Are you scanning line art or text? Line art, such as pen and ink drawings, and high-contrast images with sharp edges or type, should be scanned at the highest resolution possible. Text scans that will be processed with character-recognition software should also be scanned at high resolution for accurate translation. What halftone screen frequency will be used for printing? For continuous-tone images (photographs), a common rule of thumb is to scan at a resolution of 1.5 or at most 2 times the screen frequency. For example, for offset printing on newsprint at a screen frequency of 85 lines per inch (lpi), an image should be scanned at 128 to 170 ppi. For images printed at 133 lpi, scanning resolution should be 200 to 266 ppi. Talk with service bureaus and commercial printers about the screen frequency used for your projects. With this information, you can let Canvas calculate the optimal resolution for an image. See “Resam- pling and sharpening images” on page 32.645. Will the final image be smaller or larger than the original? If you need to enlarge the image, you should scan it at a higher resolu- tion to retain the most information when you resize it. If you will reduce the size of the image, you can scan it at a lower resolution. Tip Because resizing tends to blur an image, you can use the Unsharp Mask filter to sharpen it. For more informa- tion, see “Sharpen filters” on page 34.702. About digital images and resolution Digital images, also known as raster and paint images, are composed of tiny square pix- els. The number of pixels that fit in a linear inch or centimeter is the image resolution. The reso- lution indicates how much information is in the image, independent of the resolution used to display the image on screen or to print it. Low-resolution images have larger pixels and look more jagged than high-resolution images. However, while high- resolution images look smoother, they also require more memory and disk space. Vector 72 ppi 300 ppi 600 ppi
Canvas 8 Help: Scanning, sizing, and tracing images (5 of 18)                                       Page #637