Unlike your eyes, a digital camera does not see whites as white.
It sees the colour of the light that is reflected from the scene.
Many cameras have settings for automatic white balance, and for specific scenes like sunny, shade, tungsten, fluorescent, etc. And when you know that a scene is lit by just one predominant light source, you can help the camera by setting the white balance to the appropriate lighting.
Or you can let it figure out the scene for itself and use automatic white balance.
Automatic white balance is where the camera figures out the lighting that is illuminating the scene. It does that by comparing the scene to the many thousands of scenes programmed into its memory.
There’s a practical problem when you are taking photos in a room with mixed lighting – maybe fluorescent, with a tungsten spotlight and some daylight from a window, etc.
It is hard for the camera to set the white balance correctly and it is hard for you to choose a setting that matches the lighting.
One way to solve the problem is to have a set of white balance cards.
They are white, black, and grey. If the grey has been made properly it will be 18% grey because that is the conventional setting that cameras are set to when they are made.
The cards should be non-reflective so that they don’t pick up stray reflections.
I used to have a single grey white-balance card. I bought it in a camera shop and it was about as big as my hand. It was made of cardboard and was completely matt.
I kept it in the pocket of my camera bag and I don’t think I used it more than ten times over a number of years.
I just didn’t need it because I generally only shot portraits indoors – and I had another technique for those. More about that later.
Using a White-Balance Card: Method One
With some cameras you can set a custom white balance by pointing them at something with a known value. If so, point the camera at one of the cards and take a shot to set the custom white balance.
Then take the rest of the shots using that custom white balance.
Using a White-Balance Card: Method Two
If your camera doesn’t have a custom white balance feature, take one shot with the cards in the scene and the rest of the shots without the cards in the scene.
Then in Photoshop or whatever – put the mid-point dropper tool on the grey card in the photo and click it. That will set the white balance correctly for all the shots.
Or put the white-point dropper tool on the white card, etc.
No card? Use a piece of white copy paper.
If you are taking a portrait and don’t have a white balance card, take a reading from the person’s pupil – it’s black and non-reflective.
If taking a portrait of a sheep or a cat, don’t use that method. Animals that gather in light and bounce it around inside their eyes will bounce back the same unbalanced light.
On which subject, let me tell you about a visit to Stonehenge. My wife Tamara and I went to Stonehenge and spent the afternoon there. A couple of nights later we were passing Stonehenge and decided to see what it looked like at night.
I drove down a narrow lane parallel to the main road and saw a place to pull onto the verge. There was a gate set at an angle and I pulled off facing the gate.
What seemed like a thousand pairs of eyes were staring back at us, just eyes hovering in the night.
You can imagine what we thought.
Then as we dowsed the headlights we saw that it was a field of sheep looking to see who we were.