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.
What is DPI?
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.
What Determines the Best DPI for Scanning Documents?
Three things determine scanning resolution DPI for documents:
1. Scan speed
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.
2. File size
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.
3. Legibility
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.
What is the Recommended DPI for Scanning Documents?
Scanning resolution DPI for documents should also be set based on the type of document. Here are typical DPIs based on document type:
Text
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.
Line art
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
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.
Halftone
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.
Colour
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.
Considerations When Setting Scanning Resolution DPI for Documents
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:
- Consider the original document: When scanning high-quality documents, using a high resolution preserves the quality. When scanning poor-quality originals, however, increasing the resolution won’t improve the quality. In this case, you should avoid using higher resolution as it will bring out undesirable details like dots, yellowing, and blemishes, creating distractions that make the file difficult to read.
- Printing resolution of the original document: Knowing how the original document was printed can help. For example, inkjet printers print between 300 and 700 DPI, while a laser printer prints between 600 and 1200 DPI. By coming closer to the original DPI you will likely see better results. So, considering the original printer, the quality desired, and the size of the document can help you find a happy medium that meets all your needs.
- The number of scans: If you’re managing a bulk scanning project, you want efficiency over almost anything. In this case, you can go with our 300 DPI rule to improve efficiencies without sacrificing quality. Generally, these projects don’t require super high quality as the documents are being stored and shared digitally. However, if you work in an art department for example, and just need to do a few scans at a time, quality is more important. In this case, you have the leisure of scanning at a higher DPI to preserve the quality without worrying about the extra time it takes to scan.
- Scan purpose: The final purpose of the scans is critical. If you’re just scanning to create a digital copy for sharing, storage, or archiving, 300 DPI will suffice. However, if you need to print the document or detail is important, then always follow the recommended DPI for that type of document, file, and purpose.
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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