深入OpenCV Android应用开发中文版 – 第四章代码更新

本书中文版购书链接：京东当当

英文原版购书链接：亚马逊《Mastering OpenCV Android Application Programming》

原书所给代码以章为单位，针对的Android版本从API 19到API 21不等，同时使用的OpenCV库版本也有2.4.9和2.4.10两种。本文给出的代码是在原书代码的基础上，针对Android 7.0（API 24）与OpenCV 3.2进行了修改，适当地增加了一些预处理等操作，以使代码整体上更合理。

原书的完整代码可以在这里获取：https://www.packtpub.com/lcode_download/22299。

更新后的代码托管在GitHub：https://github.com/johnhany/MOAAP/tree/master/MOAAP-Chp4-r3。

关于在Android Studio上配置OpenCV开发环境的方法，请参考《在Android Studio上进行OpenCV 3.1开发》。

本章介绍如何在Android Studio 2上利用OpenCV开发一个人脸检测应用，涉及的算法有Haar级联分类器和LBP级联分类器。关于以上各算法的原理可以参考《深入OpenCV Android应用开发》第四章。

开发环境

Windows 10 x64

Android Studio 2.3.3（Gradle 3.3，Android Plugin 2.3.3）

Android 7.0（API 24）

JDK 8u141

OpenCV 3.2.0 Android SDK

代码及简略解释

1. 创建Android Studio项目，包命名为net.johnhany.moaap_chp4。导入OpenCV-android-sdk\sdk\java到项目中，并为app模块加载模块依赖。

2. 将app\src\main\java\net\johnhany\moaap_chp4\MainActivity.java文件修改为如下内容：

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package net.johnhany.moaap_chp4;

import android.Manifest;

import android.content.Context;

import android.content.pm.PackageManager;

import android.support.annotation.NonNull;

import android.support.v4.app.ActivityCompat;

import android.support.v4.content.ContextCompat;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.util.Log;

import android.view.Menu;

import android.view.MenuItem;

import android.view.SurfaceView;

import android.view.WindowManager;

import android.widget.Toast;

import org.opencv.android.CameraBridgeViewBase;

import org.opencv.android.OpenCVLoader;

import org.opencv.core.Core;

import org.opencv.core.CvType;

import org.opencv.core.Mat;

import org.opencv.android.BaseLoaderCallback;

import org.opencv.android.LoaderCallbackInterface;

import org.opencv.core.MatOfRect;

import org.opencv.core.Rect;

import org.opencv.core.Scalar;

import org.opencv.core.Size;

import org.opencv.imgproc.Imgproc;

import org.opencv.objdetect.CascadeClassifier;

import java.io.File;

import java.io.FileOutputStream;

import java.io.InputStream;

public class MainActivity extends AppCompatActivity implements CameraBridgeViewBase.CvCameraViewListener2 {

private static final String TAG = "OCVSample::Activity";

private CameraBridgeViewBase mOpenCvCameraView;

private boolean mIsFrontCamera = false;

private MenuItem mItemSwitchCamera = null;

private Mat mRgba;

private CascadeClassifier haarCascade;

static int REQUEST_CAMERA = 0;

static boolean read_external_storage_granted = false;

private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {

@Override

public void onManagerConnected(int status) {

switch (status) {

case LoaderCallbackInterface.SUCCESS:

{

Log.i(TAG, "OpenCV成功加载");

try{

InputStream is = getResources().openRawResource(R.raw.haarcascade_frontalface_alt2);

File cascadeDir = getDir("cascade",

Context.MODE_PRIVATE);

File mCascadeFile = new File(cascadeDir,"cascade.xml");

FileOutputStream os = new

FileOutputStream(mCascadeFile);

byte[] buffer = new byte[4096];

int bytesRead;

while((bytesRead = is.read(buffer)) != -1)

{

os.write(buffer, 0, bytesRead);

}

is.close();

os.close();

haarCascade = new CascadeClassifier(

mCascadeFile.getAbsolutePath());

if (haarCascade.empty())

{

Log.i("Cascade Error", "级联分类器加载失败");

haarCascade = null;

}

catch(Exception e)

{

Log.i("Cascade Error: ","找不到级联分类器文件");

