US3657983A

US3657983A - Graphic aid and methods related thereto

Info

Publication number: US3657983A
Application number: US36979A
Authority: US
Inventors: Elton N Baker
Original assignee: Fotel Inc
Current assignee: Fotel Inc
Priority date: 1970-05-13
Filing date: 1970-05-13
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25

Abstract

A master grid layout sheet and methods of manufacture associated therewith are disclosed for use in graphic art work such as the layout and reproduction of printed circuits and the like. In typical printed circuit work precision art work and subsequent photographic reproduction thereof are normal intermediate processing steps. The master sheet includes a pattern, usually of orthogonal reference lines, printed thereon in a predetermined critical gray or neutral monotone. The monotone has a visual density such that the reference line pattern is visible to a draftsman but the light transmission density or opacity thereof is insufficient to cause the pattern to be reproduced in a controlled photographic reproduction of the master sheet. A processing control method for forming the master grid sheet is also disclosed. The process utilizes a visual process control guide which provides a standard of comparison for obtaining the critical transmission density of the gray monotone pattern. Thus the development process by which the master grid sheet is formed may be consistently controlled to produce the critical transmission density for the reference pattern thereon. The subsequent processing of reproductions of the art work may be controlled in correlation with the critical density of the monotone pattern to cause the pattern to disappear in the final product.

Description

United States Patent Baker [54] GRAPHIC AID AND METHODS RELATED THERETO Elton N. Baker, Elgin, Ill. [73] Assignee: Fotel Inc., Villa Park, Ill. [22] Filed: May 13, 1970 [21] Appl. No.: 36,979

[72] Inventor:

[52] U.S. Cl ..95/85, 96/27 [51] Int. Cl. ..G03b 15/00 [58] Field of Search ..95/l, 85; 96/27 [56] References Cited UNITED STATES PATENTS 3,169,063 2/1965 Johnston ..96/27 3,499,377 3/1970 Esses ..95/85 FOREIGN PATENTS OR APPLICATIONS 578,363 6/1933 Germany ..352/240 Primary E.raminer.lohn M. Horan AttorneyPendleton, Neuman, Williams & Anderson 5 ABSTRACT A master grid layout sheet and methods of manufacture associated therewith are disclosed for use in graphic art work (151 3,657,983 51 Apr. 25, 1972 such as the layout and reproduction of printed circuits and the like. In typical printed circuit work precision art work and subsequent photographic reproduction thereof are normal intermediate processing steps. The master sheet includes a pattern, usually of orthogonal reference lines, printed thereon in a predetermined critical gray or neutral monotone. The monotone has a visual density such that the reference line pattern is visible to a draftsman but the light transmission density or opacity thereof is insufficient to cause the pattern to be reproduced in a controlled photographic reproduction of the master sheet.

A processing control method for forming the master grid sheet is also disclosed. The process utilizes a visual process control guide which provides a standard of comparison for obtaining the critical transmission density of the gray monotone pattern. Thus the development process by which the master grid sheet is formed may be consistently controlled to produce the critical transmission density for the reference pattern thereon. The subsequent processing of reproductions of the art work may be controlled in correlation with the critical density of the monotone pattern to cause the pattern to disappear in the final product.

11 Claims, 7 Drawing Figures PATENTED APR25 1972 SHEET 1 0F 2 FIG. 1

QPMS O 'UJ Tk. a 7.- W36 N n H I w l GRAPHIC AID AND METHODS RELATED THERETO FIELD OF THE INVENTION The invention is directed generally to methods and apparatus for graphic reproduction and more particularly to the preparation and photoreproduction of drafting in the production of electronic circuits.

I BACKGROUND OF THE INVENTION Many electronic devices such as printed circuits and the like include one or more conductors which are, for example, printed, plated, etched or formed by a chemical deposition process on a base of insulating material. Ordinarily one or more master sheets including drawings or other pictorial representations of the conductors in accurate relative registration must first be made. Prior art methods and apparatus for drafting such electronic devices often include underlay reference grid sheets or color reference lines on the master sheet itself. Similar layout grids are utilized in other areas of the graphic arts.

