john bishop images | photography | vancouver, bc

workshop assignment 2 – white balance

  colour temperature, daylight, flash, fluorescent, incandescent, tungsten, white balance

in assignment two we explore white balance, also know as gray balance, neutral balance, or colour balance.

white balance

once again we run into the man – machine conundrum discussed in the last session.  the human visual system has capabilities and a sensory range that far outstrip modern technology.

when we look at a piece of white paper under candle light, we perceive it to be white .  we “know” that same piece of paper is white when we see it under indoor incandescent or tungsten light, under fluorescent light or in the middle of the day under cloudy or clear skies.  we have a built-in colour corrector in our heads.  when we are under a particular light source and look at a white object, our brain automatically compensates so that, psychologically, we perceive white as white.  in reality, the true colour varies widely under different lighting conditions.

indeed, we often refer to a light as “warm”, a sunset as “golden”, or a sunlit field of snow “bright”.  physicists call this colour temperature and it is measured in degrees Kelvin or K.  0K (that’s “zero degrees Kelvin”, also known as absolute zero) is the amount of light emitted (i.e. none) by a theoretical “black body” radiator – think black-hole – and is about the same as -273°C or -460°F.  higher colour temperatures (5,000K or more) are cool (blueish white) colours; lower colour temperatures (2,700–3,000K) are warm (yellowish white through red) colours.

• let’s begin with an open candle flame. to our eyes, it appears red/orange and is approximately 1,800K.
• a typical indoor household incandescent light appears yellow/orange and falls between 2,700 and 3,300°K.
• most office fluorescent light bulbs fall in the 4,000K range, a greenish light, although there are also so called “daylight” (cooler) and warmer, almost pink fluorescents.
• as we move outdoors there is an increase in blue light; the colour temperature value increases.  light at the horizon during the day averages around 5,000K while average noon sunlight measures in around 5,600K depending where on the planet you are.
• modern compact fluorescents can fall anywhere between 2,700 and 5,000K – check the box as modern industry standards now require this on the label.

it’s important to note daylight and sunlight are not the same.  sunlight is the light of the sun, while daylight is light is scattered by the atmosphere.  a cloudy day has more stuff (water particles, hydrogen, nitrogen, etc.) in the air than a clear day resulting in an increase in blue light, giving an increase in colour temperature. this distinction is important – as you move from a cloudless day, to an overcast day, the colour temperature actually increases to 8,000K or higher.

all digital cameras have an automatic white balance or AWB setting.  the camera automatically compensates for varying colour temperatures by adjusting the brightest part of a scene so it will appear white. it then calculates the rest of the colors based on that white balance. if nothing in the image is “white”, the results will not be accurate.

this is unique for digital cameras; old film cameras did not have white balancing controls.  rather each lighting condition had a specific film designed for that colour temperature.  a change in lighting meant changing film.

digital cameras use these standardised symbols for the various white balance settings.  these are usually found under your MENU or FUNCTION button.

	AWB can automatically adjust between 4000K and 8000K  – that is why under tungsten or candle light our AWB adjusted photographs will take on a reddish/orange cast.
	shade white balance – the camera reduces the blue cast – 8,000K
	cloudy or overcast white balance – 6000K
	sunlight white balance – 5,200K
	fluorescent white balance – this ranges from “warm” around 4,200K to “neutral” around 5,000K to “daylight” around 6,500K
	flash white balance – 5,400K – your camera’s flash is designed to simulate sunlight or daylight colour temperature
	tungsten or incandescent white balance – 2,500K – use when taking pictures under light bulb or other tungsten light.  the camera reduces the reddish colour tones in a picture.

so is it necessary to always get the right white balance setting?  it may be a matter of opinion.   just as making compromises with dynamic range, making compromises with white balance can be a highly subjective and personal thing.   it really depends on what you are trying to achieve.  for example, this photograph of a lily, shot in auto white balance and manually white balanced.

• on the left is a digital photo as it came from the camera using auto white balance – there has been no further adjustment to color.
• on the right is the same photo using manual white balance by using a reference card in another photograph taken in the same light and from my friends “in the know” the right-hand lily this is the proper colour.

there are also situation where we want to capture the feel of the light and let the white balance wander off slightly.  this photograph was taken in my neighbourhood a mid September afternoon.  it was the warm tones and quality of the light reflecting off the bricks and white paint that spoke to me that morning.

assignment

the purpose of this sessions assignment is to explore the different white balance settings under the different light or colour temperature conditions.  using the following chart as a guide, take six photographs, each with a different white balance setting (the columns) under each lighting of five conditions (in rows) – you should have 30 photos when you are done.

rename each image file to indicate the white balance setting and lighting condition (i.e. “daylight-auto”, daylight-tungsten”, “cloudy-daylight”, “cloudy-flash”, etc.).

that’s all for session 2 – session 3 is Wednesday, February 10, 2010.