Thursday, 25 October 2007

HV20 (PAL) 1080p25 workflow solution 

Short version:

To use the HV20 in progressive mode, use the HDV1080p25 Easy Setup, but before you edit, change field dominance of all captured clips to "None".

Loooong version:

I have a Canon HV20 (PAL version). It can shoot progressive scan footage (1080p25) but it stores it in an interlaced video stream (1080i50). Note that there's no pulldown involved, and that the footage looks great without any processing.

There are several different flavours of progressive footage out there; Canon calls this one 25PF as opposed to 25F on some of their other cameras. The process is very different for NTSC frame rates going to 1080p24, which involves external programs and additional processing stages. PAL's 25p workflow is easy by comparison but issues remain in Final Cut Pro.

The issues stem from the fact that Final Cut Pro doesn't treat this footage as progressive material. Progressive-as-interlaced footage is OK for broadcast and delivery, but during post production, ugly interlacing artifacts can be introduced, for transitions and speed changes in particular. A horizontal push slide transition is probably the quickest way to see interlacing artifacts.

So, how can we treat this footage as true progressive material? Natively, it's only possible to capture this footage as 1080i50. Changing the Easy Setup to 1080p25 doesn't change the capture preset, only the device control preset and the Edit to tape/PTV output video settings. Footage is captured in 1080i50 with Upper field dominance.

It's tempting to simply create a progressive (field dominance: none) sequence and add the footage. However, Final Cut simply field-doubles the existing "progressive-as-interlaced" footage. FCP thinks the original footage is interlaced, and as the manual says: "Interlaced clips added to a progressive sequence are deinterlaced during playback." (III-688).

Here are some screenshots showing the field doubling:

field-doubled screenshot

true progressive screenshot

Note that it doesn't matter what codec the sequence uses -- HDV 1080i50, HDV 1080p25 or ProRes 422 1440x1080p -- field doubling will occur and can be easily seen at 100% in the Canvas. This occurs with luminance and is not an artifact of the low chroma resolution inherent to HDV and DV footage, nor of RT Extreme.

Finally, a solution:

1. Select your HDV clip(s) in the browser.

2. Scroll along to the field dominance column.

3. Control-click in one of the selected items where it says "Upper" and choose "None" from the popup.

If you now put one of these clips into a new ProRes 422 1440x1080 25p sequence, all will be well. No field doubling and the resulting movie can be exported directly to an HDV 1080i50 sequence if required.

Problems:

1. This doesn't work when "field dominance: none" clips are inserted directly into an HDV 1080p25 progressive sequence -- field doubling still occurs. [EDIT: Nope, HDV 1080p25 works fine as a codec. My fault. Scratch this.]

2. If you nest the ProRes progressive sequence directly into an HDV 1080i50 sequence, the interlacing lines will return.

3. Affiliate clips already in sequences are not affected by the field order change on the master clip, so every clip already in a sequence needs to be adjusted. You need to play the movie, not just move to a different frame, to update the image. This can be a tedious process via Item Properties.

There seems to be another field doubling issue when resizing HDV footage to SD DV. This is (likely) due to field order problems. Solution: if you export the ProRes sequence, you can import the resulting QuickTime movie into a DV sequence with no field doubling issues. Inserting the intermediate ProRes progressive sequence directly into a DV sequence will produce field doubling unless the DV sequence is also set to progressive.

So, it's possible to find a good workflow, but not as easy as it should be. Ideally, it would be possible to remove the field doubling de-interlacing effect in the same way that you can remove the field order filter. A capture preset that automatically sets field dominance would be valuable too.

Any feedback welcome -- and please tell me if I've missed something, basic or otherwise. Note, if you're in the US with an NTSC HV20, you can shoot 24p in a 30i stream, but the process is quite different. Look at 1080p24 from HV20 (NTSC) workflow for starters.

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