How important is the picture refresh rate?

The picture refresh rate tells you how often the picture on the screen of a flat panel TV is refreshed each second and is measured in Hz. The standard refresh rate for the PAL standard is 50 Hz (60 Hz for American NTSC), which means that a new picture can be displayed 50 times per second in line with the transmission standard.

Manufacturers are competing to provide higher refresh rates that claim to offer super smooth pictures in combination with advanced video processing software. Refresh rates of 100 Hz, 200 Hz and even up to 600Hz in plasma TV are available. It has been easier to provide higher refresh rates in Plasma TVs, but refresh rates of LCD screens have gone up considerably in the meantime.

Picture refresh rate and Frame rate

However, the rate at which new picture content is available to be displayed every second depends on the frame rate of the original recording (24 frames per second (fps) for film material, 50 fps for some video footage). It also matters how many frames per second can be transmitted via the TV signal either digitally in terestrial TV or via satelite (e.g. up to 50p fps for PAL based HDTV).

When the screen refresh rate is higher than the available frame rate, this means that the same picture will be displayed several times before the next picture is available (e.g. twice when a 25 fps recording is displayed at 50Hz refresh rate or 4 times for 100 Hz). This still may give the appearance of a smoother picture and less flicker especially for fast moving scenes but does not add more picture information.

With motion interpolation it is attempted to compute intermediate pictures between the actual recorded frames to simulate the expected motion between the frames. In combination with higher screen refresh rates this would ideally provide extremely smooth pictures. The quality of this approach depends very much on the capability of such video processors and may also lead to artifacts. Different solutions are offered by different manufacturers such as MotionFlow, ClearScan, etc.

If you like watching fast moving sports or action packed movies, a higher refresh rate and the right video processing can make some difference. It remains, however, to be seen if extremely high refresh rates can really make any more difference in picture quality when footage is recorded (and transmitted) at considerably lower frame rates and the human eye is limited in recognizing very fast changes.