US2294645A - Printing plate - Google Patents

Description

Sept. 1,1942.- F. L; wuRzBuRG, JR 2,294,645-

4 PRINTING PLATE A Original Filed July 5,A 1940 5 Sheets-Sheet l AW///// /l /7//////////// INVENTOR JW; ATTORNEY 5 Fww'kwwwjl Spt. 1, 1942. F. L. wURzBuRG, QR 2,294,645

PRNTING PLATE i original Filed July 5, 1940 .5 sheetssheet 2 kupplu INVENTOR Fw@ mida/LM 7l Q 5% mais@ ff- ATTORNEY S sept. l1,1942.

A Original Filed July 5, 1940 F. L. wURzBuRG, JR

PRINTING PLATE 5 Sheets-Sheet 3 lNVENTOR sept. 1,1942.

F. L. wuRzBuRG, JR

PRINTING PLATE ad ATTORNEY S Sept. 1, 1942. F. l.. wuRzBURG, JR 2,294,645'

l PRINTING PLATE Original -Filed July 5, 1940 5 SheetsTSheet 5 a s' "fw @www I v BY r Sit? v 05 ATTORNEYS PatentedSept. 1, 1942 2,294,645 Pnm'rmc PLATE Francis Lewis wmburk, Jr., New York, N3., u-

signor to Interchemlcal Corporation, New York, N. Y., a corporation of Ohio originsi'sppueaaon July 5, 1940, sei-m No. 343,962. Divided and uns application-August 9, 1941, serial No. 466,121

4 Claims.

This invention relates to printing plates.

The invention aims to provide for printed reproductions of continuous-tone original pictures in which the tones of the original are uniformly faithfully.represented. The printed reproductions produced in accordance with my invention differ strikingly from those heretofore made in that they faithfully reproduce the very light tones and the very dark tones of. any picture, It has heretofore been impossible to obtain uniform faithful reproductions of such'tones.

In printed pictures, the'light tones are represented by small black areas or dots on a white background, and the dark areas are represented by small white areas, which I shall also term dots, on a black background. It has long been recognized that in al1 usual methods of etching printing plates and printing from them, dots below a. definite minimum size cannot be uniformly etched and printed. The limitV varies with the method of etching and printing used and especially with the quality of the paper on which the print is made. In ordinary half-tone reproducl2,190,185 and 2,190,186, better results are ob-A tained by providing for a non-uniform spacing of the dots. This permits the obtaining of very iight tones by increasing the space between the dots without decreasing the size of the dots below the limit required for lightness of the tones which can be obtained by the Hardy plates, since a satisfactory reproduction cannot be obtained if the dots are placed too far apart to be fused by the eye.A

My invention is based in part on the observation that the diliculties which arise in etching and printing very small dots depends, not upon the area of the dot in question, but upon its shorter dimension. In the Hardy plates, the smallest dots have the form of long narrow rectangles. To etch and print properly, dots of this shape must have their shorter dimension above a predetermined limit and, in consequence, the area of such dots must be considerably larger than that of the round or square dots of a halftone plate in order to etch and printwith equivalent accuracy, This requires making .the smallest dots lof the Hardy plates of such large area (c1. lol-461.1) Y

by vproviding variably spaced dots and providingv for a variation both-dimensions of the dots,

so that the dots are of approximately uniform shape and the smallest dots may have their two 'dimensions substantially equal and at .the same time are spaced further apart than the larger dots.- In this way, I have succeeded in reprsenting very light tones by means of dots which. may be uniformly etched and printed and which, while more widely spaced than the dots of the middle tones, are nevertheless not spaced too far apart to bel fused by the eye.

