2D Goes 3D

By Industry Veteran Steve Wright

There is a paradigm shift under way in the world of compositing visual effects. More and more of the shot finishing is being pushed from the 3D department into the 2D department. The reason being, of course, costs and schedules. Revisions can be made much faster in the 2D department, so both time and money are saved by migrating the work into it. This change has introduced two major innovations, multi-pass cgi compositing and 3D compositing.

Today it is routine to render out several 3D lighting passes that are then combined, color corrected, and refined in the 2D department. A typical list of render passes would include ambient, diffuse, specular, reflection, transparency, occlusion, shadow, grunge, and fresnel. Of course, there is no upper limit here and some elaborate visual effects shots can have 20 or more passes - for each object in the scene! It has reached the point that the 3D department will set up the passes and render them out without over-fussing them or excessive test renders knowing that the 2D department will dial them in and give the shot its final look. This has considerably increased the productivity of the 3D department - and the importance of the 2D department.

Now, a whole new integration of the 2D and 3D departments is emerging as carefully selected 3D capabilities are being added to 2D compositing programs. When you switch to the 3D view in one of these advanced compositing programs you might think you are looking at Maya or 3D Studio MAX. You will see the classic 3D grid with lights, cameras, and geometry. A short list of geometric primitives are available (sphere, cube, etc.) plus the ability to add texture maps and shaders to the geometry. Not much can be done with geometric primitives alone, so there is also the ability to import massive 3D geometry databases built in real 3D systems using standard interchange file formats such as .obj or .fbx.

Match Move

One of the most important 3D compositing techniques is the match move shot. When camera tracking from the match move department is added to 3D compositing a whole new world of visual effects possibilities open up. Any 3D object can be created and “planted” into the original live action and appear to be locked to the scene without drifting around, even with a moving camera. This is an absolute necessity if you want to composite King Kong into the streets of New York.

We can follow the workflow of a match move shot using the original plate on the left (Fig 1). The mission is to add a wildly out of control sports car to an action scene. The live action plate is camera tracked to derive the position of the moving camera frame-by-frame as well as the 3D tracking markers

seen in Fig 2. With this information the 3D department can locate the street in 3-dimensional space which is then checked by placing a 3D reference grid (Fig 3) over the original plate to confirm it tracks correctly with the moving camera. The 3D car is lined up with the tracking markers and reference grid (Fig 4) then rendered with the moving camera track data provided by the match move department. Fig 5 shows the final composited shot with the 3D car perfectly tracking in the original plate even with a wildly moving camera.

Figure 1 - Original Plate

Figure 2 - Tracking Markers

Figure 3 - 3D Reference Grid

Figure 4 - 3D Car Line-Up

Figure 5 - Composited Shot

Read More about Camera Projection

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