CameraX使用ImageAnalysis分析器,可以访问缓冲区中的图像,获取视频帧数据。

准备工作

准备工作包括gradle,layout,动态申请相机权限,外部存储权限等等,大部分设置与CameraX 打开摄像头预览相同。

gradle

一些关键配置

    apply plugin: 'com.android.application'
    apply plugin: 'kotlin-android'
    apply plugin: 'kotlin-android-extensions'
    apply plugin: 'kotlin-kapt'

    android {
        compileSdkVersion 31
        buildToolsVersion "31.0.0"
        defaultConfig {
            applicationId "com.rustfisher.tutorial2020"
            minSdkVersion 21
            targetSdkVersion 31
        }
        buildFeatures {
            compose true
            dataBinding true
            viewBinding true
        }

        dataBinding {
            enabled = true
        }

        kotlinOptions {
            jvmTarget = "1.8"
        }

        compileOptions {
            sourceCompatibility JavaVersion.VERSION_1_8
            targetCompatibility JavaVersion.VERSION_1_8
        }
        composeOptions {
            kotlinCompilerExtensionVersion '1.0.1'
        }
    }

    dependencies {
        kapt "com.android.databinding:compiler:3.0.1"
        // 其他依赖...

        implementation "androidx.camera:camera-core:1.1.0-alpha11"
        implementation "androidx.camera:camera-camera2:1.1.0-alpha11"
        implementation "androidx.camera:camera-lifecycle:1.1.0-alpha11"
        implementation "androidx.camera:camera-view:1.0.0-alpha31"
        implementation "androidx.camera:camera-extensions:1.0.0-alpha31"
    }

layout

act_simple_preivew_x.xml

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

       <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
           android:layout_width="match_parent"
           android:layout_height="match_parent">

           <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
               android:id="@+id/container"
               android:layout_width="match_parent"
               android:layout_height="match_parent">

               <androidx.camera.view.PreviewView
                   android:id="@+id/previewView"
                   android:layout_width="match_parent"
                   android:layout_height="match_parent" />
           </FrameLayout>

           <LinearLayout
               android:layout_width="match_parent"
               android:layout_height="wrap_content"
               android:layout_alignParentBottom="true"
               android:gravity="center"
               android:orientation="vertical"
               android:padding="4dp">

               <LinearLayout
                   android:layout_width="match_parent"
                   android:layout_height="wrap_content"
                   android:orientation="horizontal">

                   <Button
                       android:id="@+id/start"
                       style="@style/NormalBtn"
                       android:layout_width="wrap_content"
                       android:layout_height="wrap_content"
                       android:text="打开摄像头" />

                   <Button
                       android:id="@+id/end"
                       style="@style/NormalBtn"
                       android:layout_width="wrap_content"
                       android:layout_height="wrap_content"
                       android:layout_marginStart="4dp"
                       android:text="停止摄像头" />

               </LinearLayout>

               <LinearLayout
                   android:layout_width="match_parent"
                   android:layout_height="wrap_content"
                   android:layout_marginTop="4dp"
                   android:orientation="horizontal">

                   <Button
                       android:id="@+id/enable_ana"
                       style="@style/NormalBtn"
                       android:layout_width="wrap_content"
                       android:layout_height="wrap_content"
                       android:text="setAnalyzer" />

                   <Button
                       android:id="@+id/clr_ana"
                       style="@style/NormalBtn"
                       android:layout_width="wrap_content"
                       android:layout_height="wrap_content"
                       android:layout_marginStart="4dp"
                       android:text="clearAnalyzer" />


                   <Button
                       android:id="@+id/take_one_analyse"
                       style="@style/NormalBtn"
                       android:layout_width="wrap_content"
                       android:layout_height="wrap_content"
                       android:layout_marginStart="4dp"
                       android:text="截取" />

               </LinearLayout>
           </LinearLayout>

       </RelativeLayout>
   </layout>

ImageAnalysis获取视频帧并保存到本地

androidx.camera.core.ImageAnalysis

设置分析器

先看简单的示例,在SimplePreviewXAct.java中使用ImageAnalysis

private boolean mTakeOneYuv = false; // 获取一帧 实际工程中不要这么做

private final ImageAnalysis mImageAnalysis =
        new ImageAnalysis.Builder()
                //.setOutputImageFormat(ImageAnalysis.OUTPUT_IMAGE_FORMAT_RGBA_8888)
                .setTargetResolution(new Size(720, 1280)) // 图片的建议尺寸
                .setOutputImageRotationEnabled(true) // 是否旋转分析器中得到的图片
                .setTargetRotation(Surface.ROTATION_0) // 允许旋转后 得到图片的旋转设置
                .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
                .build();

