How to change camera exposure on android?

问题

I want to perform image processing with OpenCV and android. In the first step, I need to change the camera properties like resolution, exposure, etc. By using OpenCV I only can change the resolution(mOpenCvCameraView.setMaxFrameSize(320,240);) and cannot change exposure.

By using OpenCV and camera2 When I run it, it is crashing(this code:pastebin.com/3XgvKGQN).
How can I change camera exposure?

package com.williams.drew.opencvtest;

import android.graphics.Paint;
import android.hardware.camera2.CameraDevice;
import android.hardware.camera2.CameraMetadata;
import android.hardware.camera2.CaptureRequest;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.SurfaceView;
import android.view.WindowManager;

import org.opencv.android.JavaCameraView;
import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.CameraBridgeViewBase;
import org.opencv.android.CameraBridgeViewBase.CvCameraViewFrame;
import org.opencv.android.CameraBridgeViewBase.CvCameraViewListener2;
import org.opencv.android.LoaderCallbackInterface;
import org.opencv.android.OpenCVLoader;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.imgproc.Imgproc;


public class MainActivity extends AppCompatActivity implements CvCameraViewListener2 {

    //Prefixes for logging success and failure messages
    private static final String TAG = "OCVSample::Activity";

    //Loads camera view of OpenCV for us to use. This lets us see using OpenCV
    private CameraBridgeViewBase mOpenCvCameraView;

    //Preview Builder which changes exposure (i think)
    private CaptureRequest.Builder mPreviewRequestBuilder;
    private CaptureRequest mPreviewRequest;
    private long exposureTime = 1000,frameDuration = 1000;
    private int sensitivity = 200;

    //OPENCV Variables
    Mat matRGBA;

    public MainActivity() {
        Log.i(TAG, "Instantiated new " + this.getClass());
    }

    @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.show_camera);

        mOpenCvCameraView = (JavaCameraView) findViewById(R.id.show_camera_activity_java_surface_view);
        mOpenCvCameraView.setVisibility(SurfaceView.VISIBLE);
        mOpenCvCameraView.setCvCameraViewListener(this);
    }

    @Override
    public void onPause() {
        super.onPause();

        if(mOpenCvCameraView != null) {
            mOpenCvCameraView.disableView();
        }
    }

    @Override
    public void onResume() {
        super.onResume();

        if(!OpenCVLoader.initDebug()) {
            Log.d(TAG, "Internal OpenCV library not found. Using OpenCV Manager for init");
            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_1_0, this, mLoaderCallback);
        }
        else {
            Log.d(TAG, "OpenCV library found inside package. Using it!");
            mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);
        }
    }

    @Override
    public void onDestroy() {
        super.onDestroy();

        if(mOpenCvCameraView != null) {
            mOpenCvCameraView.disableView();
        }
    }

    private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            switch (status) {
                case LoaderCallbackInterface.SUCCESS:
                {
                    Log.i(TAG, "OpenCV loaded successfully");
                    mOpenCvCameraView.enableView();
                } break;
                default:
                {
                    super.onManagerConnected(status);
                } break;
            }
        }
    };

    @Override
    public void onCameraViewStarted(int width, int height) {
        mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_OFF);
        mPreviewRequestBuilder.set(CaptureRequest.SENSOR_EXPOSURE_TIME, Long.valueOf(exposureTime));
        mPreviewRequestBuilder.set(CaptureRequest.SENSOR_SENSITIVITY, Integer.valueOf(sensitivity));
        mPreviewRequestBuilder.set(CaptureRequest.SENSOR_FRAME_DURATION, Long.valueOf(frameDuration));
        matRGBA = new Mat(width, height, CvType.CV_8UC4);
    }

    @Override
    public void onCameraViewStopped() {
        matRGBA.release();
    }

    @Override
    public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
        matRGBA = inputFrame.rgba();
        return matRGBA;
    }
}

Thank you for your answers.

回答1:

Yes, OpenCV is not exposing all the camera parameters. You can modify JavaCameraView and add the function that calls setExposureCompensation().

You want to call that function like this:

    Camera mCamera;
    mCamera = Camera.open();
    Camera.Parameters params = mCamera.getParameters();
    params.setExposureCompensation(0);

来源：https://stackoverflow.com/questions/49691541/how-to-change-camera-exposure-on-android