Roger Mueller's Raspberry Pi-Powered Coin Scanner Generates High-Resolution Models From 2D Photos

3D scanning enthusiast Roger Mueller has designed a compact high-resolution scanner designed for creating models of rare and unusual coins, using a Raspberry Pi single-board computer and the recently-launched Raspberry Pi HQ Camera Module.

"High resolution 3D scanners are not cheap," Mueller explains of the inspiration behind the project. "A while back I solved this problem with a low cost touch probe 3d scanner, but this device is painstakingly slow since every point has to be visited with a rather slow mechanical system in order to scan the entire surface of a coin."

"A far better solution is a system with just one mechanical axis (x) along which the coin is translated while the other axes (y and z) are captured by the camera. There are still faster and better methods but this is fairly easy to implement as a homemade project."

Building on an earlier Arduino-powered scanner project, Mueller set about turning a Raspberry Pi 3 Model B+ and connected HQ Camera Module — designed to offer a higher quality image than the previous Camera Module modules, while also providing support for replaceable lenses for tasks including telephoto and macro imagery — with a 3D-printed housing into a coin scanner.

"The upper knob is used to adjust the position/angle of the light," Mueller notes of the chassis. "A large incidence angle (the angle between the surface normal of the object and the light rays) offers a high vertical resolution. Too large an incidence angle leads to areas that are not illuminated and therefore not scanned. A good compromise is required in order to capture a maximum of the surface in one pass. the other knob is to manually move the carriage on which the object is positioned."

"The covers on the sides can be removed to manually adjust the focus of the lens. The lid on the left is the opening where the coin is placed onto the carriage. The lid as well as the covers are used to block most of the light coming from the outside."

The HQ Camera Module itself captures in only two dimensions; the 3D model is created from a series of these two-dimension images, taken in sequential order as the coin position is adjusted using a Python script, via a Python-based point cloud generator. The point cloud is then meshed and loaded into Blender for further processing.

"The use of a Raspberry Pi and a Raspberry [Pi] HQ Camera [Module] for a 3D coin scanner is great," Mueller writes. "The systems works very reliably and produces great results, but there are situations when the system has problems capturing the shape of the surface. This is especially true if the relief is too shallow or too deep. Color variations are another problem that can introduce image noise that ultimately leads to rough surfaces. Got a coin to scan? If it's an interesting one I'd gladly scan it. Just drop me a line!"

Full details, and 3D scans of various coins, can be found on Mueller's website.