Scanner Modifications to Scan Large Documents

Your average consumer scanner works well for scanning normal printed or handwritten documents, usually anything up to Letter or A4 size. For something a bit larger, say Legal or Tabloid size, one can try to scan the document in segments, but the scanner’s lip, which is great for aligning smaller documents, becomes a major hindrance, and one usually resorts to scanning the document using a copy machine if one has access to one. This is fine until one has a document that is too big for a copy machine, e.g. what I wanted to scan—old maps. They’re too big to fit in a scanner or copy machine even if one tried to fit part in at a time; besides, one shouldn’t try that since they’re old and irreplaceable. One could photography them, but one needs a scanning back camera to get anywhere near comparable resolution, which are really expensive. That is where this modification comes in—modifying a low-cost, off-the-shelf consumer scanner to scan arbitrarily large documents in segments, which are then assembled via software.

We start with a Canon LiDE 90 scanner, although any scanner in the Canon LiDE series will do as they’re all similar.

Unmodified Canon LiDE 90 Scanner

First, we need to remove the lid, which can be done without too much effort by pushing on the center of the piece of plastic that connects the lid to the hinge on the scanner. Next, the lip around the scan glass needs to be removed. It is attached with small plastic tabs as well as adhesive near where the control buttons are. Since we won’t be needing this anymore, it’s easiest just to pry this off. With the lid and bezel removed, observe where plastic still sticks up above the scan glass; then, carefully remove the scan glass, and put it in a safe place. Next, using whatever cutting tools seem appropriate, cut away the rest of the plastic that sticks above the glass, being careful not to cut oneself or cut away the plastic that the scan glass rests on. For this, I used a small cut-off wheel and a razor blade. Now replace the scan glass, making sure it is free of dirt and fingerprints. During disassembly, one should have noticed that the back of the bezel piece that was glued to the glass was white; this is for calibration and needs to be replaced by cutting a strip of photo paper the same size. Place the strip of photo paper above where the scan element’s home position is, printable size down. Finally, tape this strip and both end of the glass to the scanner using strips of packing tape.

One is left with a scanner that can lie flush, glass-down on a table.

Modified Scanner Front of Modified Scanner Back of Modified Scanner

To scan large documents using the modified scanner, place the document face-up on a flat surface. Then, place the scanner glass-down on top of the document and scan it in segments, ensuring sufficient overlap between scans.

Scanning a Map in Segments Detail of Scanner on Map

Finally, stitch the scanned segments together. Recommended methods include following a tutorial using Hugin or using a script I wrote to try to automate the process.

Here is a result of the process—a 1915 map of the Homewood area of Baltimore. The map was scanned in 20 segments at 600dpi, resulting in a final image resolution of just under 500 megapixel.

Thank you to Paul Espinosa at the George Peabody Library for letting me scan the map from their collection.

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12 Responses to Scanner Modifications to Scan Large Documents

  1. Pingback: Hacking a flatbed scanner to scan very large documents

  2. Mihai says:

    An excelent idea nicely explained! Thanks!

  3. Marcello says:

    Looks like an awful lot of dust is going to get below the screen and on the sensor strip?

    • Matthew Petroff says:

      It is a concern. I keep the scanner in a bag to help mitigate the risk. The glass is only held on by two strips of tape, so it’s fairly easy to remove and clean.

  4. Pingback: Scan Large Documents | WebBlog

  5. Alexander says:

    My god, this is BRILLIANT. I work in a department where we have VERY large blueprints from decades ago that are falling apart but we absolutely need to keep them for reference… Now we can scan them into a gigantic picture, and then send the origonals off to be put into long term storage.

    I think the only change I am going to make is to seal up between the glass and the mechanical insides. Maybe put a handle on the sides for ease of moving it around.

  6. Pam says:

    Have you seen the FlipPal Mobile scanner? Its battery operated, portable, 4×6 scanner with open back, so that you can use it in a similar fashion, but see where your overlapped sections are. Saves each scan to an SD card. So you don’t have to have it connected to the pc while doing the scanning. Only drawback is the number of scans it would take to do such a large format item. But I’d love to see a full size scanner made the same way. Question on your stitching the images — with a huge document like that, doesn’t it take more processing power on your computer? How do you handle the bigger and bigger file size that is created?

    • Matthew Petroff says:

      As a previous commenter pointed out, HP used to make the Scanjet 4600, which is full-sized with a window. I was able to buy one used off eBay, but it uses plastic instead of glass, so the platen scratches, and it requires external power. It would be great if a company made a full-size bus-powered scanner with a glass platen, but I don’t know of any that do. It does take a large amount of processing power and memory to stitch the scans, but I have a high-end desktop computer, so it isn’t much of an issue for me. It still takes a long time, but it’s automated. Disk space isn’t much of issue as a high quality JPEG of the results is only about 150MB.

  7. Drew says:

    As a newbie to both Python scripts AND Hugin, I have just tried to use your script.
    Apparently I don’t know how to use it – the script returns -11 – but I have no idea what it means!
    Is it meant to be run from within Hugin? This is what I did, after having the images brought into Hugin.

    Sorry, but can you help a noob out here? Tell me how to use the script?

    I have 72 scans making up four sheets of actual paper, and am desperate to make real assembled images!

    • Matthew Petroff says:

      I have no idea where that error is coming from. Normal usage is python stitch-scanned-images.py img1.jpg img2.jpg img3.jpg imgN.jpg. If it doesn’t work for you, I’d recommend using Hugin and following this tutorial.

  8. Russell says:

    I tried flipping my Epson scanner upside down and it made horrible noises. Do you know what features to look for to ensure that it can scan flipped upside down? Do all Canon LiDE models have this capability?

    • Matthew Petroff says:

      I think it has to do with the weight of the scanning module, but as I haven’t tried it with any other scanners, I’m not sure. All the Canon LiDE models I’ve seen have been built pretty much the same way, so I assume any of them should work.

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