Trapping Info:      

Spreading, choking and butting are a prepress technique, more often referred to as trapping. It mostly consists of creating small overlaps between abutting colors in order to mask registration problems.

Check out some interactive examples below.  

  When to Trap:      

Certain basic rules have to be observed.
First the decision should be made if a trap is needed between two specific inks, in other words, if these two abutting colors are printed is there a risk of gaps showing up when mis-registration happens.
In case the two colors in question are spot colors, trapping is always needed: from the moment the artwork is imaged on film or plate, they are handled separately and ultimately will be printed on two different printing units. The same applies if one of the colors is a spot, the other a process color.




Two or more colors are butted up against each other, placed side by side.  No trapping is necessary; just place the foreground object on the background object with no overprint resulting in a knockout.

Mostly use in the garment industry.  In order to keep a soft feel on a garment.  Only one layer of ink is used.  The more ink layers the thicker the feel.  

To see an example of a Butt Trap Click on Make Trap.




The background color is lighter than the foreground color.  The lighter background color is extended into the foreground color to provide a trap. No intermediate color is used.

To see an example of a Choking Trap Click on Make Trap.




The foreground color is lighter than the background color. The lighter foreground color is expanded into the background to provide a trap that does not use an intermediate color.

To see an example of a Spreading Trap Click on Make Trap.




In PostScript, every object that is placed on another object, the foreground,  will normally leave an unprinted image of itself on the background object. Trapping will be required in some cases because the “hole” is white unprinted media.

To see an example of a Knockout Click on Make Trap.




Objects printed over other objects are overprinted. The background Object Prints Completely under the Foreground Object.  This mix can result in unexpected colors.

Overprinting is the opposite of a Knockout.

Mostly used for Printing Background colors, like white, on clear media in Silk-screening Decals.

To see an example of a Overprint Click on Make Trap.




A Base/Flash is used on dark garments. It is basically a premier coat.  If a Base/Flash is not used the lighter inks will appear too dark.  A small choke trap is usually used in order to overcome registration problems.

Never Base under Black, it will wash it out.

To see an example of a Base/Flash Click on Make Trap.


Photosensitive coating, usually of silver halide grains in a thin gelatin layer, on photographic film, vellum, or glass. You always want the Emulsion side touching the Plate or Screen.

  Printer Marks:      

Crop Marks: Thin lines placed at the corners of an image or a page to indicate where to trim or cut to the final page size. Crop marks may be drawn on manually or automatically applied with some desktop publishing software programs.

Registration Marks: Is printing specific marks so that different artwork can be aligned.  Normally two crossing lines in a circle.  Also called a Target.

File Information: Prints the page title, current date and color call-outs.

Page Titles: A label on the top of the page to indicate the Company Name, Design Name and part number.  Ordinarily found in the Page Information section.

Color Call-Outs: Usually on the bottom of the page listing the color in the design.  [i.e. red PMS 485 (1 of 2), blue PMS 285 (2 of 2)]

Page Numbers: Normally on the bottom of the page.  Indicates the page number

Center Marks: Vertical lines used to indicate the center of a page. Center marks usually appear at the top and bottom edge of the page. Center marks are printed with thin lines of about 1/4 to 1/2 inches in length.

Densitometer Scale: A bar of varying shades of gray, on each separation sheet.  This  allows you to check the accuracy, quality, and consistency of the output with an instrument called a densitometer.  

Calibration Bar: A bar of 6 basic colors (red, green, blue, cyan, magenta, yellow) beside your artwork.  These color patches are used to verify the quality of the printed output.

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