Hardware Project: Refining a Multispectral Imaging System

Team

Sean McIntyre, Johannes Giorgis, Matisse Milovich, Paul Villers, Mystery

Introduction

Background

Multispectral imaging uses wavelength-specific filters to capture light at certain frequencies, to gain information about the spectrum of light reflected off an object in question. Different sets of wavelength-specific filters can provide information about the spectrum not available to the human eye either by increasing the resolution of the spectrum (using many filters) or by increasing the range of the spectrum (using UV and infrared filters). Multispectral imaging has a number of different applications. Obtaining high granularity spectral information about reflected color in a painting, for example, can distinguish between two colors that are metamers to the human eye, and therefore provide information about what pigments and dyes may have been used in different geographic zones or in different time periods to create apparently similar colors.

The goal of this project was to build a multispectral imaging system based on a rotating color filter wheel and monochrome camera. Our system components were not connected physically or electronically before we started. The first phase of the project was to design and build two adapters to fix the camera and lens on either side of the rotating filter wheel. The adapters we designed place the camera and lens as close as possible to the rotating filter wheel, to change the distance between lens and camera sensor as little as possible. The second phase of the project was to automate the photo acquisition: capturing images, rotating the filter wheel, and saving images. The automation significantly reduces the amount of human labor as well as acquisition time to capture a series of images.

Project Description

To build a multispectral imaging system based on a rotating color filter wheel and monochrome camera. The system will be used to capture images of paintings in the Cantor Arts museum. At the project outset, the components were neither physically nor electronically connected, so the camera didn't have filtering functionality. The filter wheel housing wasn't able to connect the camera or lens, because only one side of the housing had c-mount connectivity. The stock adaptor was too thick and would have increased the lens - sensor distance which would have reduced the focal range of the lens. Furthermore, the filter wheel and camera were disconnected and had manual functionality, which didn't allow one-click multispectral image acquisition.

Design Specifications

The project had two principal design specifications. The first is to use mechanical adaptors in the lens - filter - camera system to ensure that light entering through the lens would be filtered before reaching the sensor. The second is to implement an automated photo-capture system via communication between a computer, Arduino and the camera.

Components

1. Point Grey monochromatic camera with c-mount threading, USB port, GPIO port
2. Wavelength-specific filters, each with c-mount threading
3. Edmund optics Intelligent Filter Wheel (FW) with control box and housing
4. Arduino Mega 2560 Board
5. PC with FlyCap software and SDK