如何在Android camerahal中调整曝光度-乐工具技术知识

在Android Camera HAL中调整曝光度需要访问底层相机硬件接口，并对相关参数进行修改

首先确保你的Android设备支持Camera2 API。从Android 5.0 (Lollipop)开始，Camera2 API成为了官方推荐的相机编程接口。
在AndroidManifest.xml文件中添加相机权限：

在代码中创建一个Camera2 API的实例，并初始化相机预览：

private CameraDevice mCameraDevice;
private CameraCaptureSession mPreviewSession;
private ImageReader mImageReader;

private void createCameraPreviewSession() {
    try {
        List surfaces = new ArrayList<>();
        mImageReader = ImageReader.newInstance(mPreviewSize.getWidth(), mPreviewSize.getHeight(), ImageFormat.JPEG, 2);
        surfaces.add(mImageReader.getSurface());

        mCameraDevice.createCaptureSession(surfaces, new CameraCaptureSession.StateCallback() {
            @Override
            public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
                mPreviewSession = cameraCaptureSession;
                startCameraPreview();
            }

            @Override
            public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
                Log.e(TAG, "Configuration failed");
            }
        }, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

为相机预览设置一个SurfaceView或TextureView，并将其添加到相机预览会话中：

private void startCameraPreview() {
    try {
        Surface previewSurface = new Surface(mImageReader.getSurface().getNativeWindow());
        mPreviewSession.setRepeatingRequest(mPreviewRequest, previewSurface, null, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

在相机预览回调中调整曝光度。要调整曝光度，需要修改CameraCaptureRequest.Builder中的set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON)和set(CaptureRequest.CONTROL_AE_TARGET_FPS_RANGE, new Range(minFps, maxFps))参数。例如，将曝光模式设置为自动模式（AE_MODE_ON），并设置目标帧率范围为15fps至30fps：

private void setExposure() {
    try {
        CameraCaptureRequest.Builder builder = mPreviewRequest.newBuilder();
        builder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON);
        Range fpsRange = new Range<>(15, 30);
        builder.set(CaptureRequest.CONTROL_AE_TARGET_FPS_RANGE, fpsRange);
        mPreviewRequest = builder.build();
        mPreviewSession.setRepeatingRequest(mPreviewRequest, previewSurface, null, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}