New-Tech Europe Magazine | December 2018

Greater Contrast and Improved Vision for Imaging Systems POLARIZATION CAN IMPROVE IMAGE QUALITY IN LOW LIGHT CONDITIONS AND PROVIDE A MAJOR BENEFIT TO VISION APPLICATIONS FRAMOS

Making Invisible Features Visible

Often, lighting conditions and the type of object under inspection prevent vision systems from producing the best possible image. Excessive light, reflections, haze, or shiny materials can have a negative impact on the image quality; therefore, these conditions affect the results of both the image analysis and the inspection. Polarizing filters or sensors reduce the glare; reduce surface reflections; and, increase the clarity of structures, defects, and shapes. The filters eliminate reflections and light refractions, in a manner that is similar to sunglasses. Images as a result, are clearer, more vivid, and have greater contrast. What is Polarization and What Does It Achieve? In physics, light is defined as electromagnetic radiation;

in other words, a wave. The polarization of a wave describes the direction of the amplitude of the electromagnetic field, and the oscillation of the light. A distinction is made between linear, circular, and elliptical polarized waves. Generally, in image processing, polarization refers to linear polarized light. On earth, light is not naturally polarized, and light waves oscillate equally on all planes. Non-polarized light hits objects and surfaces in different states of oscillation and at different angles (see Figure 1). Then, the light can be reflected or scattered, and produces unwanted glare effects, flashes, or patches of light in image processing. These artifacts can impair or conceal important image information and compromise the analysis of captured images, and the inspection of the objects.

Polarizers filter out light waves that move in a specific direction, or on a certain polarization plane. This characteristic corresponds to approximately 50 percent of the unpolarized light reaching an object or surface (see Figure 2). If light is mirrored in a surface, one polarization plane is reflected to a greater extent than the other. A correctly optimized polarizer only allows light which is not being mirrored; therefore, this process clarifies the view of the image. These properties allow polarizing filters to be used for reducing reflections and make the image "behind" the reflections, visible. Figure 3 shows how a polarizer can reveal the rocks below the surface of the water (Annotate Figure 3 and x-ref to Figure 3-KD). Polarizing filters are ideal for both monochrome and

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