Strange Shake in Footage!

dakkio26

dakkio26

Member
Hi, I recently got myself a Canon XH A1 and the first thing I did was to shoot some footage in my back lawn. I uploaded the footage onto my PC using a firewire directly plugged in to my XH A1. I noticed that there is a strange shake at the top of my footage. I have put the footage on youtube and would really appreciate it if anybody has any idea what the reason may be, plus any other general advice you may have. I am new to digital filmmaking you see. :tongue:

http://www.youtube.com/watch?v=NDkbaSH3TDA

Thank You

Alex
 
Yeah. OK. That's weird.

But...it's not completely abnormal for the very top/bottom of video footage to be screwed up. It's outside the "safe area", so shouldn't show under normal viewing conditions.

On the other hand...it would drive me crazy...

I don't know how the Canon works. Does it take two separate frames and put them together for each "real" frame? Maybe it's a misregistration thing. (Although I'd expect to see a messed up bottom, too, in that case.)
 
It was filmed in the 25f mode, which is progressive.

When I look closely at the footage there is a horizontal black line a few pixels thick at the top of my screen. I think it could be a problem with the CCD or the tape maybe??
 
Not the tape, for sure.

But going to Adam Wilt's site (http://www.adamwilt.com/DV-FAQ-etc.html#filmlook), he says this:

"These cameras get their "proscan" images not by truly perfoming progressive readout on the chips, but rather by offsetting the green CCD's read timing by one scanline during readout -- vertical pixel-shift, if you will. In essence, an even field from R & B CCDs is blended with an odd field from the G CCD, giving you a frame that has the scanlines for both fields captured at the same instant in time. This gives a definite improvement over mere field-doubled "frames", but it's not as sharp vertically as true proscan. Each "scanline" is actually composed of two scanlines from each chip, so there is some softening vertically; also, the effective chroma resolution is halved vertically. My Technical Difficulties article "Frames and Fields" goes into a lot more detail on the topic. "

So, it does look like the two frames aren't being blended properly. (Unless that's just the way they all are, and you're expected to cut off the top line when rendering.)
 
I can tell you right away that that is not normal. Especially for a 16:9 camcorder, having a bobbing edge is not kosher at all. Have you tried other modes to see if the effect still exists?
 
The Shaking has now gone. I tried another tape and captured it using Sony Vegas 7.0 instead of 6.0 and it seems to have gone. I can only assume it was either the Tape or a capturing fault, but it seems strange for it to be either.

I'm still very interested in finding out why it happened because I'm scared that this phantom shake may re-appear.


Alex
 
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