vertical magenta lines - chromatic aberration? 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 12th, 2006, 06:38 AM   #1
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vertical magenta lines - chromatic aberration?

I have sold my Sony FX1 and am about to buy the Canon A1. After watching a lot of A1 sample clips on this forum - thanks for sharing it! - I am a quite worried about the SIGNIFICANT (chromatic?) aberration I noticed in several shots: Vertical magenta lines on the right side of dark, vertical objects (e.g. trees), mostly in the left side of the frame.

Can anyone give me more detailed information / evaluation on that?

Thanks in advance, Michael Mann

Last edited by Michael Mann; December 12th, 2006 at 07:15 AM.
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Old December 12th, 2006, 07:59 AM   #2
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It's the chroma undersampling effect, not chromatic aberration. It's caused by reduced chroma color bandwidth, which is a limitation of the HDV format. For an in-depth explanation, see this thread, specifically the posts from A.J. deLange: http://www.dvinfo.net/conf/showthread.php?t=71727
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Old December 12th, 2006, 08:20 AM   #3
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Thank you. I will study this thread. Best regards, Michael
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Old December 12th, 2006, 01:16 PM   #4
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All the cameras in this price range will occasionally show some purple fringing. It's not necessarily chromatic aberration. But it might be. If it's something that shows up on the edge of the frame but not in the center, then it may very well be C.A. If it's something that shows up against a blown-out/overexposed section of the frame, it's most likely not C.A. and is just blooming from the CCDs or some other artifact of overexposure.
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Old December 12th, 2006, 03:43 PM   #5
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Quote:
Originally Posted by Barry Green
If it's something that shows up against a blown-out/overexposed section of the frame, it's most likely not C.A. and is just blooming from the CCDs or some other artifact of overexposure.
Barry, the artifacts I was referring to are magenta/purple lines on the RIGHT side of dark, vertical objects (mostly trees) which I noticed on several A1 clips, and - that's strange! - ALWAYS on the left side of the frame. I never noticed such kind of artifacts on any of my Sony FX1 takes that I have been shooting during the last 2 years. Is there anyone with similar experience?

Thanks, Michael Mann
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Old December 13th, 2006, 01:16 AM   #6
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Hello, In Kaku Ito 24ftrpdpanoramaps9.m2t panoramic footage you can see the CA (might be a digital blooming/fringing from the CCD) in the tall buildings (Blue fringe on the right and red/magenta on the lefft corners.) I have shot with 35mm wide angle lenses (Wide angle lenses have this challenge) from Leica (15mm 2.8) and Canon (14mm 2.8L and 20mm 2.8) that have the same characteristics shooting digital color and just use Photoshop CS2 to eliminate CA in the RAW mode. I don't know if FCP has that capability to eliminate CA (fringing) in post. Possibly stopping down the aperture might help.
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Old December 13th, 2006, 01:57 AM   #7
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Both the FX1 and the A1 are built down to a 'domestic' price Michael. What this means is that corners are cut in an attempt to bring you the most mouth-watering specification sheet under the dollar deadline.

Both cameras are fine examples of the balancing act that manufacturers have to attempt. One feature is weighed against the others, such that you can have a better side-screen if you accept a 12x zoom. If you want a 20x zoom it'll have to be 1/4" chips I'm afraid, and so on.

So all the components are 'just good enough'. The colour fringing you spot will go un-noticed by many, and anyway, if your film is telling a good enough story, who the hell cares?

tom.
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Old December 13th, 2006, 04:34 AM   #8
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I agree that you get what you pay for, and you can get lenses for 2/3in CCD cameras that cost twice the price of the A1 and still display CA.

But as has been previously mentioned, this effect (which does seem quite pronounced on some shots) doesn't really look like CA. And I have my doubts about it being chroma undersampling in the codec (otherwise all HDV and DV footage would display this along vertical lines of strong contrast). So it must be something to do with the CCD... or possibly a combination of all three?

