light
Contrast
The human eye simultaneously registers a wide range of light intensity. Due to their limited latitude
image sensors are unable to do this. The difference in the level of light falling on or being refl ected
by a subject is called contrast. When harsh directional light strikes a subject the overall contrast
increases. The highlights continue to refl ect high percentages of the increased level of illumination
whilst the shadows refl ect little extra. Without contrast photographic images can appear dull
and fl at. It is contrast within the image that gives dimension, shape and form. Awareness and
the ability to understand and control contrast is essential to work successfully in the varied and
complex situations arising in photography.
Subject contrast
Different surfaces refl ect different amounts of light. A white shirt refl ects more light than black
jeans. The greater the difference in the amount of light refl ected the greater the subject contrast
or ‘refl ectance range’. The refl ectance range can only be measured when the subject is evenly lit.
The difference between the lightest and darkest tones can be measured in stops. If the difference
between the white shirt and the black jeans is three stops then eight times more light is being
refl ected by the shirt than by the jeans (a refl ectance range of 8:1).
One stop = 2:1, two stops = 4:1, three stops = 8:1, four stops = 16:1A ‘high-contrast’ image is where the ratio
between the lightest and darkest elements is
32:1 or greater.
A ‘low-contrast’ image is where the ratio
between the lightest and darkest elements is
less than 16:1.Paul Allister Mark Galer