Screen Door Effect
What is it?
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 or sometimes as a hexagonal structure.
The “Screen door effect” on DLP projectors can be corrected slightly by deliberately setting the projected image slightly out of focus, which blurs the boundaries of each pixel to its neighbor. This minimizes the effect by filling the black pixel perimeters with adjacent light. Some older LCD projectors often have a more noticeable 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.
A brighter picture will make the screen door effect easier to notice. Screen door happens in all technologies but it is easier to see with most LCDs because the gap between the pixels is larger. Screen door is a function of resolution, viewing distance, brightness, and contrast. LCOS has the smallest gap with DLP slightly behind. Going with DLP dopes not eliminate screen door but makes it harder to notice at closer viewing differences than LCD if they are about the same lumens.
Above: Screen Door Effect, notice how the appearance resembles looking out a screen