grey (gray) scale

Definition: (1) Range of grey levels or brightness steps available to or defined in a system. * E.g. the Zone System uses a grey scale with ten values; a scanner working to a depth of 8 bits digitises or quantises to a grey scale with 256 values, from 0 to 255 (black to white). (2) May be used to refer to step wedges.
When white is not so driven snow
The trouble is, no-one tells you exactly what separates one grey level from the next: a poor-quality scanner can produce 256 levels like one costing a thousand times more. The difference is, of course, that the 256 levels of a poor scanner are much closer together than those of a good one: its grey scale may be over a density range of under 3 density units, whereas a good one separates over a range of nearly 4 units -- in photographic terms, that's a difference of nearly three stops: the difference between men and boys.

Related Terms: step wedge

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