TensorFlow Object Detection
merged with grabscreen tutorial

Posted November 06, 2018 by Rokas Balsys

Object detection grab screen tutorial

This is third part of our CS:GO object detection tutorial. In this part we are going to merge jupyter API code from 1-st tutorial with code from 2-nd tutorial where we tested 3 different ways of grabbing screen. From GitHub repository you can download full code.

To begin, we're going to modify the notebook first by converting it to a .py file. If you want to keep it in a notebook, that's fine too. To convert, you can go to file > download as > python file. Once that's done, we're going to comment out the lines we don't need.

Once you have your converted object detection file, go to your TensorFlow installation folder: research\object_detection\data and grab mscoco_label_map.pbtxt file, place it to you working directory.

Next you should download pretrained model from here, I am using faster_rcnn_inception_v2_coco, so I recommend you to use the same, at least at the beginning. Take frozen_inference_graph.pb file and transfer it to your local working repository.

So we begin by importing time, CV2, MSS libraries. If you don't have them, install before moving forward.

I personally imported line to disable CUDA devices, because I wanted to run this example on CPU, because running tensorflow-gpu takes more time to startup in backend.

os.environ['CUDA_VISIBLE_DEVICES'] = '-1'

Then we don't need to import tarfile and import zipfile, because we are not working with these files, so we comment them out now. Going further we comment #from matplotlib import pyplot as plt and #from PIL import Image lines, because we are doing things our way.

Next I am importing few lines from my second tutorial for grabing screen and measuring FPS:

# title of our window
title = "FPS benchmark"
# set start time to current time
start_time = time.time()
# displays the frame rate every 2 second
display_time = 2
# Set primarry FPS to 0
fps = 0
# Load mss library as sct
sct = mss.mss()
# Set monitor size to capture to MSS
monitor = {"top": 40, "left": 0, "width": 800, "height": 640}

Because we are not using notebook anymore we are not using and these lines:


#if StrictVersion(tf.__version__) < StrictVersion('1.9.0'):
#  raise ImportError('Please upgrade your TensorFlow installation to v1.9.* or later!')

We are not using matplotlib to display image, so we are commenting line used for that:

#get_ipython().run_line_magic('matplotlib', 'inline')

There are two lines of import before going to an actual code:

from utils import label_map_util
from utils import visualization_utils as vis_util

But if you will try to use them like this, you will get an error, so add object_detection. before utils, just like this:

from object_detection.utils import label_map_util
from object_detection.utils import visualization_utils as vis_util

Next is links to paths, if you would like to have everything in same folder, just like in my tutorial, comment all these lines:

# What model to download.
MODEL_NAME = 'ssd_mobilenet_v1_coco_2017_11_17'
DOWNLOAD_BASE = 'http://download.tensorflow.org/models/object_detection/'

# Path to frozen detection graph. This is the actual model that is used for the object detection.
PATH_TO_FROZEN_GRAPH = MODEL_NAME + '/frozen_inference_graph.pb'

# List of the strings that is used to add correct label for each box.
PATH_TO_LABELS = os.path.join('data', 'mscoco_label_map.pbtxt')

And replace them with my used path lines (don't forget to add NUM_CLASSES = 99 line)

MODEL_NAME = 'inference_graph'
PATH_TO_FROZEN_GRAPH = 'frozen_inference_graph.pb'
PATH_TO_LABELS = 'mscoco_label_map.pbtxt'

Next you can comment all [6] part, because we won't use it:

#opener = urllib.request.URLopener()
#tar_file = tarfile.open(MODEL_FILE)
#for file in tar_file.getmembers():
#  file_name = os.path.basename(file.name)
#  if 'frozen_inference_graph.pb' in file_name:
#    tar_file.extract(file, os.getcwd())

Next, add 3: label_map, categories and category_index lines before detection_graph code:

label_map = label_map_util.load_labelmap(PATH_TO_LABELS)
categories = label_map_util.convert_label_map_to_categories(label_map, max_num_classes=NUM_CLASSES, use_display_name=True)
category_index = label_map_util.create_category_index(categories)

and in part [8] comment or delete category_index line:

category_index = label_map_util.create_category_index_from_labelmap(PATH_TO_LABELS, use_display_name=True)

Comment all lines in part [7] where images were loaded to numpy array:

#def load_image_into_numpy_array(image):
#  (im_width, im_height) = image.size
#  return np.array(image.getdata()).reshape(
#      (im_height, im_width, 3)).astype(np.uint8)

Next you can delete PATH_TO_TEST_IMAGES_DIR, TEST_IMAGE_PATHS and IMAGE_SIZE lines, but if you will leave them it wound effect our code:

PATH_TO_TEST_IMAGES_DIR = 'test_images'
TEST_IMAGE_PATHS = [ os.path.join(PATH_TO_TEST_IMAGES_DIR, 'image{}.jpg'.format(i)) for i in range(1, 3) ]
IMAGE_SIZE = (12, 8)

At the end of code, not to make any mistakes you can replace all [12] block code with this code:

with detection_graph.as_default():
  with tf.Session(graph=detection_graph) as sess:
    while True:
      # Get raw pixels from the screen, save it to a Numpy array
      image_np = np.array(sct.grab(monitor))
      # to ger real color we do this:
      image_np = cv2.cvtColor(image_np, cv2.COLOR_BGR2RGB)
      #image = Image.open(image_path)
      # the array based representation of the image will be used later in order to prepare the
      # result image with boxes and labels on it.
      #image_np = load_image_into_numpy_array(image)
      # Expand dimensions since the model expects images to have shape: [1, None, None, 3]
      image_np_expanded = np.expand_dims(image_np, axis=0)
      # Actual detection.
      output_dict = run_inference_for_single_image(image_np, detection_graph)
      # Visualization of the results of a detection.
      cv2.imshow(title, cv2.cvtColor(image_np, cv2.COLOR_BGR2RGB))
      TIME = time.time() - start_time
      if (TIME) >= display_time :
        print("FPS: ", fps / (TIME))
        fps = 0
        start_time = time.time()
      # Press "q" to quit
      if cv2.waitKey(25) & 0xFF == ord("q"):

So I tried to use this slow object detection method on image where you can see crowd of people walking across the street:

Crowd walking

And here is the results of frames per second working with TensorFlow CPU version. In average, it is about 7 seconds to receive one frame per second. So if we would like to use it for real time purpose, this would be impossible to do something useful with it. So we need to make it work much faster, we will do this in text tutorial.

FPS Slow

In this tutorial we learned how to export code from object detection API, and how to modify it that it could work in our python shell. Here we used pretrained model for object detection, but now our model works very slow, so in next tutorial we will clean up our code and make our code work much faster.