1 Scanning Resolution. 2  A scan at 600 dpi results in a much larger file than at 300 dpi. 3  Color Space. 4  Color and grayscale files result in much larger files than black and white files. 5  Physical dimensions of the scanned page. 6  A legal-size scan will be larger than a letter-size scan, with all other factors being equal. Color and grayscale files result in much larger files than black and white files. 2  Physical dimensions of the scanned page. 3  A legal-size scan will be larger than a letter-size scan, with all other factors being equal. 4  Compression. 5  Raw scan data can be compressed to make it smaller.