GCR Light VS. GCR Medium with a 10% UCA Boost!#$@%!

Hildebrant's picture

So--
Curious if anyone here hs any higher end experience with color seperations, specifically different levels of GCR, and what may be more appropriate for an image I am working with??

Hildebrant.

Thomas Phinney's picture

In my experience, this has a lot to do with the specific printing process you're using, as well as the particular image in question. For example, running a web press on newsprint you want to crank the GCR to the max. You can't get good shadow density anyway on newsprint. Sheetfed offset on glossy coated paper, you want pretty light GCR. But the particular image is also relevant.

The UCA will help keep the shadows dense while the GCR cleans up the midtones and allows for brighter colors.

Cheers,

T

rjohnston's picture

The usual advice is 'speak to your printer', but unfortunately printers rarely make their own separations these days (they're too used to receiving images as CMYK drum-scans from their regular repro house) and won't be able to tell you much.

GCR/UCR generally shouldn't differ from image to image, but from process to process, as Thomas says. I'm guessing you know the difference between GCR and UCR, but just in case: UCR = under colour removal; GCR = grey component replacement. In practice, UCR isn't much different to a Light GCR: it basically removes C, M and Y from deep shadows, rather than gradually replacing all neutral tones with black, as would a Medium or Heavy GCR.

Both GCR and UCR interact with the TAC, or Total Area Coverage, which is the maximum amount of ink allowed by the seaparation process in any one area of the image. Higher TAC means deeper shadows with more CMY in them; lower TAC means more neutral mixes of CMY are replaced with black.

For offset, on coated paper, typical settings would be 300-320 TAC, Light or Medium GCR or UCR. For Newsprint, TAC 250, Medium or Heavy GCR. This is obviously because a good offset press with good coated stock can stand a lot of ink and you'll maximise the dynamic range of your image by taking advantage of that; newsprint turns to mush when you apply a lot of ink so you need to compromise dynamic range to accomodate that.

There are subtler shadings -- I'll sometimes use a lower TAC (say 280) and/or a heavier GCR for lighter-weight coated stock, to avoid show-through in books (not an issue in one-sided posters etc.).

Different weights of GCR have their advantages and disadvantages, when you're in a position to choose between them. For example, say you're printing a book, offset, on good quality coated stock. Generally you would use a Light GCR or UCR. This gives the pressman a lot of control over the colours that will manifest on press, because neutrals are made predominantly from CMY, not K. Therefore he can warm up your images by pulling Cyan out or cool them down by pulling M/Y. He can lighten or darken them overall by manipulating overall CMY densities, and all this without affecting text which may be printed on the same sheet as the images, because he's not touching the black plate at all (presuming the text is printed solid black).

Conversely, with a Medium or heavier GCR, the pressman has little control over the colour of the neutrals, which are predominantly composed of K. He will have difficulty lightening or darkening images without affecting the text or making the images appear banded or washed out. So why might you want to use a Medium or heavier GCR in a case like this? Because you can't go to the press pass and you don't trust the pressman not to mess up your neutrals. If overall image density is less important than neutral neutrals, Medium or heavier GCR is the way to go, but bear in mind that if the black plate is running heavy on press that day, your images will be mud. Risky.

The last issue, as Thomas hints, is that a very few images will benefit from heavier GCR in general: four-colour greyscales are one example; computer screenshots are another. In these, you want blacks and neutrals to be pretty much black, with CMY used only to deepen shadows.

UCA is another question. I don't normally risk it as it really shouldn't be necessary and can plug up your shadows if you're not very careful. Certainly no higher than 10% anyway.

Hope that helps,

R

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