My scanner sets an output resolution at 300 dpi for a slide scanned to output dimensions of 6" x 4" - producing a file of about 6MB. I'm scanning family slides & negs to be used either as prints, say 6x4, or for showing on computer or data show. Is this sufficient or should I scan at a higher resolution (which I can set in the output screen)? Thank you.
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Our Creating guide has a formula for deciding what resolution to set your scanner at, based on how big you want to print it. The formula multiplies 300ppi by the longest side of a desired print, then divides that by the longest side of the original you are scanning. For a typical scanner to scan a 35mm slide, to get a 6"x4" print you would multiply 300ppi by 6", and divide by 1.4" original length, giving you a result of 1285ppi. The nearest standard settings on most scanners would be 1200ppi, 1600ppi or 1800ppi, and a dedicated film scanner might also offer 1400ppi. If you are not good at inches, the equivalent would be 300ppi multiplied by 150mm divided by 35mm. It is all a bit of a dark art, as the result really depends on the quality of the scanner optics, sensor and the original image. We would recommend some trial and error using different settings and getting the output printed to a photo quality. If the resolution is too low the biggest quality difference you are likely to see is the image focus will be very soft. Try to choose test images that are known to be sharp to get the best indication. Our guide to resolution is available at http://makeit.digitalnz.org/guidelines/creating-digital-content/photography-and-imaging#pixelresolution