从相机预览问题获取的位图中读取像素

Question

我正在创建一个 Android 应用程序，它要求我创建相机预览的位图，以便我可以平均预览中心的像素，但是无论相机指向什么，应用程序始终返回 0, 0, 0，作为从屏幕中心的 9x9 正方形的平均值读取的 RGB 值。 Preview.java 和主 java 文件都在那里。这是 android 的问题（如果是的话有办法解决吗），还是我的代码有问题？谢谢！ （抱歉，如果代码有点混乱）

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.hardware.Camera.ShutterCallback;
import android.os.Bundle;
import android.util.Log;
import android.view.Display;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import android.widget.FrameLayout;

public class CameraTest2Activity extends Activity {
private static final String TAG = "ZTG";
Camera camera;
Preview preview;


/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    preview = new Preview(this);
    ((FrameLayout) findViewById(R.id.preview)).addView(preview);
    final Button button = (Button) findViewById(R.id.bFire);
    button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            long timeAtStart = System.currentTimeMillis();
            TextView rgbDisplay =  (TextView) findViewById(R.id.RGBText);
            Display display = getWindowManager().getDefaultDisplay();
            int width = display.getWidth();
            int height = display.getHeight();
            Log.d(TAG, "Width and Height Retrieved As: " + width + ", " + height);
            Bitmap b = Bitmap.createBitmap(width, height, Bitmap.Config. RGB_565);
            Canvas c = new Canvas(b);
            Preview view = (Preview) ((ViewGroup) findViewById(R.id.preview)).getChildAt(0);
            view.draw(c);
            String hexValue;
            int centerX = (display.getWidth() / 2);
            int centerY = (display.getHeight() / 2);

            int test;   


            //test = b.getPixel(240, 350);
            int sampleWidth = 9;
            int sampleHeight = 9;
            int[] pixels = new int[sampleWidth * sampleHeight];
            b.getPixels(pixels, 0, 9, centerX - 4, centerY - 4, sampleWidth, sampleHeight);
            int l = 0;
            int tempNum;
            int tempBlue;
            int tempRed;
            int tempGreen;
            int blue = 0; //Color.blue(test);
            int red = 0; //Color.red(test);
            int green = 0; // Color.green(test);
            test = 0;
            Log.d("lookingFor", "test: " + pixels[1]);
            while(l < 81){
                tempNum = (Integer) pixels[l];
                Log.d("lookingFor", "Pixel Num: " + Color.blue(tempNum));
                tempBlue = Color.blue(tempNum);
                tempRed = Color.red(tempNum);
                tempGreen = Color.green(tempNum);
                Log.d("lookingFor", "current Blue: " + tempBlue);
                blue = blue + tempBlue;
                Log.d("lookingFor", "added blue: " + blue);
                red = red + tempRed;
                green = green + tempGreen;
                l = l + 1; //test g

            }
            Log.v("lookingFor", blue + " " + red + " " + green);
            blue = blue / 81;
            red = red / 81;
            green = green / 81;

            hexValue = Integer.toHexString(test);
            Log.d(TAG, "pixel at (" + centerX + ", " + centerY + " succesfully retreived! with value of: " + test);

            Log.d(TAG, "and an Hex value of: " + hexValue);
            //  blue = Color.blue(test);
            //  red = Color.red(test);
            //  green = Color.green(test);
            //this is a modification  

            Log.d(TAG, "RGB COLOR! R:" + red + " G:" + green + " B:" + blue);
            long timeAtEnd = System.currentTimeMillis();
            long totalTime = timeAtEnd - timeAtStart;
            Log.d(TAG, "Fetching the color took " + totalTime + " milliseconds");
            rgbDisplay.setText("R:" + red + " G:" + green + " B:" + blue);

        }
    });

    Log.d(TAG, "onCreate'd");
}

ShutterCallback shutterCallback = new ShutterCallback() {
    public void onShutter() {
        Log.d(TAG, "onShutter'd");
    }
};

/** Handles data for raw picture */
PictureCallback rawCallback = new PictureCallback() {
    public void onPictureTaken(byte[] data, Camera camera) {
        Log.d(TAG, "onPictureTaken - raw");
    }
};

/** Handles data for jpeg picture */
PictureCallback jpegCallback = new PictureCallback() {
    public void onPictureTaken(byte[] data, Camera camera) {
        FileOutputStream outStream = null;
        try {
            // write to local sandbox file system
            // outStream =
            // CameraDemo.this.openFileOutput(String.format("%d.jpg",
            // System.currentTimeMillis()), 0);
            // Or write to sdcard
            outStream = new FileOutputStream(String.format(
                    "/sdcard/%d.jpg", System.currentTimeMillis()));
            outStream.write(data);
            outStream.close();
            Log.d(TAG, "onPictureTaken - wrote bytes: " + data.length);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
        }
        Log.d(TAG, "onPictureTaken - jpeg");
    }
};

}

（这是主java文件）

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.hardware.Camera;
import android.hardware.Camera.PreviewCallback;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

class Preview extends SurfaceView implements SurfaceHolder.Callback {
private static final String TAG = "Preview";

SurfaceHolder mHolder;
public Camera camera;

Preview(Context context) {
    super(context);

    // Install a SurfaceHolder.Callback so we get notified when the
    // underlying surface is created and destroyed.
    mHolder = getHolder();
    mHolder.addCallback(this);
    mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}

public void surfaceCreated(SurfaceHolder holder) {
    // The Surface has been created, acquire the camera and tell it where
    // to draw.
    camera = Camera.open();
    try {
        camera.setPreviewDisplay(holder);

        camera.setPreviewCallback(new PreviewCallback() {

            public void onPreviewFrame(byte[] data, Camera arg1) {
                /*FileOutputStream outStream = null;
                try {
                    outStream = new FileOutputStream(String.format(
                            "/sdcard/%d.jpg", System.currentTimeMillis()));
                    outStream.write(data);
                    outStream.close();
                    Log.d(TAG, "onPreviewFrame - wrote bytes: "
                            + data.length);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                }*/
                Preview.this.invalidate();
            }
        });
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public void surfaceDestroyed(SurfaceHolder holder) {
    // Surface will be destroyed when we return, so stop the preview.
    // Because the CameraDevice object is not a shared resource, it's very
    // important to release it when the activity is paused.
    camera.stopPreview();
    camera = null;
}

public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
    // Now that the size is known, set up the camera parameters and begin
    // the preview.
    Camera.Parameters parameters = camera.getParameters();
    parameters.setPreviewSize(w, h);
    camera.setParameters(parameters);
    camera.startPreview();
}

@Override
public void draw(Canvas canvas) {
    super.draw(canvas);
    Paint p = new Paint(Color.RED);
    Log.d(TAG, "draw");
    canvas.drawText("PREVIEW", canvas.getWidth() / 2,
            canvas.getHeight() / 2, p);
}
}

Answer 1

您的代码对您创建的新位图 b 中的像素值进行平均，而不是相机预览或相机图片返回的像素。

我认为您需要将传递给 onPreviewFrame 的字节数组，将其从预览格式（很可能是 YUV422 或 YUV420）转换为您最喜欢的 RGB 格式，然后对 RGB 颜色进行数学计算。