Colour balance cards, called color balance cards in America, show a range of reference colours you can use to check the colour balance in photographs. When you photograph something, you include the colour balance card in the first and last image then check the colours when editing the images in Gimp or Photoshop. You can adjust the colour of your images more accurately when you have an accurate reference. The Seculine ProDisk Mini is a useful and expensive colour balance kit containing a colour balance card.
Note that the following image is not colour balanced and demonstrates why colour balancing is important. The following image has a yellow tone because the camera was not set to match the lighting.
The kit includes a grey card, which you can use to set accurate colour and exposure in cameras that adjust to a grey card reference, plus a white balance filter for adjusting white balance in other cameras.
White balance filter
A white balance filter is a diffuser you place in front of your camera lens when setting the white balance in the camera. The filter mixes incoming light across the whole image to give better average white balance readings for many cameras.
My camera has a spot meter and can white balance on a much smaller target, making the filter less useful. Most cameras can get a good reading from white paper without a special filter. You place very white paper, usually sold as presentation paper, in the spot you are photographing and measure from there.
Grey cards have a use for white balancing and for consistent exposures. You have to test your camera for both. If you run your camera's white balance setting against the grey card and get perfect colours, you can use the grey card for white balance.
Consistent exposures are made by metering exposure against a grey card every time the light changes. Film cameras look for an 18 percent grey. A lot of digital cameras look for an 11 percent grey. The Seculine ProDisk Mini does not state the percentage of grey in their card. Experiment. Adjust.
I made many fabulous outdoor photographs by exposing against grass, which is often close to density of the right grey. The problems occur when the light changes. Clouds float in front of the sun. You work under trees. You work in the early morning when there is an imbalance of blue or in the late afternoon when there is an imbalance of red. You are out on a farm in drought when the grass turns yellow. You are in the 80 percent of Australia that is too dry for grass.
Colour reference charts can contain many colours. Only a few are essential. You want white and black to set the brightest and darkest areas in the image. You want red, green, and blue to balance the colour recorded by the red, green, and blue image sensors in the camera. Everything else is decorative on screen.
Cyan, magenta, and yellow are useful when printing images because printers use those three colours. If your image has the right balance of red, green, and blue, the other colours will be right. Adding cyan, magenta, and yellow to an image simply reduces the work required to check the printing.
The following image shows the colour chart on the left and the white balance filter on the right.
Start with the price. This should be a cheap plastic item. Because it is photographic equipment and sold in Australia, it is AU$85.00 instead of $29.95. Update May 2011: Gerry Gibbs Camera Warehouse in Perth is offering the Seculine ProDisk Mini for $49.98 and the larger Seculine ProDisk II for $48.88.
The Seculine ProDisk Mini is worth the price for a professional and a professional making good money could buy the far more expensive X-rite system to fit in with the X-rite add-on products for Photoshop. The Seculine fits better in the areas of serious amateur and travellers.
The following image has the colour balanced to produce a whiter white. Compare the colours in this image to the image at the top of the page.
This is the mini version and I like it because of the smaller size. It is less weight to carry and is just big enough to be useful. There is a larger version for studio use. The more expensive X-rite alternative fits neither the small portable utility category nor the big studio category. I like the mini size.
There is a metal mirror on the back of the ProDisk Mini. You might be able to do your hair before a photograph using the mirror. The second time you pull the ProDisk mini from your camera kit, the mirror will be scratched and useless. I carry the ProDisk Mini in a zip lock plastic bag to keep scratches off the mirror and to keep rain/wine/fruit juice from wetting the colour chart.
If you spend more than a thousand dollars on your camera, keep spending to get a kit of accessories including the ProDisk Mini. For cheaper cameras, white balance against white paper and measure exposure against grey office paper or green grass.