A few scanning tips
The full calculator is just below this first one.
For reference, image sizes to fit the paper at 300 dpi are:
Aspect Ratio is the "shape" of the image - the simple ratio of the images long side to its short side, maybe long and thin or short and wide. To print it, we can always enlarge the Size, but the image Shape needs to match the paper Shape (which is a crop). If this subject is new, see Aspect Ratio.
The calculator below specifies just one paper dimension, either the short or long side. The other dimension will float (will vary, to be whatever the image shape actually is). Ideally, you will have already chosen and cropped the image shape to match the selected paper shape properly. See Image Resize about how to handle this necessary resize and/or crop.
However a shortcut for the same scaling concept is this:
The ratio of (scanning resolution / printing resolution) is the enlargement factor.
For example (in general - speaking of any size original):
Scan at 600 dpi, print at 300 dpi, for 600/300 = 2X size (to print double size or 200% size)
Scan at 300 dpi, print at 300 dpi, for 300/300 = 1X size (to print original size or 100% size)
Scan at 150 dpi, print at 300 dpi, for 150/300 = 1/2X size (to print half size or 50% size)
Or scan film at 2700 dpi, print at 300 dpi, for 2700/300 = 9X size. If from full frame 35 mm film (roughly 0.92 x 1.41 inches), then 9X is about 8x12 inches (near A4 size). Film is typically small, requiring more scan resolution for more pixels for more print enlargement. The reason to scan at high resolution is to create enough pixels to print at about 300 pixels per inch.
This is called "scaling", and this enlargement concept is true for scanning anything, photo prints, documents, film, etc.
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