When looking for a printer with a scanner, you might have noticed some technical specifications mentioning scan resolution and color depth. These two aspects affect how good your document or image looks. In the simplest terms, scan resolution refers to how detailed the scan of a physical image or document appears, and it's measured in dots per inch (DPI). Likewise, the color depth refers to how many colors a scanner can obtain from a physical image or document, and it's measured in bits.
For most people, the maximum for either of these aspects doesn't matter much. Most all-in-one printers on the market can adequately process simple items, like a black and white signed form, a page from a recipe book, or an old photo that you want to upload to social media. However, they do matter if you're scanning items with very intricate details, like a pencil sketch, handwritten notes, a photo that needs to be touched up, or a picture with many gradients.
Scan resolution and color depth isn't something most printer owners need to worry about. The specs that most entry-level printers come with are usually more than enough. That said, it might be important if you intend to work with your scanned item in photo editing software. If you want to make touch-ups or enlarge your image, you'll want to make sure your printer's scanner can process your image with the high resolution and color depth necessary for your tasks.
The maximum resolution a scanner can scan might be important for you depending on what you scan most often. If you need to scan artwork, photographs, or other highly detailed media to make printed copies afterward, you'll want to make sure your scanned document can capture as many of the original details as possible.
Scan resolution is measured in DPI, or "dots per inch": the more printed dots you scan per inch, the more detail your digital image will have. Some office printers have a lower scanner resolution, like 600 DPI, enough to capture the details in simple document scans. It's generally enough if you want to digitize some printed pictures, too; however, if you intend on blowing up a small image to a much bigger size, you'll likely want something higher, like 1200 DPI. Luckily, most home printers can achieve this maximum.
Below you can see the differences between a document scanned at 300 DPI, 600 DPI, and 1200 DPI. You can see a noticeable difference between the sharpness of the text from 300 DPI to 600 DPI, but the difference between 600 DPI and 1200 DPI isn't nearly as obvious.
You can click on the images to see the full document in a larger format. All three images are scanned at 24-bit. Your scans may vary depending on the type of paper you use and the settings your document is scanned with.
To test the scan resolution of a printer's integrated scanner, we check the provided scanning software and list the highest scan resolution indicated. Note that there's a difference between a scanner's interpolated resolution and its hardware resolution. Some scanners can increase the perceived resolution of a scan by adding extra dots between each actual scanned dot. However, we only report the hardware resolution.
If you do any professional photo retouching or editing work, then you'll want a scanner with a high color depth. Color depth is the amount of color information a scanner can retrieve from an image.
Color depth is measured in bits. Most scanners retrieve equal amounts of information from the red, blue, and green color channels, so a 24-bit scanner gets 8 bits of color information from each channel, while a 48-bit scanner retrieves 16 bits from each one. For most people, a 24-bit scanner is more than enough for most document and photo scanning needs. However, if you work with photo editing software to touch up your images, you'll want a higher color depth since it'll contain more digital information. However, because of this extra information, the 48-bit file takes up more space on your computer and might render slower, so it's best to use 24-bit for most uses unless you need something higher.
Below are two scans of a photo: one at 24-bit and one at 48-bit. As you can see, the differences between the two aren't noticeable visually at all.
You can click on the images to see the full document in a larger format. Both images are scanned at 1200 DPI. Your scans may vary depending on the type of paper you use and the settings your document is scanned with.
To test the color depth of a printer's integrated scanner, we check the scanning software settings and list the highest color depth indicated. Note that there can be a difference between a scanner's raw input (internal) and what it can output in terms of color depth (external). Some scanners can scan in 48-bit, but the resulting file is converted to 24-bit. We only report the external color depth.
To help you visualize what the scan resolution and color depth really look like, we include a sample of the printer's scanning quality in our review.
We used the Canon PIXMA TR8520 to print out this test document, and we use this same document to test every printer to make sure our results are consistent. We scan a sheet with the printer's default output resolution and color depth, even if it isn't the maximum the scanner can achieve. The document features text, monochrome graphs, color graphs, and color text to give you a picture of different kinds of work- and school-related content.
Currently, this sample serves as a reference only. We don't consider the quality of the scan when calculating the score of the Scanning Resolution and Color Depth test.
Scan resolution is measured in DPI, or "dots per inch", where one physical scanning "dot" equals one digital image pixel. These dimensions depend on the size of the physical image that was scanned, as well as the DPI it was scanned at. For example, a 4" x 6" image scanned at 300 DPI will generate a 1200p x 1800p file. You can find the pixel dimensions of a digital photo in most photo processing software programs.
Larger prints require more pixels, so if you're scanning images with the intent to reprint them in a larger format, it's important to be mindful of your scan DPI. That said, the higher the DPI, the longer the scanning time and the larger the resulting file. This means a higher DPI isn't always better. For example, an image scanned at 1200 DPI can create a file that is so large that some programs can't even open it. A scan resolution of 300 DPI is usually more than enough for letter-sized documents, while you generally shouldn't need more than 600 DPI for photos unless you intend to enlarge them significantly.
Digital photos are composed of three color channels: red, green, and blue. When these three RGB channels are added together, they can create the full-color spectrum. Most scanners assign 8-bits of color to each channel. These scanners are often called 24-bit scanners since 8-bits per channel results in 24 total bits of scan information. While this is more than enough for the human eye, sometimes it isn't sufficient for a computer when running a photo manipulation or editing program. When different photo editing effects are applied, if there isn't enough information in the file for the program to execute its command, it will often 'clip out' certain ranges of colors and shades so it can continue processing the image. This can make an image look less smooth.
To compensate for the issues associated with 24-bit scanning, some scanners assign 10 or even 16 bits of information to each RGB color channel. The resulting 30- or 48-bit files have tons of information that help mitigate the effects of clipping when performing intensive photo editing tasks. However, like scanning at a higher DPI, scanning with a higher color depth has drawbacks. Files scanned with a 48-bit color depth are massive, making them very slow to render.
There are a few things we don't test yet, like:
We're constantly considering and developing different, more effective test methods and improving our current tests to help you make a better-informed decision when buying the best printer that suits your needs.
For most tasks, the printer's scan resolution and color depth won't matter much. Most affordable all-in-one models on the market come with specs that are good enough to produce clear and sharp scans for everyday tasks. You don't need to worry about either of these aspects if you just want to digitize recipes, old photos, or signed forms for personal use. That said, if you're a professional photographer, digital artist, or designer, you'll want to keep an eye out for something with high max resolution and color depth to make sure your scanned items collect as much digital information possible.
For more information about our scanner tests, read our Scanner article.