如何使用 Android CameraX 自动对焦

Question

Android 最近几个月发布了新的 API camerax。我正在尝试了解如何让相机自动对焦。

https://groups.google.com/a/android.com/forum/#!searchin/camerax-developers/auto$20焦点|排序：date/camerax-developers/IQ3KZd8iOIY/LIbrRIqEBgAJ

这里有关于该主题的讨论，但几乎没有关于它的具体文档。

https://github.com/android/camera-samples/tree/master/CameraXBasic/app/src/main/java/com/android/example/cameraxbasic

这也是基本的 camerax 应用程序，但我找不到任何处理自动对焦的文件。

文档的任何提示或要点都会有所帮助。另外，我对 android 还很陌生，所以很可能我遗漏了一些使上述链接更有用的东西。

Answer 1

您可以在此处找到有关 Focus 的文档，因为它是在“1.0.0-alpha05”中添加的 https://developer.android.com/jetpack/androidx/releases/camera#camera2-core-1.0.0-alpha05

基本上你必须在你的视图上设置一个触摸监听器并抓住点击的位置

private boolean onTouchToFocus(View viewA, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                break;
            case MotionEvent.ACTION_UP:
                    return focus(event);
                break;
            default:
                // Unhandled event.
                return false;
        }
        return true;
    }

并将这个位置转化为点数

private boolean focus(MotionEvent event) {
        final float x = (event != null) ? event.getX() : getView().getX() + getView().getWidth() / 2f;
        final float y = (event != null) ? event.getY() : getView().getY() + getView().getHeight() / 2f;

        TextureViewMeteringPointFactory pointFactory = new TextureViewMeteringPointFactory(textureView);
        float afPointWidth = 1.0f / 6.0f;  // 1/6 total area
        float aePointWidth = afPointWidth * 1.5f;
        MeteringPoint afPoint = pointFactory.createPoint(x, y, afPointWidth, 1.0f);
        MeteringPoint aePoint = pointFactory.createPoint(x, y, aePointWidth, 1.0f);

           try {
            CameraX.getCameraControl(lensFacing).startFocusAndMetering(
                FocusMeteringAction.Builder.from(afPoint, FocusMeteringAction.MeteringMode.AF_ONLY)
                                           .addPoint(aePoint, FocusMeteringAction.MeteringMode.AE_ONLY)
                                           .build());
        } catch (CameraInfoUnavailableException e) {
            Log.d(TAG, "cannot access camera", e);
        }

        return true;
    }

Answer 2

某些 android 设备存在问题，其中相机无法使用 CameraX 自动对焦。 CameraX 团队已意识到这一点，并正在通过内部票证对其进行跟踪，希望尽快修复。

Answer 3

使用当前的 CameraX 1.0.0，您可以通过以下两种方式进行操作：

每 X 秒自动对焦：

 previewView.afterMeasured {
     val autoFocusPoint = SurfaceOrientedMeteringPointFactory(1f, 1f)
             .createPoint(.5f, .5f)
     try {
         val autoFocusAction = FocusMeteringAction.Builder(
             autoFocusPoint,
             FocusMeteringAction.FLAG_AF
         ).apply {
             //start auto-focusing after 2 seconds
             setAutoCancelDuration(2, TimeUnit.SECONDS)
         }.build()
         camera.cameraControl.startFocusAndMetering(autoFocusAction)
     } catch (e: CameraInfoUnavailableException) {
         Log.d("ERROR", "cannot access camera", e)
     }
 }

点击时专注：

 previewView.afterMeasured {
     previewView.setOnTouchListener { _, event ->
         return@setOnTouchListener when (event.action) {
             MotionEvent.ACTION_DOWN -> {
                 true
             }
             MotionEvent.ACTION_UP -> {
                 val factory: MeteringPointFactory = SurfaceOrientedMeteringPointFactory(
                     previewView.width.toFloat(), previewView.height.toFloat()
                 )
                 val autoFocusPoint = factory.createPoint(event.x, event.y)
                 try {
                     camera.cameraControl.startFocusAndMetering(
                         FocusMeteringAction.Builder(
                             autoFocusPoint,
                             FocusMeteringAction.FLAG_AF
                         ).apply {
                             //focus only when the user tap the preview
                             disableAutoCancel()
                         }.build()
                     )
                 } catch (e: CameraInfoUnavailableException) {
                     Log.d("ERROR", "cannot access camera", e)
                 }
                 true
             }
             else -> false // Unhandled event.
         }
     }
 }

afterMeasured 扩展函数是一个简单的实用程序：（感谢 ch271828n ）

inline fun View.afterMeasured(crossinline block: () -> Unit) {
    if (measuredWidth > 0 && measuredHeight > 0) {
        block()
    } else {
        viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.GlobalLayoutListener {
            override fun onGlobalLayout() {
                if (measuredWidth > 0 && measuredHeight > 0) {
                    viewTreeObserver.removeOnGlobalLayoutListener(this)
                    block()
                } 
            }
        })
    }
}

