train_object_detector.py

#!/usr/bin/python
# The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
#
#   This example program shows how you can use dlib to make an object detector
#   for things like faces, pedestrians, and any other semi-rigid object.  In
#   particular, we go though the steps to train the kind of sliding window
#   object detector first published by Dalal and Triggs in 2005 in the paper
#   Histograms of Oriented Gradients for Human Detection.  
#
#
# COMPILING THE DLIB PYTHON INTERFACE
#   Dlib comes with a compiled python interface for python 2.7 on MS Windows.  If
#   you are using another python version or operating system then you need to
#   compile the dlib python interface before you can use this file.  To do this,
#   run compile_dlib_python_module.bat.  This should work on any operating system
#   so long as you have CMake and boost-python installed.  On Ubuntu, this can be
#   done easily by running the command:  sudo apt-get install libboost-python-dev cmake

import dlib, sys, glob
from skimage import io

# In this example we are going to train a face detector based on the small
# faces dataset in the examples/faces directory.  This means you need to supply
# the path to this faces folder as a command line argument so we will know
# where it is.
if (len(sys.argv) != 2):
    print "Give the path to the examples/faces directory as the argument to this"
    print "program.  For example, if you are in the python_examples folder then "
    print "execute this program by running:"
    print "  ./train_object_detector.py ../examples/faces"
    exit(1)
faces_folder = sys.argv[1]


# Now let's do the training.  The train_simple_object_detector() function has a
# bunch of options, all of which come with reasonable default values.  The next
# few lines goes over some of these options.
options = dlib.simple_object_detector_training_options()
# Since faces are left/right symmetric we can tell the trainer to train a
# symmetric detector.  This helps it get the most value out of the training
# data.
options.add_left_right_image_flips = True
# The trainer is a kind of support vector machine and therefore has the usual
# SVM C parameter.  In general, a bigger C encourages it to fit the training
# data better but might lead to overfitting.  You must find the best C value
# empirically by checking how well the trained detector works on a test set of
# images you haven't trained on.  Don't just leave the value set at 5.  Try a
# few different C values and see what works best for your data.
options.C = 5 
# Tell the code how many CPU cores your computer has for the fastest training.
options.num_threads = 4
options.be_verbose = True 

# This function does the actual training.  It will save the final detector to
# detector.svm.  The input is an XML file that lists the images in the training
# dataset and also contains the positions of the face boxes.  To create your
# own XML files you can use the imglab tool which can be found in the
# tools/imglab folder.  It is a simple graphical tool for labeling objects in
# images with boxes.  To see how to use it read the tools/imglab/README.txt
# file.  But for this example, we just use the training.xml file included with
# dlib.
dlib.train_simple_object_detector(faces_folder+"/training.xml","detector.svm", options)



# Now that we have a face detector we can test it.  The first statement tests
# it on the training data.  It will print the precision, recall, and then
# average precision.
print "\ntraining accuracy:", dlib.test_simple_object_detector(faces_folder+"/training.xml", "detector.svm")
# However, to get an idea if it really worked without overfitting we need to
# run it on images it wasn't trained on.  The next line does this.  Happily, we
# see that the object detector works perfectly on the testing images.
print "testing accuracy: ", dlib.test_simple_object_detector(faces_folder+"/testing.xml", "detector.svm")



# Now let's use the detector as you would in a normal application.  First we
# will load it from disk.
detector = dlib.simple_object_detector("detector.svm")

# We can look at the HOG filter we learned.  It should look like a face.  Neat!
win_det = dlib.image_window()
win_det.set_image(detector)

# Now let's run the detector over the images in the faces folder and display the
# results.
print "\nShowing detections on the images in the faces folder..."
win = dlib.image_window()
for f in glob.glob(faces_folder+"/*.jpg"):
    print "processing file:", f
    img = io.imread(f)
    dets = detector(img)
    print "number of faces detected:", len(dets)
    for d in dets:
        print "  detection position left,top,right,bottom:", d.left(), d.top(), d.right(), d.bottom()

    win.clear_overlay()
    win.set_image(img)
    win.add_overlay(dets)
    raw_input("Hit enter to continue")