658 Appendix B Image Reference
Description This image has three parts. The first part consists of six (6) white circles. A large circle is
drawn in the center of the screen. Its diameter equals the lesser of the video height or
width of the display. A smaller circle is drawn at half the diameter and concentric with the
larger circle. A circle also is drawn in each of the corners of the screen. The diameter of
the corner circles equals one-fifth of the display width.
The second part of the image consists of a white crosshatch. The number of boxes in the
crosshatch depends on the physical size of the display.
The last part of the image consists of white tic marks on the horizontal and vertical center
lines of the image. The marks are one pixel thick at every other pixel location. Every fifth
mark is slightly longer. The color of the pattern can be changed with the individual video
output controls.
Test Linearity adjustment
Purpose To present an undistorted display, the horizontal and vertical sweeps of the electron beam
across the face of the CRT should be at uniform speeds. Any non-uniformity in the sweep
causes portions of an image to stretch while other portions are compressed. Non-linearity
in a monitor shows up in several ways. It may be present across the entire screen, in a
large portion of the screen, or localized in a very small area.
Method The circles in the image can be used to do a general adjustment of a monitor’s linearity
controls. Adjust the controls to form perfectly round circles. The crosshatch image can be
used to measure linearity and to make finer control adjustments. All the full boxes in the
crosshatch should be identical in size. Measure them with a ruler or a gauge made for the
monitor under test. Any deviation should be within your specification limits. Use the tic