Halftone screens associated with moiré effects below a threshold

Processing circuitry comprising:

• a screen generation module to generate a plurality of halftone screens each comprising tiles comprising cells, the cells comprising parallelograms being defined by a first vector having a first length and second vector having a second length, wherein at least one screen comprises non-orthogonal cells;
• a frequency determination module to determine for each of a plurality of screens, first and second orthogonal fundamental frequencies using a projection of the first and of the second vector for that screen into each axis of a print apparatus reference frame, the first length and the second length;
• and
• a screen selection module to test each screen for moiré effect.

A non-transitory machine readable medium comprising instructions which, when executed by a processor, cause the processor to:

• determine a non-orthogonal halftone screen comprising tiles spanning a plurality of halftone cells having a print addressable area of variable size, the halftone cells comprising non-orthogonal parallelograms being defined by a first vector having a first length and second vector having a second length;
• determine first and second fundamental frequencies for the halftone screen using a projection of the first and of the second vector into each axis of a print apparatus reference frame, the first length and the second length;
• and
• use the first and second fundamental frequencies to determine if the halftone screen is associated with perceptible moiré effects.