Shadow Removal from Image of Stained Glass Windows

Shadows may be formed on stained glass windows by structural bars supporting the leaded panels, or by external protective wire grilles, or by masonry, such as mullions or buttresses, or external objects, such as trees. The eye tends to "discount" such shadow formations when viewing the actual windows even though in the photographic images they are very clearly visible. This article introduces a method to remove shadow effects on stained-glass windows; the observed image, as captured by the camera, may be modeled mathematically as a combination of a "true stained glass image" and a "grille/bar image." A mixture model is derived, based on a theoretical model of image formation, leading to a conjectured relationship between "shadow" pixels and the neighboring "nonshadow" pixels. The resulting mixture model assumes a multiplicative relationship. If this mixture can be separated into its original components, then it should be possible to remove the unwanted shadow component from the captured image to produce the desired image of the stained glass without the shadows. The digital modeling techniques enable the shadows to be characterized and removed with a reasonable degree of success. (C) 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 223-236, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/ima.20241