Function bottomHat

This function is the black top hat (also called bottom hat). In mathematical morphology and digital image processing, top-hat transform is an operation that extracts small elements and details from given images. The black top-hat transform is defined dually as the difference between the closed and the input image. Top-hat transforms are used for various image processing tasks, such as feature extraction, background equalization, image enhancement, and others. (Wikipedia)

See

http://docs.opencv.org/2.4/doc/tutorials/imgproc/opening_closing_hats/opening_closing_hats.html

This function is the black top hat (also called bottom hat). In mathematical morphology and digital image processing, top-hat transform is an operation that extracts small elements and details from given images. The black top-hat transform is defined dually as the difference between the closed and the input image. Top-hat transforms are used for various image processing tasks, such as feature extraction, background equalization, image enhancement, and others. (Wikipedia)

See

http://docs.opencv.org/2.4/doc/tutorials/imgproc/opening_closing_hats/opening_closing_hats.html