A lot of applications as well as in the laboratory range and industrial range need a short-wave infrared imaging system. Especially multispectral imaging in that wavelength region are often enable new applications for quality assurance and monitoring of industrial processes. Due to the cost of the SWIR image sensors a multispectral imaging system should be flexible and adjustable to realize a maximum of applications. Normally push broom devices will fulfill these requirements. Disadvantages are that the sample must be moved, the spectral crosstalk and the blurring between the different channels can disturb the processing, and the correctness of spatial resolution along the scanning direction lead to uncertainties for dimensional measurements. For that reasons a twelve-channel filter-based imaging system was designed. A motor driven filter-wheel with a high precision drive will ensure that the filters will be placed in front of a SWIR Image sensor very precisely. To compensate the spectral aberrations along the optical axis a second drive positioning the image sensor into the focus plane. This enable sharp images in all spectral channels as well as high SNR (depends also on the capability of the SWIR Sensor). Furthermore, this implementation allows also to focus without changing the adjustment of the objective lens. A special designed dome light using halogen bulbs delivers very homogeneous radiation on the sample table. For the image readout, the control of the drives as well as the image presentation a software with a graphical user interface was developed. To export the image stacks in 3rd party software the imaging software saves the multispectral images in the envi-format.
Surface inspection in industrial automated processes is very often challenging. Especially the detection of transparent liquid materials such as water represent a major challenge for standard imaging systems. One approach to overcome the limitation of these imaging systems lies in the exploitation of the polarization effect. This effect surely can only be applied if the contaminants have polarizing features but can help to use invisible characteristics of light for quality inspection tasks. In this work investigations on surfaces which are contaminated with water will be presented. Therefore, an imaging system using an RGB dome light illumination was set up in combination with a four-channel polarizing camera. The dome light, which is equipped with three different LED wavelengths, will be mixed so that the illumination which hits the sample is completely unpolarized. So, any effect on the surface which leads to a polarizing effect can be observed. The system delivers a four-channel image with different polarization angles that have to be processed. Therefore, an algorithm realizes a demosaicing which separates the four different polarized pixels into individual images. Based on this, the stokes equation which allows the calculation of the degree of polarization and the angle of polarization has to be processed for the image presentation. To achieve a better visualization of the degree of polarization an HSV-transformation based on the polarization parameters was also realized.
This paper presents the latest developments on filter-wheel based multispectral imaging systems as well as their extension to making 3D images. The system, capable of producing high spatial resolution images on a spectrum spanning from 400nm to 1050nm (in 12 steps of 50nm (configurable) with 50nm or less bandwidth) can be used, without hardware change. To produce 3D image stacks where the height resolution is given by the numerical aperture of the optics used and the reproducibility of the image plane moving motor is also possible. This paper introduces the reader to spectral imaging and to 3D measurement techniques. The main parameters and relevant publications of/about the industrial monocular multispectral 3D-Imager are then presented. Correction of chromatic aberration on filter wheel system, a key idea for 3D image reconstruction, is revised. 3D imaging capabilities of the system as well as proper calibration are introduced. Selected applications and algorithms are presented towards to the end of the paper.
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