一个Camera对象可以通过

获得

val camera = cameraProvider.bindToLifecycle(
    this@Activity, cameraSelector, previewView //this is a PreviewView
)

Answer 4

请指出，要使“点击聚焦”与 PreviewView 一起使用，您需要使用 DisplayOrientedMeteringPointFactory。否则你会弄乱坐标。

val factory = DisplayOrientedMeteringPointFactory(activity.display, camera.cameraInfo, previewView.width.toFloat(), previewView.height.toFloat())

其余的请使用 MatPag 的答案。

Answer 5

我运行遇到了同样的问题，我设置了这个解决方案（即使它看起来很愚蠢）。

val displayMetrics = resources.displayMetrics
val factory = SurfaceOrientedMeteringPointFactory(
    displayMetrics.widthPixels.toFloat(),
    displayMetrics.heightPixels.toFloat()
)
val point = factory.createPoint(
    displayMetrics.widthPixels / 2f,
    displayMetrics.heightPixels / 2f
)
val action = FocusMeteringAction
            .Builder(point, FocusMeteringAction.FLAG_AF)
            .build()

try {
    camera = cameraProvider.bindToLifecycle(
        lifecycleOwner,
        cameraSelector,
        preview,
        imageAnalyzer
    )
    GlobalScope.launch(Dispatchers.Default) {
        while (workflowModel.isCameraLive) {
            camera?.cameraControl?.startFocusAndMetering(action)?
            delay(3000)
        }
    }
} catch (e: Exception) {
    Log.e(mTag, "Use case binding failed", e)
}

基本上，我在 while 循环中每 3 秒重新启动对焦动作。

isCameraLive 是我存储在我的 viewModel 中的布尔变量，当我启动相机时设置 true，当我通过调用 cameraProvider.unbindAll() 停止它时设置 false。

Answer 6

当前 1.0.0-rc03 和 1.0.0-alpha22 个工件

此解决方案假设相机已经设置好，包括 bindToLifecycle。之后我们需要在尝试对焦相机之前检查 previewView streamState 是否为 STREAMING

 previewView.getPreviewStreamState().observe(getActivity(), value -> {
        if (value.equals(STREAMING)) {
            setUpCameraAutoFocus();
        }
    });

private void setUpCameraAutoFocus() {
    final float x =  previewView.getX() + previewView.getWidth() / 2f;
    final float y =  previewView.getY() + previewView.getHeight() / 2f;

  MeteringPointFactory pointFactory = previewView.getMeteringPointFactory();
  float afPointWidth = 1.0f / 6.0f;  // 1/6 total area
  float aePointWidth = afPointWidth * 1.5f;
  MeteringPoint afPoint = pointFactory.createPoint(x, y, afPointWidth);
  MeteringPoint aePoint = pointFactory.createPoint(x, y, aePointWidth);
  ListenableFuture<FocusMeteringResult> future = cameraControl.startFocusAndMetering(
          new FocusMeteringAction.Builder(afPoint,
                  FocusMeteringAction.FLAG_AF).addPoint(aePoint,
                  FocusMeteringAction.FLAG_AE).build());
  Futures.addCallback(future, new FutureCallback<FocusMeteringResult>() {
    @Override
    public void onSuccess(@Nullable FocusMeteringResult result) {
    }

    @Override
    public void onFailure(Throwable t) {
      // Throw the unexpected error.
      throw new RuntimeException(t);
    }
  }, CameraXExecutors.directExecutor());
}

Answer 7

中的 afterMeasured 函数有一个严重的错误：它的回调经常被从不调用 。

非常简单的修复：

inline fun View.afterMeasured(crossinline block: () -> Unit) {
    if (measuredWidth > 0 && measuredHeight > 0) {
        block()
    } else {
        viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
            override fun onGlobalLayout() {
                if (measuredWidth > 0 && measuredHeight > 0) {
                    viewTreeObserver.removeOnGlobalLayoutListener(this)
                    block()
                }
            }
        })
    }
}

说明：我观察到（在生产中的应用程序中），有时视图已经测量并且没有 ui 更改，因此以后永远不会调用 onGlobalLayout。那么afterMeasured的回调将永远不会被调用，所以相机不会被初始化。

如何使用 Android CameraX 自动对焦

How to auto-focus with Android CameraX

android

kotlin

android-studio

android-camerax