What I have said as to the representation of very light tones is equally applicableto the representation of very dark (but not totally black) tones as the etching and printing of small light dots in the dark areas presents a problem similar to that of small black dots in the light. areas. Mir-invention includes a scanning method of making contrast images for producing my new printing plate. This method is characterized by using part of a photo-cell current which varies with the tone of the original picture to control the length and the spacing of the dark areas of the reproduction, and at the same time using another part of the photo-cell current to control the width of the dark areas of the reproduction in such a way that the width of the dark areas which are short and widely spaced is made less than that of those dark areas which are long and closely spaced. t

In describing my invention in detail, I shall refer to the accompanying drawings in which: Fig. l is a greatly enlarged View of part of a 40 contrast image or a diagrammatic face view of 45 face is diagrammatically represented in Fig. l,

sectioned on the line 2 3 of Fig. 1;

Fig. 3 is a view similar to Fig. 2 showing a lithographie printing plate;

Fig. 4 is a view similar to Fig. 1 showing a slightly modied contrast image embodying my invention, or a diagrammatic view of part of an inked intaglio printing plate; 'Y

Fig. 5 is an enlarged fragmentary section of an that dimculty is experienced in placing the dots intaglio printing plate whose printing surface is `diagrammatically shown in Fig. 4, sectioned on Figs. 9a, 9b, 9c are diagrams indicating the'v operation of the apparatus shown in Figs. 6, '7 and 8, each showing a position of the aperture plate with respect to the slit and the record made in that position of the aperture plate;

Fig. 10 4is a diagram of the electric circuit of a modified scanning apparatus for making contrast images;

Fig. 10a shows a modication of theelectric /circuit diagram shown in Fig. 10;

Fig. 11 is a diagrammatic perspective view of the optical system used in a scanning apparatus containing the electric circuit shown in Fig. 10 or that shown in` Fig. 10a;

Figs. 12a to 14c are diagrams illustrating the operation-of the scanning apparatus of Figs. 10 and-11, Figs. 12a, 12b and 12c being graphs show--V ing the variation in the galvanometer current, Fig, 13 a diagram indicating the relative position of the slit and aperture at different values of the and have a width only about 1/3 of the width of y the elements.

, image of Fig. 1.

Fig. 2 shows the form of a typographic plate v made from a contrast image such as that shown in Fig. 1, the plate having raised areas corresponding to the black areas of Fig. 1.

Fig. 3 shows a lithographie plate having inkreceiving areas corresponding to the black areas l of Fig. .1.

Fig. 4 shows a slight modication of a contrast 'Ihis`modication is .desirable when the image is to be used for making an intaglio plate as it avoids large unbroken indented areas in the dark portions of the picture. The elements of the areas representing different tones in Fig. 4 are the same as those in Fig. 1, but the rows of elements, instead of being contiguous as in Fig. 1, are slightly separated so as to provide white lines in the dark areas. In an intaglio galvanometer current, and Figs. 14a, 14h, 14e

ilustrating the record made when the galvanometer current has the values shown in Figs.`l2a,

- 12b, 12o respectively;

Figs. 15a,v15b and 15a are graphs similar to AFigs. 12a, 12b and 12e showing modifiedK galvanometer currents; and

Figs. 16 and 17 are diagrams similar to Fig. 13 showing modified apertures.

The character of my new printing plate is clearly shown in Fig. 1 which may be taken as representing either the inked face of a printing plate, a contrast image for producing a printing plate, or a print obtained from the plate. Fig. 1 shows the manner in which a number of different tones of a continuous-tone original are represented. 'Ihe tones represented by the different parts of the plate or printy are indicated by the figures 5, 25,` 50, 'l5 and 95 on Fig. 1 which may be taken as parts of a tone scale .from 0 to 100 and as representing the percentage of black area re quired to represent each tone.

