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.
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.
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.
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.
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.
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.
