I did some performance tests on the four histograms comparison methods that [compareHist](http://docs.opencv.org/java/org/opencv/imgproc/Imgproc.html#compareHist(org.opencv.core.Mat, org.opencv.core.Mat, int)) provides and initially found that in basic performance tests they were all about the same speed. More recently I profiled them in a real world application and found they were significantly different.

This is all using the Java OpenCV bindings.