Any contrast image may be regarded as made up of a series of elements in each of which the percentage of black area to total area represents a tone of the original. The elements of my conytra'st image, several of which are delimited by dotted lines in Fig. 1, are of uniform width to lfacilitate making of the image by a photo-electric scanning operation. The elements vary in length. As in the contrast image of the Hardy patents above referred to, the elements are shortest at the middle tone and range upwardly in length from the middle tone towards vthe lightest tone and from the middle tone towards l the darkest tone. The Variation in the length oi.' the elements is, however, not as great as in the contrast images of the Hardy patents. The dark areas of the elements in tones lighter than the middle tone diier from those of the Hardy contrast image in that they decrease in' width as well as 'in length so that the smallest black areas (those in the 5% tone)A are approximately square plate etched from the image shown in Fig. 4, the white lines in the dark areas produce narrow ridges 5 (Fig. 5) breaking up the large recesses in the plate, so that the doctor blade does not withdraw the inkcontained in them. The ridges 5 may be made so narrow that they are elimi nated by the spreading of the ink on the paper. Thus, the intaglio plate of Fig. 5, engraved from the contrast image shown in Fig. 4, may be made to produce a print substantially like the contrast image shown in Fig. 1.

My method of producing a contrast image such as that shown in Fig'. 1 may be carried out by means of various types of photo-electric scanning apparatus, such as the cylinder type shown in Hardy Patent No. 2,136,340 or the flat-bed type shown in my Patent No. V2,185,139. Various diierent electric circuits may be used, all of which, however, must include a circuit of the type shown in Hardy Patent No. 2,136,340 or some equivalent circuit. In order that the nature of my invention may be clearly understood, I will describe various diierent means for carrying out my method, beginning with one which is most Ieasily explained, although not the most desirapparatus like that shown in Hardy Patent No. V2,136,340, having a transparent picture drum I0 and a. recording drum Il which are given identical rotational and longitudinal movements through a driving mechanism l2l including a screw I3 whose pitch determines the distance between the spiral scanning bands. A constant intensity scanning lamp Il directs light through successive elements of a'continuous-tone transparent original on the drum l0 to a photo-electric cell I5. The current from the photo-cell 5 is rst passed through an amplier A which has the effect of a D. C. amplifier, although in practice it may best be composed of an A. C. amplier' and a rectier. 'Ihe amplied photo-cell current from the amplifier A is divided into two parts. One part of it is passed through a circuit H like the circuit shown in Fig. 6 of -Hardy Patent No. 2,136,340, which, for brevity,v I shall term the Hardy circuit, so as to cause intermittentlighting of the glow lamp I6 Whose light is directed vto alm F on the recording drum Il The other part of the amplied photo-cell current from the amplifier A is passed through a power circuit P and then to a device for regulatin'g-the width'of the areas on the lm F which are exposed to the glow lamp I6. VIn the form shown in Figs. 6, 1 and' 8, this device consists of a solenoid 5 whose armature I1 carries a plate I8 containing an aperture I9 of'non-uniform width. 'I'he solenoid, which is shown only diagrammatically, is of the high-response type commonly used in loud speakers. An image of the slit in the shield 2l of the glow lamp I6 is focused by a lens 22 on the aperture platel and this image is refocused by lenses 23 on the recording iilm F on the drum Il.

The operation of the apparatus illustrated in Figs. 6, 'Z and 8 is indicated in the diagram Figs. 9a, 9b. 9c which show, for three different values of the photo-cell current, the position of the aperture I9 with respect to the image 20' of the slit 20, and the resulting exposed portions of the recording film F. The diagram illustrates the making of a negative contrast image and presupposes the placing of the reversing switch of the Hardy circuit H in the position marked Neg The operation is as follows:

