Capturing camera frame in android after face detection

Question

I am working with face detection in Android and I want achieve the following:
1. Use face detection listener in Android for detecting faces on camera frame.
2. If a face is detected on the camera frame, then extract the face and save it to external storage.

After surfing through existing questions, I have found that there is no direct way to convert detected face to bitmap and store it on the disk. So now I want to capture and save the entire camera frame in which the face has been detected and I have not been able to do so.

The current code structure is as follows:

FaceDetectionListener faceDetectionListener = new FaceDetectionListener() {

    @Override
    public void onFaceDetection(Face[] faces, Camera camera) {

        if (faces.length == 0) {
        } else {
            displayMessage("Face detected!");   
            // CODE TO SAVE CURRENT FRAME AS IMAGE
            finish();
        }
    }
};

I tried to achieve this by calling takePicture in the above method but I was unable to save the frame using that approach. Kindly suggest a way in which I can save the camera frame.

Answer 1

I could not figure out a direct way to save the camera frame within FaceDetectionListener. Therefore, for my application, I changed the way in which I was handling the camera preview data. I used the PreviewCallback interface of Camera class and implemented the logic in onPreviewFrame method of the interface. The outline of implementation is as follows:

class SaveFaceFrames extends Activity implements Camera.PreviewCallback, Camera.FaceDetectionListener {

    boolean lock = false; 

    public void onPreviewFrame(byte[] data, Camera camera) {
        ...
        if(lock) {
            Camera.Parameters parameters = camera.getParameters();
            Camera.Size size = parameters.getPreviewSize();
            YuvImage image = new YuvImage(data, parameters.getPreviewFormat(), size.width, size.height, null);
            ByteArrayOutputStream outstr = new ByteArrayOutputStream();
            image.compressToJpeg(new Rect(0, 0, image.getWidth(), image.getHeight()), 100, outstr);
            Bitmap bmp = BitmapFactory.decodeByteArray(outstr.toByteArray(), 0, outstr.size());
            lock = false;
        }
    }

    public void onFaceDetection(Camera.Face[] faces, Camera camera) {
        ...
        if(!lock) {
            if(faces.length() != 0) lock = true;
        }
    }
}

This is not an ideal solution, but it worked in my case. There are third party libraries which can be used in these scenarios. One library which I have used and works very well is Qualcomm's Snapdragon SDK. I hope someone finds this useful.