![]() The spectral discrimination of colored glass filters is due to the selection of dopants added to glass material. To properly incorporate filters into a system, designers must understand the advantages and limitations of each type of filter. Neutral density and polarization filters can also improve performance for specific imaging scenarios. Interference filters provide nanometer-level control over which wavelengths are transmitted and which are not, where the control with colored glass is not nearly as precise. Interference filters also transmit specific ranges of wavelengths but are much more precise than colored glass filters. (b) Typical bandpass and notch transmission curves.Ĭolored glass filters offer an inexpensive solution for improving contrast in some applications, but are limited to applications where objects can be distinguished on the basis of broad spectral characteristics such as separating orange objects from purple ones. (a) Typical shortpass and longpass transmission curves. Within these groups, the types of each filter that are available are dependent upon the technology used to create them for example, colored glass filters are not available in the "notch" variety.įigure 1: Designers have a broad range of filter types at their disposal. ![]() Notch filters are the inverse of bandpass filters, blocking a band of wavelengths and passing the longer and shorter (Figure 1b). (Figure 1a) Bandpass filters transmit a central wavelength band while blocking longer and shorter wavelengths. Shortpass filters are the opposite, passing shorter wavelengths and blocking longer wavelengths. ![]() Longpass filters are designed to block short wavelengths and pass long wavelengths. However, if designers evaluate the spectral characteristics of the objects to be imaged, they may find that filters can improve imaging performance with minimal impact on other design elements - at a very attractive cost.ĭesigners have a range of filter types at their disposal, and they are often defined by the structure of their transmission curves. While designers who need to increase system performance can be tempted to upgrade their lighting or lenses, such options can add significant cost to a machine vision system. The choice of illumination level, aperture size, and lens quality can all increase image contrast and improve system performance. Nicholas Sischka, Optical Engineer, Edmund Optics (Barrington, NJ, USA Obtaining the highest image contrast is probably the most important factor in designing any machine vision system. ![]() Choosing the correct optical filter can improve the contrast of captured images and reduce the processing time needed to extract relevant image data. ![]()
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