Aliasing effect for object outline when panning at DVinfo.net

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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old December 23rd, 2006, 02:34 AM   #1
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Aliasing effect for object outline when panning

I have just started to test my XH A1 (PAL) last week but the quality was quite disappointing. Perhaps I shouldn't apply still photography expectation to video! The major defect I found so far is the aliasing effect on object outline and it was particularly noticeable when panning through scene even the movement was very slow.

I have tried all sort of shooting modes including easy auto, Tv, Av and Manual but they all got the same effect. Here is the list of how I got my testing footages:

- All sort of shooting modes. Tried various shutter speeds from 1/50, 1/120, 1/250 & 1/500 seconds in Tv mode as I thought the aliasing effect was caused by low shutter speed
- Shot in 1080 50i on tripod with IS off
- Tried both manual gain and WB control (problem persists)
- Captured as Quicktime movie via Final Cut Express 3.5.1 in HDV-Apple Intermmediate Codec 1080i50

I am hoping it was an operation problem but not design or faulty unit. Can you all help please.

PS: I think it would be easier for your assessment if I can post a snapshot image but it appears that I am not allowed as indicated in the "Posting Rules" box - you may not post attachments. Is this true?

Thanks all in advance.

Pele
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Old December 23rd, 2006, 04:49 AM   #2
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Are you seeing this effect on your computer monitor, or on a TV or the camcorder's LCD? Since you are used to photos and new to video, it sounds like you might be seeing interlacing. Does it look like this?

http://en.wikipedia.org/wiki/Image:Weaving.jpg

If that's what you're seeing on your computer, then its perfectly normal and your camera is fine. Try watching it on a TV instead. Your computer screen is a progressive display device and will show combing ("mouse-teeth") artifacts when viewing interlaced (50i) video.

http://en.wikipedia.org/wiki/Interla...by_interlacing

If your video is intended for progressive display (web video, film out, etc.) you should shoot progressive (25f) or deinterlace the video. If you are going to TV/DVD/broadcast, then you can choose interlaced or progressive depending on what look you're after.
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Old December 23rd, 2006, 06:21 PM   #3
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Interlacing vs Aliasing

Thanks Jason. What you showed (weaving) is exactly what I saw with my footage. I am glad that my camera is working fine.

Now it brings up one more question - if the target is to create DVD to be played on all or most DVD players including TV and computer monitors, what do most people shoot (25i/30i or 25f/30f)? If I proceed to make a video movie and cut a DVD with what I got (shot in 50i), will the weaving effect appear in the DVD cut?

Thanks in advance.

Cheers
Pele
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Old December 23rd, 2006, 08:40 PM   #4
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Hi Pele. If you make an interlaced DVD (50i) it will play back fine on an interlaced monitor such as a CRT TV. It will play back fine on most flat panel TVs too because they have been designed to handle interlaced video. It will probably not play back without jaggies on a computer monitor because it is expecting progressive scan video/graphics.

If you make a progressive scan DVD (25p/25f/30p/30f) it should play back well on all displays, BUT the caveat here is that shooting 25p etc requires more care than 50i otherwise you could end up with very juddery footage. I suggest you try searching the forums on this subject, there are a lot of worthwhile tips around on shooting progressive.

Richard
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Old December 24th, 2006, 06:11 AM   #5
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I would also add that 25p/f has an air of "quality" about it because we subconciously associate that progressive cadence with film.

And it converts more easily to 24p for distribution to NTSC than 50i does.

Personally I shoot almost everything in 25p... partly because I (personally) think it looks nicer and also partly because a lot of the projects I work on end up being for web distribution, so they're going to be watched on computers.
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Old December 24th, 2006, 07:32 AM   #6
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I was using the VLC Media Player to view a DVD a few days ago and I had the same interlacing symptons. I looked at the player setup and noticed a deinterlace filter that I switched to "blend" and the jaggies went away. I'm not sure if VLC plays the PAL formats though.
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