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 WBNeutral 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 worksYou 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.