Mathematical morphology applied to shadows and clouds detection in high resolution images

Abstract

The spatial resolution improvement of orbital sensors has broadened considerably
the applicability of their images in solving urban areas problems. But as the spatial
resolution improves, the shadows become even a more serious problem especially
when detailed information (under the shadows) is required. Besides those shadows
caused by buildings and houses, clouds projected shadows are likely to occur. In
this case there is information occlusion by the cloud in association with low
illumination and contrast areas caused by the cloud shadow on the ground. Thus,
it’s important to use efficient methods to detect shadows and clouds areas in digital
images taking in count that these areas care for especial processing. This paper
proposes the application of Mathematical Morphology (MM) in shadow and clouds
detection. Two parts of a panchromatic QuickBird image of Cuiabá-MT urban area
were used. The proposed method takes advantage of the fact that shadows (low
intensity – dark areas) and clouds (high intensity – bright areas) represent the
bottom and top, respectively, of the image as it is thought to be a topographic
surface. This characteristic allowed MM area opening and closing operations to be
applied to reduce or eliminate the bottom and top of the topographic surface.