From Photoshop, you can prepare image files for offset lithography, digital printing, gravure, and other commercial printing processes.
Generally, your workflow depends on the capabilities of the prepress facility. Before you begin a workflow for commercial printing, contact the prepress staff to learn their requirements. For example, they may not want you to convert to CMYK at any point because they may need to use prepress-specific settings. Here are some possible scenarios for preparing your image files to achieve predictable printing results:
Work entirely in RGB mode and make sure that the image file is tagged with the RGB working space profile. If your printer or prepress staff use a color management system, they should be able to use your file’s profile to make an accurate conversion to CMYK before producing the film and printing plates.
Work in RGB mode until you finish editing your image. Then convert the image to CMYK mode and make any additional color and tonal adjustments. Especially check the highlights and shadows of the image. Use Levels, Curves, or Hue/Saturation adjustment layers to make corrections. These adjustments should be very minor. Flatten the file if necessary, then send the CMYK file to the professional printer.
Place your RGB or CMYK image in Adobe InDesign or Adobe Illustrator. In general, most images printed on a commercial press are not printed directly from Photoshop but from a page-layout program like Adobe InDesign or an illustration program like Adobe Illustrator. For more information on importing Photoshop files into Adobe InDesign or Adobe Illustrator, see Adobe InDesign Help or the Adobe Illustrator Help.
Here are a few issues to keep in mind when you work on an image intended for commercial printing:
If you know the characteristics of the press, you can specify the highlight and shadow output to preserve certain details.
If you use a desktop printer to preview the appearance of the final printed piece, keep in mind that a desktop printer cannot faithfully replicate the output of a commercial printing press. A professional color proof gives a more accurate preview of the final printed piece.
If you have a profile from a commercial press, you can choose it with the Proof Setup command and then view a soft proof using the Proof Colors command. Use this method to preview the final printed piece on your monitor.
Some printers may prefer to receive your documents in PDF format, especially if the documents need to conform to PDF/X standards. See Save in Photoshop PDF format.
If you are preparing your images for commercial printing directly from Photoshop, you can select and preview a variety of page marks and other output options using the Print command. Generally, these output options should be specified only by prepress professionals or people knowledgeable about the commercial printing process.
A. Gradient tint bar B. Label C. Registration marks D. Progressive color bar E. Corner crop mark F. Center crop mark G. Description H. Star target
Prints an 11‑step grayscale, a transition in density from 0 to 100% in 10% increments. With a CMYK color separation, a gradient tint bar is printed to the left of each CMYK plate, and a progressive color bar to the right.
Calibration bars, registration marks, crop marks, and labels are printed only if the paper is larger than the printed image.
Prints registration marks on the image (including bull’s-eyes and star targets). These marks are used primarily for aligning color separations on PostScript printers.
Corner Crop Marks
Prints crop marks where the page is to be trimmed. You can print crop marks at the corners. On PostScript printers, selecting this option will also print star targets.
Center Crop Marks
Prints crop marks where the page is to be trimmed. You can print crop marks at the center of each edge.
Prints any description text entered in the File Info dialog box, up to about 300 characters. Description text is always printed in 9‑point Helvetica plain type.
Prints the file name above the image. If printing separations, the separation name is printed as part of the label.
Makes type readable when the emulsion is down—that is, when the photosensitive layer on a piece of film or photographic paper is facing away from you. Normally, images printed on paper are printed with emulsion up, with type readable when the photosensitive layer faces you. Images printed on film are often printed with emulsion down.
Prints an inverted version of the entire output, including all masks and any background color. Unlike the Invert command in the Image menu, the Negative option converts the output, not the on‑screen image, to a negative. If you print separations directly to film, you probably want a negative, although in many countries film positives are common. Check with your print shop to determine which is required. To determine the emulsion side, examine the film under a bright light after it has been developed. The dull side is the emulsion; the shiny side is the base. Check whether your print shop requires film with positive emulsion up, negative emulsion up, positive emulsion down, or negative emulsion down.
