本文主要介紹如何基于openCV來(lái)實(shí)現(xiàn)一個(gè)簡(jiǎn)單的貓臉識(shí)別應(yīng)用。

一、基礎(chǔ)準(zhǔn)備

首先需要安裝openCV，因?yàn)?a href="http://www.brongaenegriffin.com/tags/python/" target="_blank">python版的方便點(diǎn)，所以直接安裝python版openCV，通過(guò)命令sudo apt-get install python-opencv即可完成。

linaro@linaro-alip:~$ sudo apt-get install python-opencv
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  liba52-0.7.4 libdca0 libdrm-freedreno1 libdrm-tegra0
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  python-numpy python-pkg-resources
Suggested packages:
  gfortran python-dev python-pytest python-numpy-dbg python-numpy-doc python-setuptools
The following NEW packages will be installed:
  python-numpy python-opencv python-pkg-resources
0 upgraded, 3 newly installed, 0 to remove and 48 not upgraded.
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Get:2 http://mirrors.ustc.edu.cn/debian buster/main arm64 python-numpy arm64 1:1.16.2-1 [1,975 kB]
Get:3 http://mirrors.ustc.edu.cn/debian buster/main arm64 python-opencv arm64 3.2.0+dfsg-6 [478 kB]
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Preparing to unpack .../python-opencv_3.2.0+dfsg-6_arm64.deb ...
Unpacking python-opencv (3.2.0+dfsg-6) ...
Setting up python-pkg-resources (40.8.0-1) ...
Setting up python-numpy (1:1.16.2-1) ...
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安裝完成后檢查下，import cv2沒問(wèn)題就OK了。

linaro@linaro-alip:~$ python
Python 2.7.16 (default, Sep 20 2023, 07:59:17)
[GCC 8.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2
>>> exit()

二、設(shè)計(jì)和實(shí)現(xiàn)

在OpenCV中，目標(biāo)檢測(cè)使用的函數(shù)是cv2.CascadeClassifier.detectMultiScale()，它可以檢測(cè)圖像中所有的目標(biāo)。其完整定義如下：

def detectMultiScale(self, image, scaleFactor=None, minNeighbors=None, flags=None, minSize=None, maxSize=None):

image：待檢測(cè)的圖像，通常為灰度圖像
scaleFactor：表示在前后兩次相繼的掃描中，搜索窗口的縮放比例
minNeighbors：表示構(gòu)成檢測(cè)目標(biāo)的相鄰矩形的最小個(gè)數(shù)。默認(rèn)值為3，表示有3個(gè)以上的檢測(cè)標(biāo)記存在時(shí)，才認(rèn)為目標(biāo)的存在。如果希望提高檢測(cè)的準(zhǔn)確率，可以將該值設(shè)置的更大，但同時(shí)可能會(huì)讓一些目標(biāo)無(wú)法被檢測(cè)到
flags：不常用參數(shù)，一般省略。
minSize：目標(biāo)的最小尺寸，小于這個(gè)尺寸的目標(biāo)將被忽略
maxSize：目標(biāo)的最大尺寸，大于這個(gè)尺寸的目標(biāo)將被忽略
該函數(shù)的返回值是目標(biāo)對(duì)象的矩形框向量組。

OpenCV已經(jīng)自帶了貓臉的Haar特征分類器，本文選擇haarcascade_frontalcatface.xml識(shí)別分類器。

通過(guò)detectMultiScale函數(shù)返回的是貓臉的矩形框向量組，包括左上角坐標(biāo)(x,y)，長(zhǎng)寬(w,h)。而繪制貓臉矩形框則通過(guò)rectangle函數(shù)實(shí)現(xiàn)。

具體實(shí)現(xiàn)python代碼如下：

import cv2 
face_cascade = cv2.CascadeClassifier('haarcascade_frontalcatface.xml') 

img = cv2.imread("./cats.jpg")

# convert to gray 
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY) 

face_rect = face_cascade.detectMultiScale(gray, scaleFactor=1.1, minNeighbors=3)
print("number of cats: ", len(face_rect))

for (x,y,w,h) in face_rect:
    cv2.rectangle(img, (x,y), (x+w, y+h), color=(0,255,0))
cv2.imwrite("cats-1.jpg", img)
cv2.release()

三、運(yùn)行

測(cè)試的圖片是網(wǎng)上隨便下載的。

將圖片、貓臉識(shí)別分類器還有python上傳至幸狐 Core3566 模組，并運(yùn)行python腳本。

只識(shí)別出2只貓咪，看來(lái)有一只的臉不合格，要想識(shí)別出來(lái)，需要在detectMultiScale中調(diào)試參數(shù)，進(jìn)一步提示識(shí)別精準(zhǔn)度，看了看時(shí)間，都快物業(yè)了，這里就不繼續(xù)了，來(lái)個(gè)識(shí)別的結(jié)果。

看來(lái)這個(gè)黑不溜秋的不好識(shí)別。