Underlay grid sheets introduce errors because of these shortcomings: (a) accidental grid shift is possible even though the reference is pinned or taped to the master; (b) the master and reference grid must be maintained in intimate contact during the layout process; (c) maintenance of circuit component placement cannot be checked once the master is removed from the underlay grid; (d) the grid must be selected to be ofthe same size as the master to prevent misregistration; and (e) it is difficult to interrupt a project once it is begun, or make revisions, corrections or alterations thereon because of difficulties in re-establishing registration.

Producing color grid lines on master sheets, which are intended not to reproduce in subsequent photoreproduction, suffers from two manufacturing shortcomings: (a) typical color images require, in addition to regular exposure and processing, several very difficult operations: a bleach-etch process, a manual re-development for black image detail, and a manual dye application for color lines; and (b) production control of the color intensity to provide both good drafting visibility and subsequent total photographic drop out is difficult. In addition to manufacturing problems, the use of a color grid conflicts with the techniques of photographic color separation used to reproduce from a master drafted with two color tapes.

SUMMARY OF THE INVENTION Thus it is an object of this invention to provide a method and apparatus which avoids or minimizes all the aforenoted shortcomings.

It is another object ofthis invention to provide a master grid layout sheet for use in graphic art work such as the layout of printed circuits and the like where precise art work and photographic reproduction are requisite intermediate steps, the master sheet including a pattern of reference lines which are visible for circuit drafting purposes, but drop out during the processing of a photographic reproduction of the master sheet.

lt isa further object of this invention to provide a method for controlling the density of the reference lines during the I rocess of producing the master grid layout sheet, so that the qualities noted above are consistently provided.

Further and additional objects will appear from the description, accompanying drawings and appended claims.

In accordance with one embodiment of this invention, a master layout sheet is provided including a diaphanous base having both effectively opaque images which appear on both the master layout sheet and the reproduction thereof and a light gray or neutral monotone pattern disposed thereon. As

used herein the term effectively opaque means sufficiently dense to provide sharply contrasting areas in the ultimate reproduction which will determine the printed circuit pattern,

and the term neutral monotone denotes a homogeneous neutral density substantially less than effectively opaque."

The monotone pattern may comprise a network of orthogonal reference lines or the like and is of a precisely selected critical density, dense enough so that it is visible to an artist laying out a circuit design on the master sheet, and yet sufficiently transmissive so that it will not be reproduced in a properly processed photographic copy of the master. In order to precisely control the density of the monotone pattern, a visual processing control guide is incorporated in a selected area of the master layout sheet. The processing guide includes a test patch having the same density as the monotone pattern, and monotone or homogeneous in nature, and a plurality of comparator patches which are not monotone but, on the contrary are halftones or the like. One comparator patch is a standard patch having an average or effective density bearing a known relationship to the density of the monotone pattern; The remaining comparator patches have effective densities which establish predetermined upper and lower limits for the density of the monotone pattern. Further, the comparator patches, because of their non-homogeneous character develop their final effective density more quickly than the monotone test patch thus establishing a standard of comparison which may be used to control the development of the monotone test patch and thereby the pattern on the master layout sheet to precisely the proper density. I v

IN THE DRAWINGS FIG. 1 is a plan view of a master layout sheet and visual processing guide in accordance with this invention.

FIG. 2 is a detailed view ofa visual processing control guide for use in tray processing ofa master layout sheet developed in accordance with this invention.

FIG. 3 is a detailed view of an alternative processing guide for 'use in machine processing of a master layout sheet developed in accordance with this invention.

FIG. 4 is an illustration of a vacuum contact device for exposing a suitable sensitive film in producing a master layout sheet in accordance with this invention.

FIG. 5 is a partially exploded side view of the vacuum contact device shown in FIG. 4 illustrating the relative placement of the elements during exposure of the sensitive film to produce the master layout sheet.

FIG. 6 is a set of curves illustrating the relationship between development time and visual effects in the visual processing guide of FIG. 2 to achieve the optimum density of the gray monotone reference pattern on the 'master layout sheet.

