Android Camera2 开启自动曝光

首先，打开3A的总开关：

CaptureRequest.Builder builder.set(CaptureRequest.CONTROL_MODE, Camerametadata.CONTROL_MODE_AUTO);

获取支持的 AE FPS Range：

List ae_fps_ranges = new ArrayList<>();
for (Range r : characteristics.get(CameraCharacteristics.CONTROL_AE_AVAILABLE_TARGET_FPS_RANGES)) {
    ae_fps_ranges.add(new int[] {r.getLower(), r.getUpper()});
}
Collections.sort(ae_fps_ranges, new CameraController.RangeSorter());

然后，设置FPS：

builder.set(CaptureRequest.CONTROL_AE_TARGET_FPS_RANGE, ae_target_fps_range);

最后，根据 Flash_Mode 设置 AE_MODE

switch(flash_value) {
   case "flash_off":
       builder.set(CaptureRequest.CONTROL_AE_MODE, Camerametadata.CONTROL_AE_MODE_ON);
       builder.set(CaptureRequest.FLASH_MODE, Camerametadata.FLASH_MODE_OFF);
       break;
   case "flash_auto":
       // note we set this even in fake flash mode (where we manually turn torch on and off to simulate flash) so we
       // can read the FLASH_REQUIRED state to determine if flash is required
   
       builder.set(CaptureRequest.CONTROL_AE_MODE, Camerametadata.CONTROL_AE_MODE_ON_AUTO_FLASH);
       //这里FLASH_MODE可以设置为任意值，因为AE_MODE优先级高
       builder.set(CaptureRequest.FLASH_MODE, Camerametadata.FLASH_MODE_OFF);
       break;
   case "flash_on":
       // see note above for "flash_auto" for why we set this even fake flash mode - arguably we don't need to know
       // about FLASH_REQUIRED in flash_on mode, but we set it for consistency...
   
       builder.set(CaptureRequest.CONTROL_AE_MODE, Camerametadata.CONTROL_AE_MODE_ON_ALWAYS_FLASH);
       builder.set(CaptureRequest.FLASH_MODE, Camerametadata.FLASH_MODE_OFF);
       break;
   case "flash_torch":
       builder.set(CaptureRequest.CONTROL_AE_MODE, Camerametadata.CONTROL_AE_MODE_ON);
       builder.set(CaptureRequest.FLASH_MODE, Camerametadata.FLASH_MODE_TORCH);
       break;
   case "flash_red_eye":
       // not supported for expo bracketing or burst
       if( CameraController2.this.burst_type != BurstType.BURSTTYPE_NONE )
           builder.set(CaptureRequest.CONTROL_AE_MODE, Camerametadata.CONTROL_AE_MODE_ON);
       else
           builder.set(CaptureRequest.CONTROL_AE_MODE, Camerametadata.CONTROL_AE_MODE_ON_AUTO_FLASH_REDEYE);
       builder.set(CaptureRequest.FLASH_MODE, Camerametadata.FLASH_MODE_OFF);
       break;
   case "flash_frontscreen_auto":
   case "flash_frontscreen_on":
   case "flash_frontscreen_torch":
       builder.set(CaptureRequest.CONTROL_AE_MODE, Camerametadata.CONTROL_AE_MODE_ON);
       builder.set(CaptureRequest.FLASH_MODE, Camerametadata.FLASH_MODE_OFF);
       break;
}

查看每帧的曝光参数：

CameraCaptureSession.CaptureCallback{
	@Override
	public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
		long capture_result_exposure_time = result.get(CaptureResult.SENSOR_EXPOSURE_TIME);
		long capture_result_sensitivity = result.get(CaptureResult.SENSOR_SENSITIVITY);
	}
}