全文共6821字，預(yù)計(jì)學(xué)習(xí)時(shí)長(zhǎng)20分鐘

來(lái)源：Pexels

從自動(dòng)駕駛汽車檢測(cè)路上的物體，到通過(guò)復(fù)雜的面部及身體語(yǔ)言識(shí)別發(fā)現(xiàn)可能的犯罪活動(dòng)。多年來(lái)，研究人員一直在探索讓機(jī)器通過(guò)視覺識(shí)別物體的可能性。

這一特殊領(lǐng)域被稱為計(jì)算機(jī)視覺 (Computer Vision, CV)，在現(xiàn)代生活中有著廣泛的應(yīng)用。

目標(biāo)檢測(cè) (ObjectDetection) 也是計(jì)算機(jī)視覺最酷的應(yīng)用之一，這是不容置疑的事實(shí)。

現(xiàn)在的CV工具能夠輕松地將目標(biāo)檢測(cè)應(yīng)用于圖片甚至是直播視頻。本文將簡(jiǎn)單地展示如何用TensorFlow創(chuàng)建實(shí)時(shí)目標(biāo)檢測(cè)器。

建立一個(gè)簡(jiǎn)單的目標(biāo)檢測(cè)器

設(shè)置要求：

TensorFlow版本在1.15.0或以上

執(zhí)行pip install TensorFlow安裝最新版本

一切就緒，現(xiàn)在開始吧！

設(shè)置環(huán)境

第一步：從Github上下載或復(fù)制TensorFlow目標(biāo)檢測(cè)的代碼到本地計(jì)算機(jī)

在終端運(yùn)行如下命令：

git clonehttps://github.com/tensorflow/models.git

第二步：安裝依賴項(xiàng)

下一步是確定計(jì)算機(jī)上配備了運(yùn)行目標(biāo)檢測(cè)器所需的庫(kù)和組件。

下面列舉了本項(xiàng)目所依賴的庫(kù)。（大部分依賴都是TensorFlow自帶的）

· Cython

· contextlib2

· pillow

· lxml

· matplotlib

若有遺漏的組件，在運(yùn)行環(huán)境中執(zhí)行pip install即可。

第三步：安裝Protobuf編譯器

谷歌的Protobuf，又稱Protocol buffers，是一種語(yǔ)言無(wú)關(guān)、平臺(tái)無(wú)關(guān)、可擴(kuò)展的序列化結(jié)構(gòu)數(shù)據(jù)的機(jī)制。Protobuf幫助程序員定義數(shù)據(jù)結(jié)構(gòu)，輕松地在各種數(shù)據(jù)流中使用各種語(yǔ)言進(jìn)行編寫和讀取結(jié)構(gòu)數(shù)據(jù)。

Protobuf也是本項(xiàng)目的依賴之一。點(diǎn)擊這里了解更多關(guān)于Protobufs的知識(shí)。接下來(lái)把Protobuf安裝到計(jì)算機(jī)上。

打開終端或者打開命令提示符，將地址改為復(fù)制的代碼倉(cāng)庫(kù)，在終端執(zhí)行如下命令：

cd models/research \

wget -Oprotobuf.zip https://github.com/protocolbuffers/protobuf/releases/download/v3.9.1/protoc-3.9.1-osx-x86_64.zip\

unzipprotobuf.zip

注意：請(qǐng)務(wù)必在models/research目錄解壓protobuf.zip文件。來(lái)源：Pexels

第四步：編輯Protobuf編譯器

從research/ directory目錄中執(zhí)行如下命令編輯Protobuf編譯器：

./bin/protoc object_detection/protos/*.proto--python_out=.

用Python實(shí)現(xiàn)目標(biāo)檢測(cè)

現(xiàn)在所有的依賴項(xiàng)都已經(jīng)安裝完畢，可以用Python實(shí)現(xiàn)目標(biāo)檢測(cè)了。

在下載的代碼倉(cāng)庫(kù)中，將目錄更改為：

models/research/object_detection

這個(gè)目錄下有一個(gè)叫object_detection_tutorial.ipynb的ipython notebook。該文件是演示目標(biāo)檢測(cè)算法的demo，在執(zhí)行時(shí)會(huì)用到指定的模型：

ssd_mobilenet_v1_coco_2017_11_17

這一測(cè)試會(huì)識(shí)別代碼庫(kù)中提供的兩張測(cè)試圖片。下面是測(cè)試結(jié)果之一：

要檢測(cè)直播視頻中的目標(biāo)還需要一些微調(diào)。在同一文件夾中新建一個(gè)Jupyter notebook，按照下面的代碼操作：

[1]:

import numpy as np

import os

import six.moves.urllib as urllib

import sys

import tarfile

import tensorflow as tf

import zipfile

from distutils.version import StrictVersion

from collections import defaultdict

from io import StringIO

from matplotlib import pyplot as plt

from PIL import Image

# This isneeded since the notebook is stored in the object_detection folder.

sys.path.append("..")

from utils import ops as utils_ops

if StrictVersion(tf.__version__) < StrictVersion('1.12.0'):

raise ImportError('Please upgrade your TensorFlow installation to v1.12.*.')