FIG. 7 is a Hurter-Driffield characteristic curve of a sensitive film suitable for production of the master layout sheet of this invention. 1

Referring now to the drawings and in particular to FIG. I, a preferred embodiment ofa master grid layout sheet 2 is shown which is particularly suited to close tolerance printed circuit art work. The grid layout sheet is ofa diaphanous material and includes a pattern of orthogonal reference lines 10 on the surface thereof. The master can also include board corner marks 16, edge contact connectors 18 and other common features. In drafting a circuit on the master layout sheet, a draftsman applies a suitable adhesive tape to the master layout sheet 2, positioning the tape to represent theconductors of the printed circuit. The tape may be cut to desired lengths and applied to the master to represent conductors 14, using the reference network lines 10 as guides. Through-board connections and terminal points may be applied in the form of printed or diecut self-adhesive pads 15 located using intersections of the reference lines 10 as guides.

The master layout sheet 2 is purposely of large dimensions, for example, four times the desired finished board size, so that after the desired circuitry configuration is achieved, the board may be reduced in size by a photographic reproduction process with enhanced precision in the ultimate product. This reduction step causes any placement error in the printed circuit configuration as laid out on sheet 2 to be diminished in the same proportion as the master is reduced. The photographic reduction of the finished master sheet to final size is made on a camera such as a graphic arts darkroom type which reproduces the printed circuit art work with minimal distortion of its geometry and to vary precise dimensions. In a typical manufacturing process the photographic reproduction, which may be positive or negative in form, may be used to produce a silk screen mask for printing a resist on a suitable copper clad conducting board, or to expose a light sensitive resist on a conducting board. The resist selectively covers or exposes the copper circuits during plating or etching processes which remove the unwanted copper or add desired protective metallic layers in accordance with the pattern of tape on the master sheet 2.

Thus the presence of the reference lines 10 on the master grid layout sheet 2 during the art work layout process is very important in holding drafting errors to a minimum. However, should any of these reference lines appear on the photographic reproduction of the art work, an erroneous circuit connection of spurious metallic areas is produced in the printed circuit board. If the reference lines 10 are to be visible to a circuit draftsman working on the master layout sheet 2 but are not to appear on a photographic reproduction thereof, the transmission density of the lines must be held within critical limits. Density, in photographic work, is the logarithm (to the base 10) of opacity and is defined by I (incident light) T (transmitted light) Therefore, Density Log I/T. Thus if the incident light is designated as 100 percent, the following examples will illustrate the meaning of density as applied to this invention: (a) If all the light is transmitted (very nearly true of glass), then the opacity would be unit and, since the logarithm of l is 0, the density would be (b) If none'ofthe incident light were transmitted (rarely encountered in photography), the opacity and density would be infinity; (c) If 50 percent of the light is transmitted, the opacity would be 2, and the log of 2, which is 0.30, would be the density; (d) If percent of the light is transmitted, the opacity would be l0 and the density would be Opacity 1.0.0; and (e) If 0.] percent l/l0 of 1 percent) of the light is transmitted, the opacity would be 1,000 and the density would be 3.00.

A table of Common Logarithms (to the base 10) will show the above-defined relationship between opacity and density by reading opacity as the numberand density as the logarithm.

The Log l/T shall be referred to herein as transmission density. It has been determined that the reference lines 10 on the master sheet 2 should have a critical monotone density located within the general range of 0.20 to 0.40 above base density of the film, and preferably have an optimum critical transmission density of 0.30 controlled within 0.05 density abovebase density. Clear film of the type described herein has a base density of 0.05 to 0.07 which is inherently compensated for in tray processing by the fact that both the processing guide and the reference pattern are referred to the same base density. In machine processing-where transmission density readings may be taken by a densitometer, the densitometer may be calibrated to read 0 (zero) through a clear area of this base film.

Monotone density (gray) as used herein applies to a single density value of a typical photographic continuous or homogeneous tone. Effective visual density is used herein to designate the apparent density produced by the halftone technique which is used for the comparator patches of the processing guides. A halftone produces visual densities by the technique ofco ntrolling the ratio oftransmitted light to the in- I cident light, in accordance with the previous definition: Density Log UT. The halftone achieves this by the use of dots or lines having a single high density value to effectively absorb a portion of the incident light. The ratio'of transmitted light is dependent uponthe ratio of the size of high density areas to clear areas. These dots or lines occur in regular, repetitive spacing of a frequency sufficiently high to prevent visual processed as described herein. A monotone reference pattern having the prescribed critical transmission density has sufficient visual density to be visible to the naked eye and be usable in drafting the printed circuit art work as well as having a transmission density so low that the pattern will not appear in a photographic reproduction of the completed printed circuit art work when processed as describedherein. 'The'exact density value for the monotone reference pattern should preferably be maintained within a plus or minus 0.05 limitaround the critical transmission density of 0.30 above base density in order to provide visibility of the reference pattern for the draftsman without exceeding the upper density limit imposed by the exposure and processing parameters of the subsequent photographic reproduction.