}

mOpenCvCameraView.enableView();

} break;

default:

{

super.onManagerConnected(status);

} break;

}

};

@Override

protected void onCreate(Bundle savedInstanceState) {

Log.i(TAG, "called onCreate");

super.onCreate(savedInstanceState);

getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

setContentView(R.layout.activity_main);

if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CAMERA)

!= PackageManager.PERMISSION_GRANTED) {

Log.i("permission", "request READ_EXTERNAL_STORAGE");

ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.CAMERA}, REQUEST_CAMERA);

}else {

Log.i("permission", "READ_EXTERNAL_STORAGE already granted");

read_external_storage_granted = true;

}

mOpenCvCameraView = (CameraBridgeViewBase) findViewById(R.id.java_surface_view);

mOpenCvCameraView.setCvCameraViewListener(this);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

getMenuInflater().inflate(R.menu.menu_main, menu);

Log.i(TAG, "called onCreateOptionsMenu");

mItemSwitchCamera = menu.add("切换前置/后置摄像头");

return true;

}

@Override

public boolean onOptionsItemSelected(MenuItem item) {

String toastMessage;

if (item == mItemSwitchCamera) {

mOpenCvCameraView.setVisibility(SurfaceView.GONE);

mIsFrontCamera = !mIsFrontCamera;

if (mIsFrontCamera) {

mOpenCvCameraView = (CameraBridgeViewBase) findViewById(R.id.java_surface_view);

mOpenCvCameraView.setCameraIndex(1);

toastMessage = "Front Camera";

} else {

mOpenCvCameraView = (CameraBridgeViewBase) findViewById(R.id.java_surface_view);

mOpenCvCameraView.setCameraIndex(-1);

toastMessage = "Back Camera";

}

mOpenCvCameraView.setVisibility(SurfaceView.VISIBLE);

mOpenCvCameraView.setCvCameraViewListener(this);

mOpenCvCameraView.enableView();

Toast toast = Toast.makeText(this, toastMessage, Toast.LENGTH_LONG);

toast.show();

}

return true;

}

@Override

public void onRequestPermissionsResult(int requestCode, @NonNull String permissions[], @NonNull int[] grantResults) {

if (requestCode == REQUEST_CAMERA) {

// If request is cancelled, the result arrays are empty.

if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

// permission was granted

Log.i("permission", "CAMERA granted");

read_external_storage_granted = true;

} else {

// permission denied

Log.i("permission", "CAMERA denied");

}

@Override

public void onCameraViewStarted(int width, int height) {

mRgba = new Mat(height, width, CvType.CV_8UC4);

}

@Override

public void onCameraViewStopped() {

}

@Override

public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {

//Rotating the input frame

Mat mGray = inputFrame.gray();

mRgba = inputFrame.rgba();

if (mIsFrontCamera)

{

Core.flip(mRgba, mRgba, 1);

Core.flip(mGray, mGray, 1);

}

//Detecting face in the frame

MatOfRect faces = new MatOfRect();

if(haarCascade != null)

{

haarCascade.detectMultiScale(mGray, faces, 1.1, 2, 2, new Size(200,200), new Size());

}

Rect[] facesArray = faces.toArray();

for (int i = 0; i < facesArray.length; i++)

Imgproc.rectangle(mRgba, facesArray[i].tl(), facesArray[i].br(), new Scalar(100), 3);

return mRgba;

}

@Override

public void onPause()

{

super.onPause();

if (mOpenCvCameraView != null)

mOpenCvCameraView.disableView();

}

@Override

public void onResume()

{

super.onResume();

OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_2_0, this, mLoaderCallback);

}

public void onDestroy() {

super.onDestroy();

if (mOpenCvCameraView != null)

mOpenCvCameraView.disableView();

}

第48行的R.raw.haarcascade_frontalface_alt2代表预训练的分类器文件。该文件从OpenCV-android-sdk\sdk\etc\haarcascades可以找到，然后复制到项目目录的app\src\main\res\raw文件夹中（需要自己建立一个名为raw的文件夹）。在OpenCV-android-sdk\sdk\etc目录中，有两个文件夹，一个是haarcascades，包含官方提供的已经训练好的各种Haar分类器（更准确地说，是分类器的参数），可以直接用CascadeClassifier()调用进行分类；另一个是lbpcascades，包含多种预训练LBP分类器。如果想把Haar换为LBP，那么把haarcascade_frontalface_alt2替换为LBP的文件名。两种分类器都能被CascadeClassifier()加载，只不过LBP的速度稍快于Haar，而且精度低于Haar。

