Originally Posted by Chronoptimist
Flicker has nothing to do with judder.
That said, 2:2 pulldown on CRT's (24fps@48Hz CRT) and impulse displays, exhibit a flickering-edge effect -- double-edge effect that is flickering at half refresh rate. Same effect as videogame 30fps@60Hz.
Also, adding black periods between Hz, can cause the judder to look different (changes the shape of the sawtooth).
For example, 2:2 pulldown on 24fps@48Hz short-strobes such as CRT (symmetric rise-fall sawtooth) has very different-looking judder than 2:2 pulldown on 24fps@48Hz sample-and-hold LCD (asymmetric rise-fall sawtooth).
Low framerates and repeated frames introduce judder.
The motion can have different appearances (different sawtooths):
(1) Regular sawtooth, same rise-and-fall (e.g. 2:2 pulldown on CRT, 24fps@48Hz or 30fps@60Hz)
(2) Regular sawtooth, asymmetric rise-and-fall (e.g. playing 24p on sample-and-hold displays)
(3) Varying sawtooth, different peak heights for different frames (e.g. 3:2 pulldown)
For (1) the image bounces back and forth rapidly, catchup and fallback is at the same speed (e.g. symmetric flickering edge effect like playing a videogame 30fps@60Hz CRT). Symmetric rise-fall sawtooth means the image is jumping back and forth between the old and the new position, without any apparent difference in speed how it falls behind versus how it catches up.
For (2) the image slowly falls back and suddenly catches up. More easily seen at 12 frames per second than 24 frames per second, but it's quite apparent the motion is different from (1). Image falls behind gradually (as your eyes continues tracking the motion vector in an analog manner; as your eyes are not digital stepper motors), image instantly catches up to next position as the next frame is shown.
For (3), the catchup is slightly erratic-ish, because of more repeats for some frames than others. (Frame shown 3 times, then 2 times, then 3 times, then 2 times), so a frame is shown for 2/60th of a second, then 3/60th of a second, then 2/60th of a second, then 3/60th of a second. It can look different on strobed versus sample-and-hold displays, but regardless, the erraticness of 3:2 pulldown is apparent on either.
As you turn on/off strobing during 2:2 pulldown for 24fps@48Hz (comparing 48Hz LCD versus 48Hz CRT), the motion vibrating-edge effect changes between (1) and (2) - it's quite obvious that the motion vibrating-edge effect becomes more symmetric versus asymmetric. Some call this vibrating-edge effect as "judder". Some call it "judder" only when it is asymmetric ("judder" looking worse for 24p on 48Hz LCD versus 48Hz CRT). However, "judder" is a loaded word subject to misinterpretation, obviously. What's the definite truth is that the strobing (flicker) vs abscence thereof, changes the motion look enough that people do notice. And even regardless of the display's strobing (or abscence thereof), the back-and-forth vibration of motion, can create the flickering-edge effect that is seen.
Either way, flicker does affect judder/unsmoothness/motion erraticness/motion smoothness/vibrating edge look-and-feel/motion fluidity (choose your favourite word or phrase, depending on how it is defined), indirectly
, because of all the above.Edited by Mark Rejhon - 7/7/13 at 12:20pm