What did you do to the footage after you downloaded it from the camera?
A "5D" is a Canon? What format does it shoot? H264? Should be transcoded to a full-frame codec before attempting to post.
I thought rolling shutter was only a problem with horizontally moving objects; one of the many reasons I shoot HD video with a high definition video camera but that's because I've got one at my disposal.
Yep, Canon 5D MK2. I think it's more to do with only capturing every other, or every third, horizontal line of pixels... or something...
It captures as H264, and the very first thing I did was transcode to ProRes422.
I've decided to go ahead and start keyframing an inner mask to straighten them out. Still be happy to hear any other suggestions/ideas though.
I think you very much found the cause yourself - H.264 uses undersampled chroma info and that would massively show up in red areas. The way I figure it, the area between the black frame and metal casing is causing bad antialiasing and the chroma undersampling introduces colored fringes, which the keyer interprets within its tolerance range. A different BG color would obviously have helped as might have extending the black by sticking on some black tape around the perimeter of the iPad. Anyway, masking it manually doesn't seem too much of an issue, so just pursue that course of action.
It was actually a green screen, I just droped in a red solid to highlight my problem better.
But yes, it's definitely the coloured fringes and a manual clean-up is well under way.
can anyone confirm this problem is partly to do with the camera and not just my photography skills?
I can confirm that the camera and your lighting skills both contributed to your dilemma.
Because you didn't take the time to set up the shot properly when you got it, you now pay for it in post.
Because a Canon 5D Mk II records H.264 files, you have lousy color sampling (aka color resolution); I believe it's 4-2-0, which is every bit as bad as the 4-1-1 color sampling of NTSC DV.
Getting a good chroma key is all about the edges of the subject. But bad color sampling scrimps on the color information available at the edges.
And what do you need for a good COLOR key? Accurate color, perhaps?
To see what I mean, take 15 minutes out of your day. Watch the following video:
Bear in mind that your camera's color sampling is the same as the example you'll see for DV near the end of the podcast.
A DSLR might make nice pictures, but it isn't cut out for effects work. If that camera has a full-time HDMI or HDSDI out on it -- that is, the resolution doesn't change when you hit the record button -- you can drop $5,000 to get a box that will let you capture video with 4-4-4 color sampling.
Your best bet: rotoscoping the offending parts. That's how you're going to pay for your shooting haste in post.