Below. Process colour halftone screens must be applied at different angles to prevent unwanted moiré patterns. Black is normally rotated to 45o, as this
is the easiest on the eye; 90o is the most difficult to guarantee, so this reserved for the less visible yellow; cyan and magenta are rotated at approximately 105o and 75o. Unfortunately, no similarly compatible set of angles exists for six or more plates. This is one reason for using ‘stochastic’ screening, also known as
‘dithering’, where dots of a small fixed size are scattered in random positions rather than using dots of variable size in a grid. In practice, to avoid unsightly clumps and gaps, the arrangement of dots must be carefully controlled rather than completely random. Inkjet printers use dithering, although some can also reproduce halftones as a simulation of press output.