So...you've got an awesome idea that requires a green screen...and a 5D to shoot it on. For the love of all that is holy....just don't do it. Well at least don't do it unless you know what you are in for. Consider this your fair warning.
A few weeks ago, we got called in to help pull a key on some unruly 5D green screen footage for a music video. I'm not going to pull punches here...the shot was a compositor's worst nightmare. A 2.5 minute single take, a uneven green backing of different materials, a reflective piano, a bunch of semi-transparent confetti, and worst of all artificial rain. I know this is unfairly stacking the deck against the 5D, because even a much more suitable camera would struggle with all of this, but my quarrel with the footage began long before any of those things really became a factor.
Consider these stills detail stills from the footage.
The Raw Sample:
Now...just to set this up...thats supposed to be a fast moving hand. The image clearly got destroyed during A/D conversion, and I'm assuming the weird green halo is a by-product of the 4:2:0 compression in the h.264 codec. No amount of core matting or hand roto is going to fix the fact that there just isn't any data there...so without much recourse, I pulled the key as it was.
Keylight did a decent job in the solid areas, but like I said before nothing is really going to fix the lack of data where there was heavy motion blur. I know motion blur is a pain, no matter what camera you use to key, but I've never quite run into anything this bad. So I soldiered on...
This actually isn't the real final comp, because we only delivered footage with alpha's, but its close to what you could expect to see in a comp with some edge treatment and a little light wrap. I'm not even going to get into what happened once the rain and confetti started falling...
So can you easily get a decent key from a 5D? Sure...if the subject doesn't move a lot...if the green screen is perfectly lit...if there aren't any semi transparent objects...and if there aren't crazy reflections. That's a lot of ifs.
I'm not a 5D hater...I'm actually a huge fan of the image that it can produce when you work within its limitations. In fact, Charlie Harrold shot Bouquet for us on a 5D, and I think its gorgeous. We worked with the tools strengths, and got awesome results.
For more information on the strengths and weaknesses of these new DSLRs check out the Zacuto DSLR shootout. Its a lot to take in...but well worth the time.