| Scan originals at a resolution appropriate to their format
and use. Image Resolution - Photographs
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Then the rules are very simple: Scan resolution (pixels per inch) determines image size (pixels). Digital image size is dimensioned in pixels. Dpi means pixels per inch, meaning that if you scan 6 inches of object at 100 dpi, you will create 6 inches x 100 dpi = 600 pixels image size. Or scanning 1 inch at 600 dpi will also create 600 pixels. Or 2 inches at 300 dpi, or 3 inches at 200 dpi, or 12 inches at 50 dpi, or 1/2 inch at 1200 dpi, all of these also create an image with a 600 pixel dimension. Just plug in any appropriate numbers, what you have, and what you want. So planning depends on knowing what size you have to scan (inches), and knowing what size image you want from it (pixels). We simply select the appropriate scanning resolution which creates the appropriate image size to be appropriate for our goal. More resolution creates a larger image, less resolution creates a smaller image. A larger original (like a full size page) needs much less resolution than a small original (like 35 mm film). Your scanner software should compute and indicate the final image size (pixels) for your current settings (crop size and scan resolution), but of course you need to know what size image you want (pixels)? Dpi means pixels per inch, which means that if we scan 6x4 inches at 150 dpi, then we create (6 inches x 150 dpi) x (4 inches x 150 dpi) = 900 x 600 pixels. But if we are scanning 3x2 inches, then 300 dpi creates the same 900 x 600 pixels. Video screens are dimensioned in pixels too. To show the image on a 1024x768 pixel video screen, we need an image that is no larger than the 1024x768 pixel screen size (video screens vary in size, they are not all the same size). The viewing program's window will be even smaller than the full screen. Most images that are appropriately sized for printing will be too huge for the video screen. See section one and following pages about video resolution. ....So, the answer depends on the size of what you are scanning (inches) and the size of image that you want (pixels) for your purpose. Scanning dpi gives the "pixels per inch" of scanned object which determines the final image size (pixels). |
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Cornell recommends 600 ppi for 1-bit scanning or 400 ppi for 8-bit scanning of printed type to achieve preservation quality scanning. Other general recommendations for reproduction are:
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