Color trapping and overprinting
When colors are trapped, they are intentionally overlapped so that misalignments of print separations are not noticeable. In manual trapping, one color must overprint the other. Overprinting is achieved by printing one color over another. Overprint trapping works best when the top color is much darker than the underlying color; otherwise, an undesirable third color may result (for example, cyan over yellow results in a green object). In some cases, you might actually want to create a third color; for example, you can overprint two spot colors to create a third color.
How overprinted colors mix depends on the type of colors and ink you are mixing and the types of objects you are overprinting. For example, an object that uses a CMYK color overprints differently from an object that uses a spot color. Bitmaps also overprint differently from vector objects. You can preview a simulation of how overprinted colors will mix by enabling the Enhanced viewing mode and the Simulate overprints viewing mode. For more information about choosing a viewing mode, see Viewing modes. Some variation between the preview and the printed version may occur, depending on the printer you use.
When you are ready to print, you can choose to preserve overprint settings if you want to trap objects in a document, or if you want to mix the overlapping colors for effect. You can also choose to knock out the overprinted areas so that only the top color is visible. If you want to print a proof version of the file, you can simulate overprints. Simulating overprints rasterizes the file, and it prints using process colors only.
You can set a group of objects to overprint. You can allow text to overprint overlying objects. You can also overprint bitmaps; or each vector object’s fill, or outline, or both. In addition, you can overprint specific color separations and specify in which order they will print, as well as whether you want to overprint graphics, or text, or both.
The two methods for automatic color trapping include always overprinting black and auto-spreading. 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. You can adjust the threshold, if the print service provider recommends a black threshold value other than 95%.
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, are filled with a uniform fill, and have not already been designated to overprint.
For advanced trapping options, see In-RIP trapping settings.
To preserve or ignore overprints when printing
To print a simulated overprint
To overprint selected objects
You can also set an object to overprint by right-clicking the object and choosing an overprint option from the context menu.
To overprint selected color separations
The icons appear darker when the separation is set to overprint.
You can change the order in which color separations print by selecting a color separation and choosing an order from the Order list box.
To trap by always overprinting black
To set the overprint black threshold
To trap by auto-spreading
The value that you type in the Text above box represents the minimum size to which auto-spreading is applied. If you set this value too low, small text may be rendered illegible when auto-spreading is applied.
The amount of spread assigned to an object depends on the maximum trap value specified in the Maximum box and the object’s color. The lighter the color, the greater the percentage of the maximum trap value. The darker the color, the smaller the percentage of the maximum trap value.