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Beyond-visible Light Applications in Computer Vision

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Computer vision systems aren't necessarily restricted to solely analyzing the portion of the electromagnetic spectrum that is visually perceivable by humans. Expanding the analysis range to encompass the infrared and/or ultraviolet spectrum, either broadly or selectively and either solely or in conjunction with visible spectrum analysis, can be of great benefit in a range of visual intelligence applications. Successfully implementing these capabilities in traditional PC-centric hardware and software configurations is challenging enough; doing so in an embedded vision system which has stringent size, weight, cost, power consumption and other constraints is even more difficult. Fortunately, an industry alliance is available to help product creators optimally implement such vision processing in their resource-constrained hardware and software designs.

All objects emit radiation, with the type of radiation emitted primarily dependent on a particular object's temperature. Colder objects emit very low frequency waves (such as radio, microwaves, and infrared radiation), while warmer objects emit visible light or higher frequencies (ultraviolet, for example, or x-rays or gamma radiation). This spectral expanse is called the electromagnetic spectrum (EMS), and consists of all wavelengths from radio waves at the low-frequency end of the range to gamma rays at the high-frequency endpoint (Figure 1).

Figure 1. The electromagnetic spectrum encompasses wavelengths from radio waves to gamma rays, both selectively emitted and absorbed by various objects (courtesy Khan Academy).

Just as different objects emit radiation at different frequencies, different materials also absorb energy at different wavelengths across the EMS. A radio antenna, for example, is designed to capture radio waves, while humans' eyes have evolved to capture visible light. Technology has also evolved to take advantage of both the emission and absorption of EM waves. X-rays, for example, are an efficient means of imaging tissue and bone, because these particular materials exhibit high absorption at these particular wavelengths. Various applications in biology, meteorology and agriculture leverage these same transmission and absorption phenomena, albeit at different wavelengths and with different materials.

Within the EMS is a region known as the solar spectrum. Sunlight (i.e. EM radiation emitted by the sun) encompasses the infrared, visible, and ultraviolet light wavelength portions of the EMS. The solar spectrum is the particular focus of this article, which describes the technology, imaging components, and applications intended for use in these spectra. Figure 2 shows...