Getting Four-Color Separations

It is necessary to color separate your image whenever you plan to print your image to an offset press. Your image must first be in CMYK color mode (choose Image-->Mode-->CMYK Color). Then the composite color image gets digitally separated into the four-color channels — cyan, magenta, yellow, and black — and is output. (These colors are also known as process colors.) Sometimes the separation output is onto film, and sometimes, it is output directly to aluminum printing plates. The plates are put on an offset press, paper runs through each of the four inked rollers (cyan first, then magenta, yellow, and finally black), and out comes your composite image.

Getting laser separations
Before you take your image to a service bureau or offset printer to get color separations, it is wise to get what are called laser separations. Basically, you are color separating your image, not to film or plates, but to paper. If it doesn’t separate to paper, most likely it won’t to film or plates, either. This allows you to go back and troubleshoot the problem and correct it, rather than paying upwards of $80 to $150 an hour to have the service bureau or offset printer correct it for you. Consider it a cheap insurance policy.
Here are the steps to print laser separations:
1. Be sure your image mode is CMYK. If it isn’t, choose Image➪Mode➪CMYK Color.
I’m assuming your image is a four-color image. But it may also be a grayscale, duotone, tritone, or quadtone image, in which case no conversion to CMYK is necessary.
If you’re new to converting RGB images to CMYK, don’t be surprised if your vibrant colors turn muddy and flat. This is because the gamut, a fancy word for range of color, for CMYK is much smaller than it is for RGB, and Photoshop converts colors that are out of the CMYK gamut to their closest match. It’s a cold, harsh fact that we all have to live with. After the conversion, you have an image with four channels — cyan, magenta, yellow, and black.
2. Choose File➪Print with Preview. In the Print dialog box (see Figure 2-4) select the Show More Options check box and select Color Management from the pop-up menu below it.
3. Under Source Space, select Document.
It should say U.S. Web Coated (SWOP) v2.
4. Under Print Space, select Separations from the Profile pop-up menu.
This option prints each of the channels from the image to a separate plate, or in the case of laser separations, paper.
5. Select Output from the Show More Options pop-up menu. Then select additional options as desired.
6. Click the Print button.
If all goes well, four pieces of paper, one for each of the four CMYK channels, should print. If you’re printing a grayscale, duotone, tritone, or quadtone image, you get one to four pieces of paper, one for each color used. If that doesn’t happen, something’s amiss, and it’s time for troubleshooting. Be sure to take these laser separations with you when you hand over your file to the service bureau or offset printer. They’ll be appreciative of your taking the time to ensure that your file separates okay.

Output options in the Print dialog box
The following list details many of the options that are available when you choose Output from the Show More Options pop-up menu in the Print dialog box. This list covers the options that pertain to separations and options.
- Screen: Click the Screen button to create a custom halftone screen by changing the size, angle, and shape of the halftone dots. I would leave this set to Use Printer’s Default Screen. Let the service bureau or offset printer change it if necessary.
- Transfer: This option allows you to redistribute brightness levels in your image. Again, I wouldn’t mess with this setting unless you’re a prepress professional.
- Interpolation: This option is available for PostScript Level 2 or later printers to antialias low-resolution images by resampling. Leave it deselected.
- Calibration Bars: Select this option. It prints an 11-step grayscale bar outside the image area to gauge how accurately the shades are being printed. When printing separations, this option prints a gradient tint bar and color bar.
- Registration Marks: Select this option, which prints crosshair and target marks outside the image area, allowing you to line up the four plates or pages.
- Corner Crop Marks: Select this option. It adds crops marks at the corners of the image to indicate where the image should be trimmed.
- Center Crop Marks: Select this option. It adds crop marks at the center of each side of the image to indicate where the image should be trimmed.
- Labels: Select this option to print the filename and channel name on each plate or page.
- Emulsion Down: Leave this option deselected for laser separations. Emulsion is the side of the film that is light sensitive. When the service bureau or offset printer prints the separations to film or plates, it may select this option, which allows the film to be printed with the emulsion side down.
- Negative: Leave this option deselected for laser separations. When the service bureau or offset printer prints the separations to film or plates, it may select this option, which prints black as white and white as black, and every other color inverts accordingly.
- Include Vector Data: Leave this option selected if you have type or vector paths.
- Encoding: This option specifies the method of encoding used to send the image to the printer. Leave this option at the default of Binary.
Note that if you’re printing to a non-PostScript printer, some of these options may not be available. You see a preview of most of these options as you apply them to your file.