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Drop-out colour during scanning

Scanning normal paper documents is hardly a problem for electronic Document Management Systems. Even popular "all-in-one" printers with integrated printer, copier and scanner achieve good results. On the other hand trying to reliably capture documents automatically that do not have high contrast (e.g. coloured paper often used for carbon copies) is almost impossible. Here all-in-one printers do not deliver satisfactory results, which usually leads to editing the scanned documents on the computer manually.

Blind colors must not or should not be utilized in most cases since the reproduction of such a document does not match the original 100 percent. However, the employment of blind colors is justified, particularly in the application of optical character recognition (OCR) processes, because backdrop colors might be distracting and hence have a detrimental impact on the reading result. Today, scanner manufacturers make it feasible for documents to be generated twice and made available for further processing, once as a true to the original image and once as an OCR-optimized image, a method known as dual-stream scanning or multistream scanning.

Drop-out colour during scanning with Document Scanners

Specialised Document Scanners

Specialised Document Scanners can do more. They can not only automatically adjust the brightness and contrast settings for a given document to be scanned, but can also suppress predetermined colours. E.g., when scanning red carbon copies the scanner can ignore the colour red. The scanner just drops the colour out, no longer recognising it. This results in a much more readable black-and-white scan, which can achieve much better results in automatic processing later. In this example, red is the drop-out colour.

The higher the quality of the scan, the better the outcome. That appears to be self-evident. Even a decent paper document can occasionally generate a bad scan result. For instance, if the document's contrast is low, or if the text is written on colored paper - or colored carbon paper.

In this instance, the user might specify a so-called blind color to improve the scan result. If the paper is red, for example, "red" is assigned as the blind color. This means that none of the "red" data will be digitized. The scanner does this by scanning the original with a red lamp. It only identifies items that aren't red in this fashion. Of course, the other primary hues blue and yellow can also be used in this way. Not only background colors, but even pre-printed lines or frames on forms and surveys can be obscured when scanning using the blind color. As a result, the scanned files can be reduced more and processed more efficiently with OCR and ICR.

Real Document Scanners

Real Document Scanners offer even more valuable functions in contrast to regular all-in-one printers, such as automatic double intendation recognition, which recognises when two or more pages get drawn in at the same time and which can abort the scan automatically. Thus no pages get lost – a disaster when original documents do not get filed. The image quality for the DMS' downstream OCR- and barcode recognition tasks is also much better and leads to more reliable identification. This saves time which otherwise would have been needed for manual tagging.

bitfarm-Archiv DMS directly supports the special functions of some producers for document improvement, leading to first class results – without "virtual Rescan" or similar products.

Summing up, the keypoints for Drop-Out-Colour are:

  • Used for low contrast documents
  • Selected colour is ignored by the scanner
  • Improving OCR and readability

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