Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1998-03-12
2001-12-04
Garber, Wendy R. (Department: 2612)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C380S201000
Reexamination Certificate
active
06327422
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a method and apparatus for processing a video signal, and more particularly to removing (defeating) effects of phase modulation of the color burst component of the video signal.
2. Description of the Prior Art
U.S. Pat. No. 4,577,216, “Method and Apparatus For Processing a Video Signal,” John O. Ryan, issued Mar. 18, 1986 and incorporated by reference, discloses modifying a color video signal to inhibit the making of acceptable video recordings thereof. A conventional television receiver produces a normal color picture from the modified signal. However, the resultant color picture from a subsequent video tape recording shows variations in the color fidelity that appear as bands or stripes of color error. Colloquially the modifications are called the “color stripe system” or the “color stripe process”. Commercial embodiments of the teachings of this patent typically limit the number of video lines per field having the induced color error or color stripes.
Color video signals (both in the NTSC and PAL TV systems) include what is called a color burst. The color stripe system modifies the color burst. The suppression of the color subcarrier signal at the TV transmitter requires that the color TV receiver include (in NTSC) a 3.58 MHz oscillator which is used during demodulation to reinsert the color subcarrier signal and restore the color signal to its original form. Both the frequency and phase of this reinserted subcarrier signal are critical for color reproduction. Therefore, it is necessary to synchronize the color TV receiver's local 3.58 MHz oscillator so that its frequency and phase are in step with the subcarrier signal at the transmitter.
This synchronization is accomplished by transmitting a small sample of the transmitter's 3.58 MHz subcarrier signal during the back porch interval of the horizontal blanking pulse.
FIG. 1A
shows one horizontal blanking interval for color TV. The horizontal sync pulse, the front porch and blanking interval duration are essentially the same as that for black and white TV. However, during color TV transmission (both broadcast and cable) 8 to 10 cycles of the 3.58 MHz subcarrier that is to be used as the color sync signal are superimposed on the back porch. This color sync signal is referred to as the “color burst” or “burst”. The color burst peak-to-peak amplitude (40 IRE for NTSC TV as shown) is the same amplitude as the horizontal sync pulse.
FIG. 1B
shows an expanded view of a part of the waveform of
FIG. 1A
including the actual color burst cycles. During the color TV blanking intervals, such a color burst is transmitted following each horizontal sync pulse.
In one commercial embodiment of the color stripe process, no color burst phase (stripe) modification appears in the video lines that have a color burst signal during the vertical blanking interval. These are lines
10
to
21
in an NTSC signal and corresponding lines in a PAL signal. The color stripe modifications occur in bands of four to five video lines of the viewable TV field followed by bands of eight to ten video lines without the color stripe modulation. The location of the bands is fixed (“stationary”) field-to-field. This color stripe process has been found to be quite effective for cable television, especially when combined with the teachings of U.S. Pat. No. 4,631,603 also invented by John O. Ryan and incorporated herein by reference.
In NTSC TV, the start of color burst is defined by the zero-crossing (positive or negative slope) that precedes the first half cycle of subcarrier (color burst) that is 50% or greater of the color burst amplitude. It is to be understood that the color stripe process shifts the phase of the color burst cycles relative to their nominal (correct) position which is shown in FIG.
1
B. The phase shifted color burst is shown in FIG.
1
C. The amount of phase shift shown in
FIG. 1C
is 180° (the maximum possible).
Further, the amount of phase shift in the color stripe process can vary from e.g. 20° to 180°; the more phase shift, the greater the visual effect in terms of color shift. In a color stripe process for PAL TV, a somewhat greater phase shift (e.g. 40° to 180°) is used to be effective.
Other variations of the color stripe process are also possible.
U.S. Pat. No. 4,626,890, “Method and Apparatus For Removing Phase Modulation From the Color Burst”, John O. Ryan, issued Dec. 2, 1986 and incorporated by reference, discloses removing the phase modulation of the U.S. Pat. No. 4,577,216. This removal is useful in eliminating much of the effects of the process disclosed in U.S. Pat. No. 4,577,216 for recording.
SUMMARY
The present inventors have determined that improvements are possible on the teachings of above mentioned U.S. Pat. No. 4,626,890, especially pertaining to eliminating or reducing the effects of certain variants as described above of the color stripe process of U.S. Pat. No. 4,577,216.
Thus in accordance with the present invention, a circuit modifies and/or removes the color stripe process, or modifies the video signal so the color stripe process is not evident, i.e. has no influence on a television set or VCR.
In one embodiment, the video line locations of the color stripe color bursts are known. That is, it is known in which video lines the color stripe modified bursts occur, as in the above described commercial embodiment of the color stripe process. These locations are stored in a preprogrammed memory which provides signals indicating those video lines. Also, the same preprogrammed memory provides an indication of whether the entire color stripe burst or only a part of it is to be modified.
A modification circuit which also receives the video signal, and uses the information as to the location of the color stripe bursts, removes and/or modifies the color stripe bursts or otherwise modifies the video signal (i.e. modifies the horizontal sync pulse immediately preceding the color stripe burst) so that the effect of the color stripe process is attenuated or eliminated.
With regard to the present invention, it has been found that it is not necessary to completely eliminate the color stripe bursts; with typical commercially available television sets and VCRs, eliminating some of the color stripe bursts or attenuating the color stripe bursts either in terms of amplitude or duration, or removing or attenuating a portion of each or most colorstripe bursts, has been found effective to overcome the effect of the color stripe process, allowing a recordable (copiable) video signal to be produced.
Sometimes the color stripe process is not fixed in line location. Other times, even where it is so fixed, it is not desired or possible to provide the preprogrammed memory. Then instead a phase detector detects, for each video line, the presence of a color stripe burst, i.e. detects color bursts having induced phase modulation. Upon detection of the color stripe burst, the modification circuit (as above) modifies either the color burst or other portions of the video signal (i.e. the horizontal sync pulse) so as to attenuate or eliminate the effect of the color stripe burst.
It is to be understood that correcting or replacing the color stripe bursts in accordance with the invention does not require completely eliminating the phase shift (modulation); a reduction of the phase shift to some small value (e.g. 5° or less for NTSC) has been found to be effective, in that the typical viewer will not perceive the attendant color shift.
Thus, the present method and apparatus have several embodiments. There are several different methods of determining the location of the color stripe burst, either by knowing its location from prior analysis or by actual detection. Various embodiments are also disclosed herein for defeating the color stripe process. These, as described above, generally rely on first determining the video line locations of the color stripe bursts, either by knowing their location from prior analysis and programming in the location to e.g. a p
Quan Ronald
Ryan John O.
Almeida George
Garber Wendy R.
Macrovision Corp
Moe Aung S.
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