When CMYK art contains white objects on a colored background, do I need to knock-out white?

I have to design a printed poster (cmyk) for a trade show. It will be in Adobe Illustrator. The copy is all white and the logos in it are too (well, one logo is all white with some ‘less opaque’ 50% white transparent elements). The logos and all copy will be laid over a blue background, and in some places, over a photograph.

As this is white over a darker background, do I need to knockout the logos/copy? Or does the printer typically do that automatically? Is there something I need to do differently with the 50% transparent white areas of the logo? I’m not too familiar with how to knock stuff out on my own, and to be honest, I’m not sure if I need to! Do I?? I don’t have access to the printer for questions as this is outsourced.

Please advise. Thank you so much.

Answer

Knock outs refer to removing ink on one plate so that the ink from another plate can be printed straight on the stock (paper). This is done to prevent the build up of color due to multiple inks being printed in the same location.

The only reason white would ever be printed in offset printing is if you are printing on a colored stock. i.e. you have blue stock and want to print white letters on it. So, a white ink is mandatory. If you aren’t printing white…. there’s nothing to knock out.

When discussing print design… and artwork which will be printed on a white (or near white) stock… White is not printed in offset printing. Therefore anything you create in Illustrator which is white will be seen as “stock” or “invisible” when the plates are made. Simply setting the fill color of an object to white removes all ink from that area of the design. You could essentially look at white as an inherent knockout of all plates. There’s no need to specifically set white to knockout. No ink = nothing to knockout.

(In Illustrator, you do want to check that white objects are not set to overprint via the Attributes Panel. White filled objects set to overprint can create undesired results.)

As always, if you are unsure of how things will appear, you can always use the Separations Preview in Illustrator to toggle color plates on and off to see how they interact with one another. Just be certain to turn off separations preview before saving anything for the web.

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Source : Link , Question Author : efrozit , Answer Author : Scott

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