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Motion Smoothing: 120Hz and 240Hz Refresh Rates Explained

Refresh Rates
Image used with permission by copyright holder

Curious what ‘motion smoothing’ is all about in LCD displays? It’s often described in terms of 120 Hz, 240 Hz and now even 480 Hz, and boasted as a major selling point of many sets. Joseph Kane, founder of JKP Productions and creator of the Digital Video Essentials video calibration discs, explains what it all means from a layman’s standpoint:

“Refresh rates of incoming video signals are anywhere from about 24 pictures per second to 60 pictures per second. When displayed at their native rates on LCD displays you’ll often see lag in the motion. It looks as if detail is being smeared. This is because images from prior frames are still present as later frames come along. If the refresh rate is increased and frames of black added, you can often force the old image to go away before the new image comes along.

60hz-vs-240hz
Image used with permission by copyright holder

Increasing the number of frames per second opens up the possibility of ‘smoothing’ the motion, predicting what might have happened if the image had been captured at many more frames per second. Case in point, you’ve all seen the spokes of a wagon wheel going backwards in movies shot at 24 frames per second. They would go forward if the image had been captured at many more frames per second.

Enter the LCD sets with motion smoothing. In the 120, 240 or 480 Hz sets there are many frames per second. Oh, what a temptation to interpolate or smooth the motion! Accurately predicting what might have happened between images is not easy, however. The wagon might be going backwards. Then there is the issue of altering the artistic intent.

What we’ve seen of these attempts to ‘smooth’ the motion so far hasn’t been good. They introduced more motion artifacts in the picture than they resolve. The only times we’ve seen this work well is in expensive video processors. We vote for making sure you can turn this ‘feature’ off.”


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Krissy Rushing
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