注意这里的setOutputImageRotationEnabled(true),启用了旋转后,分析器会多花费一些时间(毫秒级)。
启用选择,setTargetRotation才有意义。

onCreate方法里设置setAnalyzer

// SimplePreviewXAct onCreate
final ExecutorService executorService = Executors.newFixedThreadPool(2);
mBinding.enableAna.setOnClickListener(v -> {
    Toast.makeText(getApplicationContext(), "启用分析器", Toast.LENGTH_SHORT).show();
    mImageAnalysis.setAnalyzer(executorService, imageProxy -> {
        // 下面处理数据
        if (mTakeOneYuv) {
            mTakeOneYuv = false;
            Log.d(TAG, "旋转角度: " + imageProxy.getImageInfo().getRotationDegrees());
            ImgHelper.useYuvImgSaveFile(imageProxy,  true); // 存储这一帧为文件
            runOnUiThread(() -> Toast.makeText(getApplicationContext(), "截取一帧", Toast.LENGTH_SHORT).show());
        }
        imageProxy.close(); // 最后要关闭这个
    });
});

为了更直观的看到分析器中的图片,我们想办法把图片数据保存了下来。

绑定生命周期(启动相机)的时候,把mImageAnalysis传进去

cameraProvider.bindToLifecycle(this, cameraSelector, preview, mImageAnalysis);

相机运行起来,分析器中可以得到帧数据。ImgHelper代码和SimplePreviewXAct如下文。

ImgHelper.java

新建一个工具类来处理图片格式问题。

ImgHelper.java

    import android.graphics.ImageFormat;
    import android.graphics.Rect;
    import android.graphics.YuvImage;
    import android.os.Environment;
    import android.util.Log;

    import androidx.camera.core.ImageProxy;

    import java.io.File;
    import java.io.FileOutputStream;
    import java.nio.ByteBuffer;

    public class ImgHelper {
        public static String TAG = "rfDevImg";

        // 获取到YuvImage对象 然后存文件
        public static void useYuvImgSaveFile(ImageProxy imageProxy, boolean outputYOnly) {
            final int wid = imageProxy.getWidth();
            final int height = imageProxy.getHeight();
            Log.d(TAG, "宽高: " + wid + ", " + height);

            YuvImage yuvImage = ImgHelper.toYuvImage(imageProxy);
            File file = new File(Environment.getExternalStorageDirectory(), "z_" + System.currentTimeMillis() + ".png");
            saveYuvToFile(file, wid, height, yuvImage);
            Log.d(TAG, "rustfisher.com 存储了" + file);

            if (outputYOnly) { // 仅仅作为功能演示
                YuvImage yImg = ImgHelper.toYOnlyYuvImage(imageProxy);
                File yFile = new File(Environment.getExternalStorageDirectory(), "y_" + System.currentTimeMillis() + ".png");
                saveYuvToFile(yFile, wid, height, yImg);
                Log.d(TAG, "rustfisher.com 存储了" + yFile);
            }
        }

        // 仅作为示例使用
        public static YuvImage toYOnlyYuvImage(ImageProxy imageProxy) {
            if (imageProxy.getFormat() != ImageFormat.YUV_420_888) {
                throw new IllegalArgumentException("Invalid image format");
            }
            int width = imageProxy.getWidth();
            int height = imageProxy.getHeight();
            ByteBuffer yBuffer = imageProxy.getPlanes()[0].getBuffer();
            int numPixels = (int) (width * height * 1.5f);
            byte[] nv21 = new byte[numPixels];
            int index = 0;
            int yRowStride = imageProxy.getPlanes()[0].getRowStride();
            int yPixelStride = imageProxy.getPlanes()[0].getPixelStride();
            for (int y = 0; y < height; ++y) {
                for (int x = 0; x < width; ++x) {
                    nv21[index++] = yBuffer.get(y * yRowStride + x * yPixelStride);
                }
            }
            return new YuvImage(nv21, ImageFormat.NV21, width, height, null);
        }

        public static YuvImage toYuvImage(ImageProxy image) {
            if (image.getFormat() != ImageFormat.YUV_420_888) {
                throw new IllegalArgumentException("Invalid image format");
            }
            int width = image.getWidth();
            int height = image.getHeight();

            // 拿到YUV数据
            ByteBuffer yBuffer = image.getPlanes()[0].getBuffer();
            ByteBuffer uBuffer = image.getPlanes()[1].getBuffer();
            ByteBuffer vBuffer = image.getPlanes()[2].getBuffer();

            int numPixels = (int) (width * height * 1.5f);
            byte[] nv21 = new byte[numPixels]; // 转换后的数据
            int index = 0;

