When used in portrait photography, the term “Key” refers
to the overall tone of the final photograph. The elements of the portrait
that play into the tone of it are the color of the background, the color
of clothing used and the color of any props or foreground elements.
Portraits that have a consistent key generally have much more of an
impact that those whose elements are not consistent. It is true as well
that, though rare, tones can be mixed in a photo with success. A danger
in mixing tones is that the potential for confusion on the part of the
viewer.
Generally, portraits are classified in one of three keys – low
key, middle key or high key. Low key portraits are created using a dark
background and dark clothing and props. You can identify the key of
a portrait by determining the average tone for the scene.
Generally a low key portrait would have more dark elements than bright
ones. Clothing and background might be black or dark browns giving the
feeling of drama or rigidity. Low key portraits may also be shot with
a higher lighting ratio near 3:1 as contrast is acceptable due to the
drama of a lower tone.
A high key portrait setup would involve the use of a white or off white
background and brighter clothing. A high key portrait can be challenging
as it requires a great deal of light control and has the most risk of
overexposure and loss of detail. In general they would have a low lighting
ratio near 2:1. A common background for high key portraits is paper
which is slightly overexposed resulting in a pure white seamless background
and a feeling of cleanliness. Great care is usually taken to separate
the subject from the background to eliminate shadows. These portraits
also tend to require more light and thus more power and lighting equipment
to create.
As expected, a photo which has tones in the middle of high and low
would be called a middle key portrait. Often middle key portraits will
use skin tone to set the mood. In these cases, clothing may be used
to accent the tone of the skin with contrast rather than allow all elements
to blend together. Often a high key portrait can be converted to a middle
key portrait by reducing exposure.
Often the background sets the tone for the image and as such key should
be a consideration at the beginning of a portrait setup. A background
should not take focus off of the subject, but rather help lead the eye
to the subject in the final image. Take time to identify your overall
tone, or key before you arrange the lighting setup and you will be surprised
at the results.
Low-key lighting
is a style of lighting for film or television. It attempts to create a
chiaroscuro effect. In traditional lighting design for black and white
photography, also called three-point lighting, there are a key light,
a fill light, and a back light.
Low key light shows the contours
of an object by throwing areas into light or shadow while the fill light
provides partial illumination in the shadow areas to prevent a distracting
contrast between bright and dark. For dramatic effects, one may wish the
contrast to be high — to emphasize the brightness of the sun in
a desert scene, to make a face look rugged, seamed, and old, or to isolate
details in a mass of surrounding shadow. A variety of methods can be used
to create these effects.
The key to fill ratio, as measured
using an instrument to measure light intensity, e.g., a light meter, is
the ratio of the intensity of the key light to the fill light. Low key
lighting actually has a much higher ratio, e.g. 8:1, than does high key
lighting, which can approach 1:1.
It is perfectly possible to
use fill light in these large areas of shadow, reducing the contrast.
Generally the term 'low key' refers to cases in which no such care is
taken.
Low key is also used in cinematography
to refer to any scene with a high contrast ratio, especially if there
is more dark area than light. Compare with high-key lighting.
Mood lighting is a term used
to describe the use of light to illuminate an object or background in
a deliberate manner to evoke a certain mood or emotion. This highly skilled
lighting technique is very subtle but nevertheless can achieve highly
effective outcomes. An example of this is an evil character deliberately
illuminated from beneath the chin giving them a certain eerie and demonic
appearance.
Ambient lighting refers to
the overall illumination of an environment without the addition of lighting
for photography. This includes practical lamps, overhead fluorescent,
sunlight or any previously existing light.
