Part of the upper part of the image is shown in the bottom part of the output (or vice versa). This does not happen when geometry distortion correction is switched off.


This problem has been referred to as "foldback". It arises from the fact that the processor (UTM/Megawall) needs to store a number of lines of video to be able to do vertical distortion correction. When the amount of vertical distortion is too large, this number of lines (128/250/256 depending on which product) is not sufficient to accomodate the distortion.

There are several ways to correct this:

  1. Adjust the IG vertical field of view setting to require less vertical distortion (pitch the image source up/down, or change the up/down vertical field of view, and see what happens)
  2. Physically move the projector to reduce the vertical distortion. You can experiment with the position in nControl and see what heppens before physically moving the projectors.
  3. There are also parameters that control the number of lines that are stored, see below.


See Output latency registry parameter


The Output Delay parameter has been added to the Advanced Page on Output Port, and can be set individually per channel.

NOTE: If different values are set per channel, there will be a slight variation in output latency between channels.

Megawall2/nBox Debug Command

A debug command exists that can be used to control the delay. This parameter is not persisted, and its use is no longer recommended.


output delay <n>
where <n> is number of lines.