High density (black) features which are common to a plurality of printed circuit layouts, such as edge contact connectors 18, are printed on the same master grid layout sheet.

' These features typically have a density not less than 3.00

above the density of the base. Some latitude in the density of the black features above this lower limit is permissible, with emphasis being on the quality of image geometry and the sharpness so that these features are accurately portrayed in the photographic reproduction of the 'master sheet. The parameters set forth herein are interrelated and depend in part on the available materials. Variations are possible within the functional constraints set forth herein.

The use of accurately controlled methods of exposure and development in the production of the master layout sheet insures that the monotone reference lines 10 will beeliminated in subsequent photoreproduction, whereas black features such as 18 will be sharply and clearly. reproduced. The method utilizes a processing guide 70 (shown in FIG. 1 and explained in detail below) including a test area 78 of the optimum monotone density and a plurality of

comparator patches

72, 74, 76 specially designed to provide standards by which the development of the critical low density levels may be monitored. These patches are preferably non-homogeneous halftones.

The master grid layout sheet is exposed in a vacuum contact film exposure device shown in perspective in FIG. 4. The exposure device 28 includes a base 30 having an embossed blanket 32 incorporated therein. An outlet 34 to a vacuum pump (not shown) is mounted to the underside of the base 30 and communicates with the embossing of blanket 32. Registration pins 35 and 36 and film cover sheet 38 are affixed to the upper side of the base. The base may be made of rigid acrylic plastic and the embossed blanket of black flexible vinyl plastic to provide means for air evacuation, thereby providing vacuum contact between the elements of the exposure device during the exposure process described below, while maintaining a nonreflective background for the exposure of the film therein. The cover sheet 38, which may be 0.004 inch Mylar, is used to sandwich a sensitive film 40 to be exposed and an image bearing negative 42 through which the exposure is made in intimate contact between cover 38 and blanket 32. A channel 39 provides communication between the vacuum outlet 34 and the blanket 32 to draw the cover sheet 38 down tightly on the sensitive film and master negative.

The procedure for exposing a sensitive film 40 to print thereon both the optimum density monotone pattern of reference lines and the high density standardized circuit features (which are to carry over into the final printed circuit) will now be explained in detail with reference to the partially exploded view of the'exposure device in FIG. 5. The arrangement for making an exposure places the sensitive film 40 (emulsion up) over blanket 32 covered in turn by master negative 42 (emulsion down) and cover sheet 38.

As shown in characteristic response curve FIG. 7, the emulsion and developer are carefully chosen to provide a curve portion of low gamma or contrast embracing the low density (gray) levels as well as a curve portion of high gamma so the development of a low density may be critically controlled without sacrificing the high density capability required for the black images. Kodaline Ortho Estar Base 0.007 developed in DuPont 24D meets these requirements and is the combination used for the evaluation in FIG. 7. There are other satisfactory combinations of emulsions and developers including some films which have a matte surface or are effectively translucent.

During exposure ofsensitive film 40, the master negative 42 is held in alignment overlying the film by

register pins

35 and 36. The sensitive film 40 and master negative 42 are sandwiched in overlying registration by cover 38 and the vacuum pump is started. A soft pile roller such as a paint roller sleeve may be used to assist in the evacuation of air from between film 40 and negative 42 to promote intimate contact therebetween. A first exposure of the entire image of the master negative is made from the low intensity light source 60, FIG. 4, by using a timer (not shown) to control the exposure duration.

Prior to the second exposure, without releasing the vacuum, an area mask 62 is placed in register, using register pins 35 and 36, over the corresponding areas of the master negative and squeegeed fiat to the cover sheet. Vacuum contact for the mask is not required because it contains no fine details. This mask blocks out the areas to be developed to the gray monotone density but is open in the areas for the black image details such as the edge contact connectors 18 and the comparator patches of the processing guide 70. The second exposure is made from the high intensity light 64. Both exposures are made for the same time increment, typically about seconds, controlled by a reset timer. The two

light sources

60 and 64 have a light intensity ratio of about 1 to 10 which represents 21 Log Exposure difference of L00. A switch directs the timer output to the appropriate light source. The power supply of the timer is provided by a voltage regulating transformer to insure a consistent intensity ofthe light sources.

