Improving the picture by turning up the contrast
Most digital image display systems allow one to break each primitive
colour into 256 degrees of intensity. An image that uses this entire
intensity scale, that is, that contains values coded from 0 to 255,
has excellent contrast, for the colour range will extend from black
to white and include fully-saturated colours. In contrast, an image
that uses a narrow range of numerical values will lack contrast (it
will look greyish).