Winning wth White

The sun is shining, you've been using your camera as if it is a machine gun, and you have only one exposure left when the most beautiful swan you have ever seen glides majestically into view. What are you going to do? One thing that you don't need to do is panic.

The Nightmare That Is White

Photographing a white bird, white flower or white anything is one of the biggest headache making situations known to photographers. The problem is that we are very sensitive to what looks wrong in a picture. So we have to make sure that the way a subject is recorded is an acceptable representation of what we see. Unfortunately technology comes a poor second when matched against our eyes and brains. It is physically incapable of recording the same range of tones that we can see, and so it is quite normal for a picture taken on a sunny day (where a wide range of tones are inherent) to be lacking details somewhere, either in the shadows or highlights. Slide film was notoriously challenging in this regards, unfortunately digital sensors are proving to be no better.

In our everyday world we are used to seeing little or no detail in shadows, so that looks okay, but our brain refuses to accept burnt-out highlights without complaining. So that is where we must pay most attention. The problem is made worse by the fact that in bright conditions a small change in exposure can make a big difference to the end result. There is a fine dividing line between a perfectly exposed white and rubbish.

How Meters See The World
Getting a correct exposure for white isn't too difficult if we understand how our cameras work. Camera light meters look at the world through different eyes than our own.

Nature and Wildlife Photography - winning with white
A mute swan glides majestically into view.
A typical scene has a full range of tones from ultra dark to dazzlingly light. Mix all of these together and we end up with an average tone for the world around us. On a grey scale, from black to white, the mid (half-way) tone is a shade of grey often called "mid-grey" (there is a mid-tone for any colour we may choose to consider, but the grey scale is the one that has become the standard reference for photographers). If we think of this in terms of reflectance, where black has a reflectance of 0% and white has 100%, then mid-grey falls at 18%. Giving birth to the photographic term 18% grey.

Camera meters are calibrated on the assumption that what they see averages to a mid-tone of 18% reflectance. This isn't a problem when you are dealing with an average scene, but when it comes to something away from average it's a different matter altogether. Meters will always give wrong information about non-mid-toned subjects.

Modes Of Operation
Camera designers try to overcome metering problems by the use of built-in computers. Sometimes the viewing area is divided into a multitude of segments, each of which is metered separately and an idealised exposure is calculated. This type of metering is commonly known as Evaluative or Matrix Metering. Clever as it is this can still be fooled under certain circumstances. That's why even cameras with the best metering systems still have more than one mode available.

Under difficult conditions (white subjects) the most consistently reliable method that can be used on just about any camera is to meter the subject and apply compensation. To do this the camera needs to be in manual mode and have a spot-meter facility. Otherwise a separate hand-held spot-meter will be needed.

Spot metering is where an exposure value is taken from a very small part of the frame. In camera meters this is typically an angle of view between one to five degrees. Hand-held meters usually go for the narrowest view that is practical and tend to meter at one degree. It is essential when using spot meters that your subject completely covers the spot, otherwise the indicated exposure settings will not be accurate.

Nature and Wildlife Photography - winning with white
On a bright day, deciding the correct amount of texture to record is an essential part of the decision making process.
All this talk of manual operation may seem an archaic way to go about things, but it is a method that will work with all cameras and formats. Evaluative mode is computer driven and unless you know exactly what the computer is thinking the amount of exposure compensation needed is no more than a guess, and each camera will be different. It is possible to build up a familiarity with a particular camera that allows effective use in evaluative mode with high contrast subjects, although it does take time (as does learning anything thoroughly), and many do use this method. But the instant you use a different camera you are back to ground zero on the learning curve.

How Much Compensation?
Now that we're comfortable with the idea of spot metering our subject and applying compensation the next question to ask is "how much?" Let's start from a point of 18% grey, as this is how our white will look if we take the meter reading at face value. A white that looks grey is obviously wrong, so we need to make sure that we overexpose compared to the meter reading suggested by the camera. Speaking generally of slide film we can say that by opening up one stop, and doubling the amount of light falling on our film, 18% grey becomes 36% grey (light grey), another stop gives us 72% grey (bright white), half a stop more takes us to 108% grey (blown-out white). So now we can see that a journey from mid-grey to whitest of white is a touch less than two and a half stops.

Here's another way of looking at it. Hold a sheet of white paper in your hand. This is nice and bright with a reflectance of 100%. Fold it in two. The amount of reflected light has now been halved to 50% (minus one stop). Fold it again, now we're down to 25% (minus two stops). Folding it once more gives us 12.5% (minus three stops). As mid-grey is at 18% we can see that this falls about halfway between minus two and minus three stops.

It's time to go back to our starting point of an exposure setting that will give us mid-grey. Knowing that one stop extra exposure gives light grey and two stops gives bright white with no detail, it now becomes easy to see that an ideal exposure will fall somewhere between these two settings. When our subject is white but has some texture evident it's essential to avoid over exposure to the point of burning out the detail. This is achieved by opening up something less than two stops. In fact what is required is for the exposure reading to be compensated by plus one and a half or plus one and two thirds of a stop. Which one you choose is a matter of personal preference. On an overcast day where no detail can be seen extra compensation is needed, typically plus two stops, to give a smooth white.

Nature and Wildlife Photography - winning with white
A white swan in bright light is nothing to fear for the "knowing" photographer.
Back To The Swan
The sun is shining, you've been using your camera as if it's a machine gun, and you have only one exposure left when the most beautiful swan you have ever seen glides majestically into view. What are you going to do? You're going to switch to spot metering and manual mode. Meter a brightly lit part of the swan where you can see detail in the feathers and open up by one and two thirds of a stop. All that remains is to pick your moment and fire the shutter.

Simple isn't it?

The best method for getting whites right with digital cameras, (providing you actually have more than one exposure left) is to check your camera's histogram display, and adjust your settings to avoid over exposure. This is achieved by making sure that the right hand side of the histogram is not clipped off. You take a shot, check the histogram, if it's clipped dial in some minus compensation and try again. Repeat as necessary.

As I said, "Simple isn't it?"