.An optional third exposure step may be added to the method detailed above to add patch areas of the gray monotone density outside the area of the monotone reference linesv For example, some fine details such as register marks and dimension lines which are drafted onto the master grid layout sheet require more critical exposure at the final reduction than employed for bolder high density (black) features and the drafted circuit details. The fine details can be protected from overexposure and blooming" from adjacent clear areas by including a gray patch overprinting the fine lines, the patch to be ofthe same monotone density as used for the pattern of monotone reference lines. Prior to this additional exposure, the vacuum is released and overlay mask 62 and master negative 42 are removed. A mask (not illustrated) having open areas for these patches but with complete opacity to protect all other areas is located in register in place of the master negative. The vacuum is again applied and another exposure is made from the low intensity light source 60. The vacuum is released and the film is now ready for the controlled processing procedure.

It should be understood that modifications of the exposure process may be made without departing from the invention, provided only that the interrelationship of parameters is maintained. For example, a single lamp may be used for the exposures with proper adjustment ofthe exposure times. In another method, a single exposure is made with a single light source. This method is carried out by incorporating a mask of uniform density over all areas of the master negative which are to appear in low density monotone. The density of the mask should be approximately 1.00, which will provide the necessary I to 10 exposure ratio between the low density and high density patterns of the master. A single exposure is then made using high intensity light 64. The aforementioned methods all use a single master negative. Another method uses two or more master negatives, each contributing a portion of the total image with each receiving its appropriate exposure.

In developing the exposed sensitive film 40, the density of the gray monotone portions within the optimum limits is a critical production requirement. At the same time the black features must be reproduced at the maximum transmission density to provide effective opacity. Obviously the vuse of instrumentation such as a densitometer is not possible during tray development and therefore the use of the visual control guide, FIG. 2, is imperative for manual processing. A densitometer may be used to monitor samples with machine processing; however, the visual machine processing guide, FIG. 3, appearing on each master provides an instant and convenient evaluation. Therefore, either of the processing control guides 70 in FIGS. 2 and 3 may be used in the development processing step to enable the operator to consistently produce master sheets having monotone line patterns within the optimum gray density range.

The tray processing control guide, shown in FIG. 2, preferably includes at least three comparator density patches, indicated generally at 72, 74 and 76 which quickly attain and thereafter maintain a stable visual density over a wide range of development changes during processing of film 40, and a monotone sample patch 78 which develops to transmission density at the same rate as the monotone reference pattern during the development process.

The changes in visual density with development time of the comparator patches 72-76 and the test patch 78 are illustrated in the graph of FIG. 6. As shown therein, the developing process is terminated when a predetermined ocular relationship between the density of the comparator patch 74 and the test patch 78 is achieved. In the preferred embodiment the comparator patches comprise halftone patterns of saturated high density areas interspersed with clear or low density areas to produce visual tones of a desired effective visual or optical density. The three exemplary patches are comprised of three different halftones varying in the ratio of opaque to clear area, the central patch being a halftone having an effective visual density bearing a known relationship to the gray monotone density to be used for the master sheet reference lines. The left-hand patch 72 is a submarginal halftone having an effective visual density too light to be consistently visible for use as a reference line, and the right-hand patch 76 has an effective visual density so dark that a monotone reference line of this density might carry over into a photographic reproduction of the master layout sheet. The monotone test patch 78 is matched to the halftone patch 74 of the reference pattern. As shown in the graph of FIG. 6, the comparator patches which are exposed to halftone patterns develop rapidly and then maintain a nearly constant visual density, thereby establishing the optimum density of the monotone reference pattern. These can be observed by reflection during the developing step under an appropriate safe light.

