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What is Judder?

What is judder? 
Judder is the effect that moving objects in a video or movie are not moving smoothly. In other words, objects seem to move from one point to another without being visible in between. The result is that such objects seem to jump or even shake, while moving.

 

What causes judder?
It is the direct result of the lack of pictures per seconds that is necessary to fool our human vision, to simulate a smooth moving object. Fast moving objects would need more frames than slow moving objects, however the frame rate is fixed to one value, namely 24 frames per second (fps), which has a long history and was regarded enough to generate a smooth motion impression in a cinema.
Although display technology can handle easily between 60-75fps, the recording and registration standards including BluRay still have standardized on 24fps. This quality gap between content frame rate and display frame rate is the main cause that despite the advanced display technology, there is still judder.
At about 24 fps the human vision start blending individual pictures into a smooth “motion picture”. The 24fps is always regarded at the edge and being very tiring for a human. Monitors (based on the CRT technology, having flicker) quickly moved to 60 up to 75fps to reduce the “flicker”, allowing us to work more relaxed for more hours per day.
 
Note that TV systems have 50 or 60 FIELDS per second, where a field is half the frame, either the odd or even lines. So TV systems have higher frame rates but the quality is reduced due to sending only half of the lines in each field.

How to remove judder?
There is a simple solution; use more frames per second to create a smooth motion impression. Important is that these frames are not copies because we do not intend to remove flicker. To remove judder each frame must really contribute to the motion of objects in that frame, to finally fool our human vision and create a smooth moving object impression.

NXP software’s ALL2HD can generate such “motion compensated” frames based on the standard content input frame rate of 24 fps. This feature is called Trimension Digital Natural Motion. The same technology can also generate 50/60 fps from interlaced material.  
 
How does ALL2HD remove Judder?
Using a patented technology the ALL2HD algorithm detects the motion between any set of two frames. Based on that motion an entire new frame is created in between the two originals, in which the moving objects are repositioned to match their motion path.
The result is a higher number of frames (double in this example) and because of the motion compensation, creating a very smooth motion impression.