(1) When a dark tone of the original is being scanned, the photo-cell current is low, and, under this condition, the part of the photocell current which is passed through the Hardy circuit (with its reversing switch in Neg." position) results in lighting the glow lamp lliv for brief, widely-spaced intervals, as explained in the Hardy patent. The other part of the photo-cell current which is passed through the solenoid is too weak to move the amature of the solenoid against its usual return spring, so that the plate i8 remains in its normal position in which the narrow end of the aperture I9 concides with the image 2D' of the slit 2B, as shown in full lines in Fig. 8 and Fig. 9a. As light can pass only through that part of the image of the slit which is within the aperture I9, a. narrow beam of light strikes the lnr F during the brief intervals during which the glow lamp is lighted by the Hardy circuit. This produces on the film small, widespaced, exposed areas 25 which are much narrower than the spiral scanning track 26 on the film (Whose width, as before stated, is determined by the pitch of the screw I3) y (2) When a middle tone of the original is being scanned so that the photo-cell current is at half its maximum value, the portion of the photo-cell current which passes through the solenoid moves the plate i8 so as to place the middle of its aperture i9 under the image 2li' of the slit 20, as shown in Fig. 9b. This permits a beam having the Width of the scanning band 26 to reach the recording film whenv the glow lamp is lighted. As the Hardy circuit causes equal intervals of lighting and extinguishment when the photo-cell current is at half strength, the result is to produce exposed areas 2l of the form shown in Fig. 9b.

(3) When a light-tone part of the original is being scanned so that the photo-cell current is at or near its full strength, the Hardy circuit (with its reversing switch in Neg. position) `provides, for keeping the glow lamp lighted for long periods separated by brief intervals of extinguishment. In this case, the portion of the photo-cell current passing through the solenoid positions the plate I8 with the wide end of its aperture i9 coincident with the image 20' offthe ning band leaving only short `and narrow un.

slit, as shown in dotted lines in Fig. 6 and in Fig. 9c. The result is to produce long exposed areas 28 on the recording film which are wider than the scanning band 26, so that those in one scanning band overlap those of the next scanexposed spaces.

The ,thi-ee' values of the photo-cell current whose eifect has been illustrated and described are merely indicative of the operation of the apparatus throughout the tone range.A It will be seen, therefore, that the result of this operation is to produce a negative contrast image of the sort shown in Fig. 1.

The apparatus which has been described may equally well be used to produce a positive contrast image by placing the reversing switch 24 of the Hardy circuit in Pos. position and inverting the aperture plate I8 with respect to the armature of the solenoid 8.

While the specic embodiment of my method which has been described well illustrates the principle of the method, it is by no means the most satisfactory way of carrying it out, for the expedient of obtaining narrow unexposed areas by an overlapping of the scanning lines is clumsy, and is inaccurate in case of a change in tone after a single band has been scanned.

An important feature of my invention consists in avoiding this diculty by eliminating the use of a glow lamp or equivalent, light valve with the Hardy circuit and using a mirror galvanometer to determine the length and spaclng of the exposed areas as well as the width of these areas. The method involves dividing the photo-cell current into two partsand passing one of these parts through the Hardy circuit as before, but, instead of connecting the output of the Hardy circuit with a glow lamp or light valve, it is combined with the other part of the amplified photo-cell current and the two are passed together through the coil cf the mirror` galvanometer G. The recombining of the two parts of the photo-cell current may either be by direct electrical connection as shown in Fig. l0, or by passing the two currents through separate coils of a two-coil galvalnometer G' as shown in Fig. 10a. The mirror galvanometers G and G' are of the high-response, low-inertia type used in sound recording. I prefer to use the magnetic galvanometer developed' by G. L. Dimmick. described in his article in Journal Society Motion Picture Engineers, October, 1930.

The nature of the combined current which is fed to the galvanometer coil of Fig. l0 is shown in the current diagram, Figs. 12u, 12b, 12e, which illustrates the variations in the galvanometer current at a low value, at the middle value, and at a high value, of the photo-cell current. These diagrams illustrate the elect of adding to the variable-frequency intermittent current of the Hardy circuit a direct current proportional to the photo-cell current. in the particular form shown, the current impulses of the Hardy circuit have a value of units, while the maximum value of the current from the power tube P is also 100 units. As a result, the combined current may vary between G units and 20D units as indicated in Figs. 12e, 12b and 12C.

