HDV > PAL DV... how much to crop?

NickHope wrote on 5/24/2007, 10:58 PM

I'm using some 1080i50 HDV clips shot with my Sony Z1 in a standard definition PAL DV production for TV broadcast (mixed with older PAL DV footage).

I'm hoping to exploit the extra definition of the HDV footage to crop the frame on some of the clips in order to magnify the footage. But I've read elsewhere that it's not advisable to crop all the way to a 720x576 (PAL) frame within the HDV because even thought the footage is 1080 the camera's sensors are not really capturing at that full resolution.

So I'm wondering what the advisable cropping limit would be to still hold a nice sharp image.

Comments

farss wrote on 5/25/2007, 1:01 AM

I don't think there's any simple answer to this one. From my experiences on a really good day you can almost crop down to the PAL frame. When the camera / lens is struggling the footage can get arguably worse than SD PAL, so any cropping would be not a good thing.
Bottom line, eyeball it. This isn't all the fault of the camera or the lens either. Say the camera was shooting something at a good distance with the equivalent of say a 100mm lens. You crop it down but now you've effectively doubled the focal length of the lens, crud in the atmosphere how becomes a problem, one that even the best optics and camera isn't going to help with much.

Bob.

Wolfgang S. wrote on 5/25/2007, 5:46 AM

Nick, even if the FX1 chip does not have the native HDV2 resolution in 1440x1080, your m2t material captured from the FX1 has exactly that resolution. And sure, you can crop the material to end up with 4:3 material. And you can magnify the material - but make sure that you have in your project settings for deinterlace "interpolate" or "blend", but not "none".

There has been a script for the cropping to 4:3 SD material:

http://www.sonymediasoftware.com/forums/ShowMessage.asp?MessageID=501216&Replies=2

johnmeyer wrote on 5/25/2007, 11:48 AM

This may be useful:

My workflow for HDV to SD projects

I assume that you want to keep as much of the HDV footage as possible when cropping to PAL SD.

The post above talks about mixing HDV and NTSC SD, but it turns out the calculations for PAL end up with almost the same numbers:



Format aspect ratios (for NTSC)

HDV 1080i is 1440 x 1080 which is a ratio of 1.3333

DV (PAL) is 720 x 576 which is a ratio of 1.25



Pixel aspect ratios

HDV is 1.3333

DV (PAL) is 1.0926



... the calculation  for PAL is:



1440 x (1.25 / 1.333) x (1.0926 / 1.3333) = 1106.258

This is basically the same number as for NTSC (you'll see what I mean in the post linked to above).

NickHope wrote on 5/26/2007, 10:04 AM

John, your script is fantastic. I've changed the numbers in it to the PAL numbers. Also added the event pan/crop preset.

My workflow's different because I'm archiving m2t files, not Cineform AVIs, and editing with DV proxies. So my timeline is a mixture of my old DV PAL 4:3 clips and some DV PAL 16:9 proxy clips, until I switch the latter to the m2t files with Gearshift. So for the time being I've been editing with DV PAL 4:3 project settings.

If I put your 1106.258 width preset on a 16:9 DV proxy so I can do some panning, I see black lines top and bottom. I can live with that during editing though. I wonder if the black lines will vanish when I Gearshift the m2t files back in. Or in my case should I just "match output aspect"?

I'll do some tests...

NickHope wrote on 5/26/2007, 10:19 AM

Yes, those black lines disappear.

Here's what happens...

If I "match output aspect ratio" on a DV 16:9 proxy (with PAL DV project settings) it gives 540 x 576. Then when I Gearshift to the m2t it comes in at 1080 x 1080 with thin black lines down the sides. Not good.

However if I use your 1106.258 preset on a DV proxy it automatically becomes 553.1 x 576 with thin black lines top and bottom. But when I Gearshift to the m2t it comes in at 1106.3 x 1080 with no black lines. And if I then do "match output aspect" as cross-check, nothing changes. Perfect!

You've really helped me here John. Thanks very much!