Pitty-M project aims to create a simple and cheap Polinomial Texture Maps (PTM) acquisition system.
PTM system with coin acquisition in mind.
This item was developed by Daniele Verducci as final project for the "Grafica 3D per i Beni Culturali" class at Infouma, University of Pisa.
Acquisition of big coins collections is a long and expensive work using geometry-acquisition machines, or can leave poor results if done with simle 2D cameras and paper scanners. The dense stereo matching technology is useless because of the very low profile of the engravings on the coin. The only way is using a conoscopy scanner, an heavy and expensive instrument. In the case of the camera 2D photos, by the way, the acquisition detail is very low due to the nature of the photo, able to display colorfull surfaces, but unable to represent a monochrome, engraved surface.
The right tecnique, in this case, is a relightable image of the coin. It can be acquired in few seconds, with budget instruments (a mobile light and a good camera), and it can be processed on low-power, portabile computers, even not at the same time.
The problem, in such technology, is that it need continuous human direction: someone have to move the light and take the photos. Some automatic system were developed, but they are based on big domes filled with lights and an automatically synced camera. Such systems are difficult to move and works better in a laboratoty.
The proposed system, named Pitty, sould be a cheap, compact and light alternative.
It can be built with less than 40$/30€ (price for a single system, factory production means lower prices), it weights few hundreds grams adn, when closed, represents a disc with a diameter of 15"/40cm with a thickness of few centimeters. The power supply is a rechangerable 4 AA battery pack, allowing as long as 100hours of continuous operation. In this way, it can be used in places without outlets. The system takes care of directional lighting and camera automation, and can be used for horyzontal and vertical PTMs. The operator is needed to move the arc and setup the machine. To make the machinery as cheap as possible, there isn't a system to block ambient light, so it should be used on dark environments.
Last but not the least, the system is based on open source hardware, so that the entire system could be released as open source.
The system is based on an Arduino board, an italian open source prototipyng platform based on Atmek ATMega 328. It costs under 40$ and can uses the C language.
An arc retains 10 directional white leds (18.000mcd, 20°) that lights up in a sequence to enlight the coin from different directions, managed from Arduino board. The same board takes care of shooting photos sending signals to the camera through a relais pushed by a darlington transistor. The acquisition program (auto or manual) is selected by the operator with a button.
The power supply is composed by 4 AA rechangerable batteries (4,8v), supplying current to Arduino and leds. There isn't a regulator because of the implied voltage gap: by the way, the batteries provide a regular voltage. The circuit can be powered also by a stabilized AC-DC converter.
For detail information, please see the circuit schema.
The code is released under GNU GPL 3.0 license and must be loaded onto the Arduino before the first use of the system. The prototype comes with firmware preloaded and is ready to work.
To have a lightweight chassis, I used aluminium sticks joined with screws. The base is a circle retaining an arc with LED lights. Such arc can pivot and is collapsable in order to make the item flat and easy to carry.
How to use:
Place a non-shiny support for the coin. Place the coin and the shiny ball used for light direction computation.
Place the camera on a camera support and set a macro lens. Set the maximum ISO, maximum aperture and "Sun" white balance. Plug in the camera the remote cable (see the camera user manual). With the prototype comes a Canon EOS connector.
Set the arc elevation (i.e. in case of horizontal PTM set it to 90°). Avoid covering camera lens!
Turn on the power button. You'll have a red stable light on the panel. Select mode (auto/next button for Automatic mode, manual/reset button for Manual mode).
MANUAL mode: (you have a slow blinking red light). Next key to turn on next light, reset to go back to first.
AUTO mode: (you have a fast blinking red light) Rotate dimmer to set the photo shoot time interval. The arc leds will act as time bar (1 second per led).
Press NEXT key, the camera will perform a complete acquisition lighting the leds one by one and taking syncronized photos.
If you need a complete PTM, move the ark to desidered position and press NEXT key for another round.
If you need to perform a new PTM acquisition, go to step 3. Otherwise, take down the ark and turn off the panel.
This is a Blender-rendered image of the attended result:
BUILDING THE MACHINE:
Acquisition demo (HD):
Here you can download the firmware to flash onto Arduino. (GPL v3.0 license)