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Converting 20 Frames/Second to Video


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#1 Terry Mester

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Posted 26 January 2007 - 10:25 PM

Does anyone know if it's possible to use the Telecine process according to a 2:3:3:2 Field pulldown for a 20 Frames/Second Film Rate? This would provide 5 Frames of Video for every 4 Frames of Film, and with only one Video Frame divided by two Film Frames. The other four Video Frames would correspond to one Film Frame. This pulldown would amount to 25 f/s of Video. A flat Field pulldown of 3 would provide for 30 f/s of Video with only one of every three Video Frames divided by two Film Frames. This would be of no use to 35mm cinematography, but it would be beneficial to 16mm use. Using 20 f/s would make each Film Reel last 20% longer, and provide a 17% savings in Film costs. If there were any plans to blow up a 16mm production to 35mm, then 24 f/s would have to be used.
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#2 Terry Mester

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Posted 11 April 2007 - 09:53 PM

For those who would need to convert 18 Frames / Second Film onto Telecine Video, a 3:3:3:2:3:3:3:2:3 Pulldown will fulfil 25 f/s Video, and a 3:3:4 Pulldown will fill 30 f/s Video.
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#3 Robert Houllahan

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Posted 18 April 2007 - 11:09 AM

For those who would need to convert 18 Frames / Second Film onto Telecine Video, a 3:3:3:2:3:3:3:2:3 Pulldown will fulfil 25 f/s Video, and a 3:3:4 Pulldown will fill 30 f/s Video.



As I posted in the Super8 thread any modern telecine (not chain :( ) can run the film at a desired crystal locked framerate and fit that framerate onto the output video format. For example a film run framerate of 13.987 fps can run to 25i, 30i, 24p and there will be no interlace issues and no jitter just clean images at the SDI output of the telecine/color corrector.

This process is automatic and happens in the framestore of the telecine this part is a computer essentially which builds the frame of video from the CRT/Photocells in flying spot or the CCD array in a CCD machine. The framestore is locked to a sync generator (PAL, NTSC, Tri-Level HD) and takes a frame pulse from the Digital Servo so it "knows" the desired output framerate and the rate at which pictures are being scanned from the imaging head in the telecine.

-Rob "knows too much about telecines" Houllahan-
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#4 Tim Dashwood

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Posted 30 April 2007 - 04:54 AM

Does anyone know if it's possible to use the Telecine process according to a 2:3:3:2 Field pulldown for a 20 Frames/Second Film Rate? This would provide 5 Frames of Video for every 4 Frames of Film, and with only one Video Frame divided by two Film Frames. The other four Video Frames would correspond to one Film Frame. This pulldown would amount to 25 f/s of Video. A flat Field pulldown of 3 would provide for 30 f/s of Video with only one of every three Video Frames divided by two Film Frames. This would be of no use to 35mm cinematography, but it would be beneficial to 16mm use. Using 20 f/s would make each Film Reel last 20% longer, and provide a 17% savings in Film costs. If there were any plans to blow up a 16mm production to 35mm, then 24 f/s would have to be used.

Hi Terry,

Yes it is possible, and quite easy to do in telecine transfer. The telecine will automatically figure out the exact frame rate to match 29.97 with pulldown.

I had to do this exact thing once on a short film. I shot with a Aaton XTR rented from LIFT in Toronto. The frame rate knob said 24, but was actually on 20. I learned the hard way that you have to press the display button to confirm speed on the LED readout.

Anyway, we realized this about half way through the day. We knew we would never be doing a film print so we decided to go forward and just use the 20fps we had shot. It actually looks fine and no one except me ever noticed the lower frame rate.
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#5 John Sprung

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Posted 15 May 2007 - 06:20 PM

Given 20 frame per second film going to 60 field per second video, each frame would get three fields. That should be slightly worse than 24 fps for motion resolution and skipping, but better in that the film frames each get exactly the same amount of time on screen, which should look smoother than 3-2.

The longer and more complex the step-skip sequence is, the more jarring the effect. For instance, trying to speed up 24 fps film to 50 field PAL without changing the run time means inserting two extra fields per second. Tried that once, you could sit there and snap your fingers to the beat of the motion artifact.


-- J.S.
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