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Software to rectify technical drawing scans

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  • Software to rectify technical drawing scans

    Hi everybody

    This is may first post and hope I am at the right place for my concern.

    I have recently done some scanning of technical large size drawings (sizes above DIN A2 and even A1). I used a IRIScan Book Executive 3 manual scanner as there was no large size scanner available.

    I scanned 3 to 4 scan strips the width of the scanner (about 20 cm) per drawing and have in mind to simply stitch them together using photoshop.

    Now as the attached file example shows, I managed to make some rather tilted scans I will first have to rectify before I can stitch. Does anyone know a decent and simple way to do this?

    I tried using Photoshop's perspective extraction ... with mediocre results. I believe ... or hope ... that there must be a tool that allows this sort of automatically. In allethe respective drawings, there are always several horizontal lines and always a number of vertical lines to serve as guidelines.

    Thanks for any hints in advance.
    Attached Files

  • #2
    The scans might have been tilted, which can be corrected using Photoshop's rotation tool. However, what you've posted also appears to be bent or curved.

    I needed to look up the scanner you mentioned, since I have no experience with it. Perhaps the nature of how one slides the scanner across a page resulted in some warpage of the scanned image. The scanner you used is intended to scan text from books, which doesn't match up all that well with how you've used it to scan a large technical illustration in sections.

    A better choice, if you have one, would be a flatbed scanner. Most corner copy shops that do a bit of digital printing will have flatbed -- they're very common (I have a good one here at home and one at work). Flatbed scanners with large beds are very expensive, however, and difficult to find. I've used a smaller flatbed and your technique of scanning in strips and, then, combining the results in Photoshop many times.

    These times have mostly been when I've needed to scan hand-painted acrylic illustrations, watercolors, or larger photographic prints. I've used Photoshop's feather tool to gradually and selectively blend together the overlaps (each on a separate layer), so there's no hard separation lines between the merged scans. Piecing scans together in chunks that minimize the joints between the scans crossing over critical areas helps too. This technique works quite well (with much work) since there's some room for error on the types of illustrations and photos I've scanned. This technique would likely be much less successful when merging technical illustrations that consist primarily of hard edges and geometric lines and shapes.

    Correcting distortions in the scans, like curves, bends, warps, would be difficult to fix in any case -- even with Photoshop's perspective tools. If that is a problem, my best recommendation is to use a good flatbed scanner -- even if it means paying for the scans. Rotating layers by incremental amounts to make up for not getting the imagery precisely positioned on the flatbed is easily corrected using Photoshop's rotation tool.

    Another options is an ultra-high-resolution studio photograph. Again, though, you'll be paying money for it, but you'll save a great deal of time by eliminating the need to stitch scans together.

    No matter how you go about this, though, it's not going to result in an ideal final product. A good technical illustration needs to be reproduced from the original vector artwork, but I suppose all this depends on what you'll be using it for. If it were me and top quality was a requirement, I'd likely just use the scans as templates, then redraw the illustration in Illustrator.


    • #3
      Do a search for a local document scan resource. Even some fedexkinkos locations do them. There are feed through scanners that will take engineering drawings as a feed through and reproduce quite nicely. They'll even do flat art, if the artist is ok with doing it that way.

      Or look into finding one of these or similar:

      As for what you've done here, if this is for any kind of technical archive, it isn't ever going to be good enough.
      Technical drawings are meant to be accurate.


      • #4
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