Creating high quality scans for raster to vector conversion

Last updated 7th March 2009

Raster to vector conversion: Using large format scanners to get good quality scans

During the 15 years we sold raster to vector conversion software we were constantly amazed at the poor quality of many of the scans we received.

Many of these poor quality scans were created on expensive large format scanners whose product literature glows with the promise of quick and easy high quality scans. However, as the scans we receive show, there is no guarantee of useful results when the scanner is used inappropriately for the drawing in hand.

This article sets out simple steps for ensuring high quality scans. It is aimed most specifically at users wanting to scan drawings for raster to vector conversion but once you have mastered this relatively simple process - largely a matter of learning to "read" your drawings and to use your scanner correctly - you will also be able to apply the improvements in image quality to the archiving of important drawings in order to give them and posterity the quality they deserve.

What defines a high quality or poor quality scan?

A high quality scan is one where the lines, arcs and text are clear, clean and unbroken; where close together entities are separated by clean white space; and where curves are smooth.

Here are some examples of high quality scans that can be converted using a raster to vector converter:

Suitable for raster to vector conversion - clean and clear with separated text Suitable for raster to vector conversion - separated parallel entities
High quality scans comprising unbroken entities and smooth curves. Text characters and parallel entities are separated by clean white space.

A poor quality scan is one where the lines, arcs and text are broken, have merged together, are blurry or are indecipherable even to the human eye.

While some poor quality scans can be "mended" using raster editing tools, many cannot. In this case, the scans cannot be converted using automated raster to vector conversion and the only course open to you if you need the drawings in vector format is to return to the drawing board / PC CAD system to redraw the image, or to rescan the original paper drawing if you still have it.

Here are some examples of poor quality scans of which perhaps one is "mendable". Some are unsuitable for viewing and printing, let alone raster to vector conversion. These are all real scans we have received.

Unusable for raster to vector conversion - inappropriate threshold

Entities are "blobby" and have merged into each other.

Unusable for raster to vector conversion - inappropriate threshold

Entities are broken and parts of the image are missing altogether.

Unusable for raster to vector conversion - inappropriate threshold

The lines have holes in them.

Unusable for raster to vector conversion - blurry JPEG image

Entities are blurred and have no definition.

Unusable for raster to vector conversion - too low resolution

Entities are broken and are indecipherable even to the human eye.

Unusable for raster to vector conversion - indecipherable

Entities are merged and are indecipherable even to the human eye.

So, how do you create a high quality scan for raster to vector conversion?

Here is a checklist.

[Next page]