Document scanning is an operational life-saver, providing a quick way to digitize documents and feed them into your document management pipeline. However, a scan is only as good as its quality which poses a common question for our clients: What is the right DPI for scanning documents? Here we answer this question in detail to ensure you know exactly how you can improve the quality of your scans, increase scanning efficiency, and meet the requirements of your storage limitations to create a digital document process that meets your needs.
DPI is the dots per inch used to create a digital image. Known as “resolution,” DPI determines the quality of the scanned file. The higher the resolution and DPI, the higher the quality of the scan. However, the higher the resolution, the longer it takes you to scan the document, and the larger the size of the file. These are important factors as they impact your scanning efficiency, digital document quality, and storage capabilities.
Three things determine scanning resolution DPI for documents:
Speed impacts productivity and efficiency. There are many factors contributing to scanning speed, such as your equipment, your connectivity, and the size and colour of the documents. However, suffice it to say that scanning at 75 DPI is going to take far less time than scanning at 300 or 600 DPI. For example, your timing goes from about six seconds at 75 DPI to 27 seconds at 600 DPI.
Although colour versus black and white doesn’t make much difference at 75 DPI, it slows speed from 9 seconds to 19 at 300 DPI and from 27 to 71 seconds at 600 DPI. When factoring in legibility, 75 is not much use unless it is used for something small like a preview or thumbnail. Generally speaking, as a happy medium when speed and quality are of the essence, going with 300 DPI is your best bet.
The file size is important as it impacts how long a file takes to scan, share, email, and download. Black and White scans reduce size making it a good choice for basic text documents where colour details aren’t necessary. Again, the 300 DPI scan wins, as it provides the legibility you need, and produces a reasonably sized document of about 85kb compared to 600 DPI at 368kb.
As mentioned, the higher the DPI, the better the legibility. From a basic legibility standpoint, at least 300 DPI is recommended. But you also have to consider how the documents will be used. For example, if you’re uploading it to your website or viewing the file on your computer, the typical “screen size” for images is only 72 DPI. However, if you need to print an image, at least 300 DPI is recommended.
Scanning resolution DPI for documents should also be set based on the type of document. Here are typical DPIs based on document type:
When scanning your typical text documents to share and store digitally, aim for a minimum of 300 DPI. This will provide the best quality, take less time, and also provide a reasonable file size. However, if you plan to print the document at some point, you’ll have to increase the DPI to at least 300 and preferably 600 to ensure the page is legible.
The crisp lines of line art call for good-quality resolution. If you are using line art on the web or for sharing and viewing digitally, you’ll need at least 300 DPI. However, for printing you’ll need to up the DPI substantially to 900.
Grayscale documents and images have gradient shades of black and gray, hence the name. Scans require at least 600 DPI but can be saved between 300 and 600 depending on how you intend to use them.
These images consist of tiny dots and are more likely to be found in archived images dating before digital printing technology. To capture the dot effect and image clearly, scan these at 1200 DPI or greater.
Color images and document DPI depend on what you’ll use them for. A good rule of thumb is 600 DPI. However, if you need archival-quality photos, 1200 DPI is best while screen images are fine at 300.
Here is where we get into the nitty-gritty. Although the general guidelines provided above work in most situations, other considerations will impact the final quality and file size. Use these tricks to help achieve high-quality and manageable file sizes:
Choosing the right DPI for scanning documents can help save time, produce the desired quality, and optimize your storage space. If you’re interested in investing in a higher-quality scanner or would like to learn more about the benefits of outsourcing your scanning projects, speak to the experts at MES.
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