Multispectral cameras render precise colors
APRIL 15--Accurate reproduction of colors in digital images for applications such as remote sensing, machine vision, and fluorescence imaging requires the use of multispectral imaging systems. Using cameras that sample light from objects through multiple spectral bands, these systems reproduce more accurate color images than when broadcast-standard color cameras are used.
For applications that demand greater resolution and dynamic range, Integrated Scientific Imaging (ISI; Santa Barbara, CA) has developed the CCD800 and CCD1600 cameras. Designed for low-light imaging, including fluorescence, confocal, and electron microscopy, the cameras use KAF1602E and KAF0401 CCDs from Eastman Kodak (Rochester, NY) to attain resolutions of 1024 x 1536 pixels and 512 x 768 pixels, respectively, and a dynamic range of 14 bits. With a built-in eight-position filter wheel that supports automated tricolor or multispectral imaging, both cameras can be controlled by a PC or laptop using an I/O interface card or a PCMCIA interface.
Because such filter-wheel designs use single image sensors to capture multispectral images, they are limited to applications where higher inspection rates are required. To overcome this limitation, several companies, including DuncanTech (Auburn, CA) and TVI Vision (Helsinki, Finland), have developed color cameras that use a color-separating prism to split the broadband light entering the camera through the lens into three optical channels. An optical trim filter and a CCD imaging array are then placed at each of the three exit planes of the prism.
Based on this technology, the DuncanTech MS4100 camera features three 1920 x 1080-pixel CCD imaging sensors, a rate of 5 frames/s, and a Camera Link interface. In addition to capturing RGB images, the camera can be configured with separate filters to acquire red, green, and near-infrared bands that approximate the Landsat satellite bands.
Multiple lenses, detectors, and filters are also being used in other multispectral camera designs. For example, Tetracam (Chatsworth, CA) has developed a Multiple Camera Array (MCA) camera that consists of up to four sensor channels, each of which has a detector/bandpass filter/lens mounted in a common optical block. Built as C-mount cameras, the MCA allows interchangeable lenses and customer-designated pass-band filters. The camera system can be supplied with an embedded global positioning system (GPS) receiver that permits operation with GPS-triggering software to trap the current GPS data string with each image.
For more on this, see Vision Systems Design, April 2002.