            // 复制Y的数据
            int yRowStride = image.getPlanes()[0].getRowStride();
            int yPixelStride = image.getPlanes()[0].getPixelStride();
            for (int y = 0; y < height; ++y) {
                for (int x = 0; x < width; ++x) {
                    nv21[index++] = yBuffer.get(y * yRowStride + x * yPixelStride);
                }
            }

            // 复制U/V数据
            int uvRowStride = image.getPlanes()[1].getRowStride();
            int uvPixelStride = image.getPlanes()[1].getPixelStride();
            int uvWidth = width / 2;
            int uvHeight = height / 2;

            for (int y = 0; y < uvHeight; ++y) {
                for (int x = 0; x < uvWidth; ++x) {
                    int bufferIndex = (y * uvRowStride) + (x * uvPixelStride);
                    nv21[index++] = vBuffer.get(bufferIndex);
                    nv21[index++] = uBuffer.get(bufferIndex);
                }
            }
            return new YuvImage(nv21, ImageFormat.NV21, width, height, null);
        }

        public static void saveYuvToFile(File file, int wid, int height, YuvImage yuvImage) {
            try {
                boolean c = file.createNewFile();
                Log.d(TAG, file + " created: " + c);
                FileOutputStream fos = new FileOutputStream(file);
                yuvImage.compressToJpeg(new Rect(0, 0, wid, height), 100, fos);
                fos.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

SimplePreviewXAct.java

完整的SimplePreviewXAct.java代码如下

    import android.os.Bundle;
    import android.util.Log;
    import android.util.Size;
    import android.view.Surface;
    import android.widget.Toast;

    import androidx.annotation.Nullable;
    import androidx.appcompat.app.AppCompatActivity;
    import androidx.camera.core.CameraSelector;
    import androidx.camera.core.ImageAnalysis;
    import androidx.camera.core.Preview;
    import androidx.camera.lifecycle.ProcessCameraProvider;
    import androidx.core.content.ContextCompat;
    import androidx.databinding.DataBindingUtil;

    import com.google.common.util.concurrent.ListenableFuture;
    import com.rustfisher.tutorial2020.R;
    import com.rustfisher.tutorial2020.databinding.ActSimplePreivewXBinding;

    import java.util.concurrent.ExecutionException;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;


    /**
    * @author an.rustfisher.com
    * @date 2021-12-09 19:53
    */
    public class SimplePreviewXAct extends AppCompatActivity {
        private static final String TAG = "rfDevX";
        private ActSimplePreivewXBinding mBinding;
        private ListenableFuture<ProcessCameraProvider> mCameraProviderFuture;
        private ProcessCameraProvider mCameraProvider;
        private boolean mRunning = false;

        private boolean mTakeOneYuv = false; // 获取一帧 实际工程中不要这么做

        private final ImageAnalysis mImageAnalysis =
                new ImageAnalysis.Builder()
                        //.setOutputImageFormat(ImageAnalysis.OUTPUT_IMAGE_FORMAT_RGBA_8888)
                        .setTargetResolution(new Size(720, 1280)) // 图片的建议尺寸
                        .setOutputImageRotationEnabled(true) // 是否旋转分析器中得到的图片
                        .setTargetRotation(Surface.ROTATION_0) // 允许旋转后 得到图片的旋转设置
                        .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
                        .build();

        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            mBinding = DataBindingUtil.setContentView(this, R.layout.act_simple_preivew_x);
            mCameraProviderFuture = ProcessCameraProvider.getInstance(this);
            mCameraProviderFuture.addListener(() -> {
                try {
                    mCameraProvider = mCameraProviderFuture.get();
                    Log.d(TAG, "获取到了 cameraProvider");
                    bindPreview(mCameraProvider);
                } catch (ExecutionException | InterruptedException e) {
                    // 这里不用处理
                }
            }, ContextCompat.getMainExecutor(this));
            mBinding.start.setOnClickListener(v -> {
                if (mCameraProvider != null && !mRunning) {
                    bindPreview(mCameraProvider);
                }
            });
            mBinding.end.setOnClickListener(v -> {
                mCameraProvider.unbindAll();
                mRunning = false;
            });

            mBinding.takeOneAnalyse.setOnClickListener(v -> {
                mTakeOneYuv = true;
                Log.d(TAG, "获取一帧, 输出图片旋转: " + mImageAnalysis.isOutputImageRotationEnabled());
            });

