The White Balance

Light is colourful. As a matter of a fact, it contains a varying amount of Red, Green and Blue.

We identify the colour of the light by its temperature which is measured in degree of Kelvin (k). The Kelvin scale is similar to the Celsius scale with the only difference being that its lower value [0] is not the temperature at which the water freezes but is the absolute zero which is -273.15 C. It is interesting to notice that on the contrary to what we could think, the Blue colour is dominant in high temperatures whereas Red is dominant in lower ones. The light colour is responsible for the mood in an exposure, and despite what I wrote above, an exposure with a Red tendency would have a warmer tone/mood than with a Blue which brings a cooler atmosphere.

What is the White Balance?

The colour of light depends on its temperature, so whether you are shooting under artificial light sources such as a light bulb, a neon tube, a flash or under the sun with or without clouds, your subject will be capture differently. More precisely, the white ( all colours will be affected by this, but white object is easier to spot) of your exposure will not appear as white as you can see it with your own eyes.

Why you may ask. Well, the answer is simple: you have a brain working closely with your eyes that can adapt to the light condition. Your brain has learnt to recognise white and colour in general no matter the light condition. And this is where White Balance setting on your camera comes into play; a subset of the human brain in a machine. DSLR and modern digital point and shoot cameras have a built-in feature called White Balance. Its role is to modify the light information captured by the sensor with a view to providing you with the most accurate colours of Red, Green and Blue which are the base to millions of colour (16581375). Therefore you will often see the following options for your WB setting in the camera menu: Tungsten, Fluorescent, Flash, Daylight, Cloudy, Shade and Auto. From their names you can understand which setting you should be using and when. The last setting is Auto, and while you may remember my position on leaving your camera on Automatic settings (ref The Exposure Modes), I for once must admit this Auto feature on DSLR is pretty good in most cases. Surely you may have experienced taking some shots inside your house, and the overall colour is yellowish.  Similar to this picture:

One of the beauties of Digital Photography is that you can alter your exposure in post-production with tools as basic as the one that came with your camera or more advanced such as Adobe Lightroom or the famous Photoshop. This what you can achieve in post-production by the move of a slider:

The White Balance in the shot above has been adjusted in Post Production using Lightroom 4 Undoubtedly you can see the white of the postcard and tights is whiter than before, and the resulting image is more pleasing to the eye.

How did they do before Digital?

Before Digital, the White Balance was set by using coloured filters that would screw on the front of the lens. Still, today, some photographers who use DSLR do like using coloured filters to compensate the environmental colour. The most obvious that I can think of is when shooting in Black & White.

White Balance for Monochrome exposure? 

The most common filters used for B&W Photography are Yellow, Red, Orange, Blue and Green. Those are used to increase or decrease contrast and add nuances between the Blacks and the Whites in the exposure. However, just like with White Balance, these filters can be mimicked in post-production.

Grey/White card, the other way to set the WB

Neutral Grey or White card is another way to set your WB correctly. But before explaining how to do it let’s see why the colour neutral Grey or Neutral White. As said above, the Digital sensor knows three basic colours: Red, Green and Blue. The combination of those 3 gives you all the colours the sensor can record (16581375). How does that work? Well, each basic colour is known as a channel, and each channel has a value from 0 to 255. A colour is defined by the combination of the three as this: White 255,255,255 Black 0,0,0 Neutral Grey (18%) is between 111,111,111 and 127,127,127. Using a grey or white card enables you to see how the three channels are affected by the light temperature.

Here is how it works

You first take your exposure with the Grey card in the frame (here I used my lens cloth which does act as a Grey card):

As you can see the result with the Auto WB setting gives my hand a yellowish colour which is not natural. Now you open the file in a post-production tool such as Adobe Lightroom 4:

In the top right panel “Basic”, there is a selector tool you need to click on it.

Then you go on the grey card and select a neutral tone (basically anywhere on the cloth):

Once you clicked on the spot, the WB setting is being adjusted instantly by Adobe Lightroom 4 and here is the resulting image:

There is no doubt, once the WB has been corrected in Lightroom 4, my hand skin colour, the blue of my shirt, the grey cloth have all been calibrated correctly.

Note

I did mention White card as well, but while you can still do the same procedure with it, you need to make sure your picture was properly exposed or slightly underexposed (ref: The Correct Exposure). We saw that a Correct Exposure is a perfect balance between the whites and the blacks. If you picture is over exposed, it means you will have more white than normal, and white is at the end of the RGB spectrum (255,255,2555). With grey card being in the middle of the spectrum, you can adjust lighter or darker the level of grey shade whereas with White, if you are overexposed, you WB reading will be off.

Conclusion

White Balance is the way to set either proactively (in your camera) or in post-production the correct colour of the light in your exposure. While being accurate can be critical in Portraiture where you need the skin colour to be correct, in another type of Photography the White balance can play a Creative role where you can change the mood of an exposure. As we will see later in our upcoming episode on the output format (RAW, JPEG and TIFF), setting up the WB in the camera might be better than in post-production.