Adobe 65023809 Printing Guide - Page 59

the program's "best guess" approximation of the missing pixels. There is no substitute for a correctly sized original image of the proper resolution. Compared to scaling up, scaling down an image is less likely to produce obvious loss of detail, whether the scaling is done in Photoshop, Illustrator, or InDesign. Even though image data will be discarded, the smaller size camouflages the loss. Plus, if you use the Bicubic Sharper method in Photoshop when scaling down the size of an image (which is recommended; this is discussed in the following topic), slight edge sharpening is applied to compensate visually for the discarded data. Actual versus Effective resolution The best approach to image creation (whether scanning or shooting a digital photograph) is to have the image at the proper size and resolution before using it in other applications (or printing directly from Photoshop). Generally, if you start with an image that is 300 ppi at a given size, you have some leeway; scaling up to 125% in a page layout probably won't degrade detail in an obvious way. An image without much detail (such as a background shot of a soft, gauzy sky) could still be acceptable if scaled up to 150% in a page layout. An image with a resolution of 300 ppi that is scaled up to 200% in an InDesign or Illustrator document has an effective resolution of 150 ppi. In other words, scaling an image up in InDesign decreases the resolution, and scaling an image down in InDesign increases the resolution. Conversely, a 300-ppi image that is scaled down to 50% has an effective resolution of 600 ppi. Scaling down images in InDesign or Illustrator does not reduce the amount of information included in an exported PDF, or an outgoing print stream, as no pixels are actually discarded. Processing time may increase slightly in the RIP. If just a few images are scaled down in a page layout, it's probably not worthwhile to use Photoshop to scale down the images and update them. But if most of your images are scaled down-or if images are scaled down drastically-it may be worthwhile to take the time to reduce their size in Photoshop and update them in the page layout program. Weigh the time required to scale the images against the increase in processing time-and increased storage required for oversized images-to decide whether it is necessary to create downsized images. Resampling images It's best to scan or photograph an image at the correct final size and resolution, rather than scaling it and subjecting it to interpolation. However, when scaling becomes necessary, Photoshop offers some refinements to optimize the results. Choose Image > Image Size to see the Image Size dialog box. You can resize an image by pixel dimensions or document size. Under both the pixel count and document size options, you can also specify a percentage size. If Resample Image is not selected, the Pixel Dimensions part of the dialog box is dimmed, because the pixel count won't change if the image is not resampled. Pixel Count/ Percentage (toggle) Image Size Choose options according to how you intend to resize an image- by dimensions or by pixel count. (Scaling a placed image in InDesign or Illustrator does not let you interpolate image data. ) Document Dimensions Scaling Options If the Resample Image option is selected, Photoshop must interpolate information. That is, it must manufacture image data to "fill in the blanks" if the image is scaled up. If the image is scaled down with Resample Image selected, interpolation governs what information is discarded. The scaling options include six methods for resampling, and even offers parenthetical hints about suitable uses for the methods: • Nearest Neighbor (Preserve Hard Edges): Appropriate when resizing screen shots (to avoid anti-aliasing small text), but inappropriate for photographic images. Adobe Creative Suite 4 Printing Guide 57