mid key full scale
mid key high contrast
Most successful artists define a consistent palette for their life’s work, for periods during their careers, or for individual bodies of work. It’s one of the primary things that creates an easily recognizable signature style. This is as true for black and white photographers as it is color photographers.
You can precisely describe black and white palettes by identifying the overall lightness or key (high – light, medium, low – dark) and the amount of contrast (high, medium, low, none) held in three ranges of tones – shadows (zones 0-3), midtones (zones 4-7), and highlights (zones 8-10). Put more broadly, the dominant range of tone is identified first and then each range of tone can be described as expanded or compressed; a range of tone that does not exist in an image could be described as fully compressed.