The watershed transformation is a popular image processing algorithm that is used to quickly segment an image into homogenous regions. It relies on the idea that when the image is seen as a topological relief, the homogeneous regions correspond to relatively flat basins delimited by steep edges. As a result of its simplicity, the original version of this algorithm tends to over-segment the image, which produces multiple small regions. This is why OpenCV proposes a variant of this algorithm that uses a set of predefined markers that guide the definition of the image segments.
The watershed segmentation is obtained through the use of the cv::watershed function. The input for this function is a 32-bit signed integer-marker image in which each nonzero pixel represents a label. The idea is to mark some pixels of the image that are known to belong to a given region. From this initial labeling, the watershed algorithm will determine the regions to...
