For multi-projector systems, in particular, display devices must have a low black level (i.e., project little or no light when no signal is sent to them) to allow for reasonable edge-blending between the different projector footprints. Otherwise, overlapping video images will have an additive effect, causing a complex pattern of grey to appear even when no image is being projected.
For multi-projector systems, display devices must have low black levels (i.e., minimal light emission) to enable seamless edge blending between the projectors' areas of projection. Otherwise, overlapping video images will result in an additive effect, creating a complex pattern of grey even when no image is displayed.