TheV optical system used with -the galvancmeter of this'embodiment of my invention is shown in Fig. 11. Light from a iixed intensity lamp 3i) is reflected by the mirror 3i of thegalvanometer G tervals (Fig. 12a).

cording film. An image of the aperture 33 is focused on the shield 34 by a lens 36, while an image of the slit 35 is focused on the recording lm by a lens system 31. A coniugate lens system inexposed during these long periods. During the short intervals when the current is at 95, the operture 33' crosses the slit and has coincident with the slit a divided portion (see 95 in,Fig. 13), so that two beams of light are directed upon the scanning band leaving a narrow unexposed portion 43 between them, as shown in Fig. 14c.

The three values of the photo-cell current whose effect has been illustrated and described In order to relate this diagram to the current diagram of Figs. 12a, 12b12, the slit 35 is shown at a number of different numbered positions corresponding to current valuesindicated in Figs.

12a, 12b, 12e, while the image 33' is drawn only once; but it should be understood that the different relative positions of the slit and aperture image which are shown in Fig. 13 are attained in the apparatus by movement vof the image 33' while the slit 35 remains stationary (see Fig. 1l)

The operation of this form of my. invention can readily be understood from the current diagram Figs. 12a, 12b, 12o, the slit and aperture diagram Fig. 13 and the diagram of the scanning band of the recording lm shown in Figs. 14a, 14h, 14e. As before, I will describe making a negative contrast image;

(1) When a certain dark-tone portion of the original is being scanned, the photo-cell current is so low that the galvanometer current varies between 5 and 105, remaining at the lower value for long intervals an'd the upper value for short in- 'I'he intervalsare, of course, determined by the Hardy circuit. During the long intervals during which the value of the current is at 5, the image 33 of the aperture is entirely off the slit (see 5 in Fig. 13), so that no light reaches the recording, film. During the short intervals when the current is |05, the aperture image 33' has a narrow portion coincident with the slit, as shown at |05 in Fig. 13, so that a are merely indicative'of the operation of the apparatus throughout the tone range. It will be seen, therefore, that the result of this operation is to produce a negative contrast image of the sort shown in Fig. 1. vIt should be noted that, in achieving this result, the constants of the circuit of Fig. 10 were so chosen that the maximum value of the current from the power circuit P is equalto the value of the current impulses of the Hardy circuit, and the aperture 33 is symmetrical and consists of two halves which are related to each other as a positive to a negative, that is to say, if -one half of the plate 32 were folded over on the line |00 (Fig. 13), the openings in the two halves would not overlap but would fit together to form a rectangular opening of uniform width.

The same results are obtained by passing the Hardy current and the current from the power circuit through two equal coils of a two-coil galvanometer in such direction that the two coils tend to turn the mirror in the same direction. The use of a two-coil galvanometer has the advantage of permitting greater flexibility in the choice of the constants of the circuits. Thus, if the constants are chosen so as to make the maximum value current from the power circuit different from the value of the impulses of the Hardy circuit, the turning effects of the two may be made the same by the use of different numbers of turns in the two coils of the galvanometer.l The operation of this arrangement can 12a, 12b and 12e as measuring the combined narrow band of light from the recording lamp 30 reaches the recording film during these short intervals, making short, narrow exposed areas 40,

From Fig. 13, it appears that, when the current is at 50, the aperture image 33 does not crossthe `slit (see in Fig. 13) while, when thecurrent is ,at |50, theaperture image 33' extends across the slit wi-th its widest part coincident with the slit (see |50 in Fig. 13). The result, as shown in Fig. 14h, is to produceequal exposed andunexposed areas 4|, 42 both -of which may be of the full width of the scanning band 26.'

(3) When a certain light-tone portion ofthe original is being scanned, the photo-cell current is so near its maximum that thev galvanometer current varies Ibetween 95 and' 105,. as shown in Fig. 12e.` It remates-(at the 1ower limit ss for short intervals and at the upper limit |05 for long intervals.' During the long intervals while the current is at |95, the aperture image 33 crosses the slit with its maximum width coincident with the slit (see |95 in Fig. 13), so that the entire width of the scanning track 26 is turning effect of the two currents about the axis of the galvanometer rather than reading them as values of current.

