AWB and how to deal with it

I’m old enough to remember when AWB meant “Average White Band”, a very funky Glaswegian group that sounded more Detroit than Detroit did. In photography, once you’ve taken your platform heels off, it refers to how cameras measure the colour of light.

It may come as a surprise to learn that light comes in different colours. This is particularly important to compact camera users. Our cameras guess the colour and produce jpgs that are harder to correct for the camera’s mistakes than RAW captures. The result is all too often seasick portraits under fluorescent lighting or distinctly jaundiced subjects in candlelight or tungsten lighting. If you’re old enough, you may remember getting film prints back from labs where only the first three shots were correct and everything else was strangely blue, red, green or yellow. The technician at the lab processed your film for one colour and your ancestors are remembered as livid, apoplectic people or Venusians. The phenomenon is the same but now, with digital, you can fix this.

Here’s the technical bit you can skip:

The colour of light is measured on temperature scale in degrees Kelvin (same increments as ° Celsius only starting 273° lower). The idea is to heat up an ideal “black body radiator” (think a block of iron) and measure the temperature as it changes colour when you heat it up to glowing red and more. The counter-intuitive part is that the higher the temperature, the colder light becomes. This is because the visible spectrum of light starts in the warm red and ends in the light blue before going UV.

Wikipedia has helpfully provided a rough scale:
< 2,000 K Candles, matches
2,700–3,300 K Incandescent light bulb, sunrise
3,200 K Studio lamps, photofloods, etc.
5,000 K Horizon daylight
5,500–6,000 K Vertical daylight, electronic flash
6,500 K Daylight, overcast
6,500–9,300 K LCD or CRT screen

OK, you can come back now:

The colour of light creates a colour cast. A white car under a yellow streetlight looks… yellow. We know it’s white, but our cameras don’t. Nine times out of ten they get it right. The purpose of this article is to help you get it right 99/100 times and to cope with that 100th time when they don’t.

How to confuse a digital camera:

Digital cameras from compacts to Leicas use a technology dating from the end of the 1960s to measure the colour of light. They get confused in situations where:

  1. There are several light sources (daylight + artificial lighting / stage lighting, especially strongly coloured ones)
  1. Low light (night-time, sunsets, contrasting light)
  1. They can’t focus (exposure and lighting are measured using focal points first)
  1. Flash is used. Flashlight is bright and relatively blue. It’s used, of course, when ambient light is usually low and/or red. The result is usually awful (horrible contrasts, dark shadows, zombie subjects).

The first thing to avoid is flashlight if you can. Most of us hate flash lighting because we all get it wrong. Compacts have pretty dire flash lights for various reasons not worth going into here, but the main result is harsh contrast and that bluish tinge. I try to avoid it in most cases by increasing the ISO sensitivity of my camera to make flash lighting irrelevant and I have my own version of Moore’s law: your camera’s ISO sensitivity is the same as the $ value of the camera x2. If your camera cost $400, you can safely go up to 800 ISO before it introduces horrible “noise” in your image.

Use flash lighting only in specific cases. The classic example is photographing someone against a sunset. Without the flash, your subject becomes a silhouette. If you use the flash to fill in the subject, you get both the sunset and the subject. This is why it’s called “fill-flash”. You can do this in any situation where the background is brighter than the foreground.

The second solution is to change the white balance of your camera. It’s taken me 670 words to get to the crux of the subject, but better late than never. This is particularly important if you can’t shoot in RAW. All digital cameras allow you to capture jpgs. Only DSLRs and some compacts allow to shoot in this format in which the camera does not make automatic decisions for you and allows you to correct its mistakes (and yours) in post-processing. If you can’t shoot in RAW (which is by no means compulsory), you can set your camera to shoot in more suitable circumstances. The only rule is to decide what is the dominant light in advance.

  1. If you’re indoors, set it to tungsten
  1. If you’re outdoors, set it to cloudy
  1. If you’re by the sea or in a really bright place without a cloud in the sky at midday, set it to AWB
  1. If you’re sure you’re going to use the flash, set it to flash
  1. In all other cases or if you’re not sure, leave it as AWB.

The colour of light and the colour cast determine the mood of an image and how it’s perceived by others. This is something worth considering. Alternatively, go for something funky (that’s 70s disco speak) for the hell of it, but in all cases try the various options first and get to know how your camera behaves. Olympus cameras, for example, are famous for their reds. Panasonics are considered a trifle “cold”; Canons (in my experience) can be a little flat.

All is not lost

Thank heavens (or Thomas Knoll) for digital. You can correct for tinge / cast / jaundice / seasickness. I hope I’m right in saying that every camera ships with software to correct for colour cast. The tricky bit is knowing how. You should also know that jpg images are locked and lose information as soon as you start changing them (which is another reason for shooting in RAW). Owners of Photoshop and Lightroom are probably aware of advanced techniques, but the principle is the same for all image editing software: choose the brightest (whitest) part of the image and set that as “white”. There is usually a sampling tool that does this for you. You usually need to set an absolute black and a mid-tone level. The black is easy: choose the darkest part of the image. You usually need to fiddle with the midtones to find an acceptable level of grey. In Photoshop and its Elements variant, for example, the layer adjustment is called “levels” and thoughtfully include sampler cursors to help you.

Another, very low-tech solution is to use a colour card or even a blank sheet of white paper. Do a test shoot of your subject with the card / paper in front. Then shoot the “real” version and use the sample to correct. Apply the same corrections to the “real” version and you’re good to go.

_Disclaimer

This is a work in progress and definitely needs tightening up and clarification in light of people’s understanding of my occasionally convoluted prose. Feel free to offer criticism and advice below.

I am an amateur photographer and use Canon compacts and DSLRs. No reference in the above is intended as an endorsement for any product mentioned in this article. Any errors and omissions are mine._

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