Please state the information for your system

• OpenCV version: 3.1
• Host OS: Windows 10
• Compiler & CMake: msvc 2013 & CMake 3.4.3

In which part of the OpenCV library you got the issue?

Examples:

• objdetect
• HOGDescriptor::detectMultiScale with useMeanshiftGrouping == false and hitThreshold == 1.01 on an image which includes an rectangle (object) with weight 1.013

Expected behaviour

detectMultiScale return the rectangle with weight 1.013

Actual behaviour

• before HOGDescriptor::groupRectangles gets called in HOGDescriptor::detectMultiScale the variables
  foundLocations and foundWeights include the rectangle with weight 1.013 and are of length 1.
• error: HOGDescriptor::groupRectangle returns empty foundLocations and foundWeights so HOGDescriptor::detectMultiScale returns with empty foundLocations and foundWeights
• if the variable hitThreshold is set to 0, I get a lot of false positive rectangles with my trained HOG detector. These false Positives are roughly equally distributed over the image. HOGDescriptor::groupRectangles returns only one location which is approximately the center of the image.
• What is HOGDescriptor::groupRectangles supposed to do? My proposal is to remove the call to HOGDescriptor::groupRectangles in HOGDescriptor::detectMultiScale when called with useMeanshiftGrouping == false. So the user can do the grouping himself.

Best Regards, Marcel