There are two methods for color trapping automatically: always overprinting black and auto-spreading.
Always overprinting black creates a color trap by causing any object that contains 95% black or more to overprint any underlying objects. This option is useful for artwork containing a lot of black text, but it should be used with caution on artwork with a high graphics content. If the service bureau recommends a black threshold value other than 95%, adjust the threshold.
Auto-spreading creates color trapping by assigning an outline to an object that is the same color as the object's fill and having it overprint underlying objects. Auto-spreading is created for all objects in the file that meet three conditions:
• They do not already have an outline.
• They are filled with a uniform fill.
• They have not already been designated to overprint.
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