User Manual - TRS-RenTelco

Option VGA Detailed Measurement Information
How Results are
Calculated
The leading edge position of the second white bar is determined for all three
video channels. For each pair of channels, the difference in the above values is
computed and reported. The result is also reported as a percentage of the pixel
clock period.
Color Bars Measurement
The Color Bars measurement measures the GBR color bars of a VGA card in a
PC. The Color Bars measurement measures the amplitude level (relative to back
porch) of each of the eight colors, that is, white, yellow, cyan, green, magenta,
red, blue, and black for each active channel. Therefore, this measurement makes
eight measurements on three channels for 24 total measurements. The software
assumes that G is on Channel 1, B is on Channel 2, and R is on Channel 3.
The Color Bars measurement is also used to check individual channel gain. In
addition, it can be used as a crude check of linearity because severe clipping or
other non-linear distortions will alter the measurement results from the ideal.
Signal Source
The test signal used for the Color Bars measurement is the color bars pattern
located on the Test Signal Files CD -ROM.
The color bars test signal used has nine colors. They are white, yellow, cyan,
green, magenta, red, blue, black, and white. If you generate your own color bars
test signal, it should have the first and the last bar white and the remaining seven
color bars in any order. Each of the bars should be at least 1/24 of the active line
time in duration.
If you plan to take only Color Bars measurements, use a Full Field test pattern of
the type Color Bars. Select the bitmap file that matches the format and the
refresh rate of the test. For example, use the 640x480 -ColorBars.bmp file to test
a 640x480 resolution format.
You can also use a Matrix signal as a test signal. For more information on the
Matrix signal refer to page 2 -16. For example, look for a 640x480 -Matrix.bmp
file to test a 640x480 resolution format.
Interpreting Results
The reference value of the amplitude level relative to the back porch of each of
the colors is either 0 mV or 700 mV for G, B, and R channels.
For example, relative value of 15 mV for yellow (G channel) indicates that the
measured value of the signal is greater than the reference value of the signal.
How Results are
Calculated
First, the bars are identified using the relative amplitudes of the three channels
and the specification for the selected format and colorimetry.
The amplitudes are calculated using waveform averaged values within each
identified bar relative to the back porch. Thus, it is important to ensure that the
3-42 VM5000 Automatic Video Measurement Set User Manual