Example Android Gradient

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Demonstration of how to capture and process a video stream in real-time using BoofCV on an Android device. On Android devices, video streams are accessed inside a camera preview, which require several hoops to be jumped through. What this example does is capture the image in NV21 format, convert it into an GrayU8, compute the image gradient, visualize the gradient in a Bitmap image, and display the results. Note that the example below is not entirely self contained, see the complete project for additional files.

Example File: GradientActivity.java

Complete Project: Android Project


  • Android
  • Camera Preview
  • Image Gradient

Related Tutorial:

Related Examples:

Example Code

 * Demonstrates how to use the visualize activity. A video stream is opened and the image gradient
 * is found. The gradient is then rendered into a format which can be visualized and displayed
 * on the Android device's screen.
 * This greatly simplifies the process of capturing and visualizing image data from a camera.
 * Internally it uses the camera 2 API. You can customize its behavior by overriding
 * different internal functions. For more details, see the JavaDoc of it's parent classes.
 * @see VisualizeCamera2Activity
 * @see boofcv.android.camera2.SimpleCamera2Activity
 * @author Peter Abeles
public class GradientActivity extends VisualizeCamera2Activity
	// Storage for the gradient
	private GrayS16 derivX = new GrayS16(1,1);
	private GrayS16 derivY = new GrayS16(1,1);

	// Storage for image gradient. In general you will want to precompute data structures due
	// to the expense of garbage collection
	private ImageGradient<GrayU8,GrayS16> gradient = FactoryDerivative.three(GrayU8.class, GrayS16.class);

	// Used to display text info on the display
	private Paint paintText = new Paint();

	public GradientActivity() {
		// The default behavior for selecting the camera's resolution is to
		// find the resolution which comes the closest to having this many
		// pixels.
		targetResolution = 640*480;

	protected void onCreate(Bundle savedInstanceState) {

		FrameLayout surface = findViewById(R.id.camera_frame);

		// By calling this function you are telling the camera library that you wish to process
		// images in a gray scale format. The video stream is typically in YUV420. Color
		// image formats are supported as RGB, YUV, ... etc, color spaces.

		// Configure paint used to display FPS
		paintText.setTypeface(Typeface.create(Typeface.MONOSPACE, Typeface.BOLD));

		// The camera stream will now start after this function is called.

	 * This is where you specify custom camera settings. See {@link boofcv.android.camera2.SimpleCamera2Activity}'s
	 * JavaDoc for more funcitons which you can override.
	 * @param captureRequestBuilder Used to configure the camera.
	protected void configureCamera(CameraDevice device, CameraCharacteristics characteristics, CaptureRequest.Builder captureRequestBuilder) {
		captureRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_VIDEO);
		captureRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON);

	 * During camera initialization this function is called once after the resolution is known.
	 * This is a good function to override and predeclare data structres which are dependent
	 * on the video feeds resolution.
	protected void onCameraResolutionChange( int width , int height, int sensorOrientation ) {
		super.onCameraResolutionChange(width, height,sensorOrientation);

		derivX.reshape(width, height);
		derivY.reshape(width, height);

	 * This function is invoked in its own thread and can take as long as you want.
	protected void processImage(ImageBase image) {
		// The data type of 'image' was specified in onCreate() function
		// The line below will compute the gradient and store it in two images. One for the
		// gradient along the x-axis and the other along the y-axis

	 * Override the default behavior and colorize gradient instead of converting input image.
	protected void renderBitmapImage(BitmapMode mode, ImageBase image) {
		switch( mode ) {
			case UNSAFE: { // this application is configured to use double buffer and could ignore all other modes
				VisualizeImageData.colorizeGradient(derivX, derivY, -1, bitmap, bitmapTmp);
			} break;

			case DOUBLE_BUFFER: {
				VisualizeImageData.colorizeGradient(derivX, derivY, -1, bitmapWork, bitmapTmp);

				if( bitmapLock.tryLock() ) {
					try {
						Bitmap tmp = bitmapWork;
						bitmapWork = bitmap;
						bitmap = tmp;
					} finally {
			} break;

	 * Demonstrates how to draw visuals
	protected void onDrawFrame(SurfaceView view, Canvas canvas) {
		super.onDrawFrame(view, canvas);

		// Display info on the image being process and how fast input camera
		// stream (probably in YUV420) is converted into a BoofCV format
		int width = bitmap.getWidth();
		int height = bitmap.getHeight();
				"%d x %d Convert: %4.1f (ms)",

		// Pro tip: Run in app fast or release mode for a dramatic speed up!
		// In Android Studio expand "Build Variants" tab on left.