- 1 decade agoFavorite Answer
Movies are recorded at 24 frames (pictures) per second. Most TVs (in the US) use a 60 Hz refresh rate (60 pictures per second). When you try to display 24 movie frames in a 60 frame TV refresh rate, it does not work out to a whole number (2 x 24 = 48; 3 x 24 = 72; 2.5 x 25 = 60). Ever since VHS & DVDs have been out, TVs & VHS/DVD players have used a technique called "Cinema Pulldown 3:2" to match the frame rate of a movie to the refresh rate of the TV.
With Cinema Pulldown 3:2, a DVD player will read a frame from the DVD and this will then be displayed on the TV screen 3 times. The next frame read from the DVD will now get displayed 2 times. The next read frame is repeated 3 times. The next 2 times, etc. This 3:2 repetition pattern continues throughout the entire movie. Because the alternating DVD frames are repeated at different repetition rates (3 or 2), motion is uneven on a TV screen from a DVD source. The motion actually is jittery. The term used to reference motion picture jitter is called "Judder". The term "Jitter" is reserved to describe the jittery motion you see on an LCD TV screen because of the way all LCD technology works. "Judder" is the uneven motion caused from the use of "Cinema Pulldown 3:2" to compensate for an unequal frame rate between the TV and the recorded movie.
Anti-Judder is the compensation used in a TV to correct for Judder. The typical LCD TV anti-judder technique is to increase its refresh rate to 120 Hz for movies. Now each movie frame received can be repeated on the TV screen 5 times. Since all frames use the same repetition rate (5), there is no movie Judder. Plasma TVs are doing the same except that their repetition rate is 2 because they use a refresh rate of 48 (2 x 24) for the new smooth cinema motion modes.