Tip of the Week: January 2005 Archives
Paint. This tip goes hand in hand with last weeks tip, Roto. When do you paint frames as opposed to roto? How can you decide which method will work best given the task at hand? Follow the link, and I'll help you break it down.
One thing to always remember, is that painting multiple frames to remove something is time-consuming and wasteful. There are always easier ways to get rid of a camera, or a grip, or wires. By using roto you can effectively get rid of the aforementioned items, and use your paint skills to clean up harder areas of the frame.
Paint is also not only used for clean-up, but also for creation. You can use paint strokes as lightning strikes, for electrical surges, for laser blasts. Almost anything that is dynamic in action can be created by paint. During my time on Stargate SG-1, I painted such items as staff blasts, zat hits, and electrical surges. If you take a look at my 2001 demo reel you will see some of the painted electrical arcs that I've done using paint.
A method I've seen by some beginning artists (I've done this when I started!) is to paint tracking markers out by hand. Every frame. Or paint out wires. Many wires. Things to look out for when analyzing a frame and deciding when to paint come with practice and time. Let's say I want to remove a wire rig that's holding up an actor. And for the sake of argument, it's a simple rig on a simple background. An actor suspended on bluescreen. The easiest way to remove this wire is to copy a bit of the surrounding bluescreen over the wire. You're not painting through it, you're covering it up with other bits of the frame. You'll have to track this little bit and cover the wire as it moves, but it's vastly easier than painting a clean frame and trying to match it up via grain later. However sometimes it becomes necessary to do that. Pretty soon the only areas you will need to paint and touch up are where the wires meet the body.
Rotoscoping. The technical art of tracing a frame many times. Many, many times. All of us have done it at some time or another. And if you haven't, what are you waiting for? It's a skill that should be learned, however tedious it may be. Here are some tips to help you ease the pain.
While rotoscoping moving people, I tend to use several different nodes for each part of the body. Hands, arms, legs, torso, head. Depending on your compositing package, this will make deleting or redoing any section of the person easier. Don't set keyframes on every frame, or even every 5 or 10. If you're rotoscoping a human, you'll want to match the cadence of their walk or run, so keyframe the roto on the highs or lows of their gait.
You will want to use a tool that allows you to have soft edges, so that motionblurred frames of the person will accurately be rotoed. If you're going to be rotoscoping objects, like cars, boxes, things that are usually inanimate, you can use one complete roto to cover the entire object. However, if there are extreme perspective changes, it might be better to use different roto for different parts of the object. Sometimes for objects like these, you can roto the first frame, and track the object throughout the shot duration.
When you're compositing 3D images into a film or video plate, it will rarely match up. Your job as a compositor is to dial in the color values, match the blacks, fleshtones, and so forth, until what was added and what is original blend together. Adding grain onto your final 3D is a necessary step to make the shot feel as if it was shot in one take.
Following up on last week's Tip, today I'll discuss a similar topic. Shadow density refers to the color density of an object's shadow . This shadow is usually created by using a shadow alpha created by your rendering package, or even by simple roto. The colors of a surface under shadow can vary greatly, so take great care in analyzing reference of similar shots, or similar areas in the frame that contain shadows. There are different methods of getting an accurate shadow, and using the technique of gaining our black point is probably the quickest way of getting a shadow value. Just sample the colors that fall under shadow, and dial your artificial shadow values in to match!
