BASICS 3: WHITE BALANCE

Dec 27, 2011   //   by adelia   //   Tutorials  //  No Comments

Did you know that light in different places changes colour?

Specifically that outside light is very different in colour to inside light???

Well my students at Bournemouth University used to astounded by this revelation and I could clearly see their 18 year-old minds disagreeing with such a crazy assertion.

That is until I put a piece of paper under the light and asked them what colour is was – “white” in chorus.  Now the same piece of paper by the window – what colour now “blue???”

Of course, the frequencies of light produced by electric bulbs is a different range to those produced by the sun – our eyes quickly and seamlessly adjust but cameras can’t so we need to ‘adjust the white balance’.

To adjust it manually is simple – you put a piece of white paper in front of the camera and press the white balance button.  After a second or so the camera tells you a four figure number with K on the end of it – this is the temperature of the light measured in kelvin.

On a professional camera you general get a switch with ‘preset’ ‘A’ or ‘B’ settings.  The preset setting you can adjust to the temperature you want in a menu – the A and B buttons allow you to use a piece of white paper to sample two different white balances.  This is used so that you can set one to inside and one to outside so if you are moving between the two you can smoothly switch across from A to B.

Roughly speaking, light indoors is measured at around 3200K and outside 5600K – but what does that temperature represent?  Well, it is theoretically the temperature an idealised ‘black body radiator’ would have to be at to produce that range of frequencies of light.  Although not technically correct, I think of it as the sun being a lot hotter than the surface of a filament bulb!

But what happens if you get this setting wrong?  Well it affects the colour cast of the image – we are usually aiming to have a neutral colour cast when we shoot so that all our shots match.  If we forget to set the white balance it can affect skin tones very markedly leaving people either looking:

  • Smurfed; where the whole image appears blue and cold
  • Tangoed; where the whole image appears orange and warm

So, as long as you set your white balance manually each time your light source changes you should avoid making your subjects look ‘smurfed’ or ‘tangoed’!

Just so you know exactly what I mean – here is a fantastic picture of Heston Blumenthal – correctly taken by the very talented Simon Jessop on the left and then doctored by me to demonstrate incorrect white balance in the other two shots…

AUTO WHITE BALANCE

So what should we do where our only option is to use auto white balance.  Well you guessed the rules are staying the same as if you were using auto settings for focus and exposure:

  • ‘move’ camera or location until the camera gives you a good looking shot
  • ‘don’t move’ once you are recording to prevent the settings changing mid shot

 

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