Changed the evaluate_detectors() routine so that it applies non-max suppression

to each detector individually.  This way one detector doesn't stomp on the
output of another detector.

dlib/image_processing/scan_fhog_pyramid.h

@@ -814,7 +814,9 @@ namespace dlib
         {
             for (unsigned long i = 0; i < rects.size(); ++i)
             {
-                if (tester(rects[i].rect, rect.rect))
+                // Only compare detections from the same detector.  That is, we don't want
+                // the output of one detector to stop on the output of another detector. 
+                if (rects[i].weight_index == rect.weight_index && tester(rects[i].rect, rect.rect))
                     return true;
             }
             return false;

dlib/image_processing/scan_fhog_pyramid_abstract.h

@@ -723,8 +723,9 @@ namespace dlib
               the same cell_size parameter that determines how HOG features are computed.
               If different cell_size values are used then this function will not be any
               faster than running the detectors individually.
-            - This function applies non-max suppression to the outputs from all detectors
-              and therefore none of the outputs will overlap with each other.
+            - This function applies non-max suppression individually to the output of each
+              detector.  Therefore, the output is the same as if you ran each detector
+              individually and then concatenated the results. 
             - To be precise, this function performs object detection on the given image and
               stores the detected objects into #dets.  In particular, we will have that:
                 - #dets is sorted such that the highest confidence detections come first.

dlib/test/object_detector.cpp

@@ -11,6 +11,7 @@
 #include <dlib/pixel.h>
 #include <dlib/svm_threaded.h>
 #include <dlib/array.h>
+#include <dlib/set_utils.h>
 #include <dlib/array2d.h>
 #include <dlib/image_keypoint.h>
 #include <dlib/image_processing.h>
@@ -414,11 +415,20 @@ namespace
             std::vector<rectangle> dets1 = evaluate_detectors(detectors, images[0]);
             std::vector<rectangle> dets2 = detector(images[0]);
             DLIB_TEST(dets1.size() > 0);
-            DLIB_TEST(dets2.size() == dets1.size());
+            DLIB_TEST(dets2.size()*3 == dets1.size());
+            dlib::set<rectangle>::kernel_1a_c d1, d2;
             for (unsigned long i = 0; i < dets1.size(); ++i)
             {
-                DLIB_TEST(dets1[i] == dets2[i]);
+                if (!d1.is_member(dets1[i]))
+                    d1.add(dets1[i]);
             }
+            for (unsigned long i = 0; i < dets2.size(); ++i)
+            {
+                if (!d2.is_member(dets2[i]))
+                    d2.add(dets2[i]);
+            }
+            DLIB_TEST(d1.size() == d2.size());
+            DLIB_TEST(set_intersection_size(d1,d2) == d1.size());
         }
     }