Scan2CAD raster to vector conversion software

EXPLANATION:

Large format scanner accuracy and calibration

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Conclusion

This article describes the accuracy problems you are likely to encounter when scanning with a large format scanner, why they occur and what you can do about them. Essentially all wide format scanners potentially suffer accuracy issues of some sort or another unless you look after your scanner and your documents.

  • You MUST take care of your scanner and handle it carefully.
  • You MUST be sure to calibrate your scanner frequently.
  • You MUST look after your documents and keep them as flat as possible.
  • You MUST feed your documents into the scanner with care.

If you look after your scanner and documents you are unlikely to experience accuracy problems, regardless of the make of scanner you have.

The amount of calibration your scanner needs will depend on the type of scanner it is. For example, by their very nature CCD scanners with fluorescent light systems require more calibration than CIS scanners. The amount of calibration your scanner needs also depends on what you are using it for. For example, if you are scanning technical drawings colour accuracy probably won't be important to you, so you probably won't need to bother with colour calibration.

Below is a summary of various scanner makes and scanner accuracy and calibration.

Colortrac CCD scanners

  • Colour uniformity: Colortrac scanners need to be normalised using the supplied normalisation program. Because Colortrac CCD scanners use a flourescent light source, they need to warm up before being normalised and before use to ensure colour uniformity.
  • Colour accuracy: Colour calibration is part of Colortrac's optional CopySmart software. Because Colortrac CCD scanners use a flourescent light source, they need to warm up before being colour calibrated and before use to ensure colour accuracy.
  • Stitching errors: CCD, so more prone to stitching errors. Should a stitching error occur, it can be corrected using Colortrac's automatic stitching utility.
  • Dimensional accuracy across the scan: CCD, so more prone to issues caused by scanner optics. Colortrac minimise these issues by using five cameras across the scan width instead of three or four.
  • Dimensional accuracy along the scan: Any inaccuracy can be corrected by fine-tuning the scanner's motor speed. This is part of the scanner maintenance software rather than integral to the scanning software and so is not intended for frequent use.

Colortrac CIS scanners

  • Colour uniformity: Colortrac scanners need to be normalised using the supplied normalisation program.
  • Colour accuracy: Colour calibration is part of Colortrac's optional CopySmart software.
  • Stitching errors: CIS, so less prone to stitching errors. Should a stitching error occur, it can be corrected using a stitching utility supplied with the scanner.
  • Dimensional accuracy across the scan: CIS, so not prone to issues caused by scanner optics.
  • Dimensional accuracy along the scan: Any inaccuracy can be corrected by fine-tuning the scanner's motor speed. This is part of the scanner maintenance software rather than integral to the scanning software and so is not intended for frequent use.

Contex scanners

  • Colour uniformity: Contex scanners need to be normalised. Normalisation is part of Contex's "all in one" maintenance program. Because Contex scanners use a flourescent light source, they need to warm up before being normalised and before use to ensure colour uniformity.
  • Colour accuracy: Colour calibration is part of Contex's "all in one" maintenance program. Because Contex scanners use a flourescent light source, they need to warm up before being calibrated and before use to ensure colour accuracy.
  • Stitching errors: CCD, so more prone to stitching errors. Checking and correcting camera alignment is part of Contex's "all in one" maintenance program. In addition, Contex scanners do some camera alignment checking while "resting".
  • Dimensional accuracy across the scan: CCD, so more prone to issues caused by scanner optics. Contex scanners include a check for dimensional accuracy across the scan in their "all in one" maintenance program.
  • Dimensional accuracy along the scan: Any inaccuracy can be corrected by fine-tuning the scanner's motor speed.

Graphtec scanners

  • Colour uniformity: Graphtec scanners need to be normalised using the supplied normalisation program.
  • Colour accuracy: At present, Graphtec scanners are not supplied with device profiles or software that allows device profiles to be created.
  • Stitching errors: CIS, so less prone to stitching errors. If a stitching error occurs it can be corrected using a stitching utility supplied with the scanner.
  • Dimensional accuracy across the scan: CIS, so not prone to issues caused by scanner optics.
  • Dimensional accuracy along the scan: Any inaccuracy can be corrected by fine tuning the scanner's motor speed. This is recommended if dimensional accuracy is incorrect on some media types.

Image Access scanners

  • Colour uniformity: Image Access scanners need to be normalised using the supplied normalisation program.
  • Colour accuracy: Image Access scanners are supplied with a device profile. This cannot be fine-tuned at present but Image Access are about to launch an online colour calibration service.
  • Stitching errors: CCD, so more prone to stitching errors. However, Image Access scanners automatically check and correct camera alignment before every scan and are therefore not expected to suffer stitching errors due to camera misalignment.
  • Dimensional accuracy across the scan: CCD, so more prone to issues caused by scanner optics. Image Access minimise these issues by using high quality lenses. In addition, Image Access scanners automatically check dimensional accuracy before every scan.
  • Dimensional accuracy along the scan: Image Access do not expect dimensional accuracy along the scan to be affected by different media types. Any inaccuracy can be corrected by fine tuning the scanner's motor speed.

Our thanks to Declan Tyler at Colortrac, Brian Honeycutt at Contex, Thomas and Deborah Ingendoh at Image Access and Chip Hollingsworth and Jane Hicks at Paradigm Imaging Group for their advice during the writing of this article.

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