Correlation of a waveform to a video image

Correlation between a waveform displayed on a waveform display device and the corresponding portion of a video image displayed on a monitor is achieved by brightening a portion of a video input signal from which the waveform and video image are produced. A horizontal sweep signal is compared with voltages representing the left and right edges of the waveform display device screen to determine the portion of the video input signal that is "on-screen". The on-screen signal is combined with a line select signal to produce a control signal. The control signal is used to level shift the video input signal to provide a "bright-up" feature as part of the video image on the monitor, indicating the portion of the video image being displayed as a waveform on the screen of the waveform display device.

DESCRIPTION OF THE PRIOR ART 
The present invention relates to waveform display devices, and more 
particularly to correlation of a waveform display to a video image on a 
monitor using a "bright-up" feature to indicate the portion of the video 
image that is being displayed on the screen of a waveform display device 
in order to find and identify small defects in the video image or waveform 
very accurately. 
In test and measurement of television equipment a waveform monitor is used 
to provide an analog display of a waveform representing a portion of a 
video image. The waveform monitor may display one, two or more lines 
simultaneously, or may display a series of lines in sequence. When a 
portion of a particular line is to be examined in a magnification mode, it 
is not always clear what portion of the video image the waveform 
represents. A prior method of attempting to correlate a waveform display 
with a video image is disclosed in U.S. patent application Ser. No. 
07/673,167 filed Mar. 18, 1991 by Melling et al entitled "Test Signal 
Generator Position Cursors", which is a continuation of U.S. patent 
application Ser. No. 07/340,997 filed Apr. 20, 1989. That method inserts 
cursors into a test signal that is input to a device under test. The 
position of the cursors may be controlled from the front panel of the test 
signal generator. The test signal generator also provides a trigger signal 
for a waveform display device to trigger a waveform display that is 
correlated to the position of the cursors relative to the video display on 
the monitor. However test signal generators are not always readily 
convenient to a service person while the waveform display device usually 
is. Also the cursor only indicates the starting point for the waveform 
display, and does not indicate the portion of the video image represented 
by the waveform display. 
Some current waveform monitors insert a "bright-up" line into the video 
image by shifting the video signal level of a selected line of the video 
image to add brightness to the selected video line on a monitor. However 
this does not provide an indication on the monitor of the portion of the 
video signal being displayed on a waveform display device screen when less 
than a full line is displayed. 
What is desired is correlation of a waveform on a display device with a 
video image on a monitor, the correlation being controlled from the 
waveform display device with an indication on the monitor of the portion 
of the video image that is being displayed on the display device screen. 
SUMMARY OF THE INVENTION 
Accordingly the present invention provides correlation of a waveform on the 
screen of a display device with a video image on a monitor by brightening 
up a portion of the video image corresponding to the portion of the 
waveform being displayed. A video signal is input to an amplifier within 
the waveform display device. A second input to the amplifier is coupled to 
a switch that is normally grounded. The second input is also coupled to 
the output of the amplifier. The other position of the switch provides an 
offset voltage. A control circuit for the switch compares a horizontal 
sweep signal of the waveform display device, the horizontal sweep signal 
including horizontal position and magnification information, with a pair 
of voltages indicating the left and right limits of the portion of the 
waveform being displayed on the waveform display device to determine the 
portion of the video image that is "on-screen". Line select logic 
indicates the line(s) being displayed on the waveform display device. If 
the horizontal sweep signal is between the horizontal limit voltages and 
the line(s) selected is being displayed, then the switch applies the 
offset voltage to the second input of the amplifier to produce a bright 
line signal within the video image on the monitor. 
The objects, advantages and other novel features of the present invention 
are apparent from the following detailed description when read in light of 
the appended claims and attached drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1 a waveform display device 10, such as a television 
waveform monitor, receives a video input signal VID.sub.-- IN from a video 
signal source, such as a test signal generator, device under test or the 
like. The waveform monitor 10 is adjusted to display a portion 12 of the 
video input signal, such as one, two or more lines or a magnified portion 
thereof. The waveform monitor 10 inserts into the video input signal a 
"bright-up" feature 24 corresponding to the portion 12 of the video input 
signal being displayed "on-screen" to produce a video output signal 
VID.sub.-- OUT. The video output signal is input to a monitor 20 where the 
video output signal is displayed as a video image 22. Included in the 
video image 22 is the bright-up feature 24 that indicates the portion of 
the video input signal being displayed on the waveform monitor 10. 
Within the waveform monitor 10, as shown in FIG. 2, circuitry is provided 
to insert the bright-up feature into the video input signal to produce the 
video output signal. The video input signal is applied to one input of an 
amplifier 30, the output of which is the video output signal. The video 
output signal is applied to a second input of the amplifier 30 via a 
feedback network 32. A switch 34 also is coupled to the second input of 
the amplifier 30. In the normal position of the switch 34 the video input 
signal is amplified normally by the amplifier 30 to produce the video 
output signal. In the bright-up position of the switch 34 an offset 
voltage V.sub.B is applied to the second input of the amplifier 30 to 
shift the video signal level at the output to produce the bright-up 
feature in the video output signal, i.e., to produce the bright-up feature 
24 in the video image 22 displayed on the monitor 20. 
A control circuit 40 generates a control signal for the switch 34. As is 
well known in the art the waveform monitor 10 includes a horizontal sweep 
circuit that provides a horizontal sweep signal H.sub.sweep in the form of 
a ramp to drive the horizontal deflection circuitry of the waveform 
monitor. When the waveform display is magnified, a magnification factor is 
applied to an amplifier to which the horizontal sweep signal is input to 
effectively increase the slope of the ramp. However voltages V.sub.L, 
V.sub.R that define the left and right edges of the waveform display area 
14 remain constant. The result is that the waveform display 12 expands so 
that a much smaller portion of the video input signal appears within the 
waveform display area 14. The horizontal sweep signal, after horizontal 
position and magnification have been included, is input to a pair of 
comparators 41, 43 where it is compared with the left and right voltages. 
An AND gate 44 receives the outputs from the comparators 41, 43 so that 
when the horizontal sweep signal is between the left and right voltages, 
an "on-screen" signal is produced. The on-screen signal is input to 
another AND gate together with a line select signal from conventional line 
select logic 48 within the waveform monitor 10. When the portion of the 
video input signal being displayed as a waveform 12 is within the display 
area 14 and the video input signal is at the selected line, then the 
control signal is generated from the second AND gate 46 to cause the 
switch 34 to apply the offset voltage to the second input of the amplifier 
30. Although a single line may be selected for display on the waveform 
monitor 10, the line select logic 48 may provide a select signal that 
selects several lines adjacent to the selected line to produce a 
rectangular line cursor 24 as shown in FIG. 1. In some cases a limiter 
circuit, commonly found at the input to the horizontal deflection 
amplifier, may be modified to perform the function of the comparators 41, 
43. The resulting bright-up feature 24 on the monitor 20 moves left or 
right in response to the horizontal position control and expands or 
shrinks in response to the magnification control of the waveform display 
device 10 to indicate the portion of the video image being displayed on 
the screen of the waveform display device. 
Thus the present invention provides correlation of a waveform on a display 
device to video image on a monitor by determining the portion of the video 
input signal that appears as an on-screen waveform and generating a 
brightness control signal that inserts a bright-up feature into the video 
image when the waveform is on-screen and at a selected video line(s).