While the'operation of the apparatus in making a negative contrast image has been dey scribed, the apparatus is equally adapted to making a positive contrast image. In order to do this, it is necessary only to reverse the position of the aperture plate 32, or to reverse the direction of the current through the galvanometer by means 'of the reversing switch-44 )shown in Fig. 10 or the two reversing switches 44' shown in Fig. 10a. In this ,way,'a positive is produced while the reversing switch 24 of the Hardy circuitemains in ,Neg. position. This is an ad- `vantage, since it permits simplifying the Hardy` rather delicate in operation owing to the fact that` the positions of the image of the aperture 33a and the slit 35 for making small unexposed areas and for making small exposed areas are close together (see and |05in Fig. 13). This leads to some inaccuracy in case the galvanometer` mirror oscillates slightly on a change in current before settling to its position. This diiiiculty may be avoided in accordance with my invention by making the maximum value of the direct current part of the galvanometer current considerably less than the value of the currentI impulses of the Hardy circuit, and separating the two halves of the aperture. This modication is indicated in the current diagrams, Figs, a, 15b, 15e, and the slit and aperture diagrams, Figs. 16 and 17.

Figs. 15a, 15b, 15e show theimpulse part (full lines) and the direct current part (dotted ferent values of the photo-cell current previously discussed. The two currents shown may be passed through two equal coils of galvanometer or may be passed together through a single galvanometer coil. The circuit constants are chosen so as to make the value of the current impulses of the Hardy circuit greater ,than the maximum value of the direct current. Thus, by way of example the current impulses are shown as having a value of 120 while the maximum value of the direct current is 100 although the highest value shown is 95 (Fig. 15o) Y Fig. 16 shows the image 33a of an aperture having positive and negative halves of the same shape as those of the aperture whose image is shown in Fig. 13. Thus, the negative half of the aperture shown in the lower part of Fig. 13 is identical with the negative part of the aperture shown in Fig. 16 between 0 and 100 on the scale of that figure, and the positive halfbf the aperture Yshown'in the upper half of Fig. 13 is identical with the positive part of the aperture shown in Fig. 16 between 120 and 220. Between the two separated halves of the aperture, a double slot of uniform width extends from 100 to 110 on the scale, while a single slot of uniform width A extends from 110 to 120.

(Fig. 15a), between 50 and 170 for the middle.

and between 95 and photo-cell value (Fig. 15b) 215 for the high photo-cell current (Fig.

lines) of the galvanometer current for the three difv a two-coil and the direct current part of the galvanometer current may fall below 5 units or rise above 95 units. When this oc urs with an aperture such as that shown in Fig.l 16, tones lighter than 5% produce dots of the same width as 5% tones, and tones darker than 95% produce dots of the same width as 95% tones. But the spacing of the vdots in the tones under 5% and over 95% is increased by the operation of the Hardy cir-v cuit. This may have the objection of producing dots too far apart to be fused easily by the eye. In accordance with my invention, this danger may be eliminated by use of an aperture of the type shown in Fig. 17.