3. 修改app\src\main\res\layout\activity_main.xml文件：

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

tools:context="net.johnhany.moaap_chp4.MainActivity">

<org.opencv.android.JavaCameraView

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:id="@+id/java_surface_view" />

</LinearLayout>

4. 在app\src\main\res目录下创建一个名为menu的Andorid resource directory，再在res\menu中创建一个menu_main.xml文件：

<?xml version="1.0" encoding="utf-8"?>

<menu xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto">

<item android:id="@+id/action_settings" android:title="@string/action_settings"

android:orderInCategory="100" app:showAsAction="never" />

</menu>

其实这个action_settings按钮并没有实际用途，老版本的Android Studio会默认创建这一项，我放在这儿只是为了占位：）但menu根节点是不可或缺的，因为我们在Java代码中添加了一个切换前置和后置摄像头的按钮。

5. 修改app\src\main\res\AndroidManifest.xml文件为如下内容：

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="net.johnhany.moaap_chp4">

<uses-permission android:name="android.permission.CAMERA"/>

<uses-feature android:name="android.hardware.camera" android:required="false"/>

<uses-feature android:name="android.hardware.camera.autofocus" android:required="false"/>

<uses-feature android:name="android.hardware.camera.front" android:required="false"/>

<uses-feature android:name="android.hardware.camera.front.autofocus" android:required="false"/>

<application

android:allowBackup="true"

android:icon="@mipmap/ic_launcher"

android:label="@string/app_name"

android:supportsRtl="true"

android:theme="@style/AppTheme">

<activity android:name=".MainActivity"

android:label="@string/app_name"

android:screenOrientation="landscape">

<intent-filter>

</intent-filter>

</activity>

</application>

</manifest>

6. 修改app\src\main\res\values\strings.xml文件：

<string name="app_name">第四章 - 深入OpenCV Android应用开发</string>

<string name="action_settings">Settings</string>

</resources>

同样，第二项Settings其实是无用的。

7. 修改app\src\main\res\values\styles.xml文件：

<item name="colorPrimary">@color/colorPrimary</item>

<item name="colorPrimaryDark">@color/colorPrimaryDark</item>

<item name="colorAccent">@color/colorAccent</item>

</style>

</resources>

这里保留ActionBar而没有完全全屏的原因是菜单按钮一般位于ActionBar，我们还需要通过菜单按钮来切换前/后置摄像头。

8. app\build.gradle文件修改为：

apply plugin: 'com.android.application'

android {

compileSdkVersion 24

buildToolsVersion "26.0.1"

defaultConfig {

applicationId "net.johnhany.moaap_chp4"

minSdkVersion 16

targetSdkVersion 24

versionCode 1

versionName "1.0"

testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

}

buildTypes {

release {

minifyEnabled false

proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

}

dependencies {

compile fileTree(include: ['*.jar'], dir: 'libs')

androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {

exclude group: 'com.android.support', module: 'support-annotations'

})

compile 'com.android.support:appcompat-v7:24.2.1'

compile 'com.android.support.constraint:constraint-layout:1.0.2'

testCompile 'junit:junit:4.12'

compile project(':openCVLibrary320')

}

9. openCVLibrary320\build.gradle文件修改为：

apply plugin: 'com.android.library'

android {

compileSdkVersion 24

buildToolsVersion "26.0.1"

defaultConfig {

minSdkVersion 16

targetSdkVersion 24

}

buildTypes {

release {

minifyEnabled false

proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'

}

10. 检查一下项目根目录的build.gradle文件是否为如下内容：

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {

repositories {

jcenter()

}

dependencies {

classpath 'com.android.tools.build:gradle:2.3.3'

// NOTE: Do not place your application dependencies here; they belong

// in the individual module build.gradle files

}

allprojects {

repositories {

jcenter()

}

task clean(type: Delete) {

delete rootProject.buildDir

}

运行效果

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