Does everyone see this? It seems most promenant on light shining directly into the lens (eg. silhouettes).

No more shooting into the sun?
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Last edited by Alex Leith; December 13th, 2006 at 05:27 AM.
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Old December 13th, 2006, 06:13 AM   #9
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no problem in normal life

If you pay attention you can see this in rare situations and before I saw it on the JVCHD100. But I don't see it as a problem. Besides, even in the small digital cam market you can find CA or sort alike if you take a search, but it is not bothering in 99 % of the cases. Actually, the lens has a sweet spot and you need to search for it, and use it. The image and the 20x lens are sharp.

I do not see "SIGNIFICANT (chromatic?) aberration" as Michael.
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Old December 13th, 2006, 06:58 AM   #10
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I sold my FX1 because I was - and still am - so impressed by the better sharpness of the A1. But these magenta lines parallel to the trees (i.e. beautiful Oregon clip of Devon Lyon) really jumped into my eyes. Yes, I'd call these artifacts significant - all the more I never noticed such artifacts in any of my several thousand FX1 takes, which were shot under all kind of lighting conditions. And that's what irritates me.
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Old December 13th, 2006, 07:35 AM   #11
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Quote:
Originally Posted by Mark Yamamoto
... you can see the CA (might be a digital blooming/fringing from the CCD)...
If it's in the sensor, then it's not CA. Fringing comes from a variety of causes, only one of which is chromatic aberration, and that's not even the most common cause.
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Old December 13th, 2006, 07:47 AM   #12
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Quote:
Originally Posted by Michael Mann
Yes, I'd call these artifacts significant - all the more I never noticed such artifacts in any of my several thousand FX1 takes, which were shot under all kind of lighting conditions. And that's what irritates me.
I understand your frustration, and personally I think it would be great if just one of the camera manufacturers could produce a camera with no quirks...

Still, whatever tool you're using you have to work with the limitations of that tool - be it poor low-light performance, picture noise, CA, excessive coring, lens breathing, or (in this case) fringing on high contrast.

Does this effect every camera (I can't test mine 'cause it's at the menders)? Has anyone asked Canon service about it?
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Old December 13th, 2006, 08:35 AM   #13
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Michael you have had good luck or great skill in not seeing this with your FX1. A discussion of this problem with the FX1 can be found here: http://www.dvinfo.net/conf/showthrea...4&highlight=ca
and an example here:
http://www.moronthrottle.com/images/HDVwithcannon.jpg

I have examined the footage posted from ALL the 3-chip HDV cameras and they ALL show this problem to some degree. It is a bummer and it has delayed my plunge into HDV. However I would say that, like all other HDV cameras, the A1 shows the problem--but it does not seem to be one of the worst offenders, based on examples posted to this and other boards.

I see this fringing everywhere on sample footage and it bugs me silly but if my audiences ever see it I certainly have not done my job in setting up shots (keeping the edge contrast reasonable) and telling a compelling story.

I hope post solutions become more common for dealing with the HDV fringing problem.
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Old December 13th, 2006, 08:54 AM   #14
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Alex and Bill, thanks for your evaluations and for the link. Michael
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Old December 13th, 2006, 09:01 AM   #15
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Quote:
Originally Posted by John Beale
(from the other thread)"Purple Fringe" on the other hand could be caused some kind of non-uniform saturation in the CCD chips, if the red, green, and blue chips may have different behaviors near the full-well point.
Well, that might well explain what was going on - after all I think the fringing is most evident on very contrasty edges.

Quote:
Originally Posted by John Beale
If so, this would only be present on overexposed regions, and should go away if you just reduce your exposure, but of course if it's a bright sky that may make your intended subjects too dark.
Well that's something to try. Also, I wonder what the knee settings were for the shots that display the fringing, given that fringing in the DVX was caused by an unknee'd cinegamma.
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