Capturing Light and Colour

Image sensors in digital cameras are designed to produce colours that match those in the original scene. However, there is a lot of variation among sensors and among the circuits and software that process raw images into final photographs. The results you get depend, in part, on the accuracy with which you expose the image and the match between the colour balance of the sensor and the colour balance of the light illuminating your subject.

With film cameras, photographers usually explore a wide variety of films before settling on the one or two they like best. This is because each film type has its own unique characteristics. In some the grain is small, in others it’s larger. A film may have colours that are warmer than other films, or slightly colder. These subtle variations among films are slight but noticeable and photographers gravitate to one or the other. With digital cameras, you don’t have the same choice offered by film cameras. The "film" in the form of an image sensor is built into your camera. Whatever its characteristics are, they are the characteristics you have to live with until you buy another camera.

In this chapter, we explore the world of colour and how you manage it in your photos.

Where Does Colour Come From

Why do we see colours? Light from the sun or from a lamp seems to have no particular colour of its own. It appears simply to be "white" light. However, if you pass the light through a prism, you can see that it actually contains all colours, the same effect that occurs when water droplets in the atmosphere separate light into a rainbow. A colourful object such as a leaf appears green because when white light strikes it, the leaf reflects only the green wavelengths of light and absorbs the others. A white object such as a white flower appears white because it reflects most of the wavelengths that strike it, absorbing relatively few. Inks, dyes, or pigments in colour prints also selectively absorb and reflect certain wavelengths of light and so produce the effect of colour.

Colour Balance

Although light from the sun or from a light bulb looks white to us, it not only contains a mixture of all colours, it contains these colours in varying proportions. Light from the midday sun, for example, is much bluer than light from a sunrise or a tungsten lamp. To produce what appears to us to be normal or accurate colour balance, the image we capture must contain the colours in the original scene. These colours are affected by the colour of the light source.

One way to describe the colour of a light source is by its colour temperature. The colour temperature scale is calibrated in degrees Kelvin, somewhat like a thermometer that calibrates heat temperatures in degrees centigrade. The colour temperature scale ranges from the lower colour temperatures of reddish light to the higher colour temperatures of bluish light. Daylight contains proportionately more light toward the blue end of the spectrum. Incandescent light contains more toward the red end. That’s why we describe daylight as "cooler" and incandescent light as "warmer."

"White" light actually contains light of different colours and in different proportions, the overall colour cast of the light changes as the proportions of the colours change. Although different white light sources have different "colours" you don’t see the subtle differences because your brain compensates automatically.

You can preview colour balance by looking at a scene in the LCD monitor. You can also check the colour balance of any image you’ve already taken the same way. If you examine the images closely you may notice that white areas in particular have some colour cast to them. If so, you may want to adjust white balance for subsequent shots. Many digital cameras offer a number of white balance settings, some for specific lighting situations.

• Auto (the default) works in a wide variety of lighting conditions.
• Manual lets you set white balance manually by aiming the camera at a piece of white paper.
• Daylight or Sunny is best when photographing outdoors in bright sunlight.
• Incandescent or tungsten is best when photographing indoors under incandescent lights.
• Fluorescent is best when photographing indoors under fluorescent lights.
• Cloudy is best when photographing outdoors in cloudy or overcast conditions.
• Flash is best when photographing with flash.

Colour Balance and Time of Day

In photography, there is a colour of light called "daylight." However, this type of light occurs only at a specific time of day. Over the course of the day, the light can change from a warm red at sunset, to a cold blue at noon, and then back to a warm red or orange at sunset. "Daylight" on the colour temperature scale is really set for midday sun between 10 A.M. and 2 P.M. During these hours, colours appear clear, bright, and accurately rendered in the photo.

Before and after midday, light from the sun is modified by the extra distance it travels through the Earth’s atmosphere. Some of the blue light is filtered out, leaving the light with a more reddish cast than at midday. This is easily seen very early or late in the day when the light is often quite red-orange in tone. The change in colour will affect your pictures strongly, but this reddish cast is a wonderful light to photograph in.

Sunsets and Sunrises

Sunsets and sunrises are relatively easy to expose because the exposure is not as critical as it is with some other scenes. If you underexpose the scene slightly, the colours will simply be a bit richer and darker. Slight overexposure will make the same scene slightly lighter.

The colours in the sky are often richest in the half hour before the sun rises and the half hour after it sets. It pays to be patient as you watch the sky change during these periods. For one thing, the sun itself is below the horizon and not in the image so exposure problems are greatly reduced. Also, clouds in the sky often light up dramatically and in some cases, reflect the light to other clouds until you find yourself under a wonderful canopy of reflected colour.

Every sunrise and sunset is unique and the variations can be truly amazing. It’s certainly not true that "if you’ve seen one sunrise or sunset, you’ve seen them all." If you want the sun in the photo, it’s best if it is softened and partly obscured by a mist or haze. If it rises as a hot white or yellow ball, find another subject, or turn around and photograph the scene it’s illuminating.

It’s tempting to take all of your photos of a rising or setting sun, but it often pays to turn around. The rich, warm light changes the colours of everything it hits. This is a magic time to capture images that will really stand out. Colours take on a warm, soft glow that can’t be found at any other time of the day.

