Image handling facilitating computer aided design and manufactur

Details Image handling facilitating computer aided design and manufactur Image handling facilitating computer aided design and manufactur

1992-07-13

1996-05-28

Brinich, Stephen

Facsimile and static presentation processing

Natural color facsimile

358402, H04N 146

Patent

active

055217222

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to methods and apparatus for handling digital representations of documents for example to allow sophisticated computer aided design and manufacture of a security document.
Conventional commercial colour proofing relies on the proofing media having yellow, magenta, cyan and black halftone screened colour separations which match the YMCK inks that will be used for printing. Each ink naturally has to be applied from a printing plate which contains the Y, M, C or K information.
The proofs are generally made by exposing Y, M, C and K photosensitive media to the corresponding photographic halftone colour separations, using a contact printing method. The individual colour layers are then mechanically overlaid in register.
Computer generated proofing methods are available for commercial work. One method requires Y, M, C or K halftone photographic separation films to be made which are in turn used as masks for contact imaging or proofing media. Another method exposes three or four colour sensitive media.
Problems arise with the printing of security documents. Firstly they involve different types of printing processes in the manufacture of any one document whether, say, a banknote, passport or identity card. Secondly usually one of the printing processes is different from those generally used in the printing industry or is conducted in an unusual manner e.g. intaglio printing. The printing methods often apply images only with a partial contact of the plate (such as through the use of schablones) or the inks are delivered in a special manner such as by rainbow printing from split ducts.
It is important to appreciate that most security documents are printed in continuous tone often using continuously blended colours, the blending occuring only on the ink train of the press. Security documents often make use of fine line patterns, some delivered in such "rainbow" printing fashion.
In contrast conventional full colour printing (e.g. magazine printing) will take a colour original, colour separate that, convert it into a halftone format and then print with the three subtractive colours and black. These subtractive inks are printed at full density or not at all (ie. they are not printed at continuous density levels) and their overall appearance depends on the eye blending together interspersed finely divided areas of the subtractive colours and black to give the perceived colour. This combination thus creates the perception of the original. It is however an illusion, generally unacceptable in security printed items.
Although not generally noticeable to the naked eye there has to be a sacrifice of the ultimate level of resolution because of the screening process. While coarse colour pictures of bank notes could be attempted this way, they would not survive customer's inspection and it is extremely important that the proofed security document should have a resolution similar to the final article--which will be much better than half tone processes allow. It is also important to remember that the inks delivered to the security document are not selected from four or six pots and only delivered in those colours. Rainbow printing blends the colours on the press to give continuous hues as well as continuous density.
The methods and materials used in the security printing industry are such that genuine documents can be verified such as by visual or machine authentication methods, and counterfeits or forgeries detected. The computer aided design system employed for security documents must be capable of providing visual representations to an unprecedented degree of accuracy of colour and resolution so that proofing prints can approximate more closely to the manufactured counterpart. In particular the design system must be able to simulate the effect of rainbow printing. Additionally it is highly desirable that the design system is able to provide visual indications of the placement of special markings such as invisible but ultraviolet revealable inks and magnetic inks.
For example a

REFERENCES:
patent: 4357624 (1982-11-01), Greenberg
patent: 4800380 (1989-01-01), Lowenthal et al.
patent: 4941057 (1990-07-01), Lehmbeck et al.
MicroBRIAN Resource Manual Part Two, pp. 16-22, 33 and 85-89.

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