| 摘要 |
A method of making a halftone contact screen having a plurality of discrete different optical transmittance levels by making multiple relative translations of light-sensitive material under and in close contact with a ruling mask while exposures to light through the ruling mask are made between the translations. The mask comprises a thin flat plate having an array of parallel periodic equal width opaque straight bars separated by an array of parallel equal width transparent bars. In a first process, translations are normally made perpendicular to the parallel of the bars. Two-dimensional or dot halftone contact screens are made by repeating the process wherein the light-sensitive material is rotated relative to the ruling mask, in its own plane, at an angle greater than zero to the direction of the ruling bars during the first process. Using the single process creates a line halftone contact screen; adding the second process creates a dot halftone contact screen. The effective translation distance between two successive exposures is a non-integral multiple of half of the total width of a single pair of opaque and transparent bars in the ruling mask.
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