How to generate a character on green so it keys cleanly afterwards
Tell Vizard Agent the shot is for compositing and ask it to generate the character onto a plain green field. It then measures whether that green stayed one consistent colour across the whole shot, since generated backgrounds drift as the subject moves, and tests the key against the finest edges in the design before committing to a render.
What do you type into Vizard Agent?
Say plate to Vizard Agent, not shot. The instruction that matters is that this is an element rather than a picture, because anything asked for as a good-looking shot will light the subject to a background it has just invented for itself. Give the action in seconds, and name the finest detail: whiskers, hair, feathers or lace.
Prompt
What does Vizard Agent actually do?
A character generated standing in a room is part of that room: the edges are lit by it and the shadows belong to it. On green it stays an element. But a filmed green screen is lit once, while a generated one is re-invented every frame and can drift in hue or brightness as the subject moves. In the session behind this article it:
- Opened the character reference sheet for each of a series of four-second plates and read the design.
- Generated the opening keyframe of the character on green and checked it before animating anything, since the keyframe governs everything after it.
- Animated the action from that keyframe, reviewed the frames and zoomed in on the timing of the movement.
- Measured the background green for consistency across the shot, then tested the chroma key and checked its quality at the hair, whiskers and other fine detail.
- Measured the character's position in the frame, rendered the final shot with its camera move and checked it back.
When does this not work well?
Green is a bad choice for some designs. A character wearing green, or one with translucent or reflective parts, will lose pieces of itself to the key, and a different backing colour or a generated matte is the better route. Very fine or motion-blurred detail cannot be recovered, and the longer a shot runs, the more the green drifts.
Common questions
Why not cut the character out afterwards? Because the edges are lit by the scene. Vizard Agent generates onto green instead.
Does generated green really drift? It can, because each frame is re-invented. Vizard Agent measures it.
What if my character is green? Say so and Vizard Agent uses a different backing colour.