| Summary: | 碩士 === 國立臺灣科技大學 === 資訊工程系 === 97 === Recently, an efficient algorithm based on global thresholding scheme
(GTS) was presented which uses the ratio value of the hue over the
intensity to construct the ratio map for detecting shadows of color
aerial images. Instead of only using the GTS, this thesis presents a
novel successive thresholding scheme (STS) to detect shadows more
accurately. In the proposed STS, the modified ratio map, which is
obtained by applying the exponential function to the ratio map used
in the GTS-based algorithm, is presented to stretch the gap between
the ratio values of shadow-pixels and non-shadow-pixels. By
performing the global thresholding process on the modified ratio
map, a coarse-shadow map is constructed to classify the input color
aerial image into the candidate shadow-pixels and the
non-shadow-pixels. In order to detect the true shadow-pixels from
the candidate shadow-pixels, the connected component process is
first applied to the candidate shadow-pixels for grouping the
candidate shadow regions. For each candidate shadow region, the
local thresholding process is performed iteratively to extract the
true shadow-pixels from the candidate shadow region. Finally, for
the remaining candidate shadow regions, a fine-shadow determination
process is applied to identify whether each remaining candidate
shadow-pixel is the true shadow-pixel or not. Under six testing
images, experimental results show that for the first three testing
images, the shadow detection accuracy of the proposed STS-based
algorithm is comparable to the GTS-based algorithm. For the other
three testing images which contain some low brightness objects, the
STS-based algorithm has better shadow detection accuracy when
compared to the GTS-based algorithm.
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