GB2106741A - Improvements in or relating to printing - Google Patents

Abstract

A method of reproducing a photographic image 1 in which each colour area of the reproduction comprises a plurality of component colour islands R, Y and B which together produce the colour perceived for said area. The method comprises scanning the image 1 with electronic detector means to detect the colour islands R, Y or B of a selected scanned colour. The screens 2R, 2Y and 2B (Figures 2A, 2B, 2C not shown) are prepared in respect of the scanned colours for printing the detected islands of said colour as a matrix of individual dots 6R, 6Y and 6B (see Figures 3A, 3B, 3C not shown). The screens 2R, 2Y and 2B are used successively to print a reproduction of the photographic image on a substrate (6). <IMAGE>

Description

SPECIFICATION Improvements in or relating to printing The present invention relates to printing.

Screen printing techniques are well established for the printing of textiles and the like. Such techniques are generally known as "Silk Screen Printing" although it is to be understood that the term, in modern day practice, covers the use of printing screens of materials other than the traditionally used silk, e.g. synthetic plastics, metal etc.

When it is desired to silk screen print a reproduction of a multi-colour pattern, the conventional technique is firstly to produce separate screens each for printing the areas of one colour and then to build up the print by successive screen printing of each colour using the appropriate screen.

If the print is to be a reproduction of a colour photograph, it is necessary for an artist to prepare a number of representations each showing the areas of one colour on the photograph, and separate screens are then produced each for printing one colour area. Generally 15 separate colours are selected thus requiring a corresponding number of printing operations to build-up the print. The artists work and the number of printing operations required represent time comsuming stages. There is the additional disadvantage that, because a specific number of colours are selected, it may not be possible to reproduce different shades of the same colour, so that the print lacks fidelity.

It is an object of the invention to obviate or mitigate the abovementioned disadvantages.

According to the present invention there is provided a method of reproducing a photographic image in which each colour area of the image comprises a plurality of component colour islands which together produce the colour perceived for said area, the method comprising scanning said image with electronic detector means to detect the colour islands of a selected scanned colour, preparing in respect of each scanned colour a screen for printing the detected islands of that colour as a matrix of individual dots, and printing each colour using the respective screen.

The invention is based on the fact that each colour area of a photographic image is made up of a plurality of colour islands which when perceived by the human eye produce a particular colour. Thus, for example, an area perceived as orange on a coloured photographic image will in actual fact be comprised of a plurality of individual red colour islands and a plurality of individual yellow colour islands which together suggest to the human eye the colour recognised as orange. The photographic image thus constitutes a colour separation record of the original from which the photographic image was prepared.

Such originals may be, for example, artwork, lettering, paintings, landscapes, human or animal subjects etc.

A coloured photographic image will generally comprise colour areas comprising colour islands of the primary colours (red, blue, yellow) and possibley black.

Thus, in this case, the photographic image will be scanned for the primary colours and possibly also black.

Preferably the photographic image is scanned at from 50 to 150 lines/inch (20 to 60 lines/cm). More preferably the photographic image is scanned at from 50 to 70 lines/inch (20 to 28 lines/cm) to detect colour islands at 1/50th to 1/70th inch (1/20th to 1/28th cm) spacing (i.e. image is effectively scanned at 50 x 50 to 70 x 70lines/inch2(20 x 20 to 28 x 28 lines/cm2). This has been found to be optimal for a faithful reproduction of the photographic image in the subsequent screen printing process.

The colour scanning may be effected by a Little John custom colour type 231.

As indicated above, the scanning will detect the colour islands of a particular scanned colour. The photographic image may be scanned successively or simultaneously to locate, and record in a computerised memory, the positions of the various colour islands.

Once scanning has been completed, the compute rised memory will have a record of the location of the positions of the various islands of the particular scanned colours. It is now possible to produce separate printing screens in respect of (and for printing) each of the scanned colours.

The screen for any particular scanned colour is produced such that that colour is printed as a matrix of dots corresponding in position to the islands of that colour in the photographic image. Since all colour islands (whatever the colour) are separate from each other in the photographic image, the screens for printing the various colours will have their dots through which the colours are printed at different positions (compared to a given reference point) from the dots on any of the other screens so that the various colour islands will be printed in non-overlapping relationship.

The shape of the dots is preferably such that the difference (if any) in length between the major and minor axes will not be significant. The dots may for example be circular or substantially circular (e.g.

with slight ovality), square, or hexagonal, or any other regular or substantially regular polygonal figure. Preferably the dots are polygonal (e.g. triangular or diamond shape) with radiussed corners. The maximum number of dots on any particular screen will preferably correspond to the number of lines per unit square area scanned by the colour detector.

Thus for a scanning of 50 lines/inch2 (20 lines/cm2) there will be a maximum of 50 x 50 dots/inch2 (20 x 20 dots/cm2) on the screen, the actual value depending on the number of islands of that colour per unit square area in the photographic image.

