Different places and different times of day can affect the colours you capture in a digital photograph and all image sensors are designed to reproduce a wide range of hues and tones accurately. From the harsh desert sunshine to the misty rainforest; from sunrise to dusk; indoors and out; your camera should be able to produce pictures that capture the colours and atmosphere of the place and time of day.

 

Different places and different times of day can affect the colours you capture in a digital photograph and all image sensors are designed to reproduce a wide range of hues and tones accurately. From the harsh desert sunshine to the misty rainforest; from sunrise to dusk; indoors and out; your camera should be able to produce pictures that capture the colours and atmosphere of the place and time of day.

However, there are some situations when the automatic settings on the camera struggle to produce the correct colours and tones. The most common involve artificial lighting, which is often biased to one particular colour. Incandescent lights (including halogen lamps) have a strong orange cast, while fluorescent lights are often slightly greenish. You may not notice these colour biases in everyday life but they can affect the way in which our camera reproduces the colours in a scene.

The white balance setting is used to make the colours in a digital photograph look natural under a variety of lighting conditions. The auto white balance control on a digital camera works by balancing the colour information from the camera’s sensor to produce an image in which all hues are in equal proportions.

It’s usually quite effective under normal daylight, where even landscapes with mostly green and blue hues will still look natural under the prevailing white light. However, with some kinds of artificial lighting, the balance of hues can be skewed and this will influence the appearance of the captured image. Although you may not notice these colour casts when framing a shot, your digital camera’s sensor will record them.

The most difficult type of lighting to correct for the auto white balance controls in most cameras is incandescent lighting, which has a strong orange cast. Fluorescent lighting has only slight colour casts, usually greenish in hue. Cloudy skies and open shade can produce cool-looking photos, while electronic flash often has a slight blue cast. Click here to see typical colour casts in simulated pictures.

Manual White Balance Controls
To counteract these colour casts, most digital cameras provide a range of manual presets that typically cover incandescent (‘tungsten’ or ‘halogen’), daylight, shade, cloudy, flash and fluorescent (up to three settings in some cameras).

Some cameras also let you fine-tune white balance settings along the blue/amber and magenta/green colour bands, using the camera’s LCD monitor to adjust the strength of the colour changes.

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Some cameras include controls for tuning white balance settings. Adjustments can be made on two colour axes: blue/amber and green/magenta.
Many cameras provide a manual or ‘custom’ setting. This setting lets you measure the colour of the illuminating light and use the result to remove unwanted colour casts. The process is straightforward. Simply cover the subject with a plain white object (sheet of paper or white card) and set the lens focus to manual before taking an exposure or white balance reading to capture the colour of the illuminating light. (Some cameras can record the light without taking the shot.)
White balance bracketing is provided in more sophisticated digicams and most DSLR cameras. This setting causes the camera to take three shots, varying the colour from one to the next, depending on the selected white balance mode. Bracketing is handy in mixed lighting when it is difficult for the camera’s auto or pre-set system to produce accurate colour reproduction. However, it’s just as easy to correct colour biases with image editing software.

Special Colour Effects
Many cameras include special effects settings that allow you to take black and white or sepia toned photographs. Some also include blue, green, orange and other colour conversion tools. The main problem with these incamera settings is that they discard the colour information captured by the sensor. Consequently, if you decide later that you didn’t like the effect and wanted a full-colour picture there is no way to return the image to full colour.

A better approach is to ignore the in-camera colour conversions and take all your photographs in full colour. Even the simplest image editors, such as Picasa2, include colour conversion controls. Making colour conversions with editing software allows you to keep a copy of the full-colour photograph and, at the same time, experiment with a much wider range of colour conversions on copies of your original photographs.

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Black and White conversion of a colour photograph in Picasa2.

The best monochrome prints also start off as full-colour digital images. Images that need editing should be edited in your editing software before they are converted to monochrome. Assuming all the tones in the colour original are correctly balanced, the simplest way to convert the image to black and white is to open the colour adjustment control and select Adjust Hue/ Saturation then move the Saturation slider back to -100. Make sure you save the file with its own file name so you don’t over-write the colour original.
Once the image has been converted to black and white, you can use the colour controls in the image editor to add different colour tones. The contrast tools will help you to fine-tune the tonal balance in the picture.

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Image editors generally provide a much wider range of colour effects than those offered in digital cameras. Graduated colour effects, like the one shown above, are never found as incamera conversions.

USEFUL URLs
The following websites provide additional information on the topics covered in this chapter.
www.photoreview.com.au/ contains several articles on file formats.
http://en.wikipedia.org/wiki/White_balance provides a good overview of white balance.
http://en.wikipedia.org/wiki/Graphics_file_format provides an overview of file formats plus information on image file compression.
This is an excerpt from Mastering Digital Photography Pocket Guide 2nd Edition.
Click here for more details on this and other titles in the Pocket Guide series.

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