Off to a Good Start


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 Image

Before 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:

  • At what scale factor will the image will be used? Scan the image to that size rather than scaling the image in Photoshop or a page-layout application.

  • Will the image be used at multiple sizes? If the scale factors are fairly closethe image is used at 150 percent and at 140 percent, for examplescan for the larger size and just use scaling tools in the page layout for the smaller size. But if there is a substantial difference in scale factorsan image used at 150 percent and 25 percent, for exampleit's worth making a separate scan for each use. Alternatively, scan the image for the larger scale factor, and then scale it down in Photoshop (Image > Image Size), using the Bicubic Sharper resampling option (Figure 9.1). Why have two images, when you could just place the same image twice in your page layout and scale it there? You have a bit more control over the resampling and scaling if you perform the scaling yourself in Photoshop. And you slightly reduce the processing burden on the raster image processor (RIP) that ultimately handles your job by using images that are already the correct size.

    Figure 9.1. When reducing the size of an image in Photoshop, you'll achieve better results by using the Bicubic sharper Resampling method.

  • Will the image be rotated in its final use? Scan the image at the correct angle. Photographing a subject at an angle, however, may be more challenging ("Can you stand on your head just a little bit longer?"). As with scaling, you'll achieve better results by performing the rotation in Photoshop rather than in a page-layout program. And if you don't hit the correct angle with your first try, don't perform an additional rotation. Multiple transformations (whether scaling, rotation, or distortion) can erode image detail unnecessarily. Figure out what the correct final angle should be, then undo your attempts or revert to the original version of the image and perform the rotation in one step.

  • What are the important elements in the image? If the image is a product shot, concentrate your efforts on maintaining the best detail and most faithful color rendition in the product, even if that means slightly hurting the incidental contents of the image. Worry about the red in the product package, rather than agonizing over the color of the two partial tulips accenting the upper-right corner of the shot.

  • Will the image be used on the Web, as well as for print? Consider keeping the image in RGB as you perform color corrections and retouching work. Then save an RGB version of the image to be used as the source file for Web work. Save another copy of the image as CMYK. You should also keep your RGB working file in case you need to do additional work, so that you can regenerate the Web and print images from a new parent image if necessary.

Image Resolution

The 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 Space

Our 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 CMYK

Unless 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.




Real World(c) Print Production
Real World Print Production
ISBN: 0321410181
EAN: 2147483647
Year: 2007
Pages: 132
Authors: Claudia McCue

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