Method and apparatus to improve playability in overscan areas of a TV display
A television (TV) monitor or receiver normally displays only the active portion of a video signal, and generally the HBI (horizontal blanking interval) and/or the VBI (vertical blanking interval) are not displayed. In some TV displays however, there is provision to display at least a portion of a blanking interval (overscan area). In some displays (such as monitors for professional use) the VBI is displayed as a way to allow the user to monitor test, command, and/or reference signals. If there are added pulses such as the well known copy protection signals present in blanking intervals of the video signal that cause a horizontal (or vertical) timing or recovery circuit to result in erroneous timing, then viewing is impaired of at least one blanking interval for the TV display. For example, if added copy protection pulses in the VBI region cause the horizontal phase lock loop circuit in a TV display to cause a mistiming, then viewing of signals in the VBI (overscan area) will be impaired. Such signals may include test signals and/or sync signals. A method and apparatus disclosed here improve or correct timing in TV display circuits to allow better viewing of the blanking intervals. One such method is to reposition and/or to remove or modify at least one added or other pulse in the VBI and/or HBI.
1 . A method comprising the acts of:
providing a video signal to a video display device which displays an overscan portion and an active portion of a video image associated with the video signal; and
modifying a portion of the video signal in a blanking interval thereof;
wherein as a result of the modification the displayed overscan portion exhibits improved viewability.
2 . The method of claim 1 , wherein the portion of the video signal in the blanking interval includes equalizing pulses, and the modifying includes modifying at least one equalizing pulse.
3 . The method of claim 2 , wherein the modifying includes at least one of removing, altering a duration of, altering a position of, or altering an amplitude of at least one equalizing pulse.
4 . The method of claim 1 , wherein the portion of the video signal in the vertical blanking interval includes at least one added pulse not present in a standard television signal, and the modifying includes modifying the added pulse.
5 . The method of claim 4 , wherein the added pulse is positive going or negative going with regard to the video signal.
6 . The method of claim 4 , wherein the modifying includes at least one of removing, altering a duration of, altering a position of, or altering an amplitude of at least one added pulse.
7 . The method of claim 4 , wherein the added pulse is present in a back porch region of a horizontal scan line in the vertical blanking interval.
8 . The method of claim 1 , wherein in the absence of the modifying, the displayed overscan portion exhibits distortion.
9 . The method of claim 5 , wherein the presence of the added pulses in the absence of the modification causes a voltage clamping error in the displayed overscan portion, and wherein the modification of the added pulses reduces the voltage clamping error, thereby improving viewability of the displayed overscan portion.
10 . The method of claim 1 , wherein the video display device is one of a television receiver, television monitor, video monitor, cross pulse monitor, or computer display.
11 . The method of claim 1 , wherein the modifying includes adding or inserting at least one negative going pulse prior to or after one or more horizontal sync pulses.
12 . The method of claim 1 , wherein the video signal includes a positive or negative level in a back porch region in selected horizontal scan lines in the overscan portion which causes a luminance clamp error when the video signal is displayed in the overscan portion, and wherein the video signal is modified to provide a reduced luminance clamp error in the overscan portion.
13 . Apparatus for modifying a video signal, adapted to be coupled to provide the modified video signal to a video display device which displays an overscan portion and an active portion of a video image associated with the video signal, the apparatus comprising:
an input port for receiving the video signal;
an output port adapted to be coupled to the video display device; and
circuitry coupled between the input and output ports which modifies the video signal in a blanking interval thereof;
wherein as a result of the modification the overscan portion of the video signal when displayed on the video display device exhibits improved viewability in the overscan portion.
14 . The apparatus of claim 13 , wherein the portion of the video signal in the blanking interval includes equalizing pulses, and the modifying includes modifying at least one equalizing pulse.
15 . The apparatus of claim 14 , wherein the modifying includes at least one of removing, altering a duration of, altering a position of, or altering an amplitude of at least one equalizing pulse.
16 . The apparatus of claim 13 , wherein the portion of the video signal in the vertical blanking interval includes at least one added pulse not present in a standard television signal, and the modifying includes modifying the added pulse.
17 . The apparatus of claim 16 , wherein the added pulse is positive going or negative going with regard to the video signal.
18 . The apparatus of claim 16 , wherein the modifying includes at least one of removing, altering a duration of, altering a position of, or altering an amplitude of at least one added pulse.
19 . The apparatus of claim 16 , wherein the added pulse is present in a back porch region of a horizontal scan line in the vertical blanking interval or in an overscan area.
20 . The apparatus of claim 13 , wherein in the absence of the modifying, the displayed overscan portion exhibits distortion.
21 . The apparatus of claim 17 , wherein the presence of the added pulses in the absence of the modification causes a voltage clamping error in the displayed overscan portion, and wherein the modification of the added pulses reduces the voltage clamping error, thereby improving viewability of the displayed overscan portion.
22 . The apparatus of claim 13 , wherein the video display device is one of a television receiver, television monitor, video monitor, cross pulse monitor, or computer display.
23 . The apparatus of claim 13 , wherein the modifying includes adding or inserting at least one negative going pulse prior to or following one or more horizontal sync pulses.
24 . A method of synthesizing a video copy protection signal, comprising the acts of:
providing a video signal having a set of scan lines having color burst cycles of non-normal phase in a horizontal blanking interval; and
providing another set of scan lines in the video signal containing fewer cycles of non-normal phase in a horizontal blanking interval than the first set, wherein the synthesis of the video copy protection signal provides a more effective color stripe video copy protection signal.
25 . A method of identifying a type of color processing system in a television or video display, comprising the acts of:
providing to the display a video signal having at least one cycle of incorrect phase in a color burst portion of one or more scan lines of the video signal; and
observing a color burst portion of an overscan area of the display when the video signal is displayed, wherein an observed attenuation or hanging dots in the color burst portion denotes a comb filter color processing system.
26 . A method of modifying a video signal to have a modified color burst therein, the method comprising the acts of:
providing in the video signal a color burst that includes at least one cycle of incorrect phase for a selected set of scan lines of the video signal; and
wherein the modified color burst allows identification of a color processing system of a television or video display when at least a portion of the color burst area is displayed thereon.