Function topHat

This function is the white top hat (also called top hat). In mathematical morphology and digital image processing, top-hat transform is an operation that extracts small elements and details from given images. The white top-hat transform is defined as the difference between the input image and its opening by some structuring element. 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 white top hat (also called top hat). In mathematical morphology and digital image processing, top-hat transform is an operation that extracts small elements and details from given images. The white top-hat transform is defined as the difference between the input image and its opening by some structuring element. 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