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Old 09-29-2009, 12:13 PM   #1
klok
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Default Colour saver

I would like to ask if any of you has experience with some kind of programme, that makes cmyk PDF-s more afficient in print production by generating stronger black separation and lighter other colors. Final product would be print of more vivid colors, shorter time for preparing print machine, savings in colors and thiner coat of color on the paper.
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Old 09-30-2009, 12:16 AM   #2
don Arnoldy
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Originally Posted by klok View Post
generating stronger black separation and lighter other colors.
What you're describing sounds like grey-component replacement. It is generally only done to images, and during the separation process. PhotoShop can do GCR when converting from RGB or CIE to CMYK.

I don't know of any application that can do GCR on PDFs—and it might be unwise to do so.

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Old 09-30-2009, 09:55 AM   #3
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Our firm got a test version of a software called InkSaver. So from now on we send all pdf-s from clients that include CMYK information thrue it and then we place them on print forms. We are doing that for two days now, so it is too soon to talk about saving expecialy, because most of our print producions is based on 2 to 3 color versions. Speaking of quality of print - there is a slightly difference in a positive way.
Can you tell me don Arnoldy, why would be unwised to use that sort of a software? You know, when someone wants to sell you something usually forgets to tell you that kind of unsignificul details... (smile)
Oh! Read your post again and realised, that our "orders" are to use the InkSaver before separation process... now I'm really confused...

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Old 09-30-2009, 12:33 PM   #4
don Arnoldy
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now I'm really confused...
Okay, let's start with image (photo) files. A scan or a digital photo starts life as an RGB image—always, even if the machine converts automatically to CMYK or LAB, it was an RGB file first. Converting a file from RGB to CMY is very straight-forward—C is the negative of R, M is the negative of G, and Y is the negative of B.

Printing an image in CMY on a press is problematic. Printing inks are not as pure as photographic dyes, so colors get muddy. There are mechanical issues with laying three heavy coats of ink on top of each other (picking, for instance), so dark tones are problematic. The answer to these printing issues is to add a fourth ink—black.

Now the question becomes, "How do I get that fourth color?" The process is called "black generation." One of the methods for doing this is called "grey component replacement" (GCR). In GCR, the software looks at the RGB values of a pixel, and calculates how much "grey" is in it. This process is best explained by example:

An RGB pixel with a value of 32, 32, 32 is a dark grey (the colors are all balanced, so it is a neutral. It would convert to a CMY pixel of 223,223,223 (the negative of each RGB channel). Using GCR, one could replace some amount of each or the C, M & Y values with an amount of K—one could, therefore, create a CMYK pixel of 0,0,0,223 (one could also choose to create a CMYK pixel of 222,222,222,1 or 112,112,112,111 or anything in between).

An RGB pixel with a value of 32,64,128 would convert to a CMY pixel of 223,191,127 so one could create a CMYK pixel of 96,64,0,127.

An RGB pixel with a value of 32,255,128 would convert to a CMY pixel of 223,0,127 which has no grey component, and so would become a CMYK pixel of 223,0,127,0.

One of the key questions with GCR is how agressively to do it. Do you only replace the grey component in pixels where the total CMY ink coverage would be 200% or over (and then only enough to get the total ink coverage below 200%)—or do you replace all of the grey component in every pixel that you can. There are trade-offs with either choice and often people end up somewhere between the two extremes. Which you pick depends on your presses, paper, and typical images. More aggressive GCR does mean that you use less ink, but it does not necessarily mean better-looking images (it also does not necessarily mean worse-looking image either).

Now, GCR on PDFs...

If your software looks at a PDF file, finds any RGB image data within it, converts that to CMYK image data by applying setable CGR--that could be a good thing.

If the software looks at a PDF file, and find CMYK values (like a background tint with a value of C10%,M20%,Y50%,K0%) and tries to do CGR on that, its probably a bad thing!

I hope this expination helps.

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Old 09-30-2009, 01:14 PM   #5
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don: I hope this expination helps.
I don't know if it helps klok but I found it very informative...thanks...'-}}

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