In my Canberra Times column this week I discussed 1080p24 as the ideal delivery standard for Blu-ray and HD DVD. Today I received an email on this, thus:

I had never heard of 1080p24 or even conceived that it might be possible.

But how on earth does it avoid flicker, the bane of all TVs and early computer displays? And just what kind of display device do you need to display 24 fps? Presumably the answer has a lot to do with how flat panel devices can be made to work.

Flicker is not a problem with modern digital displays. Flicker occurs on scanning displays, like CRTs, because they rely on the persistance of output from the phosphors on the screen after the scanning electron beam has passed. A slow frame rate leaves too long an interval before any given pixel is refreshed, so you get flicker. Digital displays hold all the signal data in memory until a full frame has been collected, and then switch this instantly to the display. This is then held on the display while the memory fills up with the next frame, and then this is shown.

Whether any given frame has to be held for 1/24, 1/50 or 1/60 of a second doesn’t matter, because there is no fading between frames.

I used to run my old computer CRT monitor at 85 hertz (the highest it was capable of at the resolution I was using) to avoid flicker. My new LCD monitor only runs at 60 hertz max, but there is no flicker at all. It could probably run at 10 hertz without flicker, if it were so specced, and still meet my needs, except for DVD playback.

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