Camera preview image data processing with Android L and Camera2 API

Question

I'm working on an android app that is processing the input image from the camera and displays it to the user. This is fairly simple, I register a PreviewCallback on the camera object with the setPreviewCallbackWithBuffer. This is easy and works smoothly with the old camera API

public void onPreviewFrame(byte[] data, Camera cam) {
    // custom image data processing
}

I'm trying to port my app to take advantage of the new Camera2 API and I'm not sure how exactly shall I do that. I followed the Camera2Video in L Preview samples that allows to record a video. However, there is no direct image data transfer in the sample, so I don't understand where exactly shall I get the image pixel data and how to process it.

Could anybody help me or suggest the way how one can get the the functionality of PreviewCallback in android L, or how it's possible to process preview data from the camera before displaying it to the screen? (there is no preview callback on the camera object)

Thank you!

Answer 1

Combining a few answers into a more digestible one because @VP's answer, while technically clear, is difficult to understand if it's your first time moving from Camera to Camera2:

Using https://github.com/googlesamples/android-Camera2Basic as a starting point, modify the following:

In createCameraPreviewSession() init a new Surface from mImageReader

Surface mImageSurface = mImageReader.getSurface();

Add that new surface as a output target of your CaptureRequest.Builder variable. Using the Camera2Basic sample, the variable will be mPreviewRequestBuilder

mPreviewRequestBuilder.addTarget(mImageSurface);

Here's the snippet with the new lines (see my @AngeloS comments):

private void createCameraPreviewSession() {

    try {

        SurfaceTexture texture = mTextureView.getSurfaceTexture();
        assert texture != null;

        // We configure the size of default buffer to be the size of camera preview we want.
        texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());

        // This is the output Surface we need to start preview.
        Surface surface = new Surface(texture);

        //@AngeloS - Our new output surface for preview frame data
        Surface mImageSurface = mImageReader.getSurface();

        // We set up a CaptureRequest.Builder with the output Surface.
        mPreviewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);

        //@AngeloS - Add the new target to our CaptureRequest.Builder
        mPreviewRequestBuilder.addTarget(mImageSurface);

        mPreviewRequestBuilder.addTarget(surface);

        ...

Next, in setUpCameraOutputs(), change the format from ImageFormat.JPEG to ImageFormat.YUV_420_888 when you init your ImageReader. (PS, I also recommend dropping your preview size for smoother operation - one nice feature of Camera2)

mImageReader = ImageReader.newInstance(largest.getWidth() / 16, largest.getHeight() / 16, ImageFormat.YUV_420_888, 2);

Finally, in your onImageAvailable() method of ImageReader.OnImageAvailableListener, be sure to use @Kamala's suggestion because the preview will stop after a few frames if you don't close it

    @Override
    public void onImageAvailable(ImageReader reader) {

        Log.d(TAG, "I'm an image frame!");

        Image image =  reader.acquireNextImage();

        ...

        if (image != null)
            image.close();
    }