I just came across another example of a production where you should leave the DSLR in the bag.
This time it’s something that I believe a sane person should avoid at all costs anyway. But shooting it with a DSLR? Well…
Scenario
You’re working on a project shot with DSLR cameras where a character has a scene in front of a well known landmark in a city far from the rest of your story. You look at the budget to get those shots and start talking about other ways to accomplish the scene. Someone pipes up and says, “Why don’t we just green screen it? No need to travel, we’ll shoot in the studio.”
Question
Do you check that problem off the list and schedule the time in the studio?
Reality
Green screen, blue screen, it doesn’t matter which color you use. This is a difficult production technique to pull off correctly under any circumstances. But doing it with a DSLR can make everything even more troublesome.
Pulling a good chroma key requires good chroma. That’s the color information in the video. That’s also the “4″ in the three numbers you see after some codec definitions, like Apple’s ProRes 422.
The best video for pulling a chroma key is uncompressed 10 bit video with a 4:4:4 color space. DLSR cameras produce highly compressed 8 bit video with a 4:2:0 color space. The differences are significant.
Highly compressed 8 bit video with 4:2:0 color is one reason why it’s difficult for high end film producers to embrace DSLR cameras. There’s just not as much information in DSLR video as in an uncompressed codec with 4:4:4 color space. It’s why professional color graders say it’s more difficult to grade DSLR footage. And it’s why you can’t pull great chroma keys from DSLR footage.
Besides, it’s easy to record uncompressed 4:4:4 video. Just get something like the DeckLink Extreme from Blackmagic and tap the full resolution HDMI or SD/SDI outputs of your camera.
What… your DSLR doesn’t have full resolution HDMI or SD/SDI outputs?
Neither does mine, no DSLR camera has these outputs. But you’ll find either HDMI or SD/SDI outputs on all professional camcorders, most prosumer camcorders, and even quite a few high end consumer camcorders.
If you plan to shoot much chroma key video I’d suggest going with one of these setups rather than a DSLR. You can spend about the same money and end up with a much better result. And the good news is that’s it easy to simulate the shallow DOF of a DSLR with a chroma key. Just dial in some Gaussian blur on the background.
But, just for the sake of argument, let’s assume that you take the time to set up the perfect green screen shot. You have your background loaded into your laptop with software that can generate the key. You’re able to overlay the key and view the results on a high quality monitor so you can match lighting and align the shot perfectly. You have the staff on hand to control everything for the perfect shot.
How long do you want to live with that shot on a timeline? Five seconds? Maybe a bit longer?
If you want to cut to a closeup you’ll need to shift your background to match the new camera angle. In fact, if you move the camera at all you’re going to need to adjust everything.
What if you’ve got two actors and need an over the shoulder shot? You’re going to need the reverse of your background that matches perfectly.
What if you want to pan or zoom or make any kind of live action move? You’re going to need to have a system that allows you to move the virtual camera on your background to perfectly match the live camera move.
I’m not saying that any of this is impossible. I am saying that getting great special effects shots take much more preproduction, production and post-production to pull off. If it was easy, everyone would be doing it. How many high budget films have you seen with poor chroma key effects?
On the other side of this situation, there are times when the visual design of the production makes such special effects necessary. If you have to take on such a project here’s a video with the best chroma key product I’ve seen. It will work with your clips from a DSLR and even an HDV camcorder.
Guy Cochran over at dvestore.com sells a product called Reflecmedia. Rather than paint a wall green and light it very carefully, Reflectmedia uses a special cloth that reflects light directly back to the camera. It has an LED light ring that you attach to the front of the camera. The light from the LED is very pure color and bounces off the special cloth to produce a great source for pulling a chromakey. Watch the video and Guy will show you how it works.
Reflecmedia in action – Chroma key made easy from Guy Cochran on Vimeo.
Chroma key is one of those things that people seem fascinated with and can’t wait to try. If you must include a chroma key shot in your project then the good news is that you’ll get to bill your client a lot more. If you’re the client I’d think of other ways to solve the problem than chroma key.
Tell me what you think? What’s your experience with chroma key?
