White Balance and Color Temperature

Colour temperature describes the colour of light on a line from warm to cool, measured in kelvin (K). The scale comes from physics: a perfect black body heated to about 2,000 K glows orange, around 5,500 K it glows roughly white, and hotter still it turns blue. Candles, tungsten bulbs, the sun and the open sky all sit close to that line, which is why most casts are simply “too warm” or “too cool”.

Note the inversion that confuses everyone: a camera set to 3,200 K expects warm light, so it adds blue to compensate. Lower kelvin settings on a camera therefore make the picture bluer. In the studio there is no inversion: Temperature moves the picture itself, positive towards amber and negative towards blue.

Tint is the other axis. Fluorescent tubes, cheap LED panels and some sodium and mercury street lights emit an uneven spectrum that sits off the black-body line, usually towards green. No amount of warming or cooling removes that; Tint, which runs from green to magenta, does.

Your visual system recalibrates to the light in a room within seconds. A camera has to estimate it from the picture alone, and automatic white balance relies on assumptions that are often false:

• That the scene averages out to grey. A green lawn, a red wall or a blue swimming pool drags the estimate towards the opposite colour, so the camera adds magenta to grass and cyan to the red wall.
• That the brightest area is white. At sunset the brightest area is the golden sky, so the camera neutralises the very warmth you wanted to keep.
• That there is one light. A face lit by a window on one side and a lamp on the other has no single correct balance.
• That the light stays the same. Walk from indoors to outdoors and the camera re-guesses mid-shot, so the colour drifts over a few seconds.

Fixed presets avoid the drift but are only as good as the guess: a camera left on a tungsten setting outside turns everything blue. Fortunately, as long as no channel is clipped, white balance is one of the most forgiving corrections to make afterwards.

A neutral surface reflects red, green and blue equally. If the camera recorded it with more red than blue, the difference came from the light, and since that light fell on everything, the same correction fixes the whole frame. Pick white (W) automates this: click something that should be neutral and it measures the patch in linear light, then sets Temperature and Tint to the values that neutralise it. The sliders stay editable afterwards.

Temperature works as a camera does, by scaling the channels in linear light (±100 is ±0.75 of a stop of red against blue), and it keeps the luminance of white the same, so a correction changes colour without making the shot lighter or heavier.

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Choosing a good reference

• A light or mid grey, not the brightest white: a near-white patch may have one channel clipped, which skews the reading. On the chart, the middle steps of the grey wedge are ideal.
• Lit by the same light as the subject. A white wall in the sun says nothing about a face in the shade.
• Truly neutral: cream paint, ivory fabric and “white” objects catching a coloured reflection all mislead.

Confirm on the scopes

On the Parade, the red, green and blue traces over the neutral area should now be the same height, and on the Vectorscope the neutral patches should sit on the centre dot. Check more than one level: if the mid steps of the grey wedge line up but the top or bottom steps don’t, the cast isn’t a simple white balance error, and the wheels are the better tool. See how to read video scopes for a refresher.

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Temperature and Tint constrain the correction to the axes that real light follows, which makes them fast and hard to misuse. The colour wheels are unconstrained: the puck can push in any direction, so they fix casts that don’t follow the light, and casts that are not proportional to it. The shape of the cast on the parade tells you which to reach for:

Gain multiplies, so like a light source its effect is largest in the lightest tones and zero at black; it is the wheel equivalent of a white balance, though it works on the display-encoded signal rather than in linear light. Offset adds the same amount everywhere, which is right for flare, haze or a cast baked in by a poor conversion, where colour has been added on top of the picture. The colour wheels chapter covers the maths and the R, G, B fields that show each wheel’s exact effect.

A global white balance can only neutralise one light. With daylight from a window and tungsten from a lamp in the same frame, balancing for one leaves the other warm or cool. Decide which light matters, almost always the one on the faces, and balance for that. A little warmth from a practical lamp or a little blue from a window usually reads as natural, even pleasant.

When the other light is genuinely distracting, correct it separately. In Secondary, choose Add a secondary layer, isolate the problem area with a Gradient or Circle window, or a qualifier on its colour, and use the layer’s own Temperature and Tint. Because the change lives on its own layer, it doesn’t disturb the main balance. The secondary colour correction chapter shows the technique step by step.

Neutral is a starting point, not a goal. Warm light reads as comfort, nostalgia or late afternoon; cool light as calm, clinical or cold. The craft is to make those choices deliberately rather than inherit them from the camera.

Keep correction and style apart. Neutralise on the Correction layer, then in Layers choose Add layer and warm or cool that layer with Temperature. Its Opacity becomes a dial for how much warmth you want, and you can switch it off to check the neutral version at any time. For a split between warm and cool tones, use Split toning in Creative, or start from a look: teal and orange and cinematic grades both build on a neutral base. The creative looks chapter explains how.

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