US3275445A - Photographic half-tone contact screens - Google Patents

Photographic half-tone contact screens Download PDF

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Publication number
US3275445A
US3275445A US295101A US29510163A US3275445A US 3275445 A US3275445 A US 3275445A US 295101 A US295101 A US 295101A US 29510163 A US29510163 A US 29510163A US 3275445 A US3275445 A US 3275445A
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Prior art keywords
dots
pattern
minor
screen
density
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Expired - Lifetime
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US295101A
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English (en)
Inventor
Middlemiss Herbert
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WH Howson Ltd
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WH Howson Ltd
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F5/00—Screening processes; Screens therefor
    • G03F5/14—Screening processes; Screens therefor by contact methods
    • G03F5/16—Screening processes; Screens therefor by contact methods using grey half-tone screens

Definitions

  • This invention relates to photographic halftone contact screens of the cross-lined type for use in converting an image having a variety of continuous tones into differently sized dots, for the preparation of half tone printing plates.
  • the lines on such contact screens are usually made-up from a series of dots, the dots varying in density from their centers to their edges and the lines being crisscrossed so that a chequer board pattern is produced.
  • One method of making such screens is by projecting light through a camera screen, that is a glass screen provided with a criss-cross pattern of lines, onto a photosensitive film, the light passing through any square formed by the lines being vignetted to produce the subsequent dot which forms one of the row of dots which produce the lines on the contact screen, and such contact screens are usually used in direct contact with the photosensitive material on which the final image is to be produced.
  • a contact screen has a pattern of lines of spaced dots in which the centre of each dot is in the form of a central core having a midpoint of maximum density which is surrounded by a pattern of minor dots of smaller area, these having lessening density with displacement from the central core, the minor dots being spaced apart in a regular pattern to provide areas of minimum density between them.
  • each of the dots of normal type the edges of which are of diminishing density is replaced by a dot of the kind set forth above in which the area of diminishing density is pierced in a regular pattern by areas of very low density through which light can pass.
  • the minor dots cease or are of such density as to almost cease after a predetermined distance to provide an area of minimum density between adjacent dots which is of the same area as the central cores, and the minor dots may be arranged in rows which are parallel with the rows of dots forming the screen, each minor dot being substantially square and adjacent minor dots having their corners adjacent.
  • each central core is in the shape of a number of minor dots joined together along their sides, the areas of minimum density being in the shape of the spaces left between a number of minor dots.
  • the pattern of dots is achieved by coordinating two basic patterns of dots one of which has more lines of dots to the inch, and in which the dots are of smaller area than the other in which the dots correspond to the cores of the final pattern.
  • one of the basic patterns of dots corresponds to the high density cores and the other corresponds to the rows of minor dots of lessening density with displacement from the central core.
  • one basic pattern of dots has 133 lines of dots per inch and the other has 931 lines per inch.
  • the dots on both basic patterns are substant-ially square.
  • a convenient method of making a contact screen according to the invention comprises exposing a photosensitive material to a first pattern of light projected through a cross-lined screen, said pattern of light corresponding to an area of the pattern of dots and minor dots which forms the eventual screen and then projecting a second pattern of light in place of the first in the form of a low density image of a dot or dots corresponding in area and position to the area of a larger dot or dots in the basic larger pattern projected initially, and subsequently developing the photosensitive material.
  • the first pattern of light corresponds to the pattern on the screen at the area comprising a single large dot, and provides a central area of light intensity which is surrounded bya number of areas of equal in- "ice - tensity but smaller area which are spaced apart from one another in both linear directions in a regular pattern.
  • the first pattern of light projects an image which corresponds to the eventual pattern on the contact screen but without the minor dots of smaller area being of lessening density with displacement from the central core.
  • the first pattern of light is achieved by shining the light from a light source through one of a pair of interchangeable opaque stops which are provided with apertures so shaped as to produce the patterns of light required.
  • the other stop will be used to control the second pattern of light and this stop may be provided with apertures in the form of concentric bands which are 'of diminishing width from the centre to the edge of the stop.
  • this stop provides a light pattern which simulates a vignetted dot obtained through a normal screen, and the diminishing intensity towards the edges of the spot produce the required diminishing intensity of the minor spots around the central core.
  • FIG. 1 shows a portion of the pattern on a screen according to the invention
  • FIGURE 2 is a diagrammatic illustration of part of they screen
  • FIGURE 3 is a graph showing the density of each dot on the screen in relation to the width of the dot
  • FIGURE 4 is a diagrammatic illustration of the basic. principle which is used in the production of a screen
  • FIGURE 5 is a diagrammatic illustration of the method used for producing a number of dots on the screen and
  • FIGURE 6 is another diagrammatic illustration of the method of adjusting the intensity of the dots.
  • ⁇ FIGURE 1 shows a portion of ascreen according to the invention, from which it will be seen that each dot comprises a central core E which is surrounded by a number of smaller square shaped dots F.
  • the density of the central core and of the minor dots 1F lessens with displacement from the midpoint of the central core although this is not visible in the black and white line drawing,
  • each dot is indicated by the reference letter B.
  • the central core comprises the three dots B B B which aresubstantially opaque on the screen the dot B being the midpointof maximum density.
  • the dots B and B are the minordots on each side of the central core and as will be seen their density is considerably less than that of a central core'itself, and the dots B B have a density which is lower. again. As will be seen the density between each of the dots is reduced.
  • FIGUREZ illustrates the method by which the pattern arranged as 1 3-3 lines to the inch, two of these lines being indicated at A and A and these lines also corresponding to two of the smaller spaced lines which are formed by small square or diamond shaped dots as indicated at B, B
  • minor dots B, 'D, G, I act to provide the shading of density which would normally surround a vignetted dot on a 13'? line per inch' screen. so that although a gradual shading is provided from one dot to the next as they are displaced from the midpoint of the central core .there is an 'area of lesser density between each minor dot.
  • the screen as shown in FIGURES '1, 2 and 3 can be the minor dots ends at a predetermined distance from made by the application of the arrangement shown in FIGURE 4.
  • alight. source indicated atK
  • can shine throughan opaque, stop L whichis provided with a pattern of apertures which correspond to the surrounding minordots-and core of a single major dot on the contact screen.
  • the various points B to B of greaterintensity of light. intensity on FIGURE 3 are indicated in a corresponding row of apertures across the stop.
  • Part of a crossline screen such as If a number of apertures are provided in the photographic screen M, as shown in FIGURE15 then a corre-.
  • the latent image produced in the photosensitive material by the foregoing method will show little if any of the required 1 grading of the minor dots from thecenter to the edges of the major dots. initially made of low density and subsequently strengthw ened in the required pattern by the following method;
  • FIGURE 6 thenormal vignetting type dots of V 133 line screen are indicated at Q.
  • stop Lito include morethan one basic dot. made of any convenient colour which is required.
  • a photographic half-tone contact screen comprising a member having a pattern of linearly arranged spaced first dots each of a predetermined area, each first dot being in the form of a centralcore having a midpoint of maximum density which is surrounded by a pattern of minor dots each of a smaller area than said predetermined area, said minor dots. lessening in density with displacement from ,the central core, and the minor dots. being spaced apart in a regular pattern'to provide areas of minimum density between themselves.
  • each central .core is definedby a number of plural sided minorqdots, the last-mentioned minor dotsbeing positioned in side-by-side relationship,: and the areas of minimum density being in the shape of;
  • contact screen may be I 5.
  • a method of making a contact screen comprising the steps of providing an element having a coating of light-sensitive material, forming first and second light patterns of lines of dots in which there are more light dots per inch and of a smaller area in the first pattern than in the second pattern and the light dots of the second pattern correspond in configuration to the final pattern of the contact screen, exposing the light-sensitive coating by exposing the same to the first and second light patterns, and thereafter developing the light-sensitive element.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Silver Salt Photography Or Processing Solution Therefor (AREA)
  • Photosensitive Polymer And Photoresist Processing (AREA)
US295101A 1962-07-17 1963-07-15 Photographic half-tone contact screens Expired - Lifetime US3275445A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB27340/62A GB986419A (en) 1962-07-17 1962-07-17 Improvements in or relating to photographic half-tone contact screens

