In previous DV101 columns and blog entries, I’ve discussed the principles of color temperature, understanding different wavelengths of light and how they are recorded by digital sensors.
Physiologically speaking, we see colors in the world based purely on the wavelengths of light reflecting off that object. Each object is, literally, a different color based on the light falling upon it, although the human mind has the innate ability to reconcile these differences through adaptive color interpretation and color memory. To most people, a sheet of white paper is white no matter where they see it because their mind knows that it’s supposed to be white and their brain will render it as white. In truth, that paper can be blue, orange, green or yellow, depending on the light falling on it.
Digital sensors are nowhere near as adaptive or forgiving as the human brain. The digital sensor needs to be informed as to what wavelengths of light are present in order to “correctly” render the colors in a scene. The digital sensor will see the white paper for the color it truly is at any given moment, which can be undesirable, at times.
It is important to understand that not only is “white” subjective, but white is a combination of all colors of the rainbow equally reflecting off of a surface. What we perceive as white is actually red, orange, yellow, green, blue, indigo and violet all reflecting off that surface in equal amounts. Sunlight has all of these colors in it, to varying degrees depending on the time of day, place on the globe and atmosphere. In the early morning, when the sun is just rising, the angle of light to the atmosphere filters off most of the short wavelengths in greens, blues and indigos to give a very warm light (2000°K – 3000°K). At noon, with heavy cloud cover, the atmosphere is filtering off much off the longer wavelengths, creating a very cool light (9000°K – 20,000°K).
Although digital sensors need to be “informed” as to what wavelengths of light are present at any given moment, they are extremely adaptive to rendering those specific wavelengths to a natural “white,” wherein the colors will represent, digitally, roughly as they are seen to the standard human eye.
I’m talking, of course, about white balance. This term is originally derived from old-school video cameras wherein the imager was “informed” as to what colors were available by adjusting, individually, the red, green and blue sensors and measuring the results on a waveform monitor in “parade” mode. White balance was achieved when all three signals — red, green and blue — lined up in an equal balance.
This is exactly what modern cameras are doing: they just do it automatically. When you white balance, you are forcing the camera to adjust its sensors so that red, green and blue are seen equally off that object (presumably white or neutral gray).
Most digital cameras have several white balance settings: factory preset “tungsten,” “daylight” auto white balance (AWB) and custom. Some prosumer cameras have additional settings for fluorescent, daylight shade and cloudy daylight.
Personally, I would never recommend AWB unless you’re in a completely uncontrollable run-and-gun situation where you don’t have the time to balance correctly. AWB, like auto exposure, is a compromise based on average values seen by the camera. In an AWB situation, the camera has to guess what elements of a frame are actually white in order to render them correctly. In many cases, this can lead to an acceptable setting, but rarely will it ever result in a preferred setting.
The factory presets for daylight (5500°K) and tungsten (3200°K) are handy for a number of run-and-gun situations, but will often require color correction in post to really generate the look the videographer is after. Rarely is daylight ever specifically 5500°K and rarely are artificial incandescent sources specifically 3200°K.
The real power of the digital camera is in custom white balance. The ability of the videographer or cinematographer to custom define what should be seen as white in any given scene.
What you use to white balance can be just as important as what light you white balance under.
Generally, people seem to white balance off any “white” source they have handy. I’ve been known to use typing paper on a number of occasions (or the back of a script), but to be precise with your white balance, you should use a calibrated source. Whether that be a calibrated white card or an 18% grey card (my preference). Earlier this year I reviewed an extraordinary product called the ExpoDisc — a product that I now carry with me on every shoot. It is plastic disc that goes over the camera and, when pointed at your source light, creates a perfect 18% gray scale lit by your source to white balance off of. Quick, simple and incredibly precise. In my tests, the ExpoDisc produced the most accurate whites.
