Psychtoolbox>Datapixx.{mex*} subfunction


Liquid crystal displays can exhibit an artifact when presenting 2 static images
on alternating video frames, such as with frame-sequencial 3D. The origin of
this artifact is related to LCD pixel polarity inversion. The optical
transmission of a liquid crystal cell varies with the magnitude of the voltage
applied to the cell. Liquid crystal cells are designed to be driven by an AC
voltage with little or no DC component. As such, the cell drivers alternate the
polarity of the cell’s driving voltage on alternate video frames. The cell will
see no net DC driving voltage, as long as the pixel is programmed to the same
intensity on even and odd video frames. Small differences in a pixel’s even and
odd frame luminance tend to leave the cell unaffected, and large differences in
even and odd frame luminance for short periods of time (10-20 frames?) also do
not seem to affect the cell; however, large differences in luminance for a
longer period of time will cause a DC buildup in the pixel’s liquid crystal
cell. This can result in the pixel not showing the programmed luminance
correctly, and can also cause the pixel to “stick” for several seconds after the
image has been removed, causing an after-image on the display. VPixx
Technologies has developed a strategy for keeping the pixel cells DC balanced.
Instead of alternating the cell driving voltage on every video frame, we can
alternate the voltage only on every second frame. This feature is enabled by
calling this routine. Call this routine before presenting static or
slowly-moving 3D images, or when presenting 60Hz flickering stimuli. Be sure to
call DisableVideoLcd3D60Hz afterwards to return to normal pixel driving. Note
that this feature is only supported on the VIEWPixx/3D when running with a
refresh rate of 120Hz.

###See also: DisableVideoLcd3D60Hz