Scanner Resolution and Color Depth

Evaluate these factors when choosing a scanner

If you're scanning receipts, documents, or an occasional family photo, the scanner in your all-in-one printer is probably all you need. But if your scanning demands are more complex or heavy-duty, a dedicated, stand-alone scanner may be a better choice.

Choosing a scanner isn't easy, however, and depends on your specific needs. For example, a graphic artist or photographer may need a photo scanner, while a typical office environment would likely benefit from a document 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, but there are other scanner features to consider, such as whether you need a flatbed scanner, a sheetfed scanner, or a portable scanner.

A well-dressed woman 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.

Typical optical resolution in many 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 super-high-resolution scans, however. They come with huge file sizes, taking up a lot of space on your computer. These files may take a while to open, edit, and print. Don't even think about emailing them. But with computer and cloud storage getting more inexpensive, this may not be an issue for you.

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'll select the correct resolution for the job at hand. When you select a scanner, you'll need to know how high its resolution range should be. If you're scanning only text documents, they'll 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'll be using your scans for web posts or emails, 300 dpi is more than sufficient, since most computer monitors display around 72 dpi (high-res monitors will 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're scanning photos to print out, you'll get good picture quality by scanning at 300 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 are going 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 your scanner will primarily be used for document printing, 300 dpi is more than enough resolution, and you won't need much of a resolution range in your scanner.

Consider resizing 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 you're scanning: The higher the bit depth, the more colors are used, and the better the scan will look.

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 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 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.