The major advantage of this method over the pushbroom
technique is that it does not require any moving parts. The
sample is usually illuminated with a diffuse source of NIR
light (for NIR-CI) or dilated laser source (for global
Raman Imaging). Light reflected from the sample is captured
via an imaging optic; for microscopic images a microscope
objective lens is used. The light is then passed
through a filter, which acts as a spectral encoder in this
arrangement, separating images into their spectral components.
Early staring configuration Chemical Images were
obtained using a series of bandpass filters selective to certain
wavelengths of light, which were often mounted on a
wheel for ease of switching.