OpenCV3.3で公式にサポートされたDNN(深層ニューラルネットワーク)モジュールの
Python版mobilenetサンプルを動作させてみました。

学習済みモデルは以下URLにあるはずだが、リンク切れていたため、
　https://github.com/chuanqi305/MobileNet-SSD/blob/master/MobileNetSSD_train.caffemodel
ひとまず、以下のURLから取得。
　https://drive.google.com/file/d/0BwY-lpO6tzxHRHNCdlRKczIzaEU/view?usp=sharing

動画は以下。
CPUのみでもそこそこ動く。
https://www.youtube.com/watch?v=Wg_NU0rYkMI

ソースコードは以下。
基本的には、「opencv\sources\samples\dnn\mobilenet_ssd_python.py」と同じ。
自分の環境構築が悪いのか、そのままで動作しなかったところを一部修正。


# !/usr/bin/env python
# -*- coding: utf-8 -*-

import numpy as np
import argparse

try:
    #import cv2 as cv
    import cv2                #[修正] cv2呼び出ししているため、as cvを削除
    from cv2 import dnn       #[修正] dnnモジュールをインポート
except ImportError:
    raise ImportError('Can\'t find OpenCV Python module. If you\'ve built it from sources without installation, '
                      'configure environemnt variable PYTHONPATH to "opencv_build_dir/lib" directory (with "python3" subdirectory if required)')

inWidth = 300
inHeight = 300
WHRatio = inWidth / float(inHeight)
inScaleFactor = 0.007843
meanVal = 127.5

classNames = ('background',
              'aeroplane', 'bicycle', 'bird', 'boat',
              'bottle', 'bus', 'car', 'cat', 'chair',
              'cow', 'diningtable', 'dog', 'horse',
              'motorbike', 'person', 'pottedplant',
              'sheep', 'sofa', 'train', 'tvmonitor')

if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("--video", help="path to video file. If empty, camera's stream will be used")
    parser.add_argument("--prototxt", default="MobileNetSSD_300x300.prototxt",
                        help="path to caffe prototxt")
    parser.add_argument("-c", "--caffemodel", help="path to caffemodel file, download it here: "
                             "https://github.com/chuanqi305/MobileNet-SSD/blob/master/MobileNetSSD_train.caffemodel")
    parser.add_argument("--thr", default=0.2, help="confidence threshold to filter out weak detections")
    args = parser.parse_args()

    net = dnn.readNetFromCaffe(args.prototxt, args.caffemodel)

    #if len(args.video):      #[修正] --video未指定時にlen()で長さ取得できないはずなので修正
    if args.video != None:
        cap = cv2.VideoCapture(args.video)
    else:
        cap = cv2.VideoCapture(0)

    while True:
        # Capture frame-by-frame
        ret, frame = cap.read()
        blob = dnn.blobFromImage(frame, inScaleFactor, (inWidth, inHeight), meanVal)
        net.setInput(blob)
        detections = net.forward()
        
        cols = frame.shape[1]
        rows = frame.shape[0]
        
        if cols / float(rows) > WHRatio:
            cropSize = (int(rows * WHRatio), rows)
        else:
            cropSize = (cols, int(cols / WHRatio))
        
        y1 = (rows - cropSize[1]) / 2
        y2 = y1 + cropSize[1]
        x1 = (cols - cropSize[0]) / 2
        x2 = x1 + cropSize[0]
        frame = frame[y1:y2, x1:x2]
        
        cols = frame.shape[1]
        rows = frame.shape[0]
        
        for i in range(detections.shape[2]):
            confidence = detections[0, 0, i, 2]
            if confidence > args.thr:
                class_id = int(detections[0, 0, i, 1])
        
                xLeftBottom = int(detections[0, 0, i, 3] * cols)
                yLeftBottom = int(detections[0, 0, i, 4] * rows)
                xRightTop   = int(detections[0, 0, i, 5] * cols)
                yRightTop   = int(detections[0, 0, i, 6] * rows)
        
                cv2.rectangle(frame, (xLeftBottom, yLeftBottom), (xRightTop, yRightTop),
                              (0, 255, 0))
                label = classNames[class_id] + ": " + str(confidence)
                labelSize, baseLine = cv2.getTextSize(label, cv2.FONT_HERSHEY_SIMPLEX, 0.5, 1)
        
                cv2.rectangle(frame, (xLeftBottom, yLeftBottom - labelSize[1]),
                                     (xLeftBottom + labelSize[0], yLeftBottom + baseLine),
                                     (255, 255, 255), cv2.FILLED)
                cv2.putText(frame, label, (xLeftBottom, yLeftBottom),
                            cv2.FONT_HERSHEY_SIMPLEX, 0.5, (0, 0, 0))

        cv2.imshow("detections", frame)
        if cv2.waitKey(1) >= 0:
            break

以上。