Indie Film Live

Thursday, December 08, 2005

New Pulldown Extraction Modes Explained

Both the new JVC HD100 and Canon XL H1 cameras have unique pulldown requirements for generating a true 24p capture ready editing. In these camera's MPEG modes (i.e. HDV tape,) the 24p signal is encoded either within the 60p (JVC) or 60i (Canon) transport stream, with the MPEG data kindly indicating which frames/fields are repeated and which frames/fields contain active image data. Using these MPEG flags, both Prospect HD and Aspect HD are able to cleanly extract and convert to a pure 24p CineForm Intermediate AVI. Editing is very easy from here.

The base-band acquisition from these cameras is a different story. The first downside is there are no MPEG flags indicating active or repeated fields, the upside of course is there is no MPEG, DVCPRO-HD or any other heavy compression interfering with the image. So the extraction of pulldown requires on the fly image analysis to determine the pulldown cadence of the incoming uncompressed HD signal (which I have touched on here.) This feature is controlled by the new capture panel, which tell Prospect HD which pulldown type to look for.

The most common mode will be the "2:3 (extract 24p)" mode. As we are not performing any predictive deinterlacing, the camera must be in the appropriate mode. On the Canon that is the 24F (or F2) setting and on the JVC HD100 it is the 24 frame mode. Note: this 2:3 pulldown extraction should also work on the HVX200 and Sony Z1U (there are some limitations of CineFrame 24) -- not tested yet. Even when you are capturing the a 24p stream, the incoming video format must match that of the camera's output : for the 100U use "1280 x 720 p 59.94" and for Canon use "1920 x 1080 i 29.97" (some call this 60i.)

The next two extraction types only apply to 720p sources. The "2:2 (extract 30p/25p)" is simply to half the frame when 30p is sent over 60p or 25p is sent over 50p. European users of the HD101E in 25p mode will use this pull-down type to capture a pure 25p signal. The final "1:1:1:2 (extract 48p)" is a bonus to JVC HD100 users, this allows for a perfect 48p signal for those who would like a 2X slow motion over 24p.


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