You've examined the color correction tools in depth; now it's time to move on to the bread and butter of compositing: matching foreground and background elements so that the scene appears to have been taken with the same basic light conditions.

Melding images together and eliminating all clues that they came from separate sources is as much science as art. Up to this point we've focused on optimizing source footage, which is a more subjective and artistic practice. Once the background has been properly graded, however, matching the foreground using the same tools is typically more objective (except in cases where essential clues are missing more on that in a bit). The process obeys such strict rules that you can do it without an experienced eye for color. Assuming the background (or whatever source element you're matching) has already been color-graded, you even can satisfactorily complete a shot on a monitor that is nowhere near correctly calibrated.

How is that possible?
As with so many things in visual effects work, the answer is really a question of correctly breaking down the problem. In this case, the job of matching one image to another obeys rules that can be observed channel by channel, independent of the final, full-color result.

Of course, effective compositing is not simply a question of making colors match; in many cases that is only the first step. You must also obey rules you will understand from having done the kind of careful observing of nature described in the previous chapter. And even if your colors are correctly matched, if you haven't interpreted your edges properly or pulled a good matte, or if such essential elements as lighting, the camera view, or motion are mismatched, your composite will not succeed.

These same basic techniques will work for other situations in which your job is to match footage precisely for example, color correcting a sequence to match a hero shot, a process also sometimes known as color timing.