Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

The "Impost" Scanner: With Adjustable Cradle, Able to Scan Books at Acute Angles

Built a scanner? Started to build a scanner? Record your progress here. Doesn't need to be a whole scanner - triggers and other parts are fine. Commercial scanners are fine too.
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jlev
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The "Impost" Scanner: With Adjustable Cradle, Able to Scan Books at Acute Angles

Post by jlev » 15 Apr 2017, 22:25

Hi, All!

In the year since I released my "Non-Destructive Guillotine" ("NDG") scanner design, I've thought more about de-keystoning photographs of book pages.

In many scanner designs, the book's pages are flattened by a glass or acrylic platen at 90, 100, or 180 degrees (The Archivist, for example, uses a 100-degree angle). This works well for reducing reflections and glare on two two sides of the platen, and for allowing the use of two cameras, each of which can take photographs of one side of the book straight-on.

However, in my experience, the more obtuse the angle of a platen, the less able the platen is to "dig into" the gutter of a book, and thus to flatten the pages relative to at an acute angle. Less "dig" also means that books with text close to the gutter can be difficult to scan using this type of fixed-platen design. For this reason, and considering books that are so fragile or tightly-bound that they are unable to be opened to 90+ degrees, I've been experimenting with methods for photographing books at acute angles (i.e., angles where the book is open at less than 90 degrees).

I'm thus posting this new design. I've posted a full write-up with parts list and prices (~$100 + camera) at http://adunumdatum.org/an-introduction- ... anner.html. I'm posting it here to engender feedback and conversation. For archival purposes (in case my website lasts less time than the Forums here), I've also attached that full (30+ page) post here as a PDF.

I've named this design the "Impost Scanner," after the bottom stones on which an archway rests -- because this build deals centrally with the "Keystone Effect," I named each of its elements after a part of an archway. The scanner consists of three parts:
  • A simple copystand, on which are mounted two lights and a single camera. The design can straightforwardly be modified to mount two cameras and additional lights. Like the NDG scanner, this element is constructed from 3/4-inch "Schedule 40" PVC plumbing pipe, and is thus inexpensive to build, is collapsible, and is reconfigurable.
  • A cradle, constructed from 1/2-inch plywood (or a similarly sturdy but lightweight material) and a few additional pieces of hardware, all of which can be purchased at hardware stores across the USA. This cradle, like the Archivist Scanner's, is adjustable for different book spine sizes. Additionally, unlike the Archivist design, its angle is independently adjustable for each side of the book.

    Atop the cradle lies a hinged platen, as with the NDG scanner. Like the NDG scanner, this platen allows for scanning tightly-bound and paperback books (which, with fixed platen designs, tend to close when pressure is not being applied to them); unlike the NDG scanner, this platen-cradle configuration allows scanning these types of books while still allowing the books to sit spine-down. The cradle moves laterally (to the left or right, depending on the handedness of the operator) on two wheels to allow the book's pages to be turned.
  • Software. As part of this design project, I have been working to document and add to "bookscan," a piece of software written in one day in 2012 by Yutaka Tsutano. I have added a full command-line interface and documentation to the program, and have renamed the fork "Voussoir". It should work across platforms, and can run separate from the scanning process or be built into it, depending on whether one's camera can directly deposit images into a directory that a provided example script is watching.

    Voussoir looks at images and recognizes special "Glyphs", similar to QR Codes, that are in the image. The user affixes these glyphs at the corners (or at any fixed locations along the perimeter) of the book or platen before scanning and then informs Voussoir of the dimensions of the book (Really, the user informs Voussoir of the dimensions of space between the markers). With these pieces of information, Voussoir can recognize the book's pages and digitally separate, crop, and de-keystone them, making it look as though each page were photographed face-on.
The scanner takes images like this (all downsampled for this post):
test1_original.jpg
test2_original.jpg
Using Voussoir, output images then look like this:
test1_voussoir.jpg
test2_voussoir.jpg
(Cropping is fully adjustable in Voussoir.)

The ScanTailor output of those Voussoir images look like this:
test1_scantailor.jpg
test2_scantailor.jpg
The scanner itself looks like this:
Top_View_resized_for_web.jpg
PVC_Side_resized_for_web.jpg
Cradle_Guide_Detail_Outside_resized_for_web.jpg
Cradle_Guide_Detail_Inside_resized_for_web.jpg
The platen is hinged (e.g., with a thin piece of packing tape), and moves laterally:
Platen_Use_Demonstration_Small.gif
Platen_Use_Demonstration_Small.gif (1 MiB) Viewed 3523 times
If, for some reason, it is desirable not to use a platen, but the book to be scanned sits open well when one side is flat, the cradle chain can be used to create a platen-less "teeter-totter" design:
Teeter_Totter_Cradel_Use_Demonstration.gif
Teeter_Totter_Cradel_Use_Demonstration.gif (566.22 KiB) Viewed 3523 times
In my mind, the Impost design takes the useful ideas from the NDG design while throwing out the less pragmatic ideas (including the vertical platen which could pinch pages or fingers, the camera pulley system, and the fact that gravity is pulling the left-side pages down into a curl when they're vertical). As I was drafting and then building it, I came to think about this new design as a platform rather than as a specific / static design. By that, I mean that because the hardware is so flexible (allowing different angles for each side of the cradle, teeter-tottering using the chain, different lighting configurations and camera angles and heights using such a simple (and thus extensible) copystand design), it's useful as a foundation for potentially lots of other build experiments and configurations in the future. Further, the use of software with fiducial markers divorces the hardware from much of the need for precision and calibration that would traditionally be necessary.