Selects a background color to be printed on the page outside the image area. For example, a black or colored background may be desirable for slides printed to a film recorder. To use this option, click Background, and then select a color from the Color Picker. This is a printing option only; it does not affect the image itself.
Prints a black border around an image. Type a number and choose a unit value to specify the width of the border.
Prints crop marks inside rather than outside the image. Use this option to trim the image within the graphic. Type a number and choose a unit value to specify the width of the bleed.
Reduces the jagged appearance of a low-resolution image by automatically resampling up while printing (on PostScript printers). Resampling may reduce the sharpness of the image quality.
For information on the Include Vector Data option, see Print vector data.
When preparing your image for prepress and working with CMYK images or images with spot colors, you can print each color channel as a separate page.
Separations from CMYK, Duotone, or multi-channel documents printed on non-PostScript printers may not be identical to those printed on PostScript printers.
If you are printing an image from another application and want to print spot channels to spot color plates, you must first save the file in DCS 2.0 format. DCS 2.0 preserves spot channels. This format is supported by applications such as Adobe InDesign and QuarkXPress.
Depending on the designated printer and printer drivers on your computer, these options may also appear in the Print Settings dialog box. In Windows, click the Properties button to access the printer driver options; in Mac OS, use the pop-up menu in the Print Settings dialog box that appears.
You can place a PSD file containing spot colors directly in Illustrator or InDesign without special preparation.
A trap is an overlap that prevents tiny gaps in the printed image caused by a slight misregistration on press. Contact your service provider before you do any trapping. In most cases, your print shop determines whether trapping is needed. If so, the print shop staff will tell you what values to enter in the Trap dialog box.
A. Misregistration with no trap B. Misregistration with trap
Trapping is intended to correct the misalignment of solid colors. In general, you don’t need traps for continuous-tone images such as photographs. Excessive trapping may produce an outline effect. These problems may not be visible on-screen and might show up only in print. Photoshop uses standard rules for trapping:
All colors spread under black.
Lighter colors spread under darker colors.
Yellow spreads under cyan, magenta, and black.
Pure cyan and pure magenta spread under each other equally.
You can use a number of techniques to determine the resolution at which to scan a photograph. If you are scanning photos to be printed, and you know the exact size and the printing screen frequency, you can use the following techniques to determine the scanning resolution. Often it is easiest to scan at your scanner's maximum optical resolution and then resize the image in Photoshop later.
You can determine the resolution for your scan using the original and final image dimensions and the resolution of your output device. Scan resolution translates into image resolution when you open the scanned image in Photoshop.
For laser printers and imagesetters, multiply the printer’s screen frequency by 2. To determine your printer’s screen frequency, check your printer documentation or consult your service provider.
For inkjet printers, check your printer documentation for the optimal resolution. Many dye sublimation printers and devices that print directly onto photographic paper have an optimal resolution of 300 to 400 dpi.
For example, suppose you are printing to an imagesetter with a screen frequency of 85 lpi and the ratio of the final image to the original is 3:1. First multiply 85 (the screen frequency) by 2 to get 170. Then multiply 170 by 3 to get a scan resolution of 510 ppi. If you are printing to an inkjet printer with an optimal resolution of 300 dpi, multiply 300 by 3 to get a scan resolution of 900.
Different color separation procedures might require different ratios of image resolution to screen frequency. It’s a good idea to check with your service provider or print shop before you scan the image.
You can create a dummy file to predict the file size needed for the final output of your scan.
For example, suppose you want the final image to be 4 inches wide and 5 inches high. You plan to print it with a 150‑line screen using a 2:1 ratio, so you set the resolution to 300. The resulting file size is 5.15 MB.
To produce the scan, enter the resulting file size in your scanner settings. Don’t worry about resolution or image dimensions. After you have scanned the image and imported it into Photoshop, use the Image Size command (with the Resample Image option deselected) to enter the correct width and height for the image.