Before you start slinging pixels around, do a bit of planning. You may just be stuck with a supplied image, with no control over how it began life. In that case, you may have to make some compromises for print. But if you have some control over the birth of an image, you can better prepare for a better outcome. You might glance at Chapter 4, "Preparing Raster Images," for some general image guidelines. Know the Fate of the ImageBefore you scan an image, or photograph a subject with a digital camera, it's helpful to know how the image will ultimately be used. Consider some important issues:
Image ResolutionThe rules for image resolution are the same as for image size, because the concepts are intertwined. Start with as much image information as you can. You can always discard information, but you can't convincingly create it out of nothing. Once you've determined the correct final dimensions for your image, scan the artwork or transparency to those dimensions at the appropriate resolution. What's the appropriate resolution? Generally speaking, 300 ppi at final size is sufficient for printing at 133150 line screen (see Chapter 4, "Preparing Raster Images," for a discussion of resolution, and Chapter 2, "Ink on Paper," for information about line screen). If your project will be printed at a very high line screen (175 lpi or above), and it is important to maintain a high level of detail in the contentimages of jewelry, fine art, or antiques, for exampleit may be beneficial to scan at a resolution greater than 300 ppi. If you are doing your own scans for such a projects, consult with the print service provider to determine the proper resolution to use. If the print service provider is doing the scanning, they will take care of the resolution issue. Color SpaceOur eyes see in RGB, yet we print (usually) with CMYK. As mentioned in Chapter 4, "Preparing Raster Images," RGB is the native tongue for scanners and digital cameras as well. Even though an image may be fated to printing in CMYK, there are advantages to keeping the image in RGB as you perform color correction, retouching, and compositing. The wider color gamut of RGB gives you more to work with as you make color corrections, and some interesting Photoshop effects, such as the Vanishing Point, Texturizer, and Artistic filters, are not available in CMYK images. Converting RGB to CMYKUnless you and your print service provider are working in a color-managed workflow, you'll be expected to provide CMYK images (except, of course, those images intended to print as grayscale or duotone). Ideally, you'll be given conversion settings customized for their presses, as well as instructions on applying those settings. Lacking that, you should find that Photoshop's built-in conversion settings are serviceable. Choose Edit > Color Settings and then select North America Prepress 2, or use the custom settings provided by your print service provider. Photoshop invokes these settings when you select Image > Mode > CMYK Color or Image > Mode > Grayscale. Keep this in mind if your print service provider gives you high-resolution scans to incorporate in your design. If you convert those images to RGB to perform a color correction, or apply a filter that's only available in RGB mode, your conversion back to CMYK will result in color values that differ from the original image supplied to you, although the change may not be apparent in your onscreen display. As long as your color settings are not extreme, this will probably not result in a drastic alteration of the printed piece, but it's something you should consider before you begin jumping between color spaces. |