翻译 Python 函数以将蒙版应用于图像到 Java

Question

我正在尝试将以下用于将掩码应用于图像的 Python 函数转换为 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

到目前为止，这就是我所拥有的：

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;
}

但是，它不起作用。当我尝试调用此方法时，如下例所示：

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);

（我假设这是构建一个由三个点组成的 2x3 矩阵的正确方法，每个点有两个坐标 (1,2)、(3, 4) 和 (5,6)）

我得到一个例外：

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

我正在使用 org.bytedeco.javacpp-presets:opencv-platform:3.2.0-1.3 通过 Maven Central 提供的 OpenCV。

我必须承认我在这里不知所措：与上面的 Python 函数做同样事情的惯用 Java 方式是什么？

Answer 1

好吧，我终于想通了。如果你定义你的坐标：

int[] points = new int[] {x1, y1, x2, y2, ...};

然后您可以使用以下代码简单地应用掩码：

opencv_core.Mat mask = new opencv_core.Mat(image.size(), image.type());

// Array of polygons where each polygon is represented as an array of points
opencv_core.Point polygon = new opencv_core.Point();
polygon.put(points, 0, points.length);
opencv_imgproc.fillPoly(mask, polygon, new int[] {points.length / 2}, 1, new opencv_core.Scalar(255, 255, 255, 0));

opencv_core.Mat masked = new opencv_core.Mat(image.size(), image.type());
opencv_core.bitwise_and(image, mask, masked);

其中image 是原始图像，masked 是蒙版结果。

问题在于原始点列表没有正确定义。

Answer 2

也许一些高手有完整的答案。这里值得深思：

1. Java API 是 CPP API 的直接副本：http://opencv.org/opencv-java-api.html

2. 错误std::bad_alloc 发生在您未能分配所需的存储空间时。 (http://answers.opencv.org/question/28959/cascade-training-killed-and-bad_alloc/)

3. 有两种 CPP 方法：
   • C++：void fillPoly(Mat& img, const Point** pts, const int* npts, int ncontours, const Scalar& color, int lineType=LINE_8, int shift=0, Point offset=Point() )，和
   • C++：void fillPoly(InputOutputArray img, InputArrayOfArrays pts, const Scalar& color, int lineType=LINE_8, int shift=0, Point offset=Point() )

4. 您不需要从Mat 转换为InputArray，但您可以（并且应该）只传递一个Mat 对象，其中请求InputArray (https://stackoverflow.com/a/32976883/1587329)