Created attachment 266229 [details] [review]
disable maximum object size restriction

Some time ago I found that the facedetect element had stopped finding faces in my videos.  I don't know when, exactly, this happened, but the problem hasn't resolved itself and I was finally motivated to see if I could figure out why.  I think I've identified the cause, or at least I have a patch that fixes it for me locally.

The gst_face_detect_run_detector() function includes an #if/#endif block that adds an extra argument to the cvHaarDetectObjects() call if the libopencv version is >= 2.2.  Checking the documentation at http://docs.opencv.org/modules/objdetect/doc/cascade_classification.html that final argument is described as "maxSize – Maximum possible object size. Objects larger than that are ignored".  The gstreamer facedetect element sets this argument to

cvSize (min_size_width + 2, min_size_height + 2)

i.e., it hard-codes it to 2 pixels larger in width and height than the minimum object size.  This seems to explain why the element can't find faces:  unless the user sets the minimum object size to within a few pixels of the actual size of the faces in the video they will not be found.

I have experimented and found that setting this parameter (0,0) seems to disable the max object size restriction, allowing faces to be detected once again.  This is not documented in the libopencv documentation, so who knows, but I've attached a patch that makes this change.

Note that faceblur hard-codes the maximum object size to 32x32 and also fails to find faces in my videos (which are recorded at 640x480).  I recommend setting the parameter to 0x0 in that element as well.