Sensor sharpening

Barnard K, Ciurea F and Funt B 2001 Sensor sharpening for computational color constancy. Journal of the Optical Society of America A 18(11), 2728-2743. 

The sensor s response characteristics can often be approximated by delta functions (Finlayson and Hordley 2001b). Even though each sensor responds to a range of wavelengths, in practice they are either close enough to delta functions or they can be sharpened (Barnard et al. 2001 Finlayson and Funt 1996 Finlayson et al. 1994a,b) such that this assumption is approximately correct. Assuming that the sensor s response characteristics can be described by delta functions, we have... 

Finlayson and Hordley (2001 a,b) have developed a method for color constancy at a pixel. They make two assumptions. One that the camera s sensors are sufficiently narrow band and that the illuminant can be approximated by a black-body radiator. If the sensor s response functions are not sufficiently narrow band, a sharpening technique can be used (Barnard et al. 2001 Finlayson and Funt 1996 Finlayson et al. 1994a,b). The power spectrum of a black-body radiator was described in Section 3.5. The radiance of a black-body radiator at a temperature T, measured in Kelvin, at wavelength /. is given by (Haken and Wolf 1990 ... 

A three-step procedure is used in sensor fabrication. First, the carbon fiber is sharpened using a microbumer. In... 

Figure 9. Microscopic photograph of a carbon fiber (a), Eiectron scanning micrograph (ESM) of the part of the sensor covered with a coat of isolating wax-rosin mixture (b), ESM of a thermally sharpened tip covered with polymeric TMHPPNi (c). (Reprinted with permission from Malinski T, Taha Z. Nature, 1992, 3S8 676)...

This technique employs a single thermistor serving as both a temperature sensor and a heater. Typically in this technique, either a thermistor is inserted through the lumen of a hypodermic needle, which is in turn inserted into the tissue, or the thermistor is embedded in a glass-fiber-reinforced epoxy shaft. Figure 2.4 shows the structure of a thermistor bead probe embedded in an epoxy shaft. Each probe can consist of one or two small thermistor beads situated at the end or near the middle of the epoxy shaft. The diameter of the finished probe is typically 0.3 mm, and the length can vary as desired. Because the end can be sharpened to a point, it is capable of piercing most tissues with very minimal trauma. 

Fig. 7 Intensity peaks around the dark edges (pointed out by the red arrows) introduced by the sharpening algorithms of the image sensor...

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