Scanning and Resolution Tips

These aren't hard-and-fast rules or formulas but they are tried-and-true guidelines that hold true most of the time when working with scanned images, digital images, and resolution issues.

Resolution

More is not necessarily better. Scan at no more than the output resolution or resample down to the resolution of the output device. If you are printing to a 300 dpi laser printer, scanning at 1200 dpi (ppi, see note below) results in a larger file with unneeded information that will be discarded by the printer.

On the flip side, having more resolution than you will ultimately use can be good. It gives you more pixels to work with when manipulating images in graphics software such as Adobe Photoshop. And if you find that later down the road you need a higher resolution image, you won't have to scan it again. Just keep the huge file in a safe place and when needed save it down to the desired size, saving as a new file each time.

When placing images in page layout software, use an image that has been saved at the size needed for the highest resolution output you will be using. If the image is destined for the Web, keep that 1200 ppi image on your hard drive for future use and put a lower resolution image in your layout.

DPI and LPI

The SPI should be double the LPI at which the image will be printed. Newspapers typically use 85 LPI so 170 SPI images are fine. Images in a typical magazine can be 266 SPI (133 x 2).

NOTE: DPI (dots per inch) properly refers to the printed output resolution of a device such as an imagesetter, laser printer, although in practice DPI is frequently substituted where the tersm SPI or PPI should be used. For a more detailed look at resolution see: Measuring Resolution Inch by Inch

LPI

For offset printing 85-133 LPI is typical. For other types of printing and specific types of paper see this LPI Chart

Also see Simple Guidelines That Work Most of the Time for business, software, printing, and more.