half of the time period of the back porch of the horizontal synchronisation pulse from the end of said colour burst portion to the start of said picture information portion, has elapsed. 7. A method as claimed in any one of claims 4 to 6, including inserting said further pulse after at least the commencement of the picture information portion of the video signal within said line. 8. A method as claimed in any one of the preceding claims, including varying the point of insertion of said pulse signal within said horizontal blanking interval from line to line or from frame to frame. 9. A method as claimed in claim 8 as dependent on claim 2, including varying the point of insertion of said pulse signal within said colour burst portion from line to line or from frame to frame. 10. A method as claimed in any one of the preceding claims including varying the amplitude of said pulse signal from line to line or from frame to frame. 11. A method as claimed in any one of the preceding claims including attenuating the amplitude of the horizontal synchronisation pulse and corresponding picture information portion of the video signal during the last lines of each alternate frame sufficiently such that the overcompensation of the automatic gain control of the video recording system caused by inserting said pulse signal crushes the attenuated horizontal synchronisation pulses providing a premature emulation of the vertical synchronisation pulses. 12. A method as claimed in any of the preceding claims wherein said pulse signal is not inserted into the video signal during the horizontal blanking intervals occurring during at least the vertical synchronisation pulse and post equalisation pulse sequences of the vertical blanking interval of each frame. 13. A method for decoding a treated a video signal to mitigate the ability of a Video signal recording system having an automatic gain control for adjusting the video signal level, copying an acceptable video signal for displaying therefrom, including: clamping or switching out the dc voltages of the inserted pulse signals and opposing pulse signals in the treated video signal to the video blanking level; and stabilising the amplitude of the synchronisation pulses. 14. A method as claimed in claim 13, including clamping or switching out the (dc) voltages of the inserted further pulse signals in the treated video signal to the video blanking level. 15. A method as claimed in claim 13 or 14 as dependent on claim 11, including detecting the attenuated amplitude of the horizontal synchronisation pulse and corresponding picture information portion of the last lines of the alternate frames of the treated video signal, and amplifying the amplitude of said horizontal synchronisation pulses and corresponding picture information portions to restore same to the correct video levels. 16. A method as claimed in claim 13 to 15, including: determining the amplitude of the horizontal synchronising pulses of the treated video signal; comparing said amplitude of the horizontal synchronisation pulses with said video blanking level; and adjusting the amplitude of the treated video signal to maintain the amplitude of said horizontal synchronisation pulses at the correct level. 17. An apparatus for treating a video signal to mitigate the ability of a video signal recording system, having an automatic gain control for adjusting the video signal level, copying an acceptable video signal for displaying therefrom, including: receiving means to receive the video signal; pulse generating means to generate a pulse signal of a prescribed magnitude sufficient to cause the treated video signal to overcompensate the automatic gain control of the video signal recording system when inserted into the video signal; inserting means to insert said pulse signal into the video signal during a horizontal blanking interval of a line of the video signal; and  biasing means to bias a portion of the video signal during said horizontal blanking interval to offset the (dc) voltage shift caused in the video signal by said pulse signal; wherein said inserting means is controlled to insert said pulse signal into a sufficient number of lines of the video signal to cause visual impairment of the reproduced picture information contained in a copy made of the treated video signal by said video recording system. 18. An apparatus as claimed in claim 17, wherein said inserting means is controlled to insert said pulse signal into the colour burst portion of the video signal during said horizontal blanking intervals, said pulse signal having a width sufficiently less than said colour burst portion to not affect the function of said colour burst portion during normal playing of the video signal. 19. An apparatus as claimed in claim 18 or 19, wherein said biasing means includes an opposing pulse generating means to generate an opposing pulse signal of a prescribed magnitude sufficient to achieve said offset, and said inserting means being controlled to insert said opposing pulse signal into said colour burst portion such that the resultant (dc) voltage level of said colour burst portion of the treated video signal is maintained at the same (dc) voltage level of said colour burst portion in the original video signal. 20. An apparatus as claimed in claim 19, wherein said opposing pulse signal is of a width commensurate to the remainder of the back porch of the horizontal synchronisation pulse from the commencement of said colour burst portion to the commencement of the picture information portion of the video signal and said inserting means is controlled to insert said opposing pulse signal into said back porch at the commencement of said colour burst portion. 21. An apparatus as claimed in any one of claims 17 to 20, including a further pulse generating means to generate a further pulse signal of a prescribed magnitude sufficient to cause the treated video signal to further overcompensate the automatic gain control of the video signal recording system or cause visual impairment of the reproduced picture information portion contained in a copy made of the treated video signal by said video signal recording system when inserted into the video signal, and said inserting means being controlled to insert said further pulse signal into lines of the video signal having said pulse signal, sometime after the completion of said colour burst portion and before the main displayable portion of the picture information portion of the video signal. 22. An apparatus as claimed in claim 21, wherein said further pulse is from 1 to 4 microseconds in width. 23. An apparatus as claimed in claim 21 or 22, wherein said inserting means is controlled to insert said further pulse into the video signal after at least half of the time period of the back porch of the horizontal synchronisation pulse from the end of said colour burst portion to the start of said picture information portion, has elapsed. 24. An apparatus as claimed in any one of claims 21 to 23, wherein said inserting means is controlled to insert said further pulse after at least the commencement of the picture information portion of the video signal within said line. 25. An apparatus as c