US3249437A - Contact screen and printing member produced therefrom - Google Patents

Contact screen and printing member produced therefrom Download PDF

Info

Publication number
US3249437A
US3249437A US414514A US41451464A US3249437A US 3249437 A US3249437 A US 3249437A US 414514 A US414514 A US 414514A US 41451464 A US41451464 A US 41451464A US 3249437 A US3249437 A US 3249437A
Authority
US
United States
Prior art keywords
areas
group
screen
density
groups
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US414514A
Other languages
English (en)
Inventor
Eekhout Frederick Johannes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Application granted granted Critical
Publication of US3249437A publication Critical patent/US3249437A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • 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

Definitions

  • the present invention relates to a contact screen for use in making a printing block from a picture having areas of optical density, and to a printing member, such as a printing block, produced by using the contact screen.
  • the contact screen of the present invention is of the type of contact screen having groups of small, light-transmitting areas, each group being constituted by areas of diiferent optical densities and of congruent shape, and each group having light-transmitting areas of all densities.
  • the light-transmitting areas adjoin one another and adjoining areas of adjacent groups, and each group has sub-groups the areas of which have an identical optical density. The densities of said sub-groups are different from each other.
  • This type of contact screen is described in French Patent 336,056, and can be employed for the reproduction of a picture of an object to 'be depicted in the form of one or more series of dots, all dots of one series having the same color and the same degree of transmission or reflection, the total area of the dots of a series in a certain portion of the picture being a function of the relative brightness of the corresponding portion of the object.
  • the printed dots of a series all have the same size, the number of dots in a given portion of the picture being such that this portion of the picture has the desired overall degree of reflection or transmission.
  • this known contact screen is manufactured by superposing bands of material with certain optical densities in various patterns, the optical densities of the lighttransmitting areas, as far as their mutual differences are concerned, are determined by the selection of the optical densities of the single bands used.
  • a second limitation of this prior art contact screen is that the number of density levels which can be present in the screen is determined by the number, the mutual difference in shape and optical densities, and the possibilities regarding the geometrical arrangement, of the bands. The number of levels is also limited because the geometrical configuration cannot be extended at will. If, for example, more than three bands are used, a greater number of areas of higher densities is indeed obtained, but on the other hand more and more areas of lower densities are lost.
  • a fourth restriction of the prior screen is in the number of areas of the same optical density within one group. In the prior art screen, this number is determined by the number, the optical value, and the. location of the. bands.
  • a fifth limitation of the prior screen is in the interrelation of the location of the areas of different optical densities. As a matter of fact, this is entirely determined by the arrangement of the bands. The result of these five limitations on the freedom of using the prior contact screen is that the distribution of the optical densities in the screen plate cannot be adapted to the demands to be made in connection with a true representation of the differences in brightness of the object to be depicted.
  • the contact screen according to the invention is characterized in that number of sub-groups and their densities and the number of areas in each sub-group can be selected without any limitations imposed by the fact that the screen is a configuration of intersecting bands.
  • An additional degree of freedom can be obtained, according to the invention, by varying the relative positions of the areas in the various groups. This enables a further adaptation to the requirements of a specific reproduction to be depicted.
  • the optical densities can be freely selected as far as their value is concerned, it is of importance, and it is possible according to the present invention, so to select the densities of the various areas such that the said densities constitute an arithmetical series, the logarithm of the relative number of areas of a given density being at least a substantially linear function of the said density.
  • the light transmitting areas prefferably have the shape of a regular hexagon.
  • the invention also relates to a printing block made by means of a contact screen as described herein.
  • FIG. 1 is a section, on enlarged scale, through a negative, a photographic positive material and a screen according to the invention
  • FIG. 2 is a graph showing the relationship between the magnitudes of values which play a part in the method and in the screen according to the invention
  • FIG. 3 is a greatly enlarged plan view of a preferred shape of the small light transmitting areas of the screen according to the invention.
  • FIG. 4 is an illustration of one way in which the contact screen can be built up.
  • FIG. 4A is an enlarged view of part GI of FIG. 4 showing the screen with the areas of different densities represented therein.
  • the same steps can be used as those for conventional screening methods, the contact screen according to the invention being used in the same step as the well-known screens formed by engraved optical glass.
  • the particular adjustments and auxiliary treatments, which are necessary when using the wellknown screens, are rendered superfluous by using the screen of the present invention.
  • the invention can be best understood by means of a specific example, the example here being the case where a transparent black and white negative picture is translated into dots (a screened picture) on a photo-sensitive material.
