deinterlace - technical definition

To convert an interlaced image to a progressive scan image. Also called "line doubling" and "I to P conversion," deinterlacing is built into DVD players and digital TVs. Most broadcast TV and some DVDs are interlaced, and deinterlacing fills in the missing lines so that 60 full frames per second can be displayed on HDTV sets. See interlace.

EASY: Film to Interlaced to Progressive
When movie film is converted to video, all the original content is available in the video. Each full movie frame is turned into two video half frames (see telecine for details), and the half frames can be readily converted back into one full frame for progressive scan. The deinterlacing technique analyzes the frame sequence to determine if it was originally converted from film.

DIFFICULT: Interlaced to Progressive
When shooting interlaced video, each half frame is actually captured at a different moment in time as the camera is running. As a result, the pixels in every other line are simply not there. Using various algorithms, deinterlacing methods recreate the missing lines by analyzing the pixels in the lines above and below them. This is where one algorithm can be vastly superior to another. See interlace, DCDi and telecine.