VP400 Series Video Pro
Form7343A
Operation Manual
25
they should be. If a display blooms at high luminance levels, as the contrast control is adjusted to
maximum, the top, white block in this pattern’s grayscale will become slightly wider than the
gray blocks below it.
Raster distortion at high luminance levels are caused by high voltage power supply regulation
problems. If the contrast/picture control is adjusted for a higher white level than the display
power supply is capable of fully supporting on a short-term basis, the black lines on the bottom
of the pattern will hook or bend outward.
Ideally, for an accurate picture, the contrast/picture control should be adjusted just below the
point at which either blooming, raster distortion, or yellowing of the whites is evident. In a few
cases, this may result in an unacceptably low white level for the picture, however, and a
compromise white level adjustment may have to be made between an accurate picture and a
bright picture.
Overscan
Pattern Description
:
This pattern contains a 16 horizontal line by 12 vertical line crosshatch pattern (32 horizontal by
18 vertical lines in HD modes) with chevrons pointing outward at the center of each of the four
edges. Four tic marks at the center of each of the four edges mark 5%, 10%, 15%, and 20%
overscan. A green rectangle outlines the 5% overscan area and a red rectangle outlines the 10%
overscan area. An “X” marks the electrical center of the pattern.
Pattern Usage
:
Used to check and adjust for the proper geometry
of a display, including picture centering, size,
trapezoid (keystone) correction, pincushion (bow)
correction, and linearity.
Horizontal and vertical centering controls should
be adjusted to center the pattern on the display
screen. The chevrons at each of the four edges
make it particularly easy to see whether there is
equal amount of overscan at the sides or at the top
and bottom of the pattern.
The horizontal and vertical size controls should then be adjusted for the desired amount of either
overscan or underscan. If overscan is desired, a display should usually be adjusted for slightly
less than 5% overscan. The horizontal and vertical overscan should be adjusted to be an equal
percentage, as judged by the green and red rectangles and the overscan tic marks.
Trapezoid correction control(s) should be adjusted to make the pattern’s edges parallel to the
edges of the display screen. The brighter crosses in the corners of the pattern should be adjusted
to be equal distances from the edges of the screen.
Pincushion correction controls should be adjusted to straighten the lines between the brighter
corner crosses. Use the edge of the display screen or a flexible straightedge, such as a yardstick,
