G'day Craig and others interested,
This is very interesting - I always suspected something funny was going on,
but never suspected the temporal distortion was so bad! This page explains
it nicely:
http://www.zerocut.com/tech/pulldown.html
I used to work with QuickTime, and I think I'm right in thinking that it
doesn't have these problems?
Chris
Dr. Chris Kirtley MB ChB, PhD
608 Dockside
44 Ferry St.
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Queensland 4169
Australia (GMT+10)
Tel. 61+7-3891 6644 x 1608
Fax 3891 6900
Clinical Gait Analysis: http://www.univie.ac.at/cga
Book:
http://www.amazon.co.uk/exec/obidos/ASIN/0443100098/203-6674734-4427132
On Sat, Aug 9, 2008 at 2:35 AM, Craig Angle wrote:
> Does anybody have any advice on pull down. Some of the new camcorders have
> pull down rates (see definitions below from websites). Can I assume that if
> I purchase a new camera and don't film in cinematic mode (read below) and
> the camera says it is capturing at 29.97 fps, that my velocity data is
> reliable? Normally we use more scientific cameras but with an up coming
> project we have to purchase 10 simple to use cameras on a 3000 dollar
> budget. So I am not familiar with the reliability of the low end everyday
> camcorder (JVC GR250, Cannon ZR830, and Panasonic PV GS59).
>
> When in the Cinematic Effect mode, the Sony camcorder brings video in at 30
> progressive frames per second. To get the film-like effects, the Sony
> DCR-PC350 drops every fifth frame. The camcorder then uses what's called a
> 2:3:3:2 pull down to convert the now-24p video into a signal that can be
> recorded onto a normal Mini DV tape. The Panasonic AG-DVX100 uses the same
> 2:3:3:2 pull down; however, the Panasonic is working with true 24p video,
> whereas the Sony is using 30 frames-per-second video with every fifth frame
> thrown out.
>
> *Other definitions of pull down:
> Pulldown * introducing a pulldown is the process which compensates for the
> differences in frame rates between film and video by creating new frames.
> For 24 fps film to be converted to 30 fps NTSC video, a 3/2 pulldown is used
> which creates an extra 6 frames per second.
>
> *3:2 Pulldown* The technique used to convert 24 frames per second film to
> 30 frames per second video. Every other film frame is held for 3 video
> fields, resulting in a sequence of 3 fields, 2 fields, 3 fields, 2 fields,
> etc.
>
> *3:2 Pulldown* – Movies are filmed at twenty-four frames per second (fps).
> Televisions operate at thirty frames per second. If we simply show the movie
> at 30fps it will appear to go too fast – the "Keystone Cop" effect. The "3:2
> pulldown," method repeats selected movie frames a second time to display the
> 24fps movie on the 30fps television at the right speed
>
> Thanks,
>
>
> --
> Craig Angle M.Ed, M.Ed, ATC, CSCS
> Research Associate II
> Veterinary Sports Medicine Program (www.vetmed.auburn.edu/sportsmed)
> Auburn University, College of Veterinary Medicine
> Doctoral Candidate, Biomechanics Program
> Department of Kinesiology, Auburn University
>
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