US2165169A - Means for determining the primaries - Google Patents

Description

July 4, 1939- F. L. wuRzBuRG. JR 2,165,169

MEANS FOR DETERHINING THE FRIMARIES IN A SYSTEM 0F COLOR REPRODUCTION BY PRINTING Original Filed Sept. 28, 1936 ATTORNEY Patented July 4, 1939 MEANS FOR DETERMINING THE PRIMARIES IN A SYSTEM OF COLOR REPRODUCTION BY PRINTING Francis Lewis Wrzburg, A."r., Bronxville, N.l Y.,

assignor to lnterchemical Corporation, a cor poration of Ohio Application September-28, 1936, Serial No; 102,957 Renewed October l1, 1938 5 Claims.

This invention relates to means for determining the primaries in a system of color reproduction by printing.

In co-pending application of Arthur C. Hardy.'

5 Serial No. 99,416, filed September 4, 1936, there is described and claimed a method for determining the primaries of a color reproduction system. In that method, use may be made of a differential print to. compare the color of a specified combination of colored materials with the color of other combinations in each of which the amount of one of the colored materials differs by a small increment from its amount in the specified comb-ination.

15 In applying this method to determine the primaries of a reproduction system by half-tone printing or other printing where definite screen lines or grain lines occur on the printing blocks used ior'the different colored inks, the occurthe form of an equilateral triangle consisting of two printing areas, one of which is a triangular area in one corner of the printing surface con- 35 stituting one-fourth of the whole printing surface, and the other of which is a trapezoidal area containing three-fourths of the Whole printing surface. The printing surface .is so formed that the density of the ink printed by the triangular area is slightly different from that printed by the trapezoidal area. I most desirably provide a set of such printing blocks in all of which the screen or grain lines make the same angle with the base of the'trapezoidal area.

My invention includes also the triangular and hexagonal differential prints which may be formed by such printing blocks.

The accompanying drawing shows speciiic printing blocks and prints illustrating my invention. In the drawing:

Fig. 1 is a perspective view of a printing block;

Figs. 2, 3 and 4 show three impressions from the block shown in Fig. 1;

Fig. 5 shows diagrammatically a print made by superposing the three impressions shown in Figs. 2, 3 and 4;

Fig. 6 shows six printing blocks assembled as a hexagon; and

Fig. 7 shows diagrammatically a hexagonal differential print made from the printing blocks shown in Fig. 6.

'I'he printing block I0 shown in Fig. 1 is a halftone plate having a printing surface in the form of an equilateral triangle. The printing surface is provided with the usual projections for printing half-tone dots.

The dot density of the printing surface, which I dei-lne as the proportion of the printed area which is covered by ink from the dots, is diiferent in different parts of the triangular printing surface. The printing surface consists of a triangular area s occupying one-quarter of theY total printing surface, and a contiguous trapezoidal area m occuping three-quarters of the printing surface. The dot density of the printing surface in the triangular area s is slightly different from the dot density in the trapezoidal z ea 1n. The screen lines, which may be regarded as illusl trated by the dotted lines shown in Fig. 1, run in the same direction throughout the printing surface. In the form illustrated, these lines make an angle of about 45 with the base of the trape- I sity of the printing surfaces of the different blocks may be selected as desired, but in each block the density of the triangular area is slightly diiierent from that of the trapezoidal area.

Fig. 5 shows diagrammatically a diierential print which may be made from three impressions of the block shown in Fig. 1 or by one impression'of this block and two impressions from corresponding blocks. In making the diierential print shown in Fig. 5, three impressions' of the block Ishown in Fig. l made in dierent colors may be superposed. 'Ihe way in which the block is turned in making the three impressions is shown in Figs. 2, 3 and 4. From these figures, it

is apparent that betweenthe rst and second impressions the block is rotated 120 to the left, and between the second and third impressions the block is rotated 240 to the right, that is, it is turned 120 to the right from the position which it had in the first impression, From this turning of the block, it results that the screen lines in the three superposed impressions cross each other at wide angles so that there is nov moir effect. This procedure and the form of the blocks also result in making a symmetrical differential print having central area A and three outer areas B, C, D, all four of equal size, and

so arranged that the combination of the colored inks in each one of the outer areas B, C, D is like the combination of the inks in the center area except for a slight diierence in the density of one of the three colored inks. Such a, print is have a dot density of seventy per cent. in their trapezoidal areas and a dot density of eighty per cent. in their triangular areas, and three similar printing blocks 20, in each of vwhich the density of the trapezoidal area m is zero and that of the triangular area s isa small increment above zero. for example, flve per cent. The six printing blocks may be assembled in the form of a regular hexagon as shown'in Fig.`6.

Three differently colored impressions from the assembledA blocks are then made with a turning of the assembled blocks corresponding to the turning of the single blocks. already described in connection with Figs.`2"to 5.

This procedure produces the hexagonal differential print shown in Fig. 7, containing twentyfour equal triangular areas of different colors. Assuming that the three impressions were made with yellow, magenta and blue-green inks, the area AI `shows the color of the yellow ink, the

larea A3 the color of the magenta ink, and the area A5 the color of the blue-green ink. The intermediate areas A2, A4, A6 show the colors produced by combining pairs of the inks in equal proportions. vA2 shows the color of a combination of the yellow and magenta inks, A4 of a combination of the magenta and blue-green inks, and A6 of a combination of the blue-green and yellow inks. f

The areas Bl, CI, Dl'show the changes in the color of the area AI which are produced by adding separately 'a small increment of each of the three colored inks, and they same is true of the areas surrounding each ofl the triangles from A2 to A6. 'Ihe density of eachv colored ink in each area is indicated in the following table:

lBy comparing the colors of the surrounding triangles with the colors of the triangles AI to A6, the primaries of the system for six dierent colored areas may be determined as described in the application of Arthur C. Hardy aforementioned. v f

`Ii.' desired. the plate for printing the print shown in Fig. 'I may be made in a single piece, instead of by assembling triangular printing blocks.

what I claim is: 1. Means for use in determining the primaries of a c olor reproduction system by printing. comprising a. printing block having a lined printing surface in the form of an equilateral triangle, said surface being so formed as to print a different density of ink from two parts of its printing surface, which consist respectively of an equilateral triangular area constituting one-quarter of the printing surface and a contiguous trapezoidal area constituting three-quarters of the printing surface, the lines being parallel throughout the whole printing surface.

2. Means for use in determining the primaries of a color reproduction system by printing, comprising a half-tone printing plate having a tri=' and three adjacent triangular areas in'each oneof whichA two of the colored inks have the same density as in the central area and one colored ink has a density slghtly diierent from that which it has in the central area, the lines of the three impressions crossing each other at angles of 60.

4. A differential print for determining theprimaries of a color reproduction system, consisting of superposed impressions of three differently colored inks having the form of a hexagon containing twenty-four equal differently colored areas, each in the form of an equilateral triangle, including six spaced triangular areas and six sets of three triangular areas surrounding each of said six areas and showing the effect of an increment of one of the colored inks onthe color of the area which they surround. f

5. A differential print Afor determining the primaries of a color reproduction system, consisting of superposed impressions of three diiferently colored inks having the form of a hexagon containing twenty-four equal differently colored areas, each in the form of an equilateral triangle, including six triangular areas showing the colors produced by each of the three inks separately and each of the pair of the three inks in equal proportions, and six sets of three triangular areas surrounding each of said six areas and showing the colors produced by changing the color of the area which they surround by increments yof each one Y

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