  • the transparent black and white negative will be called the negative for short and the picture thereof made on the photo-sensitive material will be called the positive.
  • the numeral 1 represents the negative and 2 the positive, both in section.
  • the numeral 3 designates a contact screen according to the invention, the construction and the operation of which Will be explained hereinafter.
  • the negative comprises a number of areas of different transmissivity.
  • the distribution of densities in the negative must be represented in the positive in a reverse sense, and according to the invention this must be effected by means of a pattern of dots, which consists of dots of equal size, the areas having differences in photographic density being reproduced in the'positive by areas having differences in the relative number of dots.
  • the half-tone positive is afterwards converted into a printing means (e.g. a half-tone block or an offset plate) which is used for printing the ultimate picture
  • a printing means e.g. a half-tone block or an offset plate
  • the positive 2 may be regarded here as if it were replaced by the printed image.
  • the object of the method of reproducing the negative is to have the positive and thus the printing means formed therefrom divided into dots in, such a manner that the number of dots per unit of surface area determines the density of the relevant portion of the image.
  • the number of printed dots actually in the area in question divided by the number of dots that could possibly be printed in'the area is equal to n, the remaining white area having no dots thereon has a size of (ln).
  • the total reflection factor then is and in general
  • the number of dots for obtaining a certain value of 1- is hence proportional to 1T, and is even substantially equal thereto.
  • the contact screen 3 which is used comprises a large number of small areas 4 of equal size and of different transmissivity, which areas are arranged in mutually identical groups, each containing sub-groups of areas having the same densities, and the diflferent sub-groups in a group of areas having different density such that each group has areas of all transmissivities that are employed.
  • the densities of the subgroups of areas within a group form an arithmetical series; in the subjoined example it is assumed that the difference in density between the successive densities of the subgroups amounts to 0.20, the extreme values being 0.00 and 2.00.
  • a zone of the positive having a certain blackening contains a number of dots which is equal to the number of dots in positive portions that are less black plus a number of additional dots, which latter number equals the number of areas of the screen of the greatest density that is still operative in this zone of the positive.
  • the number of additional dots necessary to produce each successive density level can be determined, therefore, as the difference between the total number of dots of said level and the number of dots which produce the preceding level.v
  • the relationship between the reflection factor of a portion of a printed image and the relative number of dots required therefore has already been established hereinbefore [Formula 1)].
  • Said number of dots naturally, is equal to the number of black dots in the positive which was used for manufacturing the printing means. However,.there is a difference between the extent of blackening of the positive and that of the printed image; for the printing ink used has, as was assumed, a density of 1.50, so that the maximum density. and hence the degree of blackening achievable likewise amounts to 1.50. Because in the printed image the same number of density levels must be present as in the negative, the difference in density between said levels in the printing means amounts to 0.15 instead of 0.20.
  • the subjacent table is a tabulation of the calculation outlined above; in this table Dimax is the density of the screen areas that are just operative and n, the additional number of said areas necessary for that density as compared to the area of the next preceding density level.
  • FIG. 2 is a graph in which the uppermost curve, the dots-dash curve, shows the relationship between the relative number n of printed dots and the density provided thereby.
  • the dashed-line curve shows the relationship between the relative number of n, of additional dots and the printed density
  • the full-line curve shows the relationship between it, and the density of a given set of screen areas.
  • the last-named curves turn out to be straight lines, the inclination of the latter being equal to -0.74; so that the following equation holds good:
  • the coeflicients a and b can be calculated in a corresponding manner.
  • a reversal process is used, a slightly different line of reasoning must be followed.
  • a negative image is formed first which by chemical treatment and by re-exposure is reversed into a complementary positive image. That is to say, if said provisional negative image was screened, the positive image would have a number of screen do-ts complementary to the number of dots in the negative. Consequently, the contact screen used with the provisional negative is to be adapted to produce these complementary numbers of dots.
  • the shape of the screen areas it should be noted that it is possible to use all geometrical shapes which can be arranged in adjoining relationship without any interspaces being left, examples of such shapes being triangles, squares and hexagons.
  • the latter shape is to be preferred, because owing to the alternating arrangement of the faces, the chance that lines will be seen in the screen pattern is smaller than if squares are used, while moreover the hexagon most closely approaches a circle.
  • Such a pattern is shown in FIG. 3, the faces having not yet been provided with the required grayings.
  • the formation of groups may be effected in different manners. A hexagonal circumference of the groups is most favorable owing to the symmetry and the optimum filling of a surface having a minimum area.
