Commercial Photography Technique - White Balance
White balance controls not only help capture punchier, truer colours, they can also be a powerful creative tool.
Whether you specialise in photographing people, products or the natural world in your commercial photography, the way in which you contol colour reproduction is critical. Get the colour balance spot on and your images will have more zing, more realism and more impact. Get the colour balance even slightly wrong and your images can end up awash with muddy, flat or peculiar colours and people with ghostly, sickly looking skin.
Ensuring consistently good colour reproduction is a challenge for any commercial photographer because every light source has it's own unique tint and tone, which alters the colour of the light that subjects reflect. This is because most light sources produce a mixture of all the visible wavelengths of the electromagnetic spectrum. At the same time, the exact proportions of these wavelengths vary enormously from source to source. If there's an even balance of all wavelengths the light is colourless or 'white', but if there's an imbalance of certain wavelengths, the light is coloured.
The colour temperature of light
Many involved in commercial photography use the Kelvin Colour Temperature scale to objectively quantify this colour balance. Named after the British physicist Lord Kelvin and expressed in degrees Kelvin, the scale is defined by the sequence of coloured light radiated by a metal, such as iron, as it's slowly heated from room temperature to melting point. The sequence of radiated wavelengths passes through red, orange, yellow, white and blue. Any given visible light source is allocated the same colour temperature as its colour match in the Kelvin scale. The lower the colour temperature, therefore the greater the shift towards red light. And the higher the colour temperature is, the greater the shift towards blue light. In the Kelvin scale, candlelight is rated at around 1,930K and tungsten light between 2,800K and 3,400K. Noon on a sunny day, meanwhile, is measured as 5,500K; electronic flash between 5,000K and 6,000K and blue sky between 11,000K and 18,000K.
How the Camera can be fooled
Because our brains constantly adapt our vision, the colour temperatures of different light sources are almost imperceptable to the human eye. White objects always appear white to our eyes. Cameras, on the other hand, are far less sophisticated, recording the many colour casts generated by different light sources. If you shoot a white object under a household bulb, for example, it will display a warm orange cast. A white object shot under fluorescent lighting, meanwhile, will exhibit a harsh green tint. By contrast, images taken either outdoors in the sun, shade, rain or with an electronic flash will err towards blue.
To solve this problem, digital cameras are equipped with 'white balance' technology that enables the balance of recorded colours to be shifted to compensate for the colour temperature of the dominent light source. This is achieved by adjusting the output intensity of the light sensor's red, blue and green channels in relation to a standard white colour. To correct the ugly green cast created by fluorescant lighting, for instance, a camera will simply boost the magenta levels. All digital cameras feature an automatic white balance setting, while more advanced models offer a number of additional presets related to specific lighting conditions, typically: daylight, shade, incandescant, fluorescent, cloud and flash. Leaving your camera on auto all the time might seem like a simple and convenient way to deal with changing lighting conditions, but you'll be making a huge compromise on control, consistency and accuracy.
There are several common situations in which even the most advanced automated white balance mechanisms can be fooled into making an incorrect colour assessment. Prime targets for failure are subjects featuring a predominence of certain colours; a mixture of different light sources, such as tungsten and daylight; or no natural white for the camera to use as a reference point. An automatic white balance setting also doesn't know when certain colours should be preserved, such as the sumptuous orange and red tones of a sunset. Left to its own devices in this situation, an auto setting will cool down the scene in an attempt to balance out the colours.
You can often obtain more accurate results by selecting the preset white balance mode that most closely matches the lighting conditions. But because the presets group several light sources with different colour temperatures under the same umbrella, the results will still only be approximate. Fluorescent lights range from low-temperature stadium floodlights (2,700K), right through to high-temperature mercury vapour lamps (7,200K). Tungsten lights meanwhile, can vary from 40-watt bulbs (2,600K) to halogen floodlamps (3,400K). What's more, the colour of daylight changes dramatically according to the time of day, not to mention the time of year, cloud cover, air pollution, altitude and weather conditions.
If your camera offers it, white balancing bracketing is and excellent way to improve the accuracy of white balance presets. In this mode, multiple copies of the same scene with incremental colour temperature changes are created. Alternatively, if your camera features white balance compensation, you should be able to obtain more precise results from the presets by dialling in more warmth or coolness, although you'll only have your LCD to guide you. If you want the ultimate in accuracy and consistency forget the presets and concentrate on your camera's manual white balance setting. Also known as 'custom', this facility is available on all advanced compacts and professional cameras, enabling you to match the white balance to the exact lighting used manually. Taking a manual reading involves shooting a white object under the light source in question to enable the camera to determine the reference white point. It's a straightforward enough procedure, but it must be done with care to ensure optimum results.
Why manual makes sense
Firstly, don't fall into the trap of white balancing using whatever happens to be to hand. Random subjects such as T-shirts, walls and scraps of paper are not a true white and will give you substandard, inconsistent readings. Although the human eye can never be 100% certain what's true white, a piece of clean, pure white card from an art shop or a piece of matt inkjet photo paper is an acceptable source. If you want to ensure precision, you need to invest in a spectrally neutral white card that has been scientifically engineered to reflect equal amounts of red, blue and green in all light conditions. Try the Gretag Macbeth Colourchecker Custom White Balance card.
A neutral grey object or card can also be used to measure your white balance. Using something grey to measure white balance might seem odd, but because neutral grey reflects an equal amount of red, green and blue, any colour cast introduced by the lighting can be detected and measured by the camera, just as it would be if a pure white object were used as the reference point. Again, you can make an educated guess as to what this grey should look like, but the only way to be absolutely certain is to buy a bespoke, spectrally neutral grey card, such as a Kodak 18 per cent grey card.
Once you've selected your white or grey reference, switch to custom white balance and zoom in (or set the camera to macro) so that it the reference object or card fills the entire frame. Position the card so that only light from the dominant source lands on it, moving from your shooting position if necessary. Most cameras take a couple of seconds record and process a white balance reading, so try and hold your card rock steady while it does this because unwelcome reflections can shift the reading off balance by several hundred degrees Kelvin. Ideally you should take a new white balance reading before every exposure - particularly when you're working outdoors - and, at the very least whenever you move from one light source to another. This may sound like a nuisance, but it only takes a few seconds and virtually guarantees perfect results.
Post- shoot processing
Despite all your best intentions, there will be times when you forget to recalibrate the white balance, or time constraints force you to rely on auto and preset settings. If this results in minor colour casts they usually be zapped in an image editor. If colour imbalances are more intense and your shooting JPEGs, however your ability to correct them without degrading the image quality is severely limited.
The solution? Shoot in RAW mode. The brilliant thing about RAW is that the white balance setting in force when a shot is taken is saved alongside the original photographic data as an info tag; rather than being irrevocably processed in-camera, as it is with JPEG files. Shooting in RAW also reduces the risk of unwanted noise caused by in-camera white balance conversions. RAW converters let you make manual white balance selections and corrections in a precise and non-destructive manner. This can take time, though. So always try and get the white balance right at the time of shooting wherever possible. It's also absolutely essential that you colour-manage your digital darkroom before you begin using it. Monitors, scanners and printers area all prone to colour casts and shifts and without proper calibration, all the effort you put into getting the white balance right will be squandered.
This article shows the quality and variety of techniques that customers benefit from as part of our commercial photography and architectural photography service. Call now to discuss your requirements and timescales on 079101 68536.
Copyright Adam Coupe Commercial Photography 2008
