The best resolution for scanning documents

Definition & Background

If documents are often used for scanning, the question arises as to which resolution is best. The term is often specified in DPI and stands for dots per inch. The printed picture is screened, or transformed into small dots, during the printing process. To the untrained eye, this screening is almost imperceptible. The fineness of this print screen - or, more simply, the dot density - is measured in lines per inch, or lpi. Choosing the resolution will affect the following the aspects:

• File Sizes
• Readability
• Processing speed
• Editing possibilities
  
  

Basically, scanning at a high resolution makes the scans more detailed, but it also increases the file size and hence the required storage space. The higher the DPI level, the more dots there are in the scan, and thus the more detailed it is. Thousands of sheets are frequently digitized and archived as part of file archiving and daily scanning services . Storage space is still a significant consideration nowadays because of these quantities.

Increasing the DPI value makes the document appear sharper, according to popular belief. At this stage, talking about sharpness isn't totally accurate because if the original is already blurry or out of focus, it won't alter during document scanning. When scanning, however, the higher the DPI number, the more picture information is sampled from the original, information loss is decreased, and the completed image file can be enlarged without the individual pixels becoming apparent to the human eye and the image becoming pixelated.

What is the best resolution for scanning documents?
 

For normal paper documents, a DPI value of 300 is optimal in most cases. Furthermore, for a satisfactory output, a color setting of 24 bits is necessary. Most printers have resolutions of 600 or up to 2,400 DPI, thus scanning at a greater DPI value is pointless because the printer won't be able to replicate it.

A value of 150 to 300 DPI is usually suitable in practice. This means that the files can still be modified very easily. You'll wind up with enormous files that are tough to edit if you choose a really high quality. We recommend these settings also for our free document management software, bitfarm-Archiv. Summing up, the best practises are: 

• Scan documents in black and white if possible
• A resolution of 150 to 300 DPI is sufficient for good readability
• Always choose GIF, TIFF or PDF file type for texts, JPEG for photos
  
  

Errors in character recognition can easily occur if the resolution is too low (OCR). If we differentiate resolution by color mode, black and white scans should have a resolution of 300 or 400 DPI. In most cases, 150 to 300 DPI is appropriate for grayscale and color scans. Another consideration is the document's font size. As a rule of thumb, the greater the resolution, the smaller the font.

Exception: Photo Scanning

Consider what you want to do with the scanned images before scanning them. You can then pick what resolution you require based on this information.

If you don't wish to expand the photo on paper, a scanner resolution of 300 DPI will suffice. If you wish to change it after scanning, however, a DPI of 500-600 is recommended. Even greater resolutions than 600 DPI impair image quality. After that, the image will be strewn with unattractive halftone patterns. So opt for 300 DPI if you want to:

• design photo books
• reprint in the same size
• view the photo on the screen
• archive the files
  
  

A simple computation can be used to determine the scan resolution:

Scanning resolution = target format length in cm / original format length in cm * desired resolution

For example, suppose you wish to make a 20 by 30 centimeter photo print: 30 cm (target format length) minus 15 cm (original photo length) multiplied by 300 DPI (desired resolution) equals 600 DPI scan resolution.

Are you interested in more information around the topic of document management? We glady invite you to our YouTube series (please enable english subtitles) and are looking forward to your E-Mail. In this context, we are also inviting you to check out our free open source document management system, bitfarm-Archiv.

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