Example Android Gradient

• 

  Colorized image gradient being displayed on an Android phone.

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 ImageUInt8, 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: VideoActivity.java

Complete Project: Android Project

Concepts:

• Android
• Camera Preview
• Image Gradient

Related Tutorial:

• Android Support

Related Examples:

• Image Filter

Example Code

/**
 * Demonstration of how to process a video stream on an Android device using BoofCV.  Most of the drudgery of
 * video processing is handled by {@link VideoDisplayActivity}.  This class still needs to tell it which
 * camera to use and needs to select the optimal resolution.  The actual processing is done by {@link ShowGradient}
 * which is passed into the super class when {@link #onResume()} is called.
 *
 * @author Peter Abeles
 */
public class VideoActivity extends VideoDisplayActivity
{
	@Override
	protected void onResume() {
		super.onResume();
		setProcessing( new ShowGradient());

		// for fun you can display the FPS by uncommenting the line below.
		// The FPS will vary depending on processing time and shutter speed,
		// which is dependent on lighting conditions
//		setShowFPS(true);
	}

	@Override
	protected Camera openConfigureCamera( Camera.CameraInfo cameraInfo )
	{
		Camera mCamera = selectAndOpenCamera(cameraInfo);
		Camera.Parameters param = mCamera.getParameters();

		// Select the preview size closest to 320x240
		// Smaller images are recommended because some computer vision operations are very expensive
		List<Camera.Size> sizes = param.getSupportedPreviewSizes();
		Camera.Size s = sizes.get(closest(sizes,320,240));
		param.setPreviewSize(s.width,s.height);
		mCamera.setParameters(param);

		return mCamera;
	}

	/**
	 * Step through the camera list and select a camera.  It is also possible that there is no camera.
	 * The camera hardware requirement in AndroidManifest.xml was turned off so that devices with just
	 * a front facing camera can be found.  Newer SDK's handle this in a more sane way, but with older devices
	 * you need this work around.
	 */
	private Camera selectAndOpenCamera(Camera.CameraInfo info) {
		int numberOfCameras = Camera.getNumberOfCameras();

		int selected = -1;

		for (int i = 0; i < numberOfCameras; i++) {
			Camera.getCameraInfo(i, info);

			if( info.facing == Camera.CameraInfo.CAMERA_FACING_BACK ) {
				selected = i;
				break;
			} else {
				// default to a front facing camera if a back facing one can't be found
				selected = i;
			}
		}

		if( selected == -1 ) {
			dialogNoCamera();
			return null; // won't ever be called
		} else {
			return Camera.open(selected);
		}
	}

	/**
	 * Gracefully handle the situation where a camera could not be found
	 */
	private void dialogNoCamera() {
		AlertDialog.Builder builder = new AlertDialog.Builder(this);
		builder.setMessage("Your device has no cameras!")
				.setCancelable(false)
				.setPositiveButton("OK", new DialogInterface.OnClickListener() {
					public void onClick(DialogInterface dialog, int id) {
						System.exit(0);
					}
				});
		AlertDialog alert = builder.create();
		alert.show();
	}

	/**
	 * Goes through the size list and selects the one which is the closest specified size
	 */
	public static int closest( List<Camera.Size> sizes , int width , int height ) {
		int best = -1;
		int bestScore = Integer.MAX_VALUE;

		for( int i = 0; i < sizes.size(); i++ ) {
			Camera.Size s = sizes.get(i);

			int dx = s.width-width;
			int dy = s.height-height;

			int score = dx*dx + dy*dy;
			if( score < bestScore ) {
				best = i;
				bestScore = score;
			}
		}

		return best;
	}
}