            final ExecutorService executorService = Executors.newFixedThreadPool(2);
            mBinding.enableAna.setOnClickListener(v -> {
                Toast.makeText(getApplicationContext(), "启用分析器", Toast.LENGTH_SHORT).show();
                mImageAnalysis.setAnalyzer(executorService, imageProxy -> {
                    // 下面处理数据
                    if (mTakeOneYuv) {
                        mTakeOneYuv = false;
                        Log.d(TAG, "旋转角度: " + imageProxy.getImageInfo().getRotationDegrees());
                        ImgHelper.useYuvImgSaveFile(imageProxy,  true); // 存储这一帧为文件
                        runOnUiThread(() -> Toast.makeText(getApplicationContext(), "截取一帧", Toast.LENGTH_SHORT).show());
                    }
                    imageProxy.close(); // 最后要关闭这个
                });
            });
            mBinding.clrAna.setOnClickListener(v -> {
                mImageAnalysis.clearAnalyzer();
                Toast.makeText(getApplicationContext(), "clearAnalyzer", Toast.LENGTH_SHORT).show();
            });
        }

        private void bindPreview(ProcessCameraProvider cameraProvider) {
            if (cameraProvider == null) {
                Toast.makeText(getApplicationContext(), "没获取到相机", Toast.LENGTH_SHORT).show();
                return;
            }
            Toast.makeText(getApplicationContext(), "相机启动", Toast.LENGTH_SHORT).show();
            Preview preview = new Preview.Builder().build();

            CameraSelector cameraSelector = new CameraSelector.Builder()
                    .requireLensFacing(CameraSelector.LENS_FACING_BACK)
                    .build();

            preview.setSurfaceProvider(mBinding.previewView.getSurfaceProvider());

            cameraProvider.bindToLifecycle(this, cameraSelector, preview, mImageAnalysis);
            mRunning = true;
        }

    }

运行结果

在红米9上运行,截取到的图片(效果示意图)

取消分析器

mImageAnalysis.clearAnalyzer();

ImageAnalysis相关

通过上面的示例,我们掌握了ImageAnalysis简单的用法。

Executors

setAnalyzer我们使用的是java.util.concurrent.Executors。上面的例子传入了一个定长的线程池

处理图片的方法会运行在线程池的线程里。当然这里换其他类型线程池也可以。也可以用主线程ContextCompat.getMainExecutor(getApplicationContext());

androidx.camera.core.ImageProxy

封装了android.media.Image

ImageAnalysis.Builder

用来创建ImageAnalysis

默认输出图片格式是OUTPUT_IMAGE_FORMAT_YUV_420_888,本文示例中我们使用的是默认格式。

setTargetResolution

示例中setTargetResolution(new Size(720, 1280))。我们用的是竖屏,设置成了宽度小于高度。

可以把传入的叫做“目标尺寸”。最终图片会找一个最接近的尺寸。具体由摄像头来决定。

比如把示例里的设置改成setTargetResolution(new Size(1280, 720)),最终输出的图片大小可能是720x720

setTargetResolutionsetTargetAspectRatio只能二选一

ImageAnalysis.Builder.setOutputImageRotationEnabled

setOutputImageRotationEnabled(boolean)是否启用输出图片的旋转功能。注意这是ImageAnalysis.Builder的方法。
此功能默认关闭

输出的图片可以用ImageInfo.getRotationDegrees()获得旋转的角度。

启用后,分析器会旋转每一张图片。相对而言会多耗费性能。

setTargetRotation

setOutputImageRotationEnabled(true)启用旋转后,可以设置输出图片的旋转角度。

setTargetRotation(int)接受的参数是Surface.ROTATION_0, Surface.ROTATION_90, Surface.ROTATION_180, Surface.ROTATION_270

上面的示例用的是Surface.ROTATION_0

setBackpressureStrategy

当图片产生的速度大于图片分析的速度时,分析器会采用的应对策略。Android称之为背压策略

可选值如下

STRATEGY_KEEP_ONLY_LATEST (默认)

使用最新的图片

STRATEGY_BLOCK_PRODUCER

阻止产生新的图片。
当产生的图片超过队列深度时,生产者(producer)会停止生产图片。
如果上一张图片没有调用ImageProxy.close(),生产出来的图片会去排队(queued),而不是交给分析器。
如果停止生产图片(image),其他地方也会停止,比如实时预览。

这个策略配合ImageAnalysis.Builder.setImageQueueDepth(int)使用。设置队列的长度。

获取nv21数据

例子中把YUV数据转换成nv21。

然后利用android.graphics.YuvImage,把图片存下来。

参考

12-17 17:17