In photography, a greyscale digital image is an image in which the value of each pixel is a single sample, that is, it carries only intensity information. Images of this sort, also known as black-and-white, are composed exclusively of shades of grey, varying from black at the weakest intensity to white at the strongest.
In greyscale still photography, many photographers choose to shoot in solely black-and-white since the stark contrasts enhance the subject matter.
There are a few other reasons for converting a colour street-portrait photograph into a black-and-white photograph:
- the subject’s skin colour is not coming out adequately and/or the overall white/colour balance is just plainly wrong and can’t be corrected for whatever the reason;
- the colour of the photographic lighting is unsatisfactory and can’t be changed (e.g. with fluorescent tube lighting, under a coloured market-stall awning);
- some important bright areas of the image are effectively all white or washed out (“blown-out highlights" or "clipped whites"), often if the on-camera flash has to be used;
- the background is very colourful, cluttered and distracting, to the point that it takes the focus away from the subject;
- the colours of the subject’s clothing or headgear don’t match with the colours of the background;
- the colours are too muddy, bloody or even gruesome (e.g. as a form of censorship when movies are aired on Philippine television, many gory scenes are shown in black and white, in compliance with Philippine broadcasting standards);
- the image is too noisy in colour since the camera is not set correctly (an underexposed image with unacceptable noise levels, or an overexposed image with plenty of highlights clipped);
- partial or complete colour blindness of the photographer and/or the viewer.