Processing of the sensitive film exposed by the method disclosed above to produce a master grid layout sheet having reference lines of optimum density as disclosed above can be done manually with trays or by an automatic processor. The design for a control guide for manual processing is shown in FIG. 2. The curves of FIG. 6 illustrate the relationship between development time and certain visual density characteristics of the comparator and test patches which are used to control processing. The guide is designed to give an operator controlling the developing operation a visual standard ofcomparison between three comparator densities or tones and the density or tone of the gray monotone. The ideal effective visual density value of comparator patch 74 is designated by zero (0) with upper and lower limits designated minus and plus in patches 72 and 76 to aid the operator in making an evaluation. The operator stops the developing step when the density of the monotone test patch 78 appears to have a densi ty between the plus and minus extremes of the reference patch tones 72 and 76 with the objective of achieving a visual match 88, FIG. 6, between the monotone test patch 78 and comparator patch 74, at which time the film is transferred to a stop bath and then a fixing bath.

The visual densities of the halftone comparator patches are stable over a wide time period of the development cycle, as indicated by respectively labelled curves 80, 82 and 84. The visual density or tone of gray monotone sample patch 78 slowly increases during development; the development process is stopped when a visual tone match is achieved between the tone of sample patch 78 and comparator patch 74. Observation of this guide is made under low visibility conditions, namely: reflectance from the emulsion while in the developer solution under safe light illumination. Thus the visual relationship between the monotone patch 78 and the

comparator patches

72, 74 and 76 is not the same as their measured transmission densities, as illustrated in FIG, 6. It has been determined that the observed patch 78 appears denser during development by approximately 0.20 than its actual density, This apparent increase in visual density of the monotone patch over the actual measured value of the critical transmission density is consistent throughout the development process and thus requires no other correction in the comparator and test patches of the visual processing guide than an initial adjustment of the black to white ratio in the original halftones to increase the apparent density by about 0.2. Thus the halftone comparator patch 74 should have a measured transmission density of 0.50, which is two-thirds opaque to onethird clear, to match effectively a monotone density of 0.30. The ratio of opaque to clear portions in halftone patches 72 and 76 should be about 1.5:1 and 3:1 respectively. With reference to the halftone patterns of the comparator patches ofthe processing guide, it should be noted that a line frequency of about 50 lines per inch is about the minimum which the operator sees as an effective visual tone without resolving the lines under manual processing conditions.

FIG. 3 illustrates typical comparator patches incorporated in a visual processing guide for machine processing of the film carrying the master grid layout sheet. The guide differs from that of FIG. 2 because it is used as a standard of comparison after completion of processing, and provides the operator with an evaluation useful in machine adjustments (speed and temperature) and chemistry changes (developer aging, additions or replacement) to control the development of film subsequently fed into the processor. More than three comparator patch density values are used because the magnitude of deviation should be evaluated to aid an operator in making the adjustments noted above. In FIG. 3, seven patches 90-96 are used with the center patch 93 providing a visual density match with the critical gray monotone density. A table of ratios of opaque to clear portions of these halftone patches is set out below. It should be understood that these values are disclosed as examples, and are not intended to be limiting in any way.

Patch 90 0. Patch 91 0. Patch 92 0.7 Patch 93 Patch 94 1. Patch 95 l. Patch 96 1.8

- It should also be noted that the automatic film processing guide is viewed under better conditions than the guide used in tray processing methods, Therefore, the line frequency of the automatic processing guide of FIG. 3 should be higher to prevent visual resolution. A line frequency of about 65 per inch is about minimal. Further, the apparent visual density of the test patch 78 as observed is more nearly identical to its actual transmission density so that no adjustment (as for the manual processing guide of FIG. 2) need be made. In fact, a densitometer may actually be used.

While a particular embodiment of this invention is shown above and described, and articular methods of utilization are course, that the invention is not to be limited thereto, since many modifications may be made. It is contemplated, therefore, by the appended claims, to cover any such modifications as fall within the true spirit and scope of this invention.

I claim:

1. A layout sheet having disposed thereon a master reference pattern for use in the preparation of photographic reproductions of effectively opaque effects on said sheet and oriented with respect to said master reference pattern, the effects including a plurality oforiented effectively opaque areas, said sheet comprising a generally planar member having low optical density and a master reference pattern thereon comprising neutral monotone effects disposed on a surface of said planar member, the neutral monotone effects being disposed on said surface in a pattern to facilitate the location of said of fectively opaque areas, said neutral monotone effects having an optical density sufficient to be visible during the location of said effectively opaque areas but having sufficiently low optical density that sufficient light impinging thereon can be utilized in subsequent photographic reproduction to render said neutral monotone effects photographically invisible, the optical density of said neutral monotone effects being no more than about 0.4 above the optical density of said planar member.

