In this article I will explain what white balance is, and how your camera deals with the process.
I will provide a broad outline behind the principles of white balance.
It’s for beginners and non techies who just want to learn enough for the purpose of improving their photography.
If you are a beginner you will learn exactly what is white balance in photography, in easy to understand language.
Table of contents:
- What is white balance?
- How do you know if an object is pure white?
- How colour is recorded on a cameras sensor
- How the white balance algorithms work
what does white balance mean in photography?
White balance is a setting in your camera that will attempt to correct a color cast that may be present in your image.
What’s a color cast?
Color casts occur when a single color washes over the entire photograph. It’s usually caused by the ambient light in the environment that you are photographing in.
Here’s a few reasons why you may get a color cast in an image
- Artificial lighting can introduce a color cast.
- Sunlight filtering through clouds
- Sunlight that is low in the sky and filtering through lots of atmospheric air and dust.
- Some resin filters that you may use to filter out light (eg neutral density filers) can also introduce color casts
What type of color casts are there?
The two big ones for landscape photographers are cold color casts, and warm color casts.
So, in order to explain what the white balance settings on your camera does, we need to first understand what these color casts are.
A warm color cast happens when a white object appears yellow/orange in a photograph.
The word ‘warm’ in this context refers to light that’s a yellow/orange colour.
So when yellow source light (like the Sun, late afternoon) shines on a white object, that white object will appear to be yellow (at least it will to a camera’s sensor).
Human eyes will also pick up yellow light, but our brain will do it’s own white balancing. That means that strong color casts in real life are often dampened down in our brains.
It’s not just the white objects that will look ‘warmer’ in your photo, the rest of the image will look warmer too, creating a warm yellow/orange color across the entire image.
- A color cast is where a specific color washes over an entire image, so every pixel is equally affected by the color alteration.
Any more examples?
A warming effect can also happen under artificial lighting.
Incandescent light bulbs emit a very warm, yellow light. This will cover all objects in a photograph in a yellow color cast. Sometimes a photographer may want this, and sometimes not.
What about all that blue that I get in my photos when I shoot at dusk?
A cool color cast happens exactly like a warm color cast, but the cool color cast refers to a blue color.
A blue color cast can happen naturally on a cloudy day, because clouds will filter some of the red spectrum from the Sun.
It means that the light that manages to make it through the clouds contains more of the blue spectrum in it. All the objects that the blue light falls on will create a blue color cast.
Humans may not notice how much blue there is in a scene, due to our brains interpreting light in it’s own non-linear way.
Camera technology works in a totally linear way, so lots of blue in reality will translate as lots of blue on the sensor
So how does the white balance settings on my camera have to do with all this ?
Definition of white balance in photography: The process by which a camera will attempt to remove the color cast so that white objects appear in the photograph as white.
That difference is then applied to every pixel in the image.
The theory is that this will neutralise any color cast, and the photo will look as though it was shot in pure white light. That may not be the creative outcome that you want
Is there any such thing as pure white?
The true color of an object can be defined as its color when viewed in pure white ambient light.
Pure white is difficult to come by, so some compromises have to be made. Instead of pure white, we can settle for neutral light.
Neutral light is light that may not be pure white, but is close enough to pure white not to bother the viewer.
One definition of neutral white would be the light on a sunny day when the Sun is directly overhead. So a white sheet of paper will appear as close as possible to pure white in these circumstances.
That becomes one definition of white, and that is good enough for landscape photography
How color is recorded on a camera sensor
The color of an object is defined by three events:
- the color of source/incident light falling onto an object.
- The colors of the spectrum that are naturally absorbed by the object.
- The remaining light that is reflected back into your eyes, or onto your camera’s sensor – the reflected light.
Warning! Now we get a little bit technical…
How light is recorded and interpreted in a camera
Light in digital photography is recorded as a separate number for each pixel on a cameras sensor, and each pixel contains one combined value for each of the three primary colours.
The primary colours being red, green and blue (RGB).
The value for the red channel in a pixel that contains no red at all, is 0
And the value for the red channel in a pixel that contains the brightest possible shade of red is 255.
Different shades, or brightness values of red are represented by values in-between 0 and 255.
The same goes for green values and blue values.
This means that each color channel (red, green or blue) can have a range of values between 0 (no colour), all the way to 255 (the brightest shade)
When all 3 colour channels have a maximum value of 255 for a particular pixel, when combined to form its colour, that colour will be pure white.
Please note: Each color channel (red green and blue) can each have a value between 0 and 255. That’s 256 different shades for each color channel, but that’s only how color is presented to us in post processing software like Lightroom and Photoshop.
In reality each color channel can contain many more values depending on how many binary digits represent each colour channel (12bit, 14bit or 16bit).
But that’s a bit complicated for this post, and irrelevant, as in this post we are just looking at the principles rather than the small print.
How the white balance algorithms work (in principle)
The white balance algorithm looks at the pixels it thinks should be white (or are the closest to white) and then estimates how far away from pure white those pixels are.
It then applies the difference to each pixel in the image. In the case of a white pixel, that difference should re-calculate each colour channel to 255 (white).
That difference can now be applied to every other pixel in the image and the color cast should be neutralised (in theory!).
So for example the pixel(s) with the closest value to pure white might be as follows:
In this case, in order to turn the closest to white pixels to pure white, the white balance software would add 15 to the red channel, and add 0 to the green and blue channel.
So something like this
Red: add 15
green: add 0
Blue: add 0
The white balance algorithm will then apply that difference to every pixel in the image, regardless of the existing values in each pixel.
So in this case the whole image would become a bit more red.
In this completely made up example the image should be ‘improved’ because the original image would have had too much blue and green and by adding more red everything becomes equalized and any blue/green color cast is removed.
Is that really what happens?
The precise way a camera works all this out is more sophisticated than that how I’ve explained. Understanding white balance in digital photography requires a bit of imagination! The likes of us never really know exactly what’s going on under the hood, but this is – broadly speaking – the principle of white balance.
How does this theory apply to real life?
On your camera you will have a number of settings associated with white balance.
One setting is called called Auto White Balance, and the explanation above will be roughly how the auto white balance setting works. Beware though, it isn’t always accurate.
If Auto White Balance is flawed, what else can the photographer do?
There are three main ways to set and/or change the white balance for your photograph.
How to use white balance in photography:
The first is to use Auto White balance and let the camera do everything for you. Not always accurate.
The second is to apply a physical setting on your camera, chosen from a list. The options will be something like
These settings, set on your camera will add red or blue according to what physical setting you have chosen.
The third is to use post processing software and use the temperature slider and the tint slider. This will allow you to set a perfect white balance setting for your personal tastes, that suit your vision for the photograph. For me, this is my preferred option.
The third option above really requires you to produce RAW files rather than JPG files. Don’t forget to ask questions if any of this confuses you.
Okay, then…that’s a whirlwind trip around the subject of white balance, from a technical point of view, whilst keeping everything as simple and easy to follow as possible.
For a beginner this can be a tricky subject, so if there is anything that you don’t quite understand, or need clarifying, just ask a question in the comments section.
Thanks for reading, I hope you learnt something, and don’t forget to share, as sharing is caring.