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opencv数学运算,图像加减乘除https://blog.csdn.net/u011028345/article/details/77278467

findcontours

• CV_RETR_EXTERNAL retrieves only the extreme outer contours. It sets hierarchy[i][2]=hierarchy[i][3]=-1 for all the contours.
• CV_RETR_LIST retrieves all of the contours without establishing any hierarchical relationships.
• CV_RETR_CCOMP retrieves all of the contours and organizes them into a two-level hierarchy. At the top level, there are external boundaries of the components. At the second level, there are boundaries of the holes. If there is another contour inside a hole of a connected component, it is still put at the top level.
• CV_RETR_TREE retrieves all of the contours and reconstructs a full hierarchy of nested contours. This full hierarchy is built and shown in the OpenCV contours.c demo.
  What is the retrieval method RETR_FLOODFILL?
• connected components of a multi-level image