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.
My software for image printing will be Irfanview. My OS is windows-7.