2. The layout sheet of claim 1 wherein said planar member is a diaphanous flexible sheet.

3. The layout sheet of claim 1 wherein said monotone effects and said opaque areas are of the same color.

4. The layout sheet of claim 3 wherein the neutral monotone effects have light transmission densities within the range of about 0.2 to about 0.4 abovethe light transmission density of said planar member.

5. The layout sheet of claim 4 including opaque areas having substantially the same color as neutral monotone effects and having light transmission densities of at least about 3.0 above the light transmission density of said planar member.

6. The layout sheet of claim 3 wherein the light transmission density of said planar member is substantially zero.

7. The layout sheet of claim 6 wherein the density of said neutral monotone effects is about 0.3.

8. A layout sheet having disposed thereon a master reference pattern for use in the preparation of photographic reproductions of effectively opaque effects on said sheet and oriented with respect to said master reference pattern, the effects including a plurality of oriented effectively opaque areas, said sheet comprising a generally planar member having low optical density and a master reference pattern thereon comprising neutral monotone effects disposed on a surface of said planar member, the neutral monotone effects being disposed on said surface in a pattern to facilitate the location ofsaid effectively opaque areas, said neutral monotone effects having an optical density sufficient to be visible during the location of said effectively opaque areas but having sufficiently low optical density that sufficient light impinging thereon can be utilized in subsequent photographic reproduction to render said neutral monotone effects photographically invisible, said generally planar member comprising a sheet of supporting film for a photographic emulsion, said neutral monotone effects constituting a pattern of photographic emulsion disposed on said film and reduced to a visible state.

9. The layout sheet of claim 8 wherein the neutral monotone effects have light transmission densities within the range of about 0.2 to about 0.4 above the light transmission density of said planar member. 7

10. The layout sheet of claim 8 wherein at least some of said effectively opaque areas are areas of said photographic emulsion reduced to a visible state.

11. The layout sheet ofclaim 8 wherein at least some of said effectively opaque areas are adhesively secured to said film.

Claims

1. A layout sheet having disposed thereon a master reference pattern for use in the preparation of photographic reproductions of effectively opaque effects on said sheet and oriented with respect to said master reference pattern, the effects including a plurality of oriented effectively opaque areas, said sheet comprising a generally planar member having low optical density and a master reference pattern thereon comprising neutral monotone effects disposed on a surface of said planar member, the neUtral monotone effects being disposed on said surface in a pattern to facilitate the location of said effectively opaque areas, said neutral monotone effects having an optical density sufficient to be visible during the location of said effectively opaque areas but having sufficiently low optical density that sufficient light impinging thereon can be utilized in subsequent photographic reproduction to render said neutral monotone effects photographically invisible, the optical density of said neutral monotone effects being no more than about 0.4 above the optical density of said planar member.

4. The layout sheet of claim 3 wherein the neutral monotone effects have light transmission densities within the range of about 0.2 to about 0.4 above the light transmission density of said planar member.

8. A layout sheet having disposed thereon a master reference pattern for use in the preparation of photographic reproductions of effectively opaque effects on said sheet and oriented with respect to said master reference pattern, the effects including a plurality of oriented effectively opaque areas, said sheet comprising a generally planar member having low optical density and a master reference pattern thereon comprising neutral monotone effects disposed on a surface of said planar member, the neutral monotone effects being disposed on said surface in a pattern to facilitate the location of said effectively opaque areas, said neutral monotone effects having an optical density sufficient to be visible during the location of said effectively opaque areas but having sufficiently low optical density that sufficient light impinging thereon can be utilized in subsequent photographic reproduction to render said neutral monotone effects photographically invisible, said generally planar member comprising a sheet of supporting film for a photographic emulsion, said neutral monotone effects constituting a pattern of photographic emulsion disposed on said film and reduced to a visible state.

9. The layout sheet of claim 8 wherein the neutral monotone effects have light transmission densities within the range of about 0.2 to about 0.4 above the light transmission density of said planar member.

11. The layout sheet of claim 8 wherein at least some of said effectively opaque areas are adhesively secured to said film.