2.3.2 Setting the Resolution

The right resolution for a scan primarily depends on the size of the original, the size of the scanned file to be output again later, and the output procedure or device to be used. In the "Scan dimensions" window, these three factors can be used very simply to specify the resolution needed for the scan. Once the desired dimensions or resolution have been entered, SilverFast takes care of the calculation. First, the output resolution has to be determined. For printing on a laser or inkjet printer, 300 dpi (dots per inch) is more than enough for most print shops, but some shops want to see resolutions of up to 600 dpi. In this case, you should follow the instructions from the print shop.

For output on a monitor or projector, the specification in dpi is irrelevant, since the absolute number of pixels is determined by the output device and the number of points per unit of length is not useful. An optimum output result can be obtained in this case if the dimensions (number of pixels in width by the number of pixels in height) of the scanned image are adapted to the technical specifications of the output device. A Full HD projector, for example, displays 1920 x 1080 pixels – for the best possible display, the scan should thus be adapted to these dimensions.

If the image needs to be magnified during output, a higher scan resolution is needed than for 1:1 output, to avoid artifacts in scaling such as stairstep formations. In the Preset drop-down menu, you can select the resolution that the image file should have after scanning. The Resolution slider is used to adjust the resolution to be used for scanning. The color under the slider shows how practical the currently selected resolution is from a technical standpoint. In the green area, the resolution is in a range that the scanner can still handle without problems and the files from the scans are not excessively large. In the yellow area (corresponding to the optical resolution according to the manufacturer), the scanner is at the limits of its optical and physical performance, which is usually significantly lower than the manufacturer's specifications. The resolution performance of a scanner is not only determined by the theoretical resolution of the CCD unit (usually the same as the manufacturer specifications), but also from the rest of the scanner's optical system as well as its mechanical precision while moving the CCD.

If the slider is pushed all the way to the right, the scanner will return an interpolated resolution, meaning that intermediate values will be calculated directly in the scanner if the lens can no longer detect them. The result is a file with more pixels, but no increase in the information or richness of detail in the image. The contrast, sharpness, and the color density cannot be increased in this manner at all – only the file size is larger. Users conscious of storage space can reduce the resolution of 300 dpi usually used for printing by one-fourth to a value of 225 dpi with no visible loss of quality. Since the resolution and the file size are related by a quadratic function, the size of the scanned file will be reduced by half – a significant gain in storage space.

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