The Moon

The moon, especially when full, adds a lot to an image. The best time to capture the moon is when it’s near the horizon. Because it is close to foreground objects at that time, it looks much larger than when it’s higher in the sky.

Keep in mind that the moon is relatively dim and usually requires long exposures. Since it’s moving relative to the Earth, longer exposures can actually blur it, giving it an oblong shape. To reduce the chances of this happening, shoot just before sunrise or just after sunset when there is still some light in the atmosphere from the recently set sun. (It bends around the Earth’s curvature due to refraction in the atmosphere.)

Weather

There’s no need to leave your camera home just because the sun hasn’t come out. In fact, rain, snow, fog, and mist can add interest to your pictures. Objects at a distance often appear diffused and grey in such weather, with foreground objects brighter than normal because they are seen against a muted background. Remember to take a little extra care in bad weather to protect your camera against excessive exposure to dampness.

Rainbows always make good pictures. The problem is you rarely find them where you want them, when you want them. To get better at capturing them, you should know something about how they form so you can anticipate them. Rainbows are formed by sunlight being refracted by raindrops. You’ll usually find the combination of rain and sun at the leading or trailing edge of a summer storm. You can’t see rainbows at all times of the day. To understand why, visualize the way the rainbow works. If you stand with your back to the sun while looking at a rainbow, imagine a line from the sun passing through your eye, through the Earth, and out into space. (This is called the antisolar point.) The rainbow forms a complete circle around this imaginary line, however from ground level part of it is always below the horizon. A line drawn from your eye to the top of the rainbow forms a 42-degree angle with the imaginary line from the sun through your eye. (If there is a secondary rainbow, it forms an angle of 51-degrees.) Because these angles determine the position of the rainbow in the sky, it will sink as the sun rises and rise as the sun sinks. At some points, the entire rainbow, not just the bottom half, will be below the horizon where you can’t see it. That’s why you’ll never see a rainbow at midday.

Colour Choices

The choices you make when photographing in colour, such as how to position a coloured object against its background or whether to concentrate on bright, brilliant colours or muted, soft ones, affect the mood and general impact of your pictures. Stop for a moment before you make an exposure and try to focus your attention only on the viewfinder image. Ask yourself how the colours relate to each other. Perhaps a change in camera position might bring one coloured object to a better position in relation to another. Or perhaps you should wait until sunset turns the sky a more brilliant hue. Don’t limit yourself to taking the first view of a scene that comes to your attention.

Photographing at Night

You can photograph many different things outdoors at night, so don’t put your camera away just because the sun is gone for the day. Light sources (street lights, automobile lights, neon signs, or fires) or brightly lit areas (illuminated buildings or areas under street lights) will dominate pictures at night because they stand out strongly against darker backgrounds. Plan to use these bright areas as the dominant part of your picture. A tripod will support your camera during long exposures and prevent blur caused by camera motion during the time the shutter is open.

To capture interesting images of fireworks, put people or water in the foreground. It also helps if there are identifiable objects in the image such as an illuminated building or monument to give the viewer a sense of place. Get upwind from the show since fireworks generate a lot of smoke that can become a problem if you are downwind. If you are upwind, the smoke will become part of the image, illuminated by the fireworks. Automatic exposure doesn’t work well with fireworks. Try a series of exposures of different bursts because there is a certain amount of luck involved. You might also use flash to illuminate foreground figures.

Set your exposure for fireworks by switching to aperture or shutter preferred mode and try for a setting of f/2.8 at 1/30 sec. You might also want to try increasing sensitivity, use exposure compensation, and try different combinations of aperture and shutter speed as well as those recommended here.

Light: Its Direction

The direction that light is coming from relative to your camera’s position is important because it affects the shadows that will be visible in your picture. Four main types of lighting are illustrated here: front-lighting, side-lighting, backlighting, and top-lighting. Notice the position of the shadows in these photographs and how they affect the subjects.

The direction of light can affect your automatic exposure. Backlighting, for example, can leave your subject silhouetted against a background so bright that your automatic exposure system will assume the subject is much brighter than it actually is, and so underexpose the scene and make the subject even darker. This is fine, if you want a silhouette. If you don’t, you should use exposure compensation to lighten the image.

Light: From Direct to Diffuse

Light not only has direction, it can be direct or diffused. Direct light, light coming mainly from one direction, produces relatively high contrast between bright highlights and dark shadows. Diffused light bounces onto the subject from several directions, lowering contrast. Contrast, in turn, affects the brilliance of colours, the amount of visible texture and detail, and other visual characteristics.

In direct light you may have to choose whether you want highlights or shadows to be correctly rendered because image sensors can accurately record only a limited range of contrast between light and dark areas. If this creates a problem because both highlights and shadowed areas are important, you can sometimes add fill light to lighten shadows and decrease contrast or adjust the contrast setting. In diffused light, colours tend to be softer than in direct light and textures are also softened because shadow edges are indistinct.

Using Light and Colour Creatively

Light is one of the elements of a scene that you can alter, play with, control, and make a less or more important part of your picture. Light can make a picture ominous or airy, glowing or velvety dark. To use light creatively, you may have to override your camera’s autoexposure system.

An unusual colour balance can be created with an image editing program or simply by taking advantage of the existing light on a scene. Try taking one picture in the usual way, then, before you move on; see if any other alteration of the image might be feasible.