Answer: Digital Projectors

If you’ve ever sat very close to a projection screen during a digital slideshow at work or school, there is a good chance you’ve seen the “screen-door effect” up close and personal. In digital projection, the effect is a visual artifact created by the fine lines between the individual pixels in the panel inside the projector.

The reason we can see the little lines is because the optical components of the projector (the lens system) can project the display with a greater degree of image resolution than the actual digital panel inside can create. As such, it’s like holding a powerful magnifying glass up to a printed page and seeing imperfections in the offset printing process.

Some of the tricks engineers have employed to deal with this visual artifact include depixelization, which uses various optical methods (a microlens array, for example) to eliminate the visibility of the spaces between the pixels, and setting the lens very slightly out of focus so that the individual pixels bleed into each other just enough to erase the black lines in the process.