Multispectral imaging system with interchangeable filter design

The design and calibration of a three-band image acquisition system was reported in this paper. The prototype system developed in this research was a three-band spectral imaging system that acquired two visible-band images and one NIR image simultaneously. This was accomplished by using a three-port imaging system that consisted of three identical monochrome cameras, an optical system, and three interchangeable optical filters. Spectral reflectance from an object was collimated by a front lens, and split in three ways by a cold mirror and beamsplitter: a cold mirror reflects 90% visible light and transmits 80% NIR light. The visible light was again split identically into two directions by an additional beamsplitter. Focusing lenses then projected each image onto its corresponding sensor. By incorporating an interchangeable filter design, the imaging system can measure any two visible spectral bands that range between 400 nm and 700 nm, and one NIR band that ranges between 700 nm and 1000 nm without any complicated manufacturing process. In order to co-register the three images, a system-specific calibration algorithm was developed that compensates for lens–sensor geometric misalignments.The prototype imaging system and the system calibration algorithm were tested and evaluated for image alignment accuracy. The imaging system acquired three-band images of 3D objects with 0.39 pixel misalignment error on average.