Re: [Digital BW] Re: "Ink limit" -- what is it?
2003-11-22 by Richard Corbett
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From: "Dean Beattie" <dizzyashell@...> To: <DigitalBlackandWhiteThePrint@yahoogroups.com> Sent: Saturday, November 22, 2003 5:43 PM Subject: [Digital BW] Re: "Ink limit" -- what is it? Hi David, I hope this will help you out. It is a bit technical, but it explains it we= ll. To make color separations, the three additive colors (red, green, and blue)= are translated into their subtractive counterparts (cyan, magenta, and yellow).= In theory, equal parts of cyan, magenta, and yellow combine to subtract all light refl= ected from the paper and create black. Due to impurities present in all printing inks,= however, a mix of these colors instead yields a muddy brown. To compensate for this de= ficiency in the color separation process, printers remove some cyan, magenta, and ye= llow in areas where the three colors exist in equal amounts, and they add black ink= ---------------------------------------------------------------------------- ------------------ That is I am afraid factually incorrect. It is quite possible and usual for a CYM mix to produce a neutral density but not using 100% for each colour. The required differential is usually referred to as the grey balance requirement and can typically be in the region of 100%C-85%M&Y. If you add together a typical 100%85X2% and 65% you arrive at a figure of 335% and that would be considered the maximum necessary ink coverage for that particular set of printing conditions. In real life, the inclusion of dot gain would make it necessary to reduce those figures to for instance a 95%C+80x2% for Y&M. The purpose of the black is to add density such that a typical CYM dMax will be inthe order of 1.30 but with the black added - say at about 65% - the DMax becomes 1.60 for example The actual maximum density of a four colour mix can be as high as 2.1 but that depends on the paper, ink and press characteristics. The question you could now ask is "how much Black is the right amount?" and the answer to that is simple, and rather boring to the scientifically orientated individual, in that the printer might run a series of black printer press tests in order to discover the dot% required to give the maximum DMax for the 4th colour black patch. In other words it would be trial and error. Once obtained it would hardly be necessary to change the separation requirements for any given original as the press operator could alter the level of ink subjectivly if required in order to take account of variations from job to job or sheet to sheet. UCR was originally introduced for the benefit of the Gravure industry in order to facilitate ink savings on long print runs. The problem with UCR is that it is extremely difficult ro specify exactly where a neutral will end and a colour shift begin and thus is had a relativly short trade life and it certainly was not a feature found in UK web-offset printing. GCR was introduced into the off-set industry through the facility of high end drum scanner technology where the programmer was able to specify exactly the level of grey component in any given colour, remove it from the contaminating colour and replace it with black. Now that was a very good technique because it enabled easier colour to colour register, substantial ink savings (the CYM was always more expensive than the K) and because of the register benefits, certain types of work looked sharper. GCR was certainly not originally intended to be used as a technique for improving shadow detail but, under the skilled control of the appropiate scanner operator, it often could show benefits in the shadow areas of darker images. There are of course limits to tha amount of GCR that can be applied, otherwise the problem of ink trap rears it's ugly head. This unfortualte condition occurs when one colour lays over another to a lesser degree than anticipated due to the low area coverage of the underlying colour. It is is not practicable to print only black in a particular area as the DMax of black only is always less than the DMax of Black on top of one or more colours. Although I am long retired from the printing industry I should imagine that much the same procedures are followed today as in my time because the technical improvementsa available to the offset printer are now into the slowly, slowly - tiny, tiny area of product development. All the above has nothing whatsoever to do with what happens inside an Ink jet printer, the secrets of which remain a complete mystery to moi' .....and thus endeth the first lesson Richard ---------------------------------------------------------------------------- ---------------------------- --- [This E-mail has been scanned for viruses but it is your responsibility to maintain up to date anti virus software on the device that you are currently using to read this email. ] -------------------------------------------------------- The contents of this e-mail are confidential to the ordinary user of the e-mail address to which it was addressed, or in the case of an incorrectly addressed e-mail message, the intended recipient. No-one else may copy, use, disseminate or forward all or any part of it in any form. 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