Quantum Data 801GC, 801GF, 801GX manual Adjusted Level = 255 x v / 255 1 / γ

added should analog composite sync be enabled. If you need a swing other than the default FMTN set- ting, enter it in the “User” column. In case of an RGB color signal, the swing given is common to all three color analog outputs.

Some displays require that the video output level be referenced or biased to a given voltage. The AVSB parameter sets the DC offset level. The offset is measured between ground and the blanked portion of the video signal. A postive value indicates an offset above ground.

Some displays require a blanking pedestal (i.e. a blacker-than-black level during the horizontal and vertical retrace intervals). If your display requires such a blanking pedestal, set the AVPG parameter to 1 and enter the size of the pedestal you want using AVPS. The AVPS parameter is given as a percentage of the overall peak-to-peak swing of the video signal AVSS. The default FMTN value of 7.5 represents the typical blanking level found in EIA standards.

You may need to use gamma correction if you are testing an analog video display that has a non-lin- ear light response to linear video voltage input. Most displays on the market today are of this type. Gamma correction distorts the levels output by the genera- tor so as to produce a linear light output on the face of the CRT display with varying levels of gray. The following formula shows how the value of the gamma affects the output linearity of the generator.

Adjusted Level = 255 x (v / 255) (1 / γ )

(to nearest integer value below 256 )

Where v is the uncorrected value having a range of 0 (black) to 255 (white) and γ is the gamma correc- tion factor. A gamma correction factor of 1.000 is the same as no gamma correction. The graph in the following figure shows the logarithmic variation of the output signal when gamma is set to 0.25, 0.5, 1, 2, and 3.

6-46 Chapter 6: Programming Model 801GC, 801GF & 801GX¥Rev. A