Trapping...

[Jen Marsh]

Hello everyone,

Here is the situation...we are going to get new binders printed with a printing service. We are doing the artwork ourselves. I am creating in Illustrator 9.0 and I do have colors touching. The printer said that I would need to "trap" them. I asked him what trapping was and he explained it to me. Then, I did find an article on how to do it.

Basically, I'm still a little confused on the concept and the method. If anyone can shine line on it for me, I'd be quite grateful.

I am used to Photoshop and web design, not desktop publishing!! :)

Thanks in Advance...

Jen Marsh

[tman]

this is not a subject that can be that easily addressed....the illustrator manual covers it a bit...but there are many variables....easiest way is to have printer do it for you...or 'film' or service provider...the method depends on your art...I' d have to see it to give you specifics...or describe it...

[John Slate]

Trapping is a necessary evil that hides slight misregistration on a press. If a letter is on one plate and the background is on another plate, and if the shape which is cutout (knocked out) of the background is exactly the same size as the letter itself, then the slightest movement of the letter (by misregistration) will show white slivers. A NONO.

Trapping overlaps the two color elements slightly to avoid the problem. The area of overlap would show as a stroke or outline, and the lightness/darkness of the 2 colors involved determines which color is "spread" into the other. Rule: light into dark.

As far as how to do it, tman is correct. The printer should do it. Trapping should be considered part of normal service nowadays for offset lithographers. Any printer that tells you to trap files is quite frankly, not worth the trouble.

BTW, I work for a printer.

[Mark Mathieson]

In practice trapping usually involves adding an overprinting (attributes pallet) stroke to an object. The stroke colour will depend on the situation, so for a 485 red square on a 012 yellow background you would give the square an overprinting stroke in yellow, overprinting means the stroke will not knockout of whats behind it. In this instance you have 'choked' the red square, its knockout is smaller than it. If the square was yellow and the background was red you would 'spread' the yellow square by giving it an overprinting yellow stroke. The thickness of the stroke depends on your printer. We use 0.6pt for silkscreen and 0.3pt for offset litho, but we do pretty specialist work and our tollerences are pretty fine. Remember a 0.6pt stroke falls either side of the line so you are getting a 0.3pt spread. If your printer wants a 1pt trap you will need to add 2pt as your stroke. Black can often but not always be set to overprint (overprint fill and or stroke in the attributes pallet) Trapping is a big part of my job and there is no one solution as every job is different, white out type on a red background with a black drop shadow, overprint the black and you can get a red fringe on the inside of the drop shadow. A black headline partly over a blue background, if you overprint the black it will look different depending if its on top of blue or not. Hope that helps!

[Jen Marsh]

Thanks Mark for the the description on how to do it. I do believe that will help quite a bit!!

Jen

[JasonSmith]

But still, it should be up to the printer to trap the file, every printer is different, every job is different, every substrate is different, every printing process is different.

That all comes into play when deciding how much or how little of a trap to add, and only the guy printing up the job knows the answer to that.

[Neil Meinhart]

By todays standards, most printers will have in rip trapping workflows that will automatically trap your file to their standards. Unfortunately, with the introduction of some of the new transparency features in Illustrator, it makes it almost impossible to trap this type of file with the in rip method. Many times the file will have to be trapped manually, or not at all.

regards

Neil

[john m willis]

Sometimes a pointy object or a narrow one will not stroke well for trapping. In that case use the object, offset path command which auto makes a duplicate larger or smaller (+ or - amount) then over print the larger of the two for trap. You can even change a stroked object to two objects with fills by using the outline path command and then the strokes are avoided. Delete the original shape in artwork mode and keep the outer and inner ones for the job. And then you can still offset path for trap and you can trap the inner surface and the outer surface differently if you want to. When we do stamps, no strokes are ever allowed and these methods are how we work.

[Jeffrey 65 Smith]

Why is it that a lot of designers lump the function of adding bleeds to files, together with trapping? They make the assumption that some magical device does the trap... which a RIP can perform, and some other magical piece of software goes in and blows in image area to photos... extends other extaneous matter... removes some dumb .5pt frame place precisely on the page size...

[Neil Meinhart]

My Opinion 1. Lack of communication. 2. When a piece is in the design stages, the designer sometimes isn't aware of the final trims, bleed, etc. because the client doesn't know what magazines it will all be going into. 3. With todays hectic workflows of design it today, print it tomorrow, there often isn't time to thoroughly troubleshoot every aspect of the layout. 4. There are simply some designers that are not familiar with trapping, bleeds, trims, folds, perfs, scores, etc. Therefore they cannot allow for proper file creation because of their lack of printing knowledge. So they feel it is better off left up to the printer. (which is probably a good idea) although extra $$$ can be a possibility. No offense intended to the designer, no one knows it all.

Regards

Neil