[2]:

# This isneeded to display the images.

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

[3]:

# Objectdetection imports

# Here arethe imports from the object detection module.

from utils import label_map_util

from utils import visualization_utils as vis_util

[4]:

# Modelpreparation

# Anymodel exported using the `export_inference_graph.py` tool can be loaded heresimply by changing `PATH_TO_FROZEN_GRAPH` to point to a new .pb file.

# Bydefault we use an "SSD with Mobilenet" model here.

#See https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/detection_model_zoo.md

#for alist of other models that can be run out-of-the-box with varying speeds andaccuracies.

# Whatmodel to download.

MODEL_NAME= 'ssd_mobilenet_v1_coco_2017_11_17'

MODEL_FILE= MODEL_NAME + '.tar.gz'

DOWNLOAD_BASE= 'http://download.tensorflow.org/models/object_detection/'

# Path tofrozen detection graph. This is the actual model that is used for the objectdetection.

PATH_TO_FROZEN_GRAPH= MODEL_NAME + '/frozen_inference_graph.pb'

# List ofthe strings that is used to add correct label for each box.

PATH_TO_LABELS= os.path.join('data', 'mscoco_label_map.pbtxt')

[5]:

#DownloadModel

opener =urllib.request.URLopener()

opener.retrieve(DOWNLOAD_BASE+ MODEL_FILE, MODEL_FILE)

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())

[6]:

# Load a(frozen) Tensorflow model into memory.

detection_graph= tf.Graph()

with detection_graph.as_default():

od_graph_def= tf.GraphDef()

withtf.gfile.GFile(PATH_TO_FROZEN_GRAPH, 'rb') as fid:

serialized_graph= fid.read()

od_graph_def.ParseFromString(serialized_graph)

tf.import_graph_def(od_graph_def,name='')

[7]:

# Loadinglabel map

# Labelmaps map indices to category names, so that when our convolution networkpredicts `5`,

#we knowthat this corresponds to `airplane`. Here we use internal utilityfunctions,

#butanything that returns a dictionary mapping integers to appropriate stringlabels would be fine

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

[8]:

defrun_inference_for_single_image(image, graph):

with graph.as_default():

with tf.Session() as sess:

# Get handles to input and output tensors

ops= tf.get_default_graph().get_operations()

all_tensor_names= {output.name for op in ops for output in op.outputs}

tensor_dict= {}

for key in [

'num_detections', 'detection_boxes', 'detection_scores',

'detection_classes', 'detection_masks']:

tensor_name= key + ':0'

if tensor_name in all_tensor_names:

tensor_dict[key]= tf.get_default_graph().get_tensor_by_name(tensor_name)

if'detection_masks'in tensor_dict:

# The following processing is only for single image

detection_boxes= tf.squeeze(tensor_dict['detection_boxes'], [0])

detection_masks= tf.squeeze(tensor_dict['detection_masks'], [0])

# Reframe is required to translate mask from boxcoordinates to image coordinates and fit the image size.

real_num_detection= tf.cast(tensor_dict['num_detections'][0], tf.int32)

detection_boxes= tf.slice(detection_boxes, [0, 0], [real_num_detection, -1])

detection_masks= tf.slice(detection_masks, [0, 0, 0], [real_num_detection, -1, -1])

detection_masks_reframed= utils_ops.reframe_box_masks_to_image_masks(

detection_masks,detection_boxes, image.shape[1],image.shape[2])

detection_masks_reframed= tf.cast(

tf.greater(detection_masks_reframed,0.5),tf.uint8)

# Follow the convention by adding back the batchdimension

tensor_dict['detection_masks'] =tf.expand_dims(

detection_masks_reframed,0)

image_tensor= tf.get_default_graph().get_tensor_by_name('image_tensor:0')

# Run inference

output_dict= sess.run(tensor_dict, feed_dict={image_tensor: image})

# all outputs are float32 numpy arrays, so convert typesas appropriate

output_dict['num_detections'] =int(output_dict['num_detections'][0])

output_dict['detection_classes'] =output_dict[

'detection_classes'][0].astype(np.int64)

output_dict['detection_boxes'] =output_dict['detection_boxes'][0]

output_dict['detection_scores'] =output_dict['detection_scores'][0]

if'detection_masks'in output_dict:

output_dict['detection_masks'] =output_dict['detection_masks'][0]

return output_dict

[9]:

import cv2

cam =cv2.cv2.VideoCapture(0)

rolling = True

while (rolling):

ret,image_np = cam.read()

image_np_expanded= np.expand_dims(image_np, axis=0)

# Actual detection.

output_dict= run_inference_for_single_image(image_np_expanded, detection_graph)

# Visualization of the results of a detection.

vis_util.visualize_boxes_and_labels_on_image_array(

image_np,

output_dict['detection_boxes'],

output_dict['detection_classes'],

output_dict['detection_scores'],

category_index,

instance_masks=output_dict.get('detection_masks'),

use_normalized_coordinates=True,

line_thickness=8)

cv2.imshow('image', cv2.resize(image_np,(1000,800)))

if cv2.waitKey(25) & 0xFF == ord('q'):

break

cv2.destroyAllWindows()

cam.release()

在運(yùn)行Jupyter notebook時(shí)，網(wǎng)絡(luò)攝影系統(tǒng)會(huì)開啟并檢測(cè)所有原始模型訓(xùn)練過(guò)的物品類別。來(lái)源：Pexels

感謝閱讀本文，如果有什么建議，歡迎在評(píng)論區(qū)積極發(fā)言喲~

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