Color Theory Basics – Color Correction

Film and Television has a need for accuracy with regards to color that does not translate to the stage. When on location, and shooting a scene where the primary illumination is the sun, it is often necessary to augment that light with artificial sources. The Director of Photography wants the artificial light to blend seamlessly with the natural sunlight, so they must precisely alter the color of the artificial light. Or, perhaps a scene is being shot inside a room with views to the outside. The human eye will notice the table lamp is a little more Amber and the light through the window a little more Blue. A camera will see a huge difference. In order to make the camera see these two lights as being variants on “White Light” it is necessary to use precise color filters to transform these lights into the appropriate color temperature. This is the film equivalent of Missing Color Syndrome.

Enter the world of Color Correction.

Color Correction is the general term for filters which turn incandescent lights to daylight (CTB or Color Temperature Blue), daylight to incandescent (CTO or Color Temperature Orange), fluorescent to daylight (Minus Green), and daylight to fluorescent (Plus Green). While in a filmic setting this topic could cover several posts, because I am dealing with color theory for stage lighting, we will address this all in a single essay.

CTB filters are probably the most commonly used Color Correction filters in stage lighting today. With the introduction of HMI Fresnels into live performance there arose a need to precisely balance the color of traditional incandescent lighting sources against these new Daylight discharge sources. Aside from the formal aesthetics of the light itself, these Hues provide the designer with a range of colors that look very good along the entire spectrum of human skin tones, as well as nearly all costumes. This has led to a shift in contemporary design towards a cool and clean stage picture which employs a range of CTB filters.

Let us return to our Rosco color correction from the discussion on Saturation. We can see that the colors range from nearly White to a nice cool Blue. The penultimate color, R3202, converts incandescent sources to Daylight (direct sunlight). The next color, R3220, is closer to the Blue Sky in which the sun hangs. Because different lights will be warmer or cooler we have a range of filters to fit every need.

Lee makes a similar range of colors. The difference between them is that Rosco colors tend to have a little more red in them, and are thus more recessive than the Lee colors which have a bit of Green and are more dominant. Returning to the needs of Film, Lee colors are more accurate, and are used more regularly. On the stage, the Rosco colors can be more effective because of the warmer tones on human skin. Knowing these distinctions it becomes possible to construct very clean palettes within a very tight range of colors that will give us all the effects we want from Dominant and Recessive Colors yet appears as Daylight to an audience.

Going about in this manner we might use L201 (Full CTB) in our Backlight to give a strong dominant color choice for that angle. For our Sidelight then, wanting to be a bit less saturated so as to maintain skintones and costume colors, we might choose L202 (1/2 CTB). This color has the added benefit of giving us a high dynamic range of color temperatures. When the light is at full intensity is a cool and crisp light. As we dim it, the light source gets warmer and more Amber such that we can use these lights for warm intimate scenes as well. For our Frontlight we might want something close to Clear incandescent light. But, remembering what we learned about Missing Color Syndrome would want a color in a sympathetic Hue to the rest of our Palette. Perhaps we would choose an R3216 (1/8 CTB), a more recessive version of this same family of colors.

When working with HMI, or similar discharge sources which produce a cold light, we can use these same ideas in reverse. Thus we might use a 1/8 CTO Backlight, 1/2 CTO Sidelight and Full CTO Frontlight. Similar to the CTB, the distiction between Rosco and Lee is the same. Rosco tends towards Red while Lee tends towards Green.

These same ideas and principles apply to the use of Plus Green and Minus Green filters. The Minus Green filters have the added benefit of working as a precise range of colors when solving Missing Color Syndrome or trying to balance out a followspot (which tend to be cold and a bit Green) against a majority incandescent light plot.

Just as the more visible technology we use in the lighting industry has made tremendous advances in terms of intelligent lighting, show control, rigging, and so forth, so too has the world of color technology. Time was even the level of control considered necessary for film was nowhere near as precise as it is now. Today, color technology has advanced to the level of precision where we can convert the color of newer quartz lamps (like those found in Source-4s) to traditional incandescent lamps with filters like R302.

The world of color correction is, on its own, as broad and varied as the whole world of color. Simply fine tuning color work within these ranges can be an experiment years in the making. Some designers have made whole careers with a palette that hardly diverges from this range.

If you are new to the world of Color Correction I would strongly encourage you to start exploring. Compare analogous colors like L201 and R3202 and see what distinctions you can make. Do all the colors from a particular manufacturer vary only in Saturation or is there variance in Hue as well?

I hope you found this useful. Please take any new ideas and start experimenting. We will continue to build on these concepts throughout this series. Stay tuned.

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