Scanner Resolution and Color Depth

A Deeper Understanding of Optical Resolution

using scanner in office
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If you are scanning receipts, documents, or an occasional family photo, the scanner in your all-in-one printer is sufficient. However, for other purposes, you may need a stand-alone scanner. An office environment needs a document scanner. A graphic artist or photographer may need a photo scanner

Optical Scanner Resolution

In scanners, optical resolution refers to the amount of information that the scanner can scan in each horizontal line calculated in dots per inch (dpi). A higher dpi equals higher resolution and higher quality images with more detail. Typical optical resolution in many all-in-one printer/scanners is 300 dpi, which more than meets the needs of most people. The resolution of heavy-duty office document printers is often 600 dpi. Optical resolutions can go much higher in professional photo scanners—up to 6400 dpi isn't uncommon.

A higher resolution scan doesn't always equate to a better scan. High-resolution scans come with huge file sizes. They’ll take up a lot of space on your computer and could take a while to open, edit, and print. Don't even think about emailing them.

What Resolution Do You Need?

How high a resolution you need depends on how you’re planning to use the image. A text document that is crystal clear at 300 dpi won't be any clearer to the casual viewer at 6400 dpi.

  • Web posts: Most computer monitors display 72 dpi maximum or a little higher for high-definition monitors, so if you’re scanning something that will be seen on the web or will go in an email, 300 dpi is more than sufficient. You won’t lose anything if you scan at a higher resolution, but you won’t gain anything either except in terms of file size, which could mean a lot to those on the other end of the email.
  • Photos: Unless you’re planning on enlarging photos, you’ll get good picture quality by scanning at 300 or 600 dpi. If you’re going to double the size of the original, double the dpi. However, professional photographers may need as high an optical resolution as possible, especially if they are going to enlarge the images.
  • Image editing: Follow the “double the dpi” rule if you’re planning to cut the original down by cropping it and then enlarging it.
  • Office documents: 300 dpi is more than enough for most documents. You may even want to resize the scans afterward in photo-editing software to save space.

Color and Bit Depth

Color or bit depth is the amount of information the scanner gathers about the document or photo you’re scanning: The higher the bit depth, the more colors are used and the better looking the scan will be. Grayscale images are 8-bit images, with 256 levels of gray. Color images scanned with a 24-bit scanner will have nearly 17 million colors; 36-bit scanners give you more than 68 billion colors.

The trade-off is huge file sizes. Unless you’re a professional photographer or a graphic designer, there’s not much need to worry about bit depth, since most scanners have at least 24-bit color depth.

Resolution and bit depth affect the price of a scanner. In general, the higher the resolution and bit depth, the higher the price. 

Resizing a Scan

If you own commercial photo editing software such as Adobe Photoshop, you can resize scans downward to save space and not reduce the quality significantly. So, if your scanner scans at 600 dpi and you plan to post the scan to the web where 72 dpi is the standard monitor resolution, there is no reason not to resize it. However, resizing a scan upward is a bad idea from a quality standpoint.