Screen-door effect
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The screen-door effect or fixed-pattern noise (FPN) is a visual artifact of the projection technology used in digital projectors, where the fine lines separating the projector's pixels become visible in the projected image. This results in an image that appears as if viewed through a fine screen or mesh such as those used on anti-insect screen doors. It most commonly appears as a rectangular grid (hence the name) or sometimes as a hexagonal structure.
The "Screen door effect" on DLP projectors can be mitigated by deliberately setting the projected image a little out of focus, which blurs the boundaries of each pixel to its neighbour. When done properly, this has a minimal effect on overall image sharpness with large projections (~100 inch projections at no greater than 1024x768) as each pixel occupies a moderate area. This focus minimizes the effect by filling the black pixel perimeters with adjacent light. There is current debate as to whether focusing the image in front of the plane of projection or behind the plane of projection gives superior results. Some older LCD projectors often have a more noticable screen door effect than first generation DLP projectors. Newer DLP chip designs promise closer spacing of the mirror elements which would reduce this effect, however some space is still required along one edge of the mirror to provide a control circuit pathway.
[edit] See also
- rainbow effect, an artifact associated with single-chip DLP projectors
- Silk screen effect
