I'm trying to translate the following Python function, that applies a mask to an image, into Java:

# Applies an image mask.
def region_of_interest(img, vertices):
    #defining a blank mask to start with
    mask = np.zeros_like(img)   

    #defining a 3 channel or 1 channel color to fill the mask with depending on the input image
    if len(img.shape) > 2:
        channel_count = img.shape[2]  # i.e. 3 or 4 depending on your image
        ignore_mask_color = (255,) * channel_count
    else:
        ignore_mask_color = 255

    #filling pixels inside the polygon defined by "vertices" with the fill color    
    cv2.fillPoly(mask, vertices, ignore_mask_color)

    #returning the image only where mask pixels are nonzero
    masked_image = cv2.bitwise_and(img, mask)
    return masked_image

So far, this is what I've got:

public static opencv_core.Mat applyMask(opencv_core.Mat image, opencv_core.MatVector vertices) {
  opencv_core.Mat mask = opencv_core.Mat.zeros(image.size(), opencv_core.CV_8U).asMat();

  opencv_core.Scalar color = new opencv_core.Scalar(image.channels()); // 3
  double[] colors = new double[] {
    255.0, 255.0, 255.0, 255.0,
    255.0, 255.0, 255.0, 255.0,
    255.0, 255.0, 255.0, 255.0};
  color.put(colors, 0, colors.length);

  opencv_imgproc.fillPoly(mask, vertices, color);

  opencv_core.Mat dst = new opencv_core.Mat();
  opencv_core.bitwise_and(image, mask, dst);
  return dst;
}

But, it isn't working. When I try invoking this method like in the following example:

opencv_core.MatVector points = new opencv_core.MatVector(
  new opencv_core.Mat(2, 3, opencv_core.CV_32F, new IntPointer(1, 2, 3, 4, 5, 6))
);

opencv_core.MatVector vertices = new opencv_core.MatVector(points);
opencv_core.Mat masked = LaneManager.applyMask(src, vertices);

(I'm assuming this is the right way to build a 2x3 matrix of three points with two coordinates each (1,2), (3, 4) and (5,6))

I get an exception:

java.lang.RuntimeException: std::bad_alloc
at org.bytedeco.javacpp.opencv_imgproc.fillPoly(Native Method)

I'm using OpenCV as provided by org.bytedeco.javacpp-presets:opencv-platform:3.2.0-1.3 via Maven Central.

I must admit that I'm at a loss here: What's the idiomatic Java way of doing the same thing as the Python function above?