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I'm scanning documents of different sizes and am trying to crop them in such a way that they will fit in a Letter size paper when printed (without stretching a small image, or resizing a larger image to fit in the paper).

If I know the DPI of my image (300 DPI), and the DPI that my printer prints in (600 DPI), and the size of the paper (Letter size is 8.5 by 11 inches [215.9 mm × 279.4 mm]), can I compute for the size of an image (in pixels) so that it will not need to be resized to fit the paper's width when printed, and just fit the paper width exactly? How do I do this?

In the screenshot below, what I would like to happen is for the image to fit the paper's width when I choose 'Original size (from image DPI)', so that I'll have no need to choose 'Best fit to page (aspect ratio)' or 'Stretch to page (no aspect ratio)'. This will ensure that I don't save images with resolutions higher than what my printer can print in Letter size, but high enough so that I won't need to stretch a small image. enter image description here

My software for image printing will be Irfanview. My OS is .

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If the original image is 8.5 x 11, then it will fit properly when you print it on 8.5 x 11 paper. The pixels will automatically be scaled up by a factor of two by the printer since it has twice the dpi. – psusi May 12 '12 at 19:26
@psusi I would like to know how to make my image be 8.5 x 11 inches in size, or just have 8.5 inches width (i.e. how to compute for the equivalent of 8.5 x 11 inches paper size in pixels?) – galacticninja May 13 '12 at 5:21
If the page you originally scan is 8.5 x 11 inches, then the image will be 8.5 x 11 inches. If you crop it, then you will need to resize it, in inches. Don't worry about the pixel count, that's just an implementation detail. – psusi May 13 '12 at 21:06
up vote 2 down vote accepted

If the letter size is 8.5 x 11 inches and you want to print at 600 dpi then you need an image of 8.5 * 600 by 11 * 600 pixels to avoid any scaling one way or the other.

Or more simply put 5,100 x 6,600 pixels.

The issue would be if you scanned an 8.5 x 11 inch image at 300 dpi. Then it would be converted into an image of 2,550 x 3,300 pixels - which is half the size you need. Then the image will be scaled when printed at 600 dpi to come out at the same size as the original. Either you need to scan at 600 dpi or print at 300 dpi.

The added complication (which is why you might be seeing "best fit" or "stretch") is that the printer might not be able to print right up to the edge of the paper. This would mean that your actual paper size is slightly smaller than you expect.

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Does the DPI of an image file come into the equation? For example, let's say that my image file has 300 DPI. – galacticninja May 13 '12 at 5:23
@galacticninja - I'll update the answer. – ChrisF May 13 '12 at 15:56

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