To reproduce color and continuous-tone images, printers usually separate artwork into four plates (called process colors)—one plate for each of the cyan, magenta, yellow, and black portions of the image. You can also include custom inks (called spot colors). In this case, a separate plate is created for each spot color. When inked with the appropriate color and printed in register with one another, these colors combine to reproduce the original artwork.
The process of dividing the image into two or more colors is called color separating, and the film from which the plates are created are called the separations.
To produce high-quality separations, you should work closely with the print shop that will produce your separations, consulting its experts before beginning each job and during the process.
Before you print color separations from Illustrator, it’s a good idea to perform the following prepress tasks:
Set up color management, including calibrating your monitor and selecting an Illustrator Color Setting.
Soft-proof how color will appear on the intended output device. Choose Window > Separations Preview to preview how the color separations will look.
If the document is in RGB mode, choose File > Document Color Mode > CMYK Color to convert it to CMYK Mode.
If your artwork contains color blends, optimize them so that they print smoothly (without discrete bands of color).
If your artwork requires trapping, set up appropriate overprinting and trapping.
If your artwork contains areas of transparent, overlapping colors, preview which areas will be affected by flattening and note which flattening options you want to use.
Use the Live Color dialog box to globally convert and reduce colors. For example, if you want to convert a process color document to a 2‑color spot document use the Assign portion of Live Color, and specify which colors you want and how they are assigned to existing colors.
You can preview color separations and overprinting using the Separations Preview panel.
Previewing separations on your monitor lets you preview spot color objects in your document, and check the following:
Previewing separations lets you identify areas that will print as rich black, or process black (K) ink mixed with color inks for increased opacity and richer color.
You can preview how blending, transparency, and overprinting will appear in color-separated output. You can also see overprinting effects when you output to a composite printing device.
The Separation Preview panel in Illustrator is slightly different from the Separation Preview panels in InDesign and Acrobat, for instance, the Preview panel in Illustrator is for CMYK document mode only.
To hide a separation ink on screen, click the eye icon to the left of the separation name. Click again to view the separation.
To hide all separation inks on screen except one, Alt-click (Windows) or Option-click (Mac OS) the eye icon for that separation. Alt-click (Windows) or Option-click (Mac OS) the eye icon again to view all separations again.
To view all process plates at once, click the CMYK icon .
While previewing separations on your monitor can help you detect problems without the expense of printing separations, it does not let you preview trapping, emulsion options, printer’s marks, and halftone screens and resolution. Work with your commercial printer to verify these settings using integral or overlay proofs. Setting inks to be visible or hidden on screen in the Separations Preview panel does not affect the actual separations process—it only affects how they appear on your screen during the preview.
Objects on hidden layers are not included in an on‑screen preview.
To disable printing of a color plate, click the printer icon next to the color in the Document Ink Options list. Click again to restore printing for the color.
To convert all spot colors to process colors, so that they are printed as part of the process-color plates rather than on a separate plate, select Convert All Spot Colors To Process.
To convert an individual spot color to process colors, click the spot color icon next to the color in the Document Ink Options list. A four-color process icon appears. Click again to revert the color back to a spot color.
To overprint all black ink, select Overprint Black.
To change the screen frequency, screen angle, and shape of halftone dots for a plate, double-click the ink name. Alternatively, click the existing setting in the Document Ink Options list, and make the desired changes. Note however, that the default angles and frequencies are determined by the selected PPD file. Check with your print shop for the preferred frequency and angle before creating your own halftone screens.
Tip: If your art contains more than one spot color, particularly interactions between two or more spot colors, assign different screen angles to each spot color.
In particular, you can specify how to position, scale, and crop the artwork; set up printer’s marks and a bleed; and choose flattening settings for transparent artwork.
Illustrator supports two common PostScript workflows, or modes, for creating color separations. The main difference between the two is where separations are created—at the host computer (the system using Illustrator and the printer driver), or at the output device’s RIP (raster image processor).
In the traditional host-based, preseparated workflow, Illustrator creates PostScript data for each of the separations required for the document, and sends that information to the output device.
In the newer RIP‑based workflow, a new generation of PostScript RIPs perform color separations, trapping, and even color management at the RIP, leaving the host computer free to perform other tasks. This approach takes less time for Illustrator to generate the file, and minimizes the amount of data transmitted for any given print job. For example, instead of sending PostScript information for four or more pages to print host-based color separations, Illustrator sends the PostScript information for a single composite PostScript file for processing in the RIP.
Emulsion refers to the photosensitive layer on a piece of film or paper. Up (Right Reading) means that type in the image is readable (that is, “right reading”) when the photosensitive layer is facing you. Down (Right Reading) means that type is readable when the photosensitive layer is facing away from you. Normally, images printed on paper are printed Up (Right Reading), whereas images printed on film are usually printed Down (Right Reading). Check with your print shop to determine which emulsion direction it prefers.
To tell whether you are looking at the emulsion side or the nonemulsion side (also referred to as the base), examine the final film under bright light. One side appears shinier than the other. The dull side is the emulsion side; the shiny side is the base.
Image exposure refers to whether artwork prints as a positive or negative image. Typically, print shops require negative film in the United States and positive film in Europe and Japan. If you are unsure about which image type to use, consult your print shop.
If you want to print an object on all plates in the printing process, including spot-color plates, you can convert it to a registration color. Registration marks, trim marks, and page information are automatically assigned registration colors.
To change the on‑screen appearance of the registration color from the default black, use the Color panel. The color you specify will be used for representing registration-colored objects on the screen. These objects will always print as gray on composites and as an equal tint of all inks in separations.