Fig. 1'7 shows the image 33h of an aperture whose outer parts are the same as those of the apertures of Figs. 13 and 16. The middle part of the aperture of Fig. 17 differs from those previously described. Between 95 and 110 on the scale shown in Fig. 1'7, the aperture has an opening the full width of the scanning line, while between IIU and |25 there is no opening. This aperture, when used with a galvanometer current shown in Figs. 15a, 15b, 15e produces precisely the same effect as the aperture shown in Fig. 16 so long as the direct current part of the galvanometer current does not fall below 5 or rise above 95. This is apparent from the relative positions of the image 33h of the aperture I and the slit 35 indicated by the dotted slit positions at 5, 95, |25 and 2i5 on the scale in Fig. 17, which produce light beams of the samevwidth as the corresponding relative positions shown rin Fig. 16. There is, however, a diierence in the case of tones lighter than 5%,or darker than 95%. 1f a tone is so dark that the direct current part of the galvanometer current falls to' Zero so that the combined current oscillates between 0 and 120, no light is admitted at either end of this oscillation (see dotted slit positions at 0 and 120 on the scale in Fig. 17) so that no portion of the recording lm is exposed. Conversely, if a. tone is so light that the direct current part of the galvanometer current rises to 100 so that the combined current oscillates between 100 and 220, a beam of light of the full width of the -scanning line is admitted at both ends of the oscillation (see dotted slit positions at 100 and Consequently, the relative positions of the image 33a of the aperture and the slit 35 for making y small unexposed areas and for making small exposed areas are separated by a considerable distance (note relative positions indicated by dotted slits at 95 and 25 on the scale in Fig. 16), so that a slight oscillation of the galvanometer mirror in its extreme positions does not^change the character of the exposure which is being made. y

A tone range from 5% to 95%, representing a' variation in the photo-cell current and in the direct current from the power` circuit from 5% to 95% of its maximum value, is quite sucient for ordinary reproduction. In some cases, however, where it is intended .to make reproductions within this range, it happens that the original vcontones. and, in this case, the photo-cell current 220 on the scale in Fig. 17) so that the entire scanning band is exposed. Thus, with this aperture, tones lighter than 5% and tones darker than 95% are represented by solid black or solid white without any dots. This avoids the defect of too widely spaced dots in these extreme tones.

An important feature o my invention consists in securing a strictly accurate, or as it is sometimes called linear, representation of the tones of an original, which cannot be obtained in an 'ordinary half-tone.

In accordance with my invention, a linear representation of tones is secured by combining two compensating nonlin ear representations. The Hardy circuit, when used in -my invention, is adjusted so as to produce a representation departing widely from the linear in the light and dark tones. The adjustment is made in the manner described in Hardy Patent No. 2,136,340 (p. 4, col. 2, l. 55 to p. 5, col. 1, 1. 28) except that the photo-cell and discharging currents are adjusted so as to provide for about 15% of black area in the lightest tones of the original and about of black area in the darkest tones of the original. ture is then formed in such a way that it cuts down the amount of black areav in the light tones to an amount 4proportional to the tones of the The aperoriginal, and, in the same way, increases the amount of black area in the darker tones to an amount proportional to the tone of the original. Apertures which have this eiect for all tones from 5% to 95% when the Hardy circuit is adjusted as described are shown in Figs. 13, 16 and 17. 'I'he result is' to produce a truly linear representation of the tones of the original.

This is a division of,my application Serial No. 343,962, iiled July 5, 1940.

The methods and apparatus and the contrast images described herein are not claimed in this application as they form the subject-matter respectively oi' my said parent application Serial No. 343,962, iiled July 5, 1940, and my application Serial No. 406,120, led August 9, 1941, as a. division of said parent application.

What I claim is:

1. A printing plate having variably-spaced, rectangular printing areas which vary both in length and in width.

2. A printing plate having a light-tone part containing small, widely-spaced. approximately square, printing areas. a dark-tone'part having a printing area containing small, Widely-spaced, approximately square, non-printing areas, and a middle-tone part having closely-spaced printing areas whose widths and' lengths are greater than the dimensions of the printing areas in the light-,tone part.

3. A relief printing plate having in its middletone part closely-spaced raised dots, in its lighttone part widely-spaced raised dots which are both shorter and narrower tha-n the dots in the middle-tone part.

4. An intaglio printing plate having printing -indentations varying in size and spacing in a'ccordance with the tones of the picture -andl having a series of narrow parallel ridges extending across the indentations of large area which occur in the dark-tone parts. 1

FRANCIS LEWIS WRZBURG, Ja.

Images