适用于Android的Canny Edge检测器

Question

I am trying to implement the canny edge detection algorithm using Tom Gibaras implementation(changed for Android) in my Android App. The App uses the camera to capture the picture, the camera works fine and the picture is taken, the problem lies for when I want to pass it to the algorithm and display the result.Instead of the image being processed and edges detected then displayed, the App returns to the home screen The code below is my activity so far.I can provide any additional code requested, can you help me please?

/**
 * ShootActivity demonstrates capturing camera images
 * - user presses button to capture an image using the device camera
 */
public class ShootActivity extends Activity {
public static final int ACTION_TAKE_PHOTO_B = 1;

public String mCurrentPhotoPath;
public static final String BITMAP_STORAGE_KEY = "viewbitmap";
public static final String IMAGEVIEW_VISIBILITY_STORAGE_KEY = "imageviewvisibility";
public ImageView mImageView;
public Bitmap mImageBitmap;
public static final String JPEG_FILE_PREFIX = "IMG_";
public static final String JPEG_FILE_SUFFIX = ".jpg";

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mImageView = (ImageView) findViewById(R.id.imageView1);
    mImageBitmap = null;

    Button picBtn = (Button) findViewById(R.id.btnIntend);
    setBtnListenerOrDisable( 
            picBtn, 
            mTakePicOnClickListener,
            MediaStore.ACTION_IMAGE_CAPTURE
    );

}
/**
 * Click method to handle user pressing button to launch camera
 */

Button.OnClickListener mTakePicOnClickListener = 
        new Button.OnClickListener() {
        public void onClick(View v) {
            dispatchTakePictureIntent(ACTION_TAKE_PHOTO_B);
        }
    };


public File createImageFile() throws IOException {
    // Create an image file name
    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
    String imageFileName = JPEG_FILE_PREFIX + timeStamp + "_";
    //File albumF = getAlbumDir();
    File imageF = File.createTempFile(imageFileName, JPEG_FILE_SUFFIX);
    return imageF;
}

public File setUpPhotoFile() throws IOException {

    File f = createImageFile();
    mCurrentPhotoPath = f.getAbsolutePath();

    return f;
}

public void setPic() {

    /* There isn't enough memory to open up more than a couple camera photos */
    /* So pre-scale the target bitmap into which the file is decoded */

    /* Get the size of the ImageView */
    int targetW = mImageView.getWidth();
    int targetH = mImageView.getHeight();

    /* Get the size of the image */
    BitmapFactory.Options bmOptions = new BitmapFactory.Options();
    bmOptions.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(mCurrentPhotoPath, bmOptions);
    int photoW = bmOptions.outWidth;
    int photoH = bmOptions.outHeight;

    /* Figure out which way needs to be reduced less */
    int scaleFactor = 2;
    if ((targetW > 0) || (targetH > 0)) {
        scaleFactor = Math.min(photoW/targetW, photoH/targetH); 
    }

    /* Set bitmap options to scale the image decode target */
    bmOptions.inJustDecodeBounds = false;
    bmOptions.inSampleSize = scaleFactor;
    bmOptions.inPurgeable = true;

    /* Decode the JPEG file into a Bitmap */
    mImageBitmap = BitmapFactory.decodeFile(mCurrentPhotoPath, bmOptions);
    CannyEdgeDetection detector = new CannyEdgeDetection();
    detector.setLowThreshold(0.5f);
    detector.setHighThreshold(1f);
    detector.setSourceImage(mImageBitmap);
    detector.process();
    Bitmap edges = detector.getEdgesImage();
    /* Associate the Bitmap to the ImageView */
    mImageView.setImageBitmap(edges);
    mImageView.setVisibility(View.VISIBLE);
}

public void galleryAddPic() {
        Intent mediaScanIntent = new Intent("android.intent.action.MEDIA_SCANNER_SCAN_FILE");
        File f = new File(mCurrentPhotoPath);
        Uri contentUri = Uri.fromFile(f);
        mediaScanIntent.setData(contentUri);
        this.sendBroadcast(mediaScanIntent);
}

public void dispatchTakePictureIntent(int actionCode) {

    Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

        File f = null;

        try {
            f = setUpPhotoFile();
            mCurrentPhotoPath = f.getAbsolutePath();
            takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(f));
        } catch (IOException e) {
            e.printStackTrace();
            f = null;
            mCurrentPhotoPath = null;
        }


    startActivityForResult(takePictureIntent, 1102);
}
public void handleBigCameraPhoto()
{
    if (mCurrentPhotoPath != null) 
    {
        setPic();
        galleryAddPic();
        mCurrentPhotoPath = null;
    }
}
/**
 * Handle user returning from capturing the image
 */
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) 
{
    if(requestCode == 1102 && resultCode == Activity.RESULT_OK)
    {
        if(data != null)
        {
        handleBigCameraPhoto();
        }
    }

