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	Scanning Input and Output Resolution Resolution for input devices and for output devices is an important consideration in the printing process. Several measurements are used to describe image characteristics in the process: ppi, or pixels per inch, is a measure of the amount of information scanned in from an image or captured using a digital camera.The higher the resolution capability of the input device. The higher the possible scan resolution, which is critical to image quality. dpi, or dots per inch, is a measure of the resolution of the printer, imagesetter, platesetter, or other output device. lpi, or lines per inch, is a measure of the frequency of the halftone screen used to print an image. The specific lpi chosen is a function both of the printing process and of the substrate on which the job is being printed A guideline to use in determining the input scan resolution is as follows: (Intended Output Size Ratio) x (Screen Ruling) x 2 = Minimum Scanning Resolution Example 1: Intended output size ratio = 1.00 (100% size of original) Intended screen ruling = 100 lpi Scanner input resolution = 1.00x 100 lpi x 2 = 200dpi Example 2: Intended output size ratio = 4.00 (400% size of original) Intended screen ruling = 100 lpi Scanner input resolution = 4.00 x 100 lpi x 2 = 800 dpi Example 3: Intended output size ratio = 4.00 (400% size of original) Intended screen ruling = 133 lpi Scanner input resolution = 4.00 x 133 lpi x 2 = 1064 dpi Scanning resolution is also affected by the input/output size ratio and the screen ruling required of the output image. A scan-to-screen ruling ratio of 2:1 is recommended, although industry experts suggest that a ratio as low as 1.5: can be acceptable. A ratio of less than 1.5:1 could create coarse, uneven halftones and a fuzzy printed appearance. The scanner used and subject matter being scanned have an impact on this ratio as well. Scanning operators are encouraged to test any scan-to-output ratio that is less than 2:1. Table 2 suggests scanning resolutions for different lines-per-inch levels, assuming that the image output size is the same-100%-as the image scan size. Scaling Scaling scanned images changes the effective resolution and can adversely affect quality and file sizes. Enlarging a halftone image after it has been scanned may result in loss of sharpness and clarity. enlarging images more than 110% may result in pixelization, or a breaking apart, of the image. SNAP suggests re-scanning the original at a higher resolution if the scan is to be output at a size larger than 110%. Users may wish to test the 110% threshold to confirm whether the quality is acceptable.

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