How to turn background black and white but keep characters in color?

[Michael29035730wwsz]

Hello all, I am a student working on a short film and I am workshopping some ideas for its visual style. One idea I had, after looking at this music video, is turning the background black and white for a few scenes while keeping the characters in color. Is this possible for a film where the camera and actors will be moving a lot and how do you do it? Any help would be appreciated.

[Rick Gerard]

To create that effect, you need to duplicate the footage layer, rotoscope the top layer so that the background is removed, and apply a black-and-white filter to the bottom layer.

Depending on the footage, you may be able to use Rotobrush to remove the background. If the edges of the foreground person (or object) match the background colors, you may have to rotoscope the shot manually. Mocha AE can help simplify manual rotoscoping. 

Without seeing at least a frame of the shot you want to work on, it is impossible to suggest the most efficient workflow. The only thing I can tell you for sure is that the comp you create for that kind of shot should only be as long as the effect lasts. In the music video you shared, I didn't see a single shot of the woman in color with a black-and-white background that was longer than 2 seconds. If you need the effect for five to seven seconds, it can be quite doable. If you need the effect in a shot that is 2 minutes long, you're looking at a long and tedious process and you will probably need to break up the shot into manageable sections to get the shot completed.

[Michael29035730wwsz]

Thanks Rick! This is super helpful. There are certainly going to be some longer shots, but right now the entire project is probably going to be less than 20 minutes. I'm a complete novice at After Effects though, so I'm sure it will be difficult but good to know its possible.

[Mylenium]

As Rick said, depending on what you shoot, this could be a lot of work. At the same time it could be easy - if you are still in the planning phase, you can mold your shoot to facilitate the later work by e.g. dressing your actors suitably so they can be treated with simple color corrections without much masking. Either way, without even a hint of a story board or reference frame it's impossible to advise on the best strategy. Ultimately anything is doable even in a clunker like AE, it just depends on your skill level and how much work you want to invest.

Mylenium

[Michael29035730wwsz]

So dress my actors in colors that contrast well against the black and white, or against the native environment? Thanks for the feedback.

[Rick Gerard]

The most important part of shooting for Rotoscope or Rotobrush is to make sure that your subject is in focus. Sufficient depth of field is critical. If the subject is going to be moving quickly, you should also decrease the exposure time from the standard of about 1/50 of a second to at least 1/100. Motion blur is going to make a good roto extremely difficult or sometimes impossible. Then, you want to ensure that there are sufficient contrast or color differences between the foreground (actor) and the background. A shot like this one will be extremely difficult to work with. 

 All of those arrows point to places where the background and foreground colors are so close that Rotobrush is not going to be able to figure out where the edges are.

This shot will be much easier to deal with. There are still a few places where the foreground and background colors are very close. It's mostly in the shadows. 

Here's a quick look at the cleanup I had to do on the second shot:

I didn't even bother with the first shot because Rotobrush would not work on that shot. The dark background, dark shirt, dark parts of his hair, and a bunch of other problems tell me that it is not a shot that will work with Rotobrush. 

Make sure that your shot is trimmed so you don't waste time working on frames that will not appear in the final edit. When the shot is trimmed, you have decided if you need to apply some color correction to improve the edge detail, pre-compose the layer, move all attrites to the new composition, and trim the new comp to the length of the layer. After the Roto is complete and frozen (locked), you can turn off the color correction you applied to the shot to help Rotobrush find the edges.

I looked at about 20 Rotobrush tutorials and didn't find a really good one. Most had some good suggestions, but none of them emphasized trimming and pre-composing. That can be a critical, time-saving step. 

When I shoot with a fast shutter speed to reduce motion blur, I will usually Pre-compose my Rotobrushed comp again, moving all attributes and turning off color correction, then render the Pre-composed Roto comp. I can then add CC Force Motion Blur or Pixel Motion Blur to bring some motion blur back into the composite and make it look better.

I hope this helps. I'm including an in-depth Roto and Masking series of tutorials in my new tutorial series. Look for it here in a couple of weeks: My Quick Tips Playlist

[Michael29035730wwsz]

This is extremely helpful, and I'll absolutely be on the lookout for your tutorials. Final question--would shooting at 1/100+ of a second, applying the rotoscoping effects, and then lowering the frame rate in post to 24 fps for rendering to give it a more "cinematic" quality work?

[Rick Gerard]

I didn't say 100 fps, I said increase the shutter speed to reduce motion blur when you are going to need to do rotoscoping or use Rotobrush. It is much easier to add motion blur after creating the matte than dealing with it before. The same goes for focus. Make sure that the depth of field covers the subject. Because displays and television are 60 HZ in NTSC countries and 50Hz in PAL countries, the easiest frame rates to deal with are 30 fps (29.97 for broadcast) and 25 fps. If you are creating for theatrical release, then it's 24fps in the NTSC (most of the world) and 25 in PAL countries. Because 99.9999% of theaters use video projectors, those lines are a little less rigid. 

It's also important to know for your shot design workflow that streaming services (YouTube, Vimeo, Instagram, and the rest) throttle the frame rates and resolution depending on bandwidth. If you upload a 60fps 4K H.264 video to YouTube, only part of your audience is going to see it in 4K and 60 fps. Most of the audience is probably going to get an HD, 30 fps video. A 4K 60 fps video has 16 times more data than an HD 30 fps video. It's a matter of economics and bandwidth.