Is white not white? Why is white balance important for photography? Our light varies not only in brightness (light intensity), but also in color temperature. What is color temperature and what does it have to do with photography?
For a deeper understanding we need a small trip into physics, so that we can grasp the used terms.
Our visible light is physically seen electromagnetic radiation with a wavelength in the range of 380 to 750 nanometer. Shorter wavelengths have a higher proportion of blue (high color temperature) - long wavelengths have a range of 600 to 700 nanometer and account for the red component of light.
White light is a composition of different wavelengths. As a reminder: in physic classes white light got refracted into its colors with a Prisma - that way the colors become visible.
Color temperature is measured in kelvin. Please think about a glowing iron - it has depending on the temperature different colors. Light with a low color temperature has a high share of longwave light.
For assessing the different specifications:
|Light situation||Color temperature in kelvin|
|Light bulb (60 W) from the good old days||2680 K|
|light bulb (100 W)||2800 K|
|halogen lamp||3000 K|
|Morning sun / evening sun||5000 K|
|Mid-morning sun/ afternoon sun||5500-5600 K|
|Midday sun, clouds||5500-5800 K|
|Overcast sky||6500-7500 K|
Not only the source of the light, but also the surrounding surfaces have an influence on the color. Surfaces absorb or reflect light and possibly add a coloring. A red wall on one side of a portrait photography can lead to a red coloring. And when we think of looking at the sun then we realize that the sun does not reach the earth unfiltered. Clouds and the air's composition tint the light and give it a coloring. Thereby different colorings occur in the course of a day, because the sunlight hits the atmosphere of the earth different and thus its color temperature changes.
Our brain changes the in the eye accrued pictures and makes a "White Balance (WB)". From experience we know, that a book as generally white pages. That is the reason why a book page still looks white in the evening even when we look at it in the yellow light of an old light bulb. It becomes critical, when the book has colored paintings, they can look quite disparate in the yellow light of the bulb.
The „automatic white balance“ of a humans is called color constancy and is a feature of the human color perception system.
In the analogues photography there were different film types depending on application - daylight films or artificial light films. A fast change was very unedifying. Fortunately, this became much easier in the development of digital cameras.
The automatic white balance (WB) of digital cameras has generally the abbreviation AWB - automatic white balance, sometimes only WB for "White Balance". In a technically simplified explanation following happens - the camera software looks for the area of the picture which is white (or nearly white). If there is no white in the picture (for example a green forest), then the software picks the brightest spot of the picture (in the hope, that it is a grey). When there is no uniform grey area (photo on a green meadow without a sky) then the white balance of a camera will have problems. That means, when the brightest area of the picture is colored and not neutral grey the taken picture will have a color cast!
On the other hand, the white balance works in standard situations astonishingly reliable - but fails when there are difficult light situations and also in mixed-light situations. When there is daylight and additional different artificial light with the same brightness, then the white balance of most cameras become pure luck. If the camera had no luck in guessing the photographer gets a picture with a color cast. However, the camera is unbeatable by a fast change of light situations (for example fast changing weather like a windy day with overcast sky with blue areas).
Because of this there is additional to the automatic white balance an important manual white balance, which is in difficult light situations the ideal solution. Mostly, cameras have standard selections with more or less meaningful symbols - to be strictly accurate it is a half-manual white balance. Good digital cameras allow to make an own white balance - either with a gray card or by directly choosing a kelvin number. More about it later on.
Good cameras offer the possibility to do a white balance series (White Balance Bracketing). That way, the camera does several photos with varied White Balance settings.
It is good to know, that depending on the chosen saving format an unintentional wrong set white balance can be more problematic. If you save your pictures in jpg format, then a later white balance with a software will lead to a loss of quality. That is one of the reasons why I recommend the RAW format.
Check beforehand if your camera supports the RAW format or not. Many cheap consumer cameras only offer the space-saving JPG format. Generally, RAW is offered by digital SLR cameras (it must be set on it). Many RAW formats save the data "raw" - that way a later color adjustment, i.e.: a white balance with a software does not lead to a immense quality reduction as when using JPG.
Depending on your cameras the operating steps are different. First, take a gray card and hold it into the picture. Important is, that the gray card has the same angle to the light source as the object or person you want to take a picture off. In portrait photography, you can also hand the card to the portrayed one and the person holds it under his nose in the direction of the camera. If the light situation changes a new white balance is needed.
Sometimes you can read, that a simple sheet of paper is a good-enough substitution for a white balance with a grey card. Hands off! Depending on the paper manufacturer there are different brighteners inside the paper which emits a high amount of blue content. These are not noticeable with the human eye (because of chromatic adaption). Certainly, you do not deliver pure white to camera, but something and might even cause a color cast with that method.
Author: Axel Pratzner
Translator: Felix Pratzner