Scanning – What DPI to Use for Old Photos

Most likely this has to do with mechanics; a new "line" requires precise action from the roller that moves paper; a new "column" on the other hand is purely about timing and software. My understanding is that the laser ray moves at pretty much constant speed across the page, and getting more precision on that direction is just a matter of turning laser on and off at higher frequency.

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.