In photography, the term key refers to the overall tone of a photograph. There are two types of keys or tones, low and high. Low key images have very little light, their contrast is high and the lighting hard. High key images on the other hand have a predominance of white or very light tones and tend to look light and airy, the contrast in these images is low and the lighting soft. CONTRAST Contrast is one of the most important concepts in photography; simply put contrast is the difference between the lightest and the darkest areas in a photo.
The greater the difference between the lightest and the darkest areas in a photo, the higher the contrast will be. For example, an image made up of mostly black and white tones is contrasty whereas an image composed mostly of middle gray tones is flat. When we talk about contrast in photography, we refer to both tonal contrast as well as colour contrast.
Tonal contrast is seen in black and white images, and colour contrast is found in colour images. In black and white photography, contrast is created by the difference in subject tones. Subjects portray a number of different tones and when captured in black and white these tones move from white to grey to black. In colour photography tone does not create contrast, but rather contrast is created by colour.
Contrast can be low, high, or normal. A high contrast photograph is made up of white and black areas with little or no grey. High contrast images convey a sense of hardness, power, and strength. A low contrast image is flat, as there is little difference in the density of the tones in the highlight and the shadow areas, all colours and tones in the scene are very similar in appearance. Low contrast images portray softness and gentleness.