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 ScanTailor output of those Voussoir images look like this:
- Platen_Use_Demonstration_Small.gif (1 MiB) Viewed 7995 times
- Teeter_Totter_Cradel_Use_Demonstration.gif (566.22 KiB) Viewed 7995 times
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.
AD_VNVM_DATVM_An_Introduction_to_the _Impost_ Book Scanner_using_Voussoir2.pdf- (1.97 MiB) Downloaded 388 times
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.