White balance

Learning goal

You will understand how the camera finds white, and be able to set white balance for the scene at the moment of shooting. You will explain that the number you enter in white balance tells the camera the color of the light, and in which direction the photo will shift if this number differs from the light; you will recognize the scenes where the automatic setting goes wrong; you will use presets and entering a Kelvin value for consistent color across a series; you will take a custom white balance with a gray card; and in a frame where people of different skin tones stand in the same light, you will know why setting color not by one person's skin but by a neutral reference lets everyone keep their own color.

The question

In a textile workshop, you are photographing three women working at sewing machines. Long fluorescent lamps on the ceiling, a window in one corner. Of the frames you take with auto white balance, in one everything is greenish, in another the fabrics have shifted to a pale blue, and in the frame you take near the window the colors are very warm. The same workshop, the same minutes, three separate colors.

Why do my photos come out orange or blue? Because in every frame the camera has to answer this question: what is white in this scene? In this lesson we will talk about how the camera answers this question, how to correct it when it gives the wrong answer, and how you can tell it the answer.

Context

In Lesson 11.1 we saw that light has a color, and that this color is described in Kelvin. The eye quietly adapts to the color of the light in front of it; you see white paper as white both in an incandescent room and on a cloudy street. The camera, on the other hand, records light as it is, and to show white as white it has to take the color of the light into account. This calculation is called white balance.

In Lesson 7.4 we learned to correct color afterward in the editing program. In Lesson 4.7 we also saw the white balance control in the phone's pro mode. This lesson carries the job to the moment of shooting: getting color right from the start, keeping a series the same color from start to finish, and reducing the work left for editing.

Simple explanation

What does the number you enter in white balance say?

When you set white balance to 3200 Kelvin, you tell the camera this: this scene is lit by a 3200 Kelvin light, that is, an orange light. The camera, to neutralize this orange, adds the opposite color, blue, to the image. If the light really is 3200 Kelvin, whites come out white. If you photograph a sunny street with the same setting, the camera keeps adding blue even though there is no orange on the street to neutralize, and the photo shifts to blue.

The rule in short is this: if white balance is set to a number lower than the light, the photo shifts to blue; if it is set to a higher number, it shifts to orange. When you photograph an incandescent room with the 5600 Kelvin daylight setting, the room comes out orange; when you shoot in daylight with the 3200 Kelvin incandescent setting, everything turns blue. The size of this shift, as in Lesson 11.1, depends not on the Kelvin difference but on the mired difference. White balance doesn't change the light itself; it only changes how the camera will interpret that light.

Where does the automatic setting go wrong?

Auto white balance (AWB) looks at the scene and guesses the color of the light, assuming the average should be neutral. In most scenes this guess works well. But if a single color dominates the scene, the guess goes off: in a kitchen painted yellow or a hall with a red carpet, the camera takes the color of the wall for the color of the light, erases it, and adds an opposite color to the image. At sunset, in a similar way, it can count the orange light as a mistake, press it down, and take away the warmth you wanted.

Another problem of the automatic setting is consistency. Because it guesses again in every frame, as the colors in the frame change, the guess changes too. In the workshop, when you turn the camera to a roll of green fabric, then to a rack of blue thread, the color of the photos shifts from frame to frame even though the light stays the same. For a single frame this may not matter; for a series, a product catalog or a family album it is a problem.

What are presets and Kelvin for?

Most cameras have presets shown with sun, cloud, shade, bulb, fluorescent and flash icons. Each white balance preset corresponds to an approximate Kelvin value and neutralizes for the light it is named after. The fluorescent setting usually also corrects the green shift a little. When you choose a preset according to the scene's light, color doesn't move from frame to frame the way it does with the automatic setting.

Entering the Kelvin value directly goes one step further. If you know the light's value, or have found it with a few test frames, you fix that number and shoot the whole series in the same color. Presets and Kelvin can also be used for a conscious choice: choosing the cloud or shade setting in daylight warms the photo, keeping Kelvin lower than the light cools it. This isn't a mistake, but a decision about the feeling the color tells, and it is enough to know that the decision is yours.

What is a gray card for?

The most accurate way is to show the camera what is neutral in the scene. A gray card is a colorless card made to reflect all colors equally. You hold the card where the subject stands, facing the light the subject gets; in the camera's custom white balance menu you photograph the card filling the frame and choose this frame as the reference. The camera now applies whatever is needed for the card to be gray in that light. If you don't have a card, a white sheet of paper can do the job too, but some papers contain whitening agents and can shift slightly to blue depending on the light.

