Optimizing Scans for the Task at Hand

1.	Choose an Appropriate Resolution While raising the scan resolution makes it possible to print at higher resolutions or in larger sizes, it also increases the processing time (scan time) and the amount of hard disk space consumed. This section describes the resolutions appropriate to different tasks to help save time and storage space.
	Scanning for Output on an Inkjet Printer : Printers for home use generally employ multiple ink dots to express a single colour individual halftones and colors ("simulated halftones"). Consequently, the printer's specified resolution (usually of 720 or 1440 dpi) is not the same as that required to print photographic images (color or grayscale images). Adequate quality can be obtained at a resolution of from one-third to one-quarter (depending on the printer resolution) of that stated in the specifications. To date, experience has shown an effective resolution of around 240 dpi to be sufficient for most printers.
	Scanning for Output on a Dye-Sublimation Printer : Printers that operate by means of dye sublimation or photographic processes express each color with a single dot ("continuous halftones"). Consequently, the resolution given in the printer catalogue specifications is the same as that required to ensure adequate. For example, images destined for printing on Nikon's NP-200 dye-sublimation printer (resolution 306 dpi) should be scanned at 306 dpi.
	Commercial Printing : When scanning images destined for commercial printing, keep in mind that most common commercial processes generally use from 150 to 175 lines per inch (lpi), while the target scan resolution is usually (although not necessarily) around twice this number. If you are printing images at 150 lpi, for example, scan at 300 dpi.
	Scanning for Display on a Monitor : For images destined primarily for monitor viewing, scan in full color at the monitor resolution of 72 dpi (Macintosh monitors). Example file sizes for scanned images : Scanned for Approximate file size 13" monitor ( 640 x 480 pixels) 920 KB 16" monitor ( 832 x 624 pixels) 1.6 MB 19" monitor (1,024 x 768 pixels) 2.4 MB A5 page printed in full color at 150 lpi (300 dpi) 10 MB A4 page printed in full color at 150 lpi (300 dpi) 20 MB
Note :	Images destined for display on standard Windows monitors should be scanned at 96 dpi.
2.	Scale (Output Size) In certain jobs, the scanner settings are decided by specifying a "scale" which relates the dimensions of the output image to those of the original. For example a scanning job might be to make an output file that is five times the size of the original, at a certain resolution. Such a requirement may arise if it is known that the original will withstand only certain degree of magnification before quality becomes affected. Alternatively, if the magnification is not an issue, the actual size of the required output dimensions might be given, for example so that the scanned image fits into a space in a magazine or web page. In this case, the user can simply enter these output dimensions and set the resolution according to the needs of the printer or monitor (see above). The relationships between size, scale, resolution, and the number of pixels can be expressed as follows: scale = size of image as printed (output) divided by size of original resolution (dpi) x size (inches) = number of pixels Scanner (or input) resolution may be expressed as: output resolution x scale = input resolution For example, although an image scanned at settings of 72 dpi and 200% has the same input resolution and number of pixels as it would when scanned at settings of 144 dpi and 100%, when printed an image scanned at 72 dpi and 200% will be twice the size of the original.
Image scanned at 144 dpi, scale 100% (file size 74 KB)
Image scanned at 72 dpi, scale of 200% (file size 74 KB)
Note :	When output on a printer, two bitmap images with the same dimensions but different resolutions will print at the same size, although the quality of the two images will differ. When making a scan, keep in mind the appropriate resolution for your printer (the printer's effective resolution), together with the desired size.
3.	Adjusting Resolution If you are unable to scan an image at the desired resolution, you can use imaging software such as Adobe Photoshop to adjust the resolution of (resize) the image. The resize operation is generally used to go from a larger to a smaller size, or from a higher to a lower resolution. It is thus necessary to scan the image at a higher than required resolution before performing this operation. Resizing in the other direction (enlarging) will tend to result in an image where the boundaries between pixels become visible, although, an enlargement of 2x may be acceptable depending on the viewing conditions.

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