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Silicon Imaging SI-2K
2/3" 1080p IT-integrated 10-bit digital cinema w/direct-to-disk recording.

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Old December 10th, 2006, 12:25 AM   #16
Inner Circle
Join Date: Jun 2003
Location: Toronto, Canada
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In an extremely bizarre test pattern situation, you could have bands of different saturated colors with the same luminance values (i.e. to the camera, if it were looking at big areas of those colors alone). If those two colors were to alternate at a high frequency, those colors would alias into luminance information.
Ok so I tried tested my idea there, and I'm not sure about that anymore. I tried running a zone plate pattern with roughly equal luma. My camera was a Panasonic GS70, 3 X 460,000 pixel shifted CCDs. What I saw was that:

Zone plate of alternating green + magenta (roughly equal luma; in retrospect I perhaps should have tried for equal luminance):
Very little aliasing.
Chroma resolution absolutely terrible (in vertical and horizontal directions; horizontal chroma is munged by 4:1:1 to begin with).

This perhaps suggests that there is very heavy filtering applied (presumably to avoid aliasing?). In regards to whether pixel shifting increases aliasing, I think this quick test was inconclusive.

Zone plate of just black + white:
Visible aliasing, which is to be expected. I didn't test carefully here. Aliasing from components above the sampling frequency is completely unavoidable, I believe that was in my test pattern.

Significantly greater resolution in luma than chroma (maybe 4X?? just guesstimating, I did not try to measure this).

2- It looks to me that pixel shifting simply shifts the information around to favor luminance over color. So there isn't really "more" information, but more useful information. My test result seems to indicate this.

Other information from Adam Wilt:
http://dv.com/columns/columns_item.j...leId=187202363 (registration required)

I don't believe Adam Wilt tested for color aliasing?

Glenn, I think I mentioned > 70%, and I think you'd probably have the AA filter factor in there too.
My mistake, I was working off memory there.
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Old December 11th, 2006, 06:55 PM   #17
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Join Date: Nov 2006
Location: Fife Wa.
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Thx Graeme

Thank you for the clear and understandable answer to my question Graeme.
I was guessing that it went a little deeper than just frame rate.
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