Although cameras with manual white balance measurement systems can provide almost cast-free colour photographs, there are times when additional colour reference tools should also be used to ensure you achieve a correct colour balance in any shooting situation. Including a colour balance reference target in shots is particularly handy if you shoot JPEGs. It’s less important for raw file shooters because colour tweaking is possible when converting raw files to editable formats. However, having a target in a reference shot can make the task quicker and easier when you’re editing image files.

 

Although cameras with manual white balance measurement systems can provide almost cast-free colour photographs, there are times when additional colour reference tools should also be used to ensure you achieve a correct colour balance in any shooting situation. Including a colour balance reference target in shots is particularly handy if you shoot JPEGs. It’s less important for raw file shooters because colour tweaking is possible when converting raw files to editable formats. However, having a target in a reference shot can make the task quicker and easier when you’re editing image files.

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Reference_Target350

Including a reference target in the first shot in a sequence will make it easier to obtain the correct colour balance, particularly if you shoot JPEG files. Many cards come with software to help you use the reference shot in your workflow environment.

A target will enable you to ensure JPEGs are captured with the correct white point (ie, no colour casts) and eliminate potential errors that may not be correctable at the editing stage. It will also save time and money when you come to print your pictures – particularly if they are printed by somebody else. For these reasons, professional photographers usually include a white balance target in the first shot when photographing subjects where accurate colour reproduction is critical.

Some examples of situations where reference targets are useful include fashion shoots, product shots and reproductions of artworks or fabrics. Scientific and technical photographs may also require accurate colour reproduction. Architectural photographs – either outdoor or indoor – containing mixed lighting will also be easier to colour balance in post-capture editing when a colour reference target is included.

In contrast, scenes such as sunsets and landscape shots under blue skies don’t require precise colour corrections. Each photographer should know the effect they want to achieve and be able to adjust colours accordingly and, since most people like rich, saturated colours for these types of shots, a slight over-adjustment of colours is usually acceptable.

Remember to include a target whenever you change lenses and shooting angles. Colour balances may change, simply because of what is included or excluded from the frame.

Colour reference tools range from simple do-it-yourself targets to accurately calibrated and printed colour references. Colour accuracy is the key feature to look for. The colour patches should be large enough to use for visual assessment (targets with tiny patches can only be ‘read’ with a densitometer).

Colour targets are required if you wish to profile your camera (but that’s a complex subject for the future). In most situations, a simple tonal target containing black and white plus a series of neutral grey patches should provide good results.

Using a reference target is simple; just position it in the shot where it will receive the same light intensity and colour as the subject. Have the subject hold the target in portrait shots or prop it up against the subject when shooting three-dimensional objects. Lie the target on top of the subject for flat artworks, fabrics and similar materials.

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Perfect-Pixs350

A reference target is valuable when shooting fabrics and other items where colour must be documented correctly. Place the target on the subject where it receives the same light distribution and include it in the first shot.

Check the exposure of the target immediately after shooting. Adjust the exposure until you can discern all of the grey patches individually. If the light patches appear the same, reduce the exposure level. If the dark patches look identical, increase exposure levels.

Using Greyscale Targets
It’s important to start with a calibrated monitor and use the appropriate colour space in your image editor. Most reference cards are calibrated for sRGB colour (which is the display colour space for most monitors and printers), so that is the colour space you should use.

Open the image file containing the target and enlarge the target. Compare it with the original reference card. Note: expect the reference card to look less vibrant than the on-screen image because printed images have a shorter dynamic range.

Look for colour casts and then check them by measuring the RGB values with the eyedropper tool in your software. The RGB values should match to within about five increments, as shown in the illustration below.

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Eyedropper350

The eyedropper tool is positioned on the third target from the left and the measured RGB colour values can be seen circled in the dialog box above the grey patch strip. The figures show no significant colour cast is present in the reference image.

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Yello_Cast350

This reference shows a yellow cast, which is confirmed by the relatively low Blue value (which is approximately 30 increments below the Red and Green values).

To correct colour casts, use the target in the image to set the white, black and grey points in your image editor. Open the Levels adjustment and click on the White eyedropper then select the white patch in the reference target. This sets the white point. Do the same with the Black eyedropper and the black patch in the reference target. This sets the black point. (The middle eyedropper is used to set the grey point on the mid-grey patch.)

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Grey_points350

Adjusting white, black and grey points in editing software.

Colour Target Options
The simplest and cheapest colour target is a sheet of white Styrofoam, some opaque white paper, a white table napkin or a piece of white card, which can be positioned in front of the subject and used as a colour reference.

Plusses: It’s cheap, the materials are readily available and this option can be used whenever you forget to pack a ‘proper’ target.

Minuses: It’s not calibrated so you can’t tell whether there are inherent colour casts. Contrary to popular belief, the human eye is a poor judge of colour contamination with black and white because it quickly adapts to seeing any very light tone as ‘white’ and any very dark tone as ‘black’.

A step up from the DIY option is calibrated reference cards and reflector targets. Depending on their size and the number of different targets included in the pack, prices for these products range from less than $5 for an 8.5 x 11-inch grey card (which may not be precisely calibrated) to more than $100 for a complete kit of fully-calibrated colour and greyscale reflectors. Cards containing calibrated colour reference patches range from under $20 to over $500.

Plusses: Calibrated cards provide an accurate reference value that can be used when adjusting your images. Many systems are portable and easy to pack into your camera bag so you can use them whenever you wish.

Minuses: High price tags are the main deterrent to buying the more expensive systems, although they are more durable than cards and will remain usable a great deal longer. Cards require extra care when you pack them into a camera bag. Bent cards won’t lie flat and marks can interfere with the accuracy of RBG measurement.

Colour targets are produced by several manufacturers and available through most professional photographic equipment suppliers and some camera stores.

Leading products – and their distributors:

. Perfect-Pixs reference cards are among the cheapest calibrated reference tools on the market. Distributed by Vanbar; www.vanbar.com.au/catalogue/index.php.

. Lastolite produces a range of EzyBalance, XpoBalance and TriBalance flexible, fold-down grey reference targets. Distributed by Kayell; www.kayellaustralia.com.au.

. X-Rite ColorChecker targets that range from the portable ColorChecker Passport to the classic 21.59 x 27.94 cm and mini-sized calibrated colour patch, greyscale and white reference cards. Multi-patch cards for profiling with 140 reference patches are also on offer. Distributed by DES Pty Ltd; www.des-pl.com.au/.

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Perfect-Pixs_ZoneCard350
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Perfect-Pixs_GraduatedCard350

Greyscale and colour patch reference cards from Perfect-Pixs represent some of the most affordable calibration targets available. They are supplied with full instructions.

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X-Rite_colorchecker-passport350

The X-Rite ColorChecker Passport provides several durable calibrated targets in a protective wallet that is easy to carry. Full software support and usage instructions are included.
This is an article from Photo Review Magazine Issue 42.
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