All of our concepts stems from the film lab processes known as color timing. Originally this described the person who knew how long to leave the negative in the chemical bath to achieve the desired results (the “timer”). Once the industry figured out to manipulate color in the negative-to-positive printing process, the “color timer” was the person who controlled the color analyzer and who dialed in degrees of density and red/blue/green coloration. The Dale Grahn Color iPad application will give you a good understanding of this process. Alexis Van Hurkman also covers it in his “Color Correction Handbook”.
Electronic video color correction started with early color cameras and telecine (film-to-tape transfer or “film chain”) devices. These were based on red/blue/green color systems, where the video engineer (or “video shader”) would balance out the three components, along with exposure and black level (shadows). He or she would adjust the signal of the pick-up systems, including tubes, CCDs and photoelectric cells.
RCA added circuitry onto their cameras called a chroma proc, which divided the color spectrum according to the six divisions of the vectorscope – red, blue, green, cyan, magenta and yellow. The chroma proc let the operator shift the saturation and/or hue of each one of these six slices. For instance, you could desaturate the reds within the image. Early color correction modules for film-to-tape transfer systems adopted this same circuity. The “primary” controls manipulated the actual pick-up devices, while the “secondary” controls were downstream in the signal chain and let you further fine tune the color according to this simple, six-vector division.
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Oliver Peters breaks down some of the history behind color correcting and grading and the basic terminology.