Publications (1)

Publication Number Publication Date
US3275445A true US3275445A (en) 1966-09-27

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ID=10257990

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Application Number Title Priority Date Filing Date
US295101A Expired - Lifetime US3275445A (en) 1962-07-17 1963-07-15 Photographic half-tone contact screens

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US (1) US3275445A (zh)
BE (1) BE635095A (zh)
DE (1) DE1255492B (zh)
GB (1) GB986419A (zh)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3885971A (en) * 1973-08-01 1975-05-27 Fuji Photo Film Co Ltd Contact screen and method for nonlinear transformations and filtering in coherent optical systems
DE3339396A1 (de) * 1983-10-29 1985-05-09 Helmut 4800 Bielefeld Jahn Kontaktraster fuer die reproduktionstechnik

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4600666A (en) * 1983-01-12 1986-07-15 Zink Edmund S Integrated photoscreen for making a halftone reproduction printing plate from a photograph

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE15494C (de) * WÜRTTEMBERGISCHE METALLWAARENFABRIK in Geifslingen Neuerungen in der Herstellung kupfer plattirter Eisenbleche
CH31757A (de) * 1905-01-27 1905-08-31 Theodor Dittmann Raster zur Herstellung von Autotypien
NL21929C (zh) * 1926-11-04
US1995958A (en) * 1933-03-03 1935-03-26 Photo Cast Inc Universal screen for preparing half-tones
DE716362C (de) * 1940-08-21 1942-01-31 Johannes Wimmer Verfahren zur Herstellung von Kopiervorlagen fuer den autotypischen Tiefdruck
US2478444A (en) * 1946-05-18 1949-08-09 Eastman Kodak Co Manufacture of photographic contact screens
DE958529C (de) * 1955-06-23 1957-02-21 Herbst & Illig Kontakt-Raster
DE1105721B (de) * 1959-09-22 1961-04-27 Herbst & Illig Kontakt-Tiefdruckraster

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3885971A (en) * 1973-08-01 1975-05-27 Fuji Photo Film Co Ltd Contact screen and method for nonlinear transformations and filtering in coherent optical systems
DE3339396A1 (de) * 1983-10-29 1985-05-09 Helmut 4800 Bielefeld Jahn Kontaktraster fuer die reproduktionstechnik

Also Published As

Publication number Publication date
BE635095A (zh)
GB986419A (en) 1965-03-17
DE1255492B (de) 1967-11-30

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