Above is a screen shot from Adobe’s OnLocation, a program that analyzes DV signals and puts them through software-simulated analysis devices. In this case, I’m showing a spectrum analysis (red, green, blue and luminance), a waveform in “parade mode” (showing luminance, RY and BY) and a vectorscope. In this first image, this is a custom color balance from a Canon XL2 set with the ExpoDisc under natural daylight through the window in the late afternoon. Note how extraordinarily close the image analysis is — red, green and blue are nearly identical. In the waveform, we’ve achieved a perfect white balance with all three signals (luminance, red and blue) lining up in the center. Finally, the vectorscope signal is dead center — perfect neutral.
Above is the camera’s auto white balance setting — still through the ExpoDisc, meaning the entire image is a perfectly calibrated 18% gray, but the AWB cannot render it cleanly. There’s considerably more blue in the image and much less red. The waveform doesn’t line up and you can see the vectorscope signal biasing toward blue/cyan.
In this final capture, we see the preset “daylight” (5500°K) and, below that, the “tungsten” (3200°K) settings. Obviously the tungsten setting is way off and will be very, very blue. But even the daylight setting is off because the natural daylight at that time in the afternoon was warmer than 5500°K.
Setting a custom white balance for any given location will help render the scene as the videographer wishes it to be experienced. That doesn’t always mean making it “white.” Sometimes having a scene that appears warmer or cooler than white is desirable. If you’re shooting a scene at sunset, the last thing you want to do is white balance under the setting sun and “correct” out the warmth of the sunset! In that instance, it’s best to utilize the standard “daylight” camera setting, which will render the sunset in a pleasing orange/red warmth.
On a number of occasions, I have white balanced through a piece of color correction gel — CTO (orange) or CTB (blue) of varying strengths to bias the camera in the opposite direction.
The scene in the frame below with actress Jennifer Taylor was lit with natural sunlight on a bright afternoon.
Instead of white balancing “clean” or using the preset “daylight” setting, I white balanced through a 1/2 CTB filter to fool the camera’s sensor that the lighting was cooler than it really was so that it would bias the scene in a warmer direction.
The opposite of this, in this shot, actress April Adamson is lit with tungsten light with a 1/2 CTB on the lamp (to partially color the light for effect while not losing as much light to the gel as I would with a full CTB). The director, Jamie Neese, wanted a very deep blue, so in addition to the coloring of the lamp, I white balanced the scene through a full and a half CTO to create a very deep blue cast. This was a very early DV project for me, shot with the JVC DV-GY500, and I admittedly pushed the white balance effect too far. Although we achieved exactly the color the director wanted, I also introduced a considerable amount of noise by pushing the camera’s internal circuitry so far into the blue range. I learned that if I were to do this again, I would achieve the same look by going halfway on set, in-camera, and getting the rest of the hyper-saturated look in color correction in post.
In another use of white-balance effects, this also for Mindgame, directed by Jamie Neese — the light coming through the vertical blinds is actually natural daylight. I have a layer of neutral density 1.2 on the window beneath the blinds, and I’m lighting the room with tungsten lights with 1/2 CTO on them. I white balanced under the tungsten lights WITH the CTO so that those lights would appear “white” and the natural daylight would appear very deep blue, as if it were moonlight.
When balancing through gels, I’ve found the Lee Cinematographer swatchbook to be very handy as the gel pieces are 2″ square, sizeable enough to fit over most lenses.
As an alternative, a couple of manufacturers make specially calibrated white balance cards with warm or cool tints built in to achieve the same effects. DSC Labs (www.dsclabs.com) offers a calibrated white balance card and a warm balance, which gives the effect, roughly, of an 81A filter. Vortex Media (www.vortexmedia.com) offers WarmCards 2.0, cards that are calibrated in various strengths of warm or cool bias.
Always make sure, if you’re using gels for effect, to white balance WITHOUT the gels; otherwise, the camera will counteract the effects.
It is also, sometimes, preferable to utilize the incorrect white balance setting. Is the natural sky a little too overcast and grey or looking for your scene? Want a really deep blue sky? Set the camera to tungsten balance, light your shot with tungsten fixtures and the natural daylight will naturally render a much deeper blue.
Hopefully this little white balance opus provides you with some new thoughts on a relatively boring step in your videography.