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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 April 18th, 2008, 09:36 AM   #1
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Join Date: May 2003
Location: Virginia Beach, VA
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channel softness problem

I am looking for input on a problem I'm having (or maybe it isn't a problem). When shooting with the XHA1, I sometimes see what looks like a horizontal offset of either the red or green channel. I've attached two frame caps to show the problem. The tree branches are magnified about 400%, but the shot of the Washington Monument is the original frame...though I forgot the correct the pixel aspect ratio. You can only see the problem when you have a high-contrast back lit vertical (in the attachments, the edges of the tree branches against the white stone sill or the edges of the Washington Monument against the sky), and it appears as a band of green on the left side of the vertical and a band of red on the right side.

When I first noticed the problem I thought maybe there was some slight misalignment of the chips, but I've tried shooting test footage with two different XHA1s, and they both do the same thing, which makes me think that this is an inherent characteristic of this camera rather than a problem with my particular camera. However, I'm using footage from this camera in a documentary I'm making with a colleague who shot some B-roll on his little Sony HDV palmcorder. Embarrassingly enough, when we both shot footage of back lit verticals, his shots look great, whereas mine have this slight muddiness about them.

So, two questions:

1) Does anyone know what might be causing this, and is there something I can do about it?

2) Is there anything that can be done in post to clean up such shots. I thought maybe shifting the red channel to the left by one pixel would help, but I can't find a filter in Premiere Pro that will let me do that.

Oh, I should probably add that the footage was shot 1080/60i, and we're editing in native HDV.

Thanks in advance for any help you might be able to give me.

Attached Thumbnails
channel softness problem-wm.jpg   channel softness problem-01_c2.jpg  

Stu Minnis is offline   Reply With Quote
Old April 18th, 2008, 11:16 AM   #2
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Hi Stu........

Well, I've given both of those grabs a pretty thorough scrute, and either I'm going blind (hey, anything's possible), my screen is rubbish (ditto) or there really ain't much there to see.

If, as you say, there really is something there, I can only assume it's CA caused by shutting the aperture down too far. Keep it wider than about f5.6 and you shouldn't have a problem.

There is, as far as I am aware, no "generic" problem with the A1 optics/ sensors. If you have seen this with two different cameras, it either isn't there or is self inflicted/ system/ operator error.


Last edited by Chris Soucy; April 18th, 2008 at 12:11 PM. Reason: Whoops
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Old April 19th, 2008, 02:46 AM   #3
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I can see it, and it looks like ordinary chromatic abberation to me.

You'll see it usually when you've got a bright part of the picture against a dark part, usually more obvious on vertical objects, and usually more obvious on one side of the subject than the other.

It hard to avoid if you've got a bright pale sky in the background, so I try to avoid shooting in these conditions - wait for a blue sky if I can (easier said than done here).

With digital stills you can get rid of a lot of it with software, don't know about video though.
Canon XH A1; Canon XF100; Nikon D800
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