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Question

25ips camera on 60HTZ progressive scan TV

Sep 15, 2013 3:03PM PDT

Can someone please tell me what, if any effect of using a 25ips camera on a 60Htz sceen or 30ips on a 50Htz screen.

I know it was relevant in interlaced technology of odd and even lines and PAL 25ips 50Htz and NTSC 30ips 60Htz. and refresh rates vs frame rates etc.

Does this still apply to HDTV and progressive scan. What visual differences would I expect to see. if using 25 ips on 50htz, vs 60Htz

Discussion is locked

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Answer
Depends on whether the display is flickerfree
Oct 4, 2013 5:19PM PDT

Depends on whether the TV is sample-and-hold (flickerfree LCD) or impulse-driven (plasma, scanning backlight).

For sample-and-hold, you won't see much of a difference. You can use a camera at almost any framerate on an LCD. Static images won't show perceptible differences. Motion on the display itself will show strange stutters (framerate interference between framerate of camera and framerate of the display being videoed). That's why television studios often use LCD panels as background screens, they're pretty co-operative to being filmed, as long as the backlights are not flickering.

For impulse-driven, you will see udulations caused by the flicker of the display, much like CRT's. Plasma being filmed, especially at the wrong framerate/exposure, will show ugly flickering effects when being filmed. You pretty much need to treat them like CRT's, by filming them synchronized with the camera's shutter speed.

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PWM
Oct 4, 2013 5:21PM PDT

One minor complication: Some LCD's use scanning backlights, or PWM-driven dimming. So turn these features off, and set brightness to 100% (if your LCD uses PWM dimming). This gives you a flicker-free LCD.