White Balance

The paper on your desk looks white under a desk lamp, white by a window, and white in a fluorescent office — but a camera pointed at the same sheet records three distinctly different colors. White balance is the correction that reconciles what light actually does with what your brain insists it saw, and it's the single adjustment that most often separates a healthy-looking face on a call from a sickly one.

Light has a color

Every light source has a spectral character, and for most practical sources it's summarized by color temperature, measured in kelvin. The scale comes from physics: heat an idealized black body and it glows first red, then orange, then white, then blue-white as it gets hotter. A candle flame sits around 1900 K — deep orange. A tungsten studio lamp is standardized at 3200 K, still distinctly warm. Midday daylight is around 5600 K, roughly neutral, and an overcast sky runs higher still, into the blue. Counterintuitively, the "warm" colors have low temperatures and the "cool" blue light has high ones — the vocabulary of feeling runs opposite to the physics of glowing metal.

This means there is no such thing as neutral light in the wild. Any scene is bathed in a color, and every surface in it reflects that color mixed with its own. A white shirt under tungsten light is, measurably, an orange shirt. Some common sources complicate the picture further — fluorescent tubes and cheap LEDs emit spiky, uneven spectra that no single temperature describes, which is why corrections often need a second axis, tint, running green to magenta at right angles to the warm–cool one.

Your eyes correct; sensors don't

You rarely notice any of this, because the human visual system performs chromatic adaptation: it continuously discounts the color of the prevailing illumination, recalibrating so that objects keep stable colors as the light changes. Walk from sunlight into a tungsten-lit room and, within moments, white paper looks white again. The adaptation is so complete that most people are genuinely surprised the effect exists — the orange cast is invisible from inside it.

A camera sensor has no such reflex. Its photosites report the light that arrived, cast included, with mechanical honesty. Point an uncorrected camera at that tungsten-lit room and the recording is orange, because the light was orange. White balance, then, is the camera's substitute for the adaptation your brain does for free: an estimate of the illumination's color, and a correction that removes it so neutral objects come out neutral.

Film's answer and digital's answer

Photochemical film could not adapt at all — its color response was fixed in the emulsion at the factory — so the industry balanced around two standards. Tungsten-balanced stocks were formulated for 3200 K studio lamps and daylight-balanced stocks for sunlight; shoot one under the other's light and the results skewed heavily orange or blue. Bridging the gap was the job of filters and gels: a CTO (color temperature orange) gel warmed daylight down toward tungsten, and a CTB (color temperature blue) gel cooled tungsten up toward daylight — sheets of colored plastic clipped over lights or windows so that every source in the frame agreed with the film. The correction was physical, chosen in advance, and expensive to get wrong.

Digital cameras answer differently. A sensor sees through red, green and blue filtered photosites, and warm light simply drives the red channel harder than the blue. White balancing is therefore a matter of per-channel gain: amplify blue and rein in red under tungsten, the reverse under shade, until a neutral surface produces equal red, green and blue values. Because it's applied to the raw channel data before any of the lossy processing that follows, a sensor-level balance is clean — it rescales the channels rather than stretching an already-compressed image. The gels became two multipliers.

Where auto white balance fails

Since digital correction is just gains, cameras estimate it automatically. Auto white balance typically leans on a gray-world assumption — that the scene, averaged out, should be neutral — refined with heuristics for skin and sky. Most of the time this works. Its failures, though, cluster exactly where video calls live. Mixed lighting is the classic one: a desk lit by a blue-ish window on one side and a warm lamp on the other has no single correct answer, so the camera picks a compromise that leaves one half of your face cool and the other warm. Dominant colors break the gray-world premise — a large green plant wall or a strongly painted room reads as a color cast to be removed, so the camera shifts your skin the opposite way. And because auto white balance is continuous, it drifts: clouds pass, a screen's content changes, someone opens a door, and your face slowly slides between warm and cool over the course of a call — a shift your viewers perceive even if they can't name it. The fix for all three is the same: measure once, under the light you'll actually use, then lock the balance so it stops guessing. Locked balance trades adaptability for stability — exactly the right trade when you sit in one chair under one set of lights.

At the sensor or in software

There are two places to correct color, and they are not equivalent. Fixing it at the sensor — setting the camera's own channel gains — happens before compression and before any downstream processing, so it costs nothing in quality and everything after it inherits a neutral image. Fixing it in software means transforming pixels that have already been processed and compressed; a mild correction is harmless, but dragging a badly-cast image back to neutral amplifies noise and banding in the starved channel. The engineering rule follows directly: correct as early in the chain as you can, and use software adjustment for what it's genuinely good at — fine trim, and deliberate creative warmth on top of an already-correct image, not rescue.

In DeskBroadcast

DeskBroadcast applies that rule by working at both layers. On UVC-compliant USB webcams, it drives the camera's own hardware white balance — auto, or manual and locked — which is a sensor-level correction applied inside the camera before any compression or processing touches the image. That's the right place to make neutral actually neutral, and locking it there ends mid-call drift at the source. On top of that, the software Look pipeline offers warmth and tint controls for every camera, including built-in ones that expose no hardware controls. These sit deliberately at the other end of the philosophy: they're a creative choice — a touch of warmth to flatter skin, a tint trim for stubborn fluorescents — layered over a corrected image rather than substituting for correction. Both layers are previewed live in the menu-bar panel, so you can lock the hardware balance, add exactly the warmth you want, and know that the virtual camera is sending Zoom, Meet or Teams precisely what you're looking at.