Canon EOS mag

24

Technique Custom white balance

LEE BEEL

The custom white balance setting exists for those situations where you need absolutely accurate white balance. An example of this could be product photography, where the client demands that the colours are accurate. Another example is if you are photographing a colourful subject such as a flower and want to capture the colour accurately. If you leave it to the camera’s auto white balance setting it could easily be fooled by a strong colour into a false reading. You could correct it in post-processing – but how would you know when the colour was accurate? If you are photographing a red flower, were the petals a deep red, light red, or perhaps dark pink or light purple? If you use custom white balance at the time you take the photo you won’t have to worry about how accurate your colours are – the camera will capture them. Another situation where custom white balance comes in useful is when you are photographing a subject under fluorescent lighting. Fluorescent tubes are becoming more common as tungsten bulbs are phased out. While your camera has a white balance setting for fluorescent light, in practice this is not always accurate because the white balance of light emitted by fluorescent tubes varies widely depending on the type of tube used. Some fluorescent tubes produce light with a green colour cast – which is what the white fluorescent light white balance setting is designed to correct – but other tubes emit a white or warm light similar to tungsten bulbs. By using custom white balance, you can record colour accurately every time. Custom white balance also comes in handy when you use the JPEG format, as you can’t easily adjust the white balance in post- processing. You can adjust the colour balance, Custom white balance

Colour icons These are the EOS colour balance settings.

Auto White Balance 3000 to 7000 K

Daylight 5200 K

Above When a single colour dominates an image auto white balance struggles to produce the correct colour.

Shade 7000 K

Cloudy 6000 K

Tungsten 3200 K

White fluorescent 4000 K

Above Setting custom white balance, as described below, give colours much closer to those of the subject. EOS 600D, EF 100mm f2.8 Macro, 1/160 second at f8, ISO 100, subject in photographic tent using studio flash.

How do you know if the colours in your photos are accurate? One way is to switch from auto white balance (AWB) to custom white balance. Andrew Gibson shows you how to handle this useful feature of your digital camera. Custom colour

Electronic flash 6000 K

Custom 2000 to 10000 K

but it is much better if the colour is accurate to start with. If you use the RAW format you can adjust white balance in post-processing, but that doesn’t mean that custom white balance isn’t useful. It saves you work to get the white balance correct at the time that you take the photo. It also removes any doubt that the colours are accurate.

Colour temperature 2500 to 10000 K (not available on all models)

One of the advantages of digital cameras is that you can set the white balance to control colour. With film, the white balance is determined by the type of film you use, which in most cases is daylight balanced. Digital cameras let you set the white balance yourself and change it from shot to shot if you wish. Film cameras lack this flexibility, forcing you to use coloured filters for fine colour correction. EOS cameras come with several white balance presets: daylight, shade, cloudy, tungsten light, white fluorescent light and flash. You can choose one of these according to the type of light that is illuminating your subject. You can also use the auto white balance (AWB) setting, and the camera will usually do a reasonable job of setting white balance to match the light. But there are times when more accuracy is required – and that’s when you need custom white balance.

Above and below How accurately do the colours in these photographs match original? Custom white balance helps you record colours faithfully, even when a dominant colour fills the frame.

Colour temperature Colour balance is needed because the colour of light varies. Daylight is warmer in the early morning than in the middle of the day, while light from tungsten bulbs is yellow. These different types of light are assigned a colour temperature where yellowish light has a lower value than blue light (see panel on opposite page). When we look at a sheet of white paper it looks white under tungsten light or daylight. That’s because our brain processes the data before creating the image we see. Digital cameras can also balance the light using auto white balance (AWB) to make white paper look white, but cameras are not as good as our brains and sometimes need help.

Setting custom white balance

The only piece of extra equipment you need to obtain a custom white balance reading is a sheet of white card or paper (or you can use an 18% grey card). Place the card in the same light that is going to illuminate your subject. (This is very important, otherwise you won’t get an accurate reading.) Move in close, so that the card fills

at least the spot metering circle in the viewfinder. Focus manually, make sure the exposure is correct (set exposure compensation to +2 stops if the card fills the frame) and take a photo. This works with any Picture Style except Monochrome. Follow the instructions below to obtain a reading (screens from EOS 50D).

TONY TODD

1 Go to the Custom WB command on the menu and press Set.

2 Select the image that you took to test the white balance and press Set.

3 Select OK on the next screen to import the white balance data.

4 Go to the white balance command on the menu and press Set.

5 Select the icon for custom white balance and press Set.

24 Reproduced from EOS magazine April-June 2012

Reproduced from EOS magazine April-June 2012 25