Scanner Resolution and Color Depth

Evaluate these factors when choosing a scanner

Choosing a scanner depends on your specific needs. If you scan receipts or documents, the scanner in your all-in-one printer may be all you need. If you're a graphic artist or photographer, you may need a photo scanner. If you manage an office, you might benefit from a document scanner.

Scanner resolution and color depth are key factors to understand when considering a scanner purchase. Here's a look at what these terms mean, and how to assess your scanning needs to purchase the right device.

Resolution and color depth are important considerations. However, there are other scanner features to consider, such as whether you need a flatbed scanner, a sheetfed scanner, or a portable scanner.

A shopper using a large flatbed scanner inside a retail store
zoranm / Getty Images

Optical Scanner Resolution

In scanners, optical resolution refers to the amount of information the scanner can gather in each horizontal line. In other words, resolution is the amount of detail a scanner can capture. Resolution is measured in dots per inch (dpi). A higher dpi means higher resolution and higher-quality images with more detail.

The typical optical resolution in multifunction printers with scanning capabilities 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, for example, up to 6400 dpi.

There are downsides to high-resolution scans. These come with huge file sizes, taking up a lot of space on a computer. These files may take a while to open, edit, and print. Also, high-resolution scans are too large to email. However, with computer and cloud storage getting more inexpensive, this may not be an issue.

If you scan photos at the highest resolution possible, you can crop the images and still maintain high image quality for printing and sharing.

Evaluate the Resolution You'll Need

Most scanners offer a variety of resolution options, and you can choose the correct resolution for the job. When you select a scanner, you'll need to know how high its resolution range should be. If you scan only text documents, these will be crystal clear at 300 dpi and won't look any clearer to the casual viewer at 6400 dpi.

Web, Email, or Internet Use

If you use your scans for web posts or emails, 300 dpi is more than sufficient, since most computer monitors display around 72 dpi (high-res monitors display at a higher dpi). If you scan something at a higher resolution, you won't lose anything, but there's no real benefit.

Photo Scanning and Printing

If you scan photos to print, you'll get good picture quality by scanning at 300 dpi or 600 dpi. If you plan to enlarge the photos, use a higher dpi. Professional photographers may need as high an optical resolution as possible, especially if they plan to enlarge the images.

A good rule of thumb for printing, editing, cropping, and resizing images: If you're going to double the size of the original, double the dpi.

Document Printing

If you need a scanner primarily for document printing, 300 dpi is more than enough resolution, and you won't need much of a resolution range in the scanner.

Resize scans in photo-editing software to save space on your hard drive.

Color and Bit Depth

Color or bit depth is the amount of information the scanner gathers about the document or photo being scanned. At higher bit depths, more colors are used, and the scan looks better.

For example, 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, while 36-bit scanners give more than 68 billion colors.

The trade-off is large 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 a scanner's price. 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, resize scans downward to save space without significantly reducing image quality. For example, 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's no reason not to resize it. However, resizing a scan upward is a bad idea from a quality standpoint.