Camera2 api with Preview

Question

I am using the Camera2 api to show a preview form the camera. I also want to implement a ImageReader to process the images. I have a Start preview function. When I call it the preview is just black. If I remove "mimageReader.getSurface()" from Arrays.asList() I am able to see the camera preview. How can I have a camera preview show up and also use ImageReader?

 private void startPreview() 
  {
        List<Surface> outputSurfaces = new ArrayList<>();
        List surfaces = new ArrayList<>();

        SurfaceTexture surfaceTexture =  textureView.getSurfaceTexture();
        surfaceTexture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
        Surface previewSurface = new Surface(surfaceTexture);

        try {
            mCaptureRequestBuilder = _cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);




           mCaptureRequestBuilder.addTarget(previewSurface);

            _cameraDevice.createCaptureSession(Arrays.asList(previewSurface,mimageReader.getSurface()),
                    new CameraCaptureSession.StateCallback() {
                        @Override
                        public void onConfigured(CameraCaptureSession session) {
                            Log.d("", "onConfigured: startPreview");

                            try {
                                session.setRepeatingRequest( mCaptureRequestBuilder.build(),null,mthreadhandler);
                            } catch (CameraAccessException e) {
                                e.printStackTrace();
                            }
                        }

                        @Override
                        public void onConfigureFailed(CameraCaptureSession session) {
                            Log.d("", "onConfigureFailed: startPreview");

                        }
                    }, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

score 0 · Answer 1 · answered Jul 05 '17 at 02:23

You have to create a new instance of ImageReader, set its onImageAvailableListener(you can process the preview frames here) and add it to PreviewRequestBuilder. For example:

mImageReader = ImageReader.newInstance(
                mPreviewSize.getWidth(), mPreviewSize.getHeight(), ImageFormat.YUV_420_888, 2);

mImageReader.setOnImageAvailableListener(mOnGetPreviewListener, mBackgroundHandler);

mPreviewRequestBuilder.addTarget(mImageReader.getSurface());

score 0 · Answer 2 · answered Jul 25 '19 at 09:43

It may be because your function startPreview() is not called, it can happens when we don't get surfaceTexture values at time.

This is my startPreview method

protected void createCameraPreview() {
    try {
        SurfaceTexture texture = textureView.getSurfaceTexture();
        assert texture != null;

        texture.setDefaultBufferSize(imageDimension.getWidth(), imageDimension.getHeight());
        Surface surface = new Surface(texture);

        captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);

        captureRequestBuilder.addTarget(surface);
        cameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback(){
            @Override
            public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
                //The camera is already closed
                if (null == cameraDevice) {
                    return;
                }
                // When the session is ready, we start displaying the preview.
                cameraCaptureSessions = cameraCaptureSession;
                updatePreview();
            }
            @Override
            public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
                Toast.makeText(MainActivity.this, "Configuration change", Toast.LENGTH_SHORT).show();
            }
        }, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

Then i call updatePreview function to restart the preview

protected void updatePreview() {
    if(null == cameraDevice) {
        Log.e(TAG, "updatePreview error, return");
    }
    captureRequestBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
    try {
        cameraCaptureSessions.setRepeatingRequest(captureRequestBuilder.build(), null, mBackgroundHandler);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

Camera2 api with Preview

2 Answers2