If you shoot RAW, you can photograph the card once in the scene and then, in editing, correct the whole series the same way by clicking on the gray point in that frame. This path is especially valuable for frames with people in them. If you set color by looking at one person's skin, you also erase that skin's own warmth or coolness, and shift the skin of the people next to them by the same amount. A correction made by the gray card, on the other hand, erases the color of the light and leaves every skin, light or dark, with its warm or cool undertone as it is.

Visual evidence

You go back to the workshop. You lean beside the woman working at the middle machine, a dark-skinned, middle-aged woman in a headscarf, hold the gray card at the level of her face, facing the fluorescent lamps, and take custom white balance from this card. At the neighboring tables a light-skinned young woman and an olive-skinned older woman are working; all three under the same fluorescent lamps.

In the frame you take with the new setting, the greenish veil has lifted. The dark-skinned woman's face is a warm, glowing brown; the white of her headscarf is truly white. The young woman's light skin is pinkish, the older woman's skin a beige leaning toward gold; each stands in her own color. When you turn the camera to the rolls of fabric and the thread racks, the colors don't move from frame to frame. When you want to photograph the same workshop by the window, though, you hold the card in the window light this time and take a new setting, because that is a different light.

Common mistakes

Summary

White balance is the setting that tells the camera the color of the light lighting the scene: a value lower than the light shifts the photo to blue, a higher value to orange. The automatic setting can go wrong in scenes with a dominant color and gives inconsistent color across a series; presets and Kelvin fix the color and allow a conscious choice of warmth. A custom white balance taken with a gray card erases the color of the light and leaves each person of different skin tones with their own undertone.

Mini assignment

In this assignment you will photograph the same scene with different white balance methods and compare them.

1. Photograph a room lit by an incandescent or warm lamp with auto, the bulb preset and the daylight preset.
2. In front of a single-colored, dominant surface, for example a colored wall, take five frames with the automatic setting and look at whether the color moves between frames.
3. Hold a gray card or a white sheet of paper in the subject's light, take a custom white balance, and photograph the same scene again.
4. Photograph two people of different skin tones in the same light; set color once by one person's skin and once by the card, and compare the two results.

Check yourself

• Were you able to guess in advance which way the frame you took in the incandescent room with the daylight setting would shift?
• In the frame set by the card, are white objects truly white?
• In the frame set by the card, did the two people's skins stay different from each other, in their own colors?

Glossary

Mini quiz

1. If a sunny street is photographed while white balance is set to 3200 Kelvin, which way does the photo shift?

• A) To orange
• B) To green
• C) To blue
• D) In no direction

2. Why can auto white balance go wrong in a kitchen painted yellow?

• A) It takes the wall's color for the light's color, erases it, and adds an opposite color
• B) Because there is no light at all in the kitchen
• C) Because the automatic setting can't see yellow
• D) Because the wall spoils the exposure

3. To photograph a series in the same color in a place where the light doesn't change, which is least suitable?

• A) Fixing the Kelvin value
• B) Taking a custom white balance with a gray card
• C) Choosing the right preset
• D) Leaving it on auto white balance

4. In a frame with three people of different skin tones, why is it a problem to set color by the skin of the person in the middle?

• A) The exposure changes
• B) That skin's undertone is erased, and the others' skins shift by the same amount
• C) Focus slips
• D) The gray card can no longer be used

Answers

1. C — The camera assumes an orange light and adds blue; because the light is actually daylight, the added blue stays in the photo.
2. A — The automatic setting counts the scene's average as neutral; it takes the dominant yellow wall for the color of the light and presses it down with blue.
3. D — The automatic setting changes its guess as the frame changes; the others keep the color fixed.
4. B — Skin isn't a neutral reference; a correction made by it shifts that person's color and the others' colors.

Summary card

• White balance tells the camera the color of the light; it doesn't change the light.
• If the setting is lower than the light, blue; if higher, orange.
• The automatic setting goes wrong with a dominant color and makes color move across a series.
• A preset or Kelvin fixes the color; a conscious warmth is a choice too.
• Hold the gray card in the subject's light; every skin stays in its own color.

Bridge to the next lesson

While setting white balance, we kept going back and forth between the same two colors: we added blue to neutralize orange, and orange to neutralize blue. Why do these two colors erase each other so easily, and why do they bring each other forward when they stand side by side in the same frame? The next lesson arranges colors on a wheel and talks about complementary, analogous and triadic color relationships, and how these relationships are read in a photo.