Another image for Auntie’s Ghastly Gallery!

The sender of this image was particularly interested in converting the text.

Our Scan2CAD raster to vector converter has a capability for converting raster text to vector text using OCR. When you convert raster text using Scan2CAD’s OCR, the vector text is proper editable text rather than a series of uneditable lines and arcs. However, Scan2CAD’s OCR only recognizes raster text where certain conditions are met.

The first condition – which this image fails – is that the text is easily legible. Can you read the text in the portion of the image shown below?

(For a list of the other conditions, see the Raster Text Quality Checklist on our main web site.)

Essentially, the image has been scanned at too low a resolution.

As with our previous ghastly image, it is worth remembering that not only is this scan utterly useless for raster to vector conversion, it is utterly useless as an archive scan as well. The information that the original drawing contained has been irretrievably lost.

Again, I’m going to stress the importance of careful scanning by knowledgable operators. Careless scanning, or scanning by operators who don’t know what constitutes a good scan or how to produce one, leads to utterly useless scans.

For more information on how to produce useful scans, see the following article on our Scanners4CAD web site:
Creating high quality scans for raster to vector conversion

Yesterday, one of the images I was emailed to do a sample raster to vector conversion on was so ghastly I was inspired to write this post.

Here is a zoomed in view of part of the image.

What is so ghastly about it, you might ask. After all, the lines look quite obvious.

Essentially, there are three issues that make this image so poor – and completely unsuitable for raster to vector conversion:

1. The text is illegible (e.g. red arrow).
2. The text and linework touch (e.g. blue arrow).
3. The background dirt touches the linework and so cannot be easily cleaned away from it – see the image below, which shows a more zoomed view of the area enclosed in the green rectangle:

    
   

A raster image is made up of pixels that form a shape. The exact nature of this shape is usually obscured by odd pixels that stick out (are these part of the shape or should they be ignored?), by breaks or by other shapes that touch or cross it. As a human being, you can usually unscramble the bits and make sense of it. But all the raster to vector converter sees is a conglomeration of little squares that it somehow has to convert into sensible and correct lines and text characters.

For raster to vector conversion to work you need an image that contains unambiguous shapes. If the image contains a lot of overlapping or touching information, like this one, the shapes become confusing to the raster to vector converter and you will not get a good conversion.

This image is by no means the ghastliest image we have seen, and to be fair parts of the image were better quality than the section shown here.

However, it is not only raster to vector conversion that the image is unsuitable for. Just imagine if it was one of the images in your archive and the original drawings had been destroyed. Although the linework can be made sense of by a human being, the text is illegible and has been irretrievably lost.

I have not seen the original drawing that this was scanned from, but assuming it was legible and reasonably clean there is every possibility that if it had been scanned at a slightly higher resolution using a good adaptive threshold, the raster image quality would have been fine.

I’m hoping that seeing images like this will stress the importance of careful scanning by knowledgable operators, and make companies who pay untrained staff low wages to scan drawings en masse on scanners that are sold on the promise of scanning “400 drawings per hour” think twice.

I will add other ghastly images to this gallery as I receive them.