Method of making halftone contact screens

A method of manufacturing a two-dimensional halftone contact screen having a plurality of discrete optical transmittance levels in each of its unit cells, comprising the steps of:

• (a) exposing a flat light-sensitive material through a ruling mask having an array of parallel periodic equal width opaque straight bars separated by an array of parallel equal width transparent bars for a first predetermined period of time while the ruling side of the ruling mask is in close contact with the light-sensitive side of the light sensitive material;
• and
• (b) translating the light-sensitive material relative to the ruling mask along a direction in the plane of light-sensitive material making an angle .theta., where 0.degree.<.theta..ltoreq.90.degree. effectively, to the direction of the parallel of the opaque bars a distance d such that the distance dsin.theta. is a non-integral multiple of one-half of the sum of the widths of one opaque bar and one transparent bar;
• and
• (c) exposing said light-sensitive material through said mask for a second predetermined period of time;
• and,
• (d) repeating said translation-exposure process a predetermined non-zero number of times;
• and
• (e) changing the orientation of the light-sensitive material in its own plane relative to the ruling mask an angle .phi., where 0.degree.<.phi..ltoreq.90.degree., effectively;
• and,
• (f) repeating said steps (a) through (d) above, and
• (g) developing said light-sensitive material, producing a two-dimensional halftone contact screen consisting of a matrix of identical parallelograms on the developed light-sensitive material, each of the said parallelograms having a plurality of discrete and different optical transmittance levels.

A method of manufacturing a two-dimensional halftone contact screen having a plurality of discrete different optical transmittance levels in each of its unit cells, comprising the steps of:

• (a) exposing a flat light-sensitive material through a ruling mask having an array of parallel periodic equal width opaque straight bars separated by an array of parallel equal width transparent bars for a first predetermined period of time while the ruling side of the ruling mask is in close contact with the light-sensitive side of the light sensitive material;
• and
• (b) translating the light-sensitive material relative to the ruling mask along a direction in the plane of the light-sensitive material making an angle .theta., where 0.degree.<.theta..ltoreq.90.degree. effectively, to the direction of the parallel of the opaque bars a distance d such that the distance dsin.theta., is a non-integral multiple of one-half of the sum of the widths of one opaque bar and one transparent bar;
• and
• (c) exposing said light-sensitive material through said mask for a second predetermined period of time;
• and
• (d) repeating said translation-exposure process a predetermined non-zero number of times;
• and
• (e) changing the orientation of the light-sensitive material in its own plane relative to the ruling mask an angle .phi., where 0.degree.<.phi..ltoreq.90.degree., effectively;
• and
• (f) repeating said steps (a) through (d) above;
• and
• (g) further repeating said step (e) with angle .phi. different from any previous angle .phi., and said step (f) at least one further time;
• and
• (h) developing said light-sensitive material, producing a two-dimensional halftone contact screen consisting of a matrix of identical polygons on the developed light-sensitive element, each of said polygons having a plurality of discrete and different optical transmittance levels.

The method of manufacturing a halftone contact screen having a plurality of discrete different optical transmittance levels in each of its unit cells, comprising the steps of:

• (a) exposing a light-sensitive material through a ruling mask having a periodic array of opaque geometrically-shaped bars bounded by other than straight lines separated by transparent interstices for a first predetermined period of time while the ruling side of the mask is in close contact with the light-sensitive side of the light-sensitive material;
• and
• (b) translating the light-sensitive material relative to the ruling mask along a direction in the plane of the light-sensitive material an amount such that the said mask is offset with respect to its original position a distance equal to a non-integral multiple of 1/2 of the periodic distance of the said geometrically-shaped bars;
• and
• (c) exposing said light-sensitive material through said mask for a second predetermined period of time;
• and
• (d) repeating said translation-exposure process a predetermined non-zero number of times;
• and
• (e) Selectably repeating the translation-exposure process of said steps (a) through (d) above Q times where Q is any integer including zero, and wherein the orientation of said light-sensitive material, in the plane of the material, relative to the said ruling mask, is changed by an angle .phi., 0.degree.<.phi..ltoreq.90.degree., effectively, between each translation-exposure process;
• and
• (f) developing said light-sensitive material, producing a one-dimensional screen when Q is zero and a two-dimensional halftone screen when Q is greater than zero consisting of a matrix of identical geometric shapes on the developed light-sensitive material, each of said geometric shapes having a plurality of discrete and different optical density levels.