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Old November 27th, 2007, 07:31 AM   #1
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Fast Panning with HDV - "Ventian Blind Effect"

Hi,

I mentioned this at the end of a recent thread but posting it as a new topic now. I have been wondering what is causing this effect (look at the edge of the guys head in the crude screen shot jpg I've attached below as I fast pan past him to follow the plane at Duxford Flying Legends Airshow this summer.)

I only get it with "hard edges" when doing a fast pan and also see it on high speed revolving propellers close up. Is this a HDV (1440x1080i) to MPEG2 (720x576) downconversion motion artifact or is it something else?

It was with a Sony HC1 (PAL) and downconverted to std. def (in Vegas 7) for DVD output. I left the shutter speed on the camera on auto - a bright sunny day - by the way in case this is important to know.

I get the same effect if I render out the file as UFF or as Progressive Scan but don't seem to get this effect when I view the native High Def .m2t video on my editing PC. I just get a slight double image but without the "ventian blind" effect and it is near on impossible to see it - unless you pause the video and view it frame by frame!!! However, it's moderately easy to see the ventian blind effect on the downconverted video even if not paused (and it often looks like jagged/sawtooth edges.) Hopefully my desciption and the screen shot gives enough info. The DVD's are good (at least to my eyes) and it's all tolerable but I just want to know what it is and how I might avoid it.

I'm sure someone can explain to me what this effect is and if there is any way I can remove it in my downconversion to std. def!

Many thanks in advance for inputs.
Attached Thumbnails
Fast Panning with HDV - "Ventian Blind Effect"-duxford-venitian-blinds-fast-pan-effect.jpg  
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Old November 27th, 2007, 08:45 AM   #2
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Looks like interlacing artifacts, so you'll need to experiment with different options for minimizing that depending on the delivery format.
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Old November 27th, 2007, 11:55 AM   #3
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welcome to progressive HD!

Andy,

I'm afraid that this is one of the drawbacks when your content is progressive HD.

To save me explaining the ins and outs of why this happens please read this excellent article by UK cameraman Mike Brennan

http://www.jvcpro.co.uk/getResource2...ar.pdf?id=6118

You'll learn that when shooting in this format there are plenty of things to avoid! One of which is contrasting straight edges when viewed in a moving shot. The second is to just avoid panning altogether!!

I've been shooting a few things in HD recently and I've really had to apply completely different techniques. It means thinking more like a cinematographer rather than a video cameraman! You'll find however, that being forced to use these techniques will improve the quality of your output. The conventions for broadcast news and entertainment TV really don't work in film. For example, zooming and panning is everywhere on TV, but it's a NO NO in cinema! Eliminate them from your video work, and put that extra effort in your still shots, framing and lighting and your output will look better.

I was trained in broadcast news and light entertainment. Friday night TV and kids programmes is full of whip pans and wide angles! It can become habitual. Move over into HD and it's time to change your ways! For the better!!!!
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Old November 27th, 2007, 01:01 PM   #4
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Stuart,

Thanks so much for the excellent advice and equally excellent article in the link by Mike. I now understand the nature of this so much better.

This will help me a lot in developing good working camera techniques to make the best of this HDV format I'm now using!

Thanks again!
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