White Balance and Color Temperature

The Kelvin scale.

Geeky moment – this scale represents what colour a certain metal (don’t know which one, I’m not that geeky) goes when heated to a certain temperature. Whilst it seems a bit weird, it equates to real world situations – tungsten lights, fluorescent tubes, sunny daylight, cloudy skies, etc. Look at the chart below, and how it starts at orange on the extreme left, with low numbers, then moves through yellow, and into blue as the numbers get higher:

White Balance - The Kelvin Scale

Setting the white balance

So, you need to set your camera to the right white balance for the light you’re in. How to do this will vary from camera to camera, but you’re looking for “WB” usually, and then the icons should look like the situation you’re in – a bulb for tungsten, a sun for daylight etc. The auto setting isn’t bad, but like auto exposure, it can vary from shot to shot depending on how you compose the shot, even if the lighting stays the same, as the camera may react differently to larger or smaller areas of a certain colour. Your best option, and what I do, is to pick the white balance that’s closest, stick to that one and then batch convert in RAW (more info on RAW files coming very soon.)

Getting white balance accurate

Splash out and buy yourself a grey card, or a white balance card, and then shoot a frame with it in exactly the lighting you’re using. This card should have no colour tone to it at all, and functions as a neutral reference point. It can then be selected afterwards in whatever software you’re using to ensure your whites are white, and everything else should fall into place. Beware using what you think is white for a reference – lots of white paint has colour casts in, and if you try and pick that as a neutral, you may end up with a very strong cast.

When shooting in mixed lighting – your camera can only pick one, don’t forget, so you need to choose which one you think is dominant, and accept that some areas of the frame will have a colour cast. When you get really clever you can start adding gels to your own lights, and then they’ll all be the same colour as the ambient, or you can deliberately pick the wrong white balance to create dramatic shifts in colour, but we’re getting ahead of ourselves..    

Don’t panic too much if your images do have a cast – in RAW mode it’s no problem at all, and even in jpeg it’s not the end of the world and can be quickly corrected in software with only a tiny loss in image quality.

Colour casts

Our eyes are great at adapting, so often we don’t see these shifts in colour. We tend to notice them only when there’s a contrast, such as when we’re coming inside from outside, or walking down a street as night is falling and looking into a room lit by household bulbs.

An important thing to remember is that your camera can only be in one white balance at once. If you’re set for the wrong one, your images will have a colour cast, sometimes a very strong one. This is caused by the light falling on your subject being warmer or cooler than the colour temperature (white balance) you have set.

Here’s an image shot in daylight, with the camera set to daylight white balance:

And here’s the same image, in the same light, with the white balance on the camera set to tungsten:

The blue colour cast is caused by the light falling on the subject being much bluer than the colour temperature the camera is set for.    

Here’s the same situation in reverse. First, an image in tungsten light, with the camera set to tungsten white balance:

White Balance - Tungsten White Balance, Tungsten Light

And here’s what happens if we stay under tungsten light, but change the white balance on the camera to daylight:

White Balance - Daylight white balance under tungsten light

Hopefully, by now you’ve twigged that the orange cast is caused by the light falling on the subject being much warmer than the white balance the camera is set to. Play around with this yourself, and you’ll soon get a feel for it.

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