OpenCV with Android SDK Camera

Original Post Here – Using Android SDK Camera with OpenCV on my blog.

So I’m currently working on HTC Evo V 4G and was desparately trying to obtain images from both the camera. One thing was sure that I couldn’t use OpenCV’s Java Camera or Native Camera (it doesn’t even work with ICS). I decided to use Android SDK Camera. I tried posting question on stackoverflow and OpenCV forum, but couldn’t find any proper solutions. I tried taking pieces of code from wherever I could and wrote something, but it wouldn’t work. I also found a perfectly working code but it was giving me Static Linkage Errors. It meant the OpenCV manager couldn’t be loaded in the application. I had done everything step by step but it wasn’t working.

Since my phone has two back cameras (stereoscopic), I was finding it very difficult to access both the cameras and convert it to OpenCV images (Mat format). Someone adviced me to use HTC Open Sense SDK to access both the cameras. So I downloade HTC Open Sense SDK and installed it as mentioned on HTC Website. I loaded one of the example applications on the phone and started using it. It worked alright. I browsed the source and found a code which used 3D camera. You can find it on HTC Website

So, I used it as the base of my code. Tried it and switced off the 2D view. So far so good. The applicaiton was working fine. Dan advised me to use Camera Intent. I tried Camera Intent and it turned out to be very good. It started a new thread/application which captured image on pressing the button and also asked whether you wanted to save it or not. Pretty useful application. But it couldn’t be used in my case becuase whenever I used Intent, it started the camera in 2D mode, i.e. only one camera was capturing the image. So I had to look for some other solution.

There’s a similar question on stackoverflow which proved to be very useful. Using the code provided to capture images and store it in bytes, I used OpenCV Mat’s put instance to store the data in OpenCV Mat. Plus, I edited the HTC code a bit for my own use so that I could use both cameras and store the image data in bytes.

Whenevr I pressed on text/button, using onTouchEvent, I’d use addCallbackBuffer and setPreviewCallbackWithBuffer to get the raw image data in bytes.

public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
    //  toggle();
        //Intent cameraIntent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE); 
        //startActivityForResult(cameraIntent, 1337);
        int bufferSize = width * height * 3;
        byte[] mPreviewBuffer = null;

        // New preview buffer.
        mPreviewBuffer = new byte[bufferSize + 4096];

        // with buffer requires addbuffer.
    return true;

Now, the function where I’d store the bytes data in OpenCV Mat.

private final Camera.PreviewCallback mCameraCallback = new Camera.PreviewCallback() {
public void onPreviewFrame(byte[] data, Camera c) {
    Log.d(TAG, "ON Preview frame");
    img = new Mat(height, width, CvType.CV_8UC1);
    gray = new Mat(height, width, CvType.CV_8UC1);
    img.put(0, 0, data);        
    Imgproc.cvtColor(img, gray, Imgproc.COLOR_YUV420sp2GRAY);
    String pixvalue = String.valueOf(gray.get(300, 400)[0]);
    String pixval1 = String.valueOf(gray.get(300, 400+width/2)[0]);
    Log.d(TAG, pixvalue);
    Log.d(TAG, pixval1);
        // to do the camera image split processing using "data"

The image that we get from Android SDK Camera is in YUV420s Colorspace and we wanted it in BGRA/Grayscale corolspace. So we tried converting it, but we were getting only 0.0 as the data, so we figured there was some problem with YUV420s colorspace format. We looked up on the google and realized that OpenCV requires only 1 channel (not 4 or 3 channel) Mat to store YUV420S colorspace image. So, now we have both the images stored in Mat. Both images are places side by side. We can use both the images by splitting the Mat in half.

So this is a way to use Android SDK Camera to take image and convert it OpenCV Mat. I have posted the solution on stackoverflow. You can find it here.

P.S. More posts to come on image stitching and Android.


Super Sunday

A super sunday :
sleep at 4 in morning. Wake up at 1:15 because there is a BANG on your door . Eat lunch and ice cream. Read and pretend that you are actually doing something about Java. But the truth is you are not. You are just lost in your thoughts, your imagination. Wondering about “the girl”, listening to music, but you are so much engrossed in your imagination that you don’t even recognize that the loudest iron maiden song is playing on full volume until you snap out of your imagination just because you have another random thought !!
Masala dosa for snacks. And cheese maggi for after snacks. 😛
Then you come back to your room and start doing some random things on your laptop. You do random searches on twitter and bump into a bitsian profile and go to his blog. Coincidentally the blog is so good that you get lost in it and read it from bottom to top. Still you have no sense of time. You keep on reading it further and laugh occasionally because you feel the story resembles to your life a bit. Then you finish reading it and think to write something as cool as that blog. But again you are lost in some other thoughts and totally forget about it. The Beatles, Pink Floyd, The Doors, Iron Miaden, Dio are on your playlist adding upto total of more than 800 songs with some hindi music, but you still don’t recognize what music is being played or maybe you don’t even care !!
Time is passing by, you are lazing in your room, you hear some random shouts as manu  vs liverpool match and india vs ireland match is going on, but you don’t care. you don’t even care that random music is being played since you woke up. You just want to lie in bed and do nothing but gaze ! And also you want to post all this.
You don’t care that your room is so messed up. You don’t care that temperature is so high that you are sweating. You just want to lie in bed and indistinctively listen or just pretend to listen what song is being played. You don’t even care about dinner ! Just close your eyes and gaze at whatever you can see. And do not try to think anything.
Aah… this is a super sunday !!
Now, I don’t even care to write more.
P.S. This post is updated via Android