Many photography hobbyists love to click monochromatic high contrast or high key pictures. There is simplicity in such pictures in the way that the tones reside in them for a visual impact. It is said that subjects with highly contrasted pictures tend to contain more impact and elicit more visual reaction.
To produce highly contrasted images, use little light to see that everything is not evenly lit. The key is to have distinct areas of light and dark. One light, placed at a high angle in relation to your subject or angled to the side of the subject, will throw interesting shadows across the subject.
These contrasting shadows can be easily augmented during the conversion to monochrome, resulting in a highly contrasted image. In visual perception, contrast is determined by the difference in the brightness of the object and other objects within the same field of view.
It needs to be kept in mind that the light or white subject matter is composed in the frame to mainly have white tonalities to make it the high key picture. Therefore, it is advisable to light the subject and have a white background without detail. A white wall will do with uneven light falling on the subject.
Faces of living things or people, high key images are used quite often for headshots to give the clean and sharp feel to these images of the subject. The dark areas or solid blacks have to be less as compared to the white ones.
In visual perception, contrast is determined by the difference in the brightness of the object and other objects within the same field of view.