  • the size of the screen areas depends on the demands which are made on the reproduction and the lower limit of said size is determined by the surface properties of the paper to be printed. It is possible to achieve a diameter of 0.05 mm. and even less.
  • FIG. 4 is will be seen that there are two vertical columns of figures, the left column containing 7 figures and the right column 6. Furthermore there is a subdivision into horizontal rows which from the top downwards are designated by the letters AG inclusive. Consequently, the figure in the bottom right hand corner will be designated by GII etc.
  • FIG. 4 is a greatly enlarged portion of a contact screen. Adjacent portions of the contact screen will generally be built up in the same manner, i.e. according to the same pattern, but this is in principle not necessary. All areas of the sub-group of dark areas contained in the group of areas in FIG. AI, thirteen in this example, have the same photographic density. The same applies to the darkened areas forming the sub-groups of areas shown within a group of areas the same size as the group of areas in FIG. AI in the right column, i.e. sub-group B2 (containing twelve areas) to sub-group G2, inclusive.
  • the photographic density of the areas forming a sub-group is the same for all areas, of the sub-group
  • the photographic density of the overall group of areas increases step-wise from AI to G2.
  • the areas of the sub-group are uniformly distributed over the space occupied by the overall group of areas. This distribution is such, however, that as each of the various sub-groups is superposed upon the preceding sub-groups, the darkened and undarkened areas form a regular, and preferably homogenous, pattern.
  • group AI has a regular pattern as does group B2.
  • FIG. B1 which again has a regular and homogenous pattern, i.e.
  • FIG. AI has thirteen areas forming the sub-group. It would also be possible, however, to begin with a sub-group of five areas, namely, one in each corner and one in the center. It will be evident that this would also necessitate a change in the pattern of the succeeding sub-groups having different densities.
  • One of the advantages of the method and the preferred embodiment of the contact screen according to the invention is that in the case of multi-color printing it is not necessary to change the screening direction, for the chance of a visible moir-effect is much less than with the conventional screen pattern, the pattern according to the present invention containing many more dots.
  • the contact screen can be adapted in a simple manner to the materials used or to produce particular effects.
  • the positive will acquire the same photographic density as the negative; however it Will be clear that the distribution of dots may be so effected that the photographic density of the screened element, i.e. the positive, is greater or less than that of e the starting material, i.e. the negative.
  • the contact screens according to the invention may be made of any suitable transparent material e.g. glass, cellulose tri-acetate, and the like.
  • a contact screen the flexibility of which is opposite to that of the photographic printing material, i.e. in the case of photographic plates, a film screen, and in the case of films, a plate screen, so as to ensure a good contact and therefore an absence of interference figures. Because of the fact that in the graphic art vacuum cassettes are conventionally used, this is not an objection.
  • the contact screens according to the invention can be made in :a relatively simple manner by first drawing or printing a master screen on a greatly enlarged scale and blackening the areas into which said screen is to be subdivided according to the required pattern. Subsequent- 1y said screen is photographically reduced.
  • the degree of blackening of the areas of the master screen is to be adapted to the density curve of the photographic material which, if said curve is accurately known and if the reflection and transmission factors of the blackening agents used in the master screen have been accurately measured, does not give rise to special difliculties. If the color-sensitiveness of the photographic material used is accurately known, it is also possible to provide the areas of the master screen with such different colors that the desired blackening of the photographic material is obtained,
  • a contact screen for forming a printing means for printing a picture said screen having identical groups of small light transmitting areas, each group being made up of congruent areas, said light transmitting areas adjoining one another and the areas on the edges of the groups in parts of the screen other than the edges thereof adjoining areas of adjacent groups, each group of areas having subgroups of areas with the photographic density of each area in a subgroup being identical to the photographic density of the other areas in the subgroup, the densities of the areas in the respective subgroups being different from the density of the areas in each of the subgroups within said group of areas and there being a subgroup corresponding to each photographic density in a series of photographic densities, the areas of each subgroup being distributed over the total area ofthe corresponding group in a regular homogeneous optical pattern and the areas of each subgroup within a group together with the areas of the other subgroup-s within the group having a lower photographic density forming a regular homogene-ousoptical pattern.
  • A'contact screen as claimed in claim 1 in which the arrangement of the areas in the groups is mutually different.
  • a contact screen as claimed in claim 1 in which the densities of the different subgroups of areas Within a group are in an arithmetical series, and in which the logarithm of the relative number of areas in a subgroup is at least a substantially linear function of said density.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Printing Methods (AREA)
  • Manufacture Or Reproduction Of Printing Formes (AREA)
US414514A 1959-03-05 1964-11-23 Contact screen and printing member produced therefrom Expired - Lifetime US3249437A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL236806 1959-03-05

