Color Fringing or "Aliased Fringe"
Posted 26 February 2012 - 04:54 PM
I'm noticing some pretty extreme rainbow pattern high frequency moire in a situation involving hard edges and bright light, like shooting directly at a window from inside of a darker room and exposing for what's outside and focusing for the edge of that window. It is a fine pattern of red, green and blue high frequency noise.
I tried this test across a number of lenses, primes and zooms, both motion stabilized or not, handheld, and at varying ISO levels with ND on and off. It was only happening in areas with very hard edges that were at or near the limits of exposure, say 90 to 95% on up. I was shooting canon c-log. Also, none of this showed up on the monitors, which is somewhat distressing - I used the canon monitor as well as a separate SmallHD monitor that gives me bigger and better picture quality for focusing, but I could not see it. The room had a stained glass window in it and I'm betting this may be the culprit, as I can't think of any other options within the camera that could have produced this effect.
I'm assuming this is a very minor limitation of the sensor, but it is not like typical 7D or 5D moire. I have been shooting with this camera constantly for the last week and it's the first time I've seen anything like it, so it's not going to come up often, but it's a weird issue as you can't ever see it. If you're shooting in a cathedral with stained glass someday, I might suggest you review footage shot on your monitors to make sure this isn't happening. :-)
Anyone care to explain? I couldn't get rid of this noise in post easily -- it was very prominent and all the tricks i typically use didn't help it.
Posted 26 February 2012 - 11:43 PM
I have tried pushing the C300 to get the camera to produce moire patterns - mostly on fine line drawings - and so far I haven't seen any moire/aliasing to speak of. Would be interesting to see what you're looking at.
Posted 07 March 2012 - 06:40 PM
As far as I can tell this pattern is not an instance of ISO settings, user settings, or anything else. It's something that the sensor is resolving due to light patterns. The footage was shot using Canon Raw (user settings totally disabled), multiple ISOs, multiple lenses, multiple ND settings, imported as Prores or MXF, all with the same results, which is a localized sort of rainbow moire pattern. I think it has something to do with the quality of light coming through a stained glass window directly behind what I was shooting, but that is just a non-scientific hunch and nothing more.
The file is 35 meg, it was converted to h264 for viewing purposes but this pattern is NOT an artifact of that. Showing on vimeo doesn't make it as clear as what I'm seeing off the camera in its raw state so I had to post it this way instead.
Posted 13 March 2012 - 02:42 PM
I did pass your issue to the C300 team Director who is stationed here in Hollywood 'til NAB.....he said he would pass it on to Japan so, hopefully, they can put a fix out if it is a problem they can replicate.
Camera Department Manager
Posted 06 April 2012 - 11:32 AM
Apparently, dialing down the sharpness can be helpful as well.
Shooting C-Log is also helpful. EOS Standard is sharpened by comparison and more saturated, thus more likely to show the issue.
Ultimately the best thing to do for now is avoid pushing the camera with harshly contrasted blowouts that cause the issue, but of course it is impossible to always avoid. Hopefully we will hear a reply from Canon soon, would be great if this was possible to fix with firmware...
Posted 19 November 2012 - 12:30 PM
I suspect that a black stocking stretched very tight might be the perfect solution. Going to try some more tests soon.
Posted 19 November 2012 - 02:28 PM
Posted 20 November 2012 - 02:29 AM
Posted 20 November 2012 - 11:00 PM
I recently had this issue whilst shooting a sunset across some mountains. It resulted in red/green - lines/pixels across the high contrast part of the image where the sun dipped behind the mountains. I sent the camera back to Canon complaining of this issue along with another problem that I was experiencing with the camera. To cut a long story short I ended up with a new camera along with a firmware upgrade 18.104.22.168.00 which apparently deals with the fringing issue. Can't guarantee 100% but had no problems since and have tried to recreate with other high contrast scenes!
New firmware...? very interesting. have you taken note of any other changes?
Posted 26 November 2012 - 04:26 PM
On a side note, I learned that Canon typically makes repairs or upgrades on an individual basis unless complaint statistics (many complaints) warrant a global response. The number of complaints about issues i wanted addressed -- color fringing and lens hot swaps -- have not risen to that level. So, even though there are some issues that seem to affect all C300 cameras, it is up to each owner to resolve these issues individually with Canon service.
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