8/26/2019 Print Trapping Tutorial
Where colors printed from separate platesoverlap or adjoin one another, press misregistration can cause gapsbetween colors on the final output. To compensatefor potential gaps between colors in artwork, print shops use a techniquecalled trapping to create a small area of overlap (calleda trap) between two adjoining colors. You can use aseparate, dedicated trapping program to create traps automatically,or you can use Illustrator to create traps manually.
There are two types of trap: a spread, in whicha lighter object overlaps a darker background and seems to expandinto the background; and a choke, in which a lighterbackground overlaps a darker object that falls within the backgroundand seems to squeeze or reduce the object.
A 'trap' is a method of overlapping abutting colored objects to compensate for the imperfect registration of printing presses. Because registration, even on good presses with good operators, can be off by a quarter point or more,abutting elements in your publication may not end up abutting perfectly when the publication is printed by your commercial printer. Acrobat can automatically trap color documents with the Adobe In-RIP Trapping engine, which is available on Adobe PostScript output devices that support Adobe In-RIP Trapping. Adobe In-RIP Trapping can precisely calculate and apply any necessary adjustments to the edges of type and graphics throughout your document.
When overlapping painted objects share a common color, trappingmay be unnecessary if the color that is common to both objects createsan automatic trap. For example, if two overlapping objects containcyan as part of their CMYK values, any gap between them is coveredby the cyan content of the object underneath.
Trapping type can present special problems. Avoid applying mixedprocess colors or tints of process colors to type at small pointsizes, because any misregistration can make the text difficult toread. Likewise, trapping type at small point sizes can result inhard-to-read type. As with tint reduction, check with your print shopbefore trapping such type. For example, if you are printing blacktype on a colored background, simply overprinting the type ontothe background may be enough.
The Trap command creates traps for simpleobjects by identifying the lighter-colored artwork—whether it’sthe object or the background—and overprinting (trapping) it intothe darker artwork. You can apply the Trap command from the Pathfinderpanel or as an effect. The advantage of using the Trap effect isthat you can alter the trap settings at any time.
A. Area of overprinting B. Area ofknockout C. Background color D. Foregroundcolor
In somecases, the top and bottom objects may have similar color densitiesso that one color is not obviously darker than the other. In thiscase, the Trap command determines the trap based on slight differencesin color; if the trap specified by the Trap dialog box is not satisfactory,you can use the Reverse Trap option to switch the way in which theTrap command traps the two objects.
Specifies a stroke width between 0.01 and 5000 points. Checkwith your print shop to determine what value to use.
Specifiesthe trap on horizontal lines as a percentage of the trap on verticallines. Specifying different horizontal and vertical trap valueslets you compensate for on‑press irregularities, such as paper stretch.Contact your print shop for help in determining this value. Thedefault value of 100% results in the same trap width on horizontallines and on vertical lines. To increase the trap thickness on horizontallines without changing the vertical trap, set the Height/Width valueto greater than 100%. To decrease the trap thickness on horizontallines without changing the vertical trap, set the Height/Width valueto less than 100%.
Height/Width set to 50% (left) compared to 200% (right)
Reducesthe tint of the lighter color being trapped; the darker color remainsat 100%. This option is useful when trapping two light-colored objects,where the trap line may show through the darker of the two colors, resultingin an unsightly dark border. For example, if you trap alight yellow object into a light blue object, a bright green borderis visible where the trap is created. Check with your print shopto find out what percentage of tint is most appropriate given thetype of press, inks, paper stock, and so on being used.
Tint reduction value of 100% (trap contains 100% of lightercolor) compared to tint reduction value of 50% (trap contains 50%of lighter color)
Convertsspot-color traps to equivalent process colors. This option createsan object of the lighter of the spot colors and overprints it.
Traps darker colors into lighter colors. This option doesnot work with rich black—that is, black that contains additionalCMY inks.
Affects how precisely an object's path is calculated. Themore precise the calculation, the more accurate the drawing andthe more time is required to generate the resulting path.
Removes unnecessary points.
Formore precise control of trapping and for trapping complex objects,you can create the effect of a trap by stroking an object and settingthe stroke to overprint.
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