Publications (1)

Publication Number Publication Date
US3249437A true US3249437A (en) 1966-05-03

Family

ID=19751604

Family Applications (1)

Application Number Title Priority Date Filing Date
US414514A Expired - Lifetime US3249437A (en) 1959-03-05 1964-11-23 Contact screen and printing member produced therefrom

Country Status (4)

Country Link
US (1) US3249437A (xx)
CH (1) CH435978A (xx)
GB (1) GB951233A (xx)
NL (2) NL111394C (xx)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3493381A (en) * 1966-01-27 1970-02-03 Eastman Kodak Co Halftone screens having more than one type of dot
US4083632A (en) * 1976-04-05 1978-04-11 Xerox Corporation Multi-frequency screen

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3913728A1 (de) * 1989-04-26 1989-12-07 Hubert Marcel Brobst Raster und dessen autotypieverfahren von halbtonbildern und zeichnungen, geeignet insbesondere fuer den textildruck

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US805244A (en) * 1897-03-25 1905-11-21 Barmen Bank Verein Hinsberg Fischer & Comp Weaving-diagram and method of making the same.

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US805244A (en) * 1897-03-25 1905-11-21 Barmen Bank Verein Hinsberg Fischer & Comp Weaving-diagram and method of making the same.

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3493381A (en) * 1966-01-27 1970-02-03 Eastman Kodak Co Halftone screens having more than one type of dot
US4083632A (en) * 1976-04-05 1978-04-11 Xerox Corporation Multi-frequency screen

Also Published As

Publication number Publication date
NL111394C (xx)
CH435978A (de) 1967-05-15
NL236806A (xx)
GB951233A (en) 1964-03-04

Similar Documents

Publication Publication Date Title
DE3004749A1 (de) Vorrichtung und verfahren zur digital gesteuerten herstellung von druckformen unter verwendung eines lasers
US3249437A (en) Contact screen and printing member produced therefrom
US3643597A (en) Method of making screen printing articles
US4308326A (en) Halftone contact screen and photographic method of making the screen
US3085878A (en) Half-tone screen for color separation
US3674488A (en) Method of making matching photoprinting masters
US2189751A (en) Method for obtaining in projection images in color
US3258341A (en) Contact screen
US4188225A (en) Halftone screen with cell matrix
JP2961949B2 (ja) グラビア版
US2482638A (en) Photogravure
US2957766A (en) Method for the preparation of tinting patterns for plastic sheeting
US3024111A (en) Gravure
US4269932A (en) Process for preparing an original information carrier for zero-order diffraction
US1919481A (en) Photographic screen
US4278755A (en) Halftone screen and method of using same
US2150805A (en) Method of preparing halftone negatives with variable-density screens
US2468680A (en) Halftone screen for use in the
US1161824A (en) Photographic screen for half-tone work.
US3788200A (en) Exposure device for manufacturing colour picture tubes
US3666479A (en) Print containing different numbers of dots in light and dark tonal areas
US2014513A (en) Apparatus for making printing surfaces
JPS62169181A (ja) 光書き込みプリンタ
US2959484A (en) Method for preparing art copy for relief or offset printing
US2984566A (en) Method of preparing a printing surface