Voussoir's source code and marker glyphs are available under a permissive license on GitHub. The GitHub repository also contains example scripts for (a) watching a folder for auto-processing images, and (b) invoking the program with several of its features. I've been adding to the program in what feels like a primarily custodial way; I would be happy to collaborate on additional contributions to it!

As with the NDG scanner last year, I am releasing this scanner hardware design into the Public Domain (or its nearest equivalent internationally) via the Creative Commons CC0 dedication, following Daniel Reetz' advice on the topic. This write-up (and the attached PDF) and the images that are part of it are released under a Creative Commons Attribution-ShareAlike 4.0 license; if you would like to arrange a different license to re-use these materials, please contact me.

jlev
Posts: 24
Joined: 04 Mar 2014, 00:52
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Country: USA
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Re: The "Impost" Scanner: With Adjustable Cradle, Able to Scan Books at Acute Angles

Post by jlev » 15 Apr 2017, 22:28

Note also that exciting and related development is currently being performed by duerig in the program "marker-crop." marker-crop also uses glyphs and is intended to simplify the process of cropping images. To my knowledge, it does not currently support de-keystoning of images. duerig and I began working on these programs separately at approximately the same time, and have been in contact about feature development and collaboration.

I think that the use of fiducial markers is a really useful area for further research, since it removes so much need for precise calibration!

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Mohib
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Re: The "Impost" Scanner: With Adjustable Cradle, Able to Scan Books at Acute Angles

Post by Mohib » 16 Apr 2017, 18:32

I've almost got a comprehensive demo video of my scanner complete in which I perform various tests -- including a 1 min scan (22 pages/min or 1320 pages per hour) of a brand new paperback without cracking, creasing or damaging the spine (I show a picture of the spine after). This is precisely because I am able to scan with books at acute angles, opening them no more than you would have to when reading them carefully.

Similarly, scanning text very tight into the gutter is not an issue as I posted here: viewtopic.php?f=14&t=2549&start=20#p20567

And an improvement to my scanner I've been thinking about is to have a 45 degree bevel on the left edge of the platen would help the platen slide snugly into the binding (provided it doesn't create some other unforeseen problem) and improve the performance when scanning of these types of books.

However, there are times when even this can be too much and so in those cases I think your idea to deliberately introduce a keystone to allow scanning of fragile and other very tightly bound books without damaging the spine is a clever one. So I tried it out with my scanner! :) I simply replaced the support post with a shorter one and tilted the smart-phone to 30 degrees (as measured on a bubble-level app). Normally, I lay the iPhone on the book, zero out the level (no matter what it reads), mount the iPhone and adjust the ball joint till it reads within a degree of 0 in x and y and that solves my key-stoning no matter the angle of the table/book. So this was an interesting twist to deliberately push it off 30 degrees.

The setup and results, after using auto-dewarp in Scan Tailor (but I think first processing the images with your Voussoir script will be better), are below.

I am in complete agreement with your notion of using calibration markers. I myself have modified (see here viewtopic.php?f=14&t=3401&start=40#p20574) the script dtic provided, to resolve the image scale problem with my scanner, to use calibration pages. I think if a simple calibration marker -- say a 4" black square on a white page -- was scanned first, before the first page, and then last after the last page, it could be auto analysed for scaling and key-stoning corrections and both applied at the same time in Step 5 of Scan Tailor as part of the scaling it does there when applying margins and save extra processing (and image degradation) as I think all scales and corrections could be incorporated into one calculation.
DSC03613 - acute angle - side (book angle) - 25%.jpg
DSC03613 - acute angle - side (book angle) - 25%.jpg
DSC03613 - acute angle - side (book angle) - 25%.jpg (363.67 KiB) Viewed 3492 times
DSC03615 - acute angle - control - 25%.jpg
DSC03615 - acute angle - control - 25%.jpg
DSC03615 - acute angle - control - 25%.jpg (361.09 KiB) Viewed 3492 times
DSC03617 - acute angle - side - 25%.jpg
DSC03615 - acute angle - control - 25%.jpg
DSC03617 - acute angle - side - 25%.jpg (307.19 KiB) Viewed 3492 times
IMG_2162 - iPhone 4s tilt for acute angle test - 50%.png
IMG_2162 - iPhone 4s tilt for acute angle test - 50%.png
IMG_2162 - iPhone 4s tilt for acute angle test - 50%.png (134.04 KiB) Viewed 3492 times
IMG_2161 - 25%.jpg
IMG_2161 - 25%.jpg
IMG_2161 - 25%.jpg (367.86 KiB) Viewed 3492 times
IMG_2161 - (Scan Tailor TIF converted to JPG) -  50%.jpg
IMG_2161 - (Scan Tailor TIF converted to JPG) - 50%.jpg

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Mohib
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Re: The "Impost" Scanner: With Adjustable Cradle, Able to Scan Books at Acute Angles

Post by Mohib » 18 Apr 2017, 23:09

Will there be a Windows version of Voussoir? I'd like to try some tests.

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