Online Seminars from Photoshop Tips & Tricks...

Photoshop 5.5
Spot Color Trapping
by Joyce Evans


We will trap the sample we did in Spot Color Knockout and then change the percentage of the Spot Color for print. If you don't fully understand the principles of "knockouts" and trapping, see Fred's article "Trapping: Dangerous Subject" in the Graphics department of DT&G.
__ Whenever you have two colors which vary as much as these do you'll need to trap them. The knockout we made and the spot color are the exact same size. If the press gets the registration a tad off (which almost always happens) you'll have a white hairline showing through. To solve this you need to either make the knockout a bit smaller or expand the spot color.
PHOTOSHOP Seminars - Color Trapping__ We are going to expand the spot color. Don't even try to use the trapping that Photoshop has because it won't work in the Spot Color Channel, you have to do it manually. It isn't all that difficult.

Most offset printing applications require about .25 points of trap. There are 72 points in an inch. To determine how many .25 points there are in an inch, divide 72 by.25 which is 288.

Now we need to determine how to get this into pixels. Divide your resolution (ours is 200) by 288. Multiply the result by 2 and round off to the nearest whole number to determine the stroke width. (always round up)

Based on our calculations above we need to stroke 2 pixels


CTRL+Click (Option+Click) on the Spot Color channel to select it.
PHOTOSHOP Seminars - Color Trapping

Be sure you have your foreground color set to the color of your Spot
color, so the stroke is the same color.


From the menu bar choose Edit|Stroke and enter a value of 2 pixels and
center, click OK.


You probably think you just increased the size by 2 pixels but in fact
it was only one because we choose center which put one pixel on the
current selection and one outside.

Now that wasn't so bad was it? You have just trapped your Spot Color.



Joyce Evans is a freelance reviewer. If you have software or hardware you would like reviewed please send press releases or contact at: Joyce@je-ideadesign.com. Copyright 2000 All Rights Reserved Joyce Evans



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