}
@Override
protected void onSaveInstanceState(Bundle outState) {
    outState.putParcelable(BITMAP_STORAGE_KEY, mImageBitmap);
    outState.putBoolean(IMAGEVIEW_VISIBILITY_STORAGE_KEY, (mImageBitmap != null) );
    super.onSaveInstanceState(outState);
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    mImageBitmap = savedInstanceState.getParcelable(BITMAP_STORAGE_KEY);
    mImageView.setImageBitmap(mImageBitmap);
    mImageView.setVisibility(savedInstanceState.getBoolean(IMAGEVIEW_VISIBILITY_STORAGE_KEY) ? ImageView.VISIBLE : ImageView.INVISIBLE);
}
public static boolean isIntentAvailable(Context context, String action) {
    final PackageManager packageManager = context.getPackageManager();
    final Intent intent = new Intent(action);
    List<ResolveInfo> list =
        packageManager.queryIntentActivities(intent,
                PackageManager.MATCH_DEFAULT_ONLY);
    return list.size() > 0;
}


public void setBtnListenerOrDisable( 
        Button btn, 
        Button.OnClickListener onClickListener,
        String intentName
) {
    if (isIntentAvailable(this, intentName)) {
        btn.setOnClickListener(onClickListener);            
    } else {
        btn.setText( 
            getText(R.string.cannot).toString() + " " + btn.getText());
        btn.setClickable(false);
    }
}

}

03-27 02:47:37.310: E/AndroidRuntime(6513): FATAL EXCEPTION: main
03-27 02:47:37.310: E/AndroidRuntime(6513): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1102, result=-1, data=null} to activity {com.example.f_y_p/com.example.f_y_p.ShootActivity}: java.lang.NullPointerException
03-27 02:47:37.310: E/AndroidRuntime(6513):     at android.app.ActivityThread.deliverResults(ActivityThread.java:3182)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at android.app.ActivityThread.handleSendResult(ActivityThread.java:3225)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at android.app.ActivityThread.access$1100(ActivityThread.java:140)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1275)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at android.os.Looper.loop(Looper.java:137)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at android.app.ActivityThread.main(ActivityThread.java:4898)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at java.lang.reflect.Method.invokeNative(Native Method)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at java.lang.reflect.Method.invoke(Method.java:511)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at dalvik.system.NativeStart.main(Native Method)
03-27 02:47:37.310: E/AndroidRuntime(6513): Caused by: java.lang.NullPointerException
03-27 02:47:37.310: E/AndroidRuntime(6513):     at com.example.f_y_p.CannyEdgeDetection.setSourceImage(CannyEdgeDetection.java:75)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at com.example.f_y_p.ShootActivity.setPic(ShootActivity.java:114)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at com.example.f_y_p.ShootActivity.handleBigCameraPhoto(ShootActivity.java:153)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at com.example.f_y_p.ShootActivity.onActivityResult(ShootActivity.java:166)
03-27 02:47:37.310: E/AndroidRuntime(6513):     at android.app.Activity.dispatchActivityResult(Activity.java:5390)    
 032702:47:37.310:E/AndroidRuntime(6513):atandroid.app.ActivityThread.deliverResults(ActivityThread.java:3178)
03-27 02:47:37.310: E/AndroidRuntime(6513):     ... 11 more

03-27 02:47:48.535: I/Process(6513): Sending signal. PID: 6513 SIG: 9

Answer 1

Crash :

Your app returns to the home screen because there is a crash. The crash is probably due to a NullPointerException .

It may be because of this line:

Bitmap mBitmap = (Bitmap) data.getExtras().get("data");

Logcat :

You can determine exactly where the crash is occurring by looking at the LogCat output. Please post the LogCat output or just scan through it and determine where the app is crashing.

Photo Location :

Now for the bad news. You cannot get the photograph taken from the camera via the Extras Bundle in the manner you attempted. At most this function will return a small thumbnail that will not be suitable for your image processing algorithm. Your image is more likely to be located at the location you specified by outputFileUri .

How to Capture and Optionally Choose from Gallery :

Please see this post: Allow user to select camera or gallery for image . Look for the answer titled: " How to launch a single Intent to select images from either the Gallery or the Camera, or any application registered to browse the filesystem ". You are going to have to use this or a similar method to get the path to your image from the camera.

Scale :

Additionally, there is another problem that you are going to have to deal with. It will most likely be impossible to open a single full-size Bitmap representation of your image. It is just too big to fit into the available heap memory of the Android device. Therefore, you will have to open a scaled down version of your image. Fortunately, this is not very difficult to do using BitmapFactory.decodeFile(String pathName, BitmapFactory.Options opts) .

Example:

BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 4; // Arbitrary, your mileage may vary.
return BitmapFactory.decodeFile(path, options);

You can scale the image by 1, 2, 3, etc. times smaller using inSampleSize . There are even ways of calculating inSampleSize such as to keep the Bitmap below a particular byte size.