Reflectance Images from Image Sequences

Weiss (2001) describes how a reflectance image may be obtained from an image sequence taken with a stationary camera. Obviously, if the camera is stationary and no moving objects 

If the illuminant is constant, we can remove the influence of the illuminant by computing the first derivative. This works if two neighboring pixels have the same illuminant. If two neighboring pixels have a different illuminant, then we probably have a shadow edge between the two pixels. Weiss suggests simply applying a median filter to the first derivatives to eliminate the influence of the illuminant. 

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Fig. 25.3 Time sequence of droplet formation in response to one pulse (Vp = 29 V). The ink is ejected rightward, and the vertical line shows the location of orifice. Meniscus distortion appears at t 30 is. Mirror images due to reflection from the printhead are visible on the right side of the orifice. Images from a solid ink printhead (Phaser 860 provided by Xerox Corporation, Rochester, NY) with orifice diameter of 20 pm (Reproduced from [28]. With permission. Copyright 2008)...

Fig. 3.43a, b. BOLD sequence on a normally functioning renal graft. The coronal Tlw gradient echo image shows the normal cortico-medullary differentiation. On the calculated R2 map, higher values of R2 are displayed in the medulla reflecting lower pOj. [Reprinted with permission from Sadowski et al. (2005) Radiology 236 911-919]... 

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