The screens for printing each colour (assumed to be the primary colours and possibly black) may be produced from the computerised memory as follows. Firstly, and using conventional techniques, a matrix of opaque islands (corresponding in position to the colour islands to be printed) is produced on a transparent film. Secondly, the film is laid onto a printing screen mesh coated with a cross-linkable emulsion and the screen is irradiated through the film to cross-link the emulsion otherwise than at the locations of the opaque islands. Thirdly, the film is removed and the screen washed to remove the non-cross-linked resin thereby producing a screen for printing colour islands at the required locations.

If desired the screens may be repared to produce a print which is of different size from the original pattern. This may be effected by a Little John "Magnacolour" unit. Also if desired the screen mesh may be angled with respect to the printing direction (e.g. by 10 ) to eliminate morn' effects.

Each screen is now used to print its respective primary colour (or black) using conventional screen printing techniques. In this way the primary colours (and possibly black) are applied to the material being printed. Areas of colour which, on the original pattern, were mixtures of primary colours, are printed as areas built up of, in the ideal case, non-overlapping islands of the primary colour components and the effect to the eye is a faithful reproduction of the corresponding colour area in the original print. In practice, a small amount of ink bleed may occur (depending on the nature of the material being printed and/or the consistency of the ink) so that the colours merge together, although this may be tolerated.

The result is a faithful and clear reproduction of the original pattern which is far superior to the images produced by the conventional technique of the above described technique of colour separation by an artist. Additionally, the method of the invention requires only the printing of a maximum of four colours as compared to fifteen or so used in the prior art.

It is also possible to reproduce a black and white pattern. If the print is to be laid on white material then the pattern need only be scanned for black since the material will provide the white print areas.

If the print is to be laid on coloured material, the white is scanned for primary colours and printed as described above.

The invention may be used for printing textile or other materials and may also be used for printing textile garments, e.g. T-shirts.

The invention is illustrated with reference to the accompanying drawings which schematically indicate the individual printing screens formed from a multi-colour photographic image and the formation of the final print. In the drawings: Figure 1 represents a multi-colour photographic image (e.g. in the form of a transparency) a part of which has been greatly enlarged; Figures 2A - 2C illustrate parts of printing screens for printing colour island locations detected in the imageof Figure 1; and Figures 3A - 3C represent the build up of the print from the screens shown in Figures 2A - 2C.

Figure 1 shows a muiti-colour photographic (e.g.

transparency) 1 on an area which is shown greatly enlarged in the circle to illustrate the individual colour islands. These individual islands are designated in Figure 1 as R for red, Yfor yellow and B for blue.

To produce the printing screens for each colour, the photograph 1 is scanned by the technique discussed more fully above, to detect the individual colour islands. Printing screens 2R, 2B and 2Y (shown in Figures 2A - 2C respectively) are then produced as described above for the colours red, yellow and blue respectively. Figures 2A - 2C only show the areas of the screens corresponding to the encircled area in Figure 1. It will be seen that screen 2R is opaque save for dots 3 through which ink may pass and corresponding in position to the red colour islands in the encircled area of photograph 1.

Similarly screens 2B and 2Y have dots 4 and 5 in the position of the yellow and blue colour islands respectively in the encircled area of photograph 1.

Printing of a substrate 6 may now commence using conventional techniques and each of the screens 2R, 2B and 2Y. Printing of the colours will generally be in the order red, blue, yellow.

After printing of the red colour, the substrate 6 has red dots 6R (Figure 3A). After printing of the blue colour, the substrate 6 has red dots 6R and blue dots 6B (Figure 3B). Finally, after printing of the yellow colour, the substrate 6 has yellow dots 6Y in addition to dots 6R and 6B.

It will thus be seen that the pattern of dots 6R, 6B and 6Y on substrate 6 corresponds to the pattern of colour islands R, B and Yin Figure 1 so that the photograph 1 is reproduced.

Claims (9)

1. A method of reproducing a photographic image in which each colour area of the image comprises a plurality of component colour islands which together produce the colour perceived for said area, the method comprising scanning said image with electronic detector means to detect the colour islands of a selected scanned colour, preparing in respect of each scanned colour a screen for printing the detected islands of that colour as a matrix of individual dots, and printing each colour using the respective screen.

2. A method as claimed in claim 1 wherein the colours scanned are the primary colours.

3. A method as claimed in claim 2 wherein black is additionally scanned.

4. A method as claimed in any one of claims 1 to 3 wherein the image is scanned at 20 - 32 lines/cm (50 - 80 lines/inch).

5. A method as claimed in any one of claims 1 to 4 wherein the dots are circular, substantially circular, square, hexagonal or other polygonal figure.

6. A method as claimed in any one of claims 1 to 5 wherein the screen is of synthetic plastics material.

7. A method as claimed in claim 6 wherein the screen is of nylon.

8. A method as claimed in any one of claims 1 to 7 wherein the screen mesh is at an acute angle with respect to the printing direction.

9. A method or reproducing a photographic image substantially as hereinbefore described.