java - 错误，还是用户错误？在裁剪后的 Mat Image 上创建边框不会正确渲染最右边的边框线

Question

我正在为 OpenCv 使用 Java 绑定(bind)，并尝试为已裁剪的图像添加边框。然而，虽然边框在完整图像上按预期绘制了 100%，但如果我裁剪源图像，它不会正确绘制左侧。

例如:不爽猫

现在，为了添加边框，我或多或少地复制了 OpenCV border tutorial 中的代码。 .

例如

public class main {
   public static void main( String[] args )
   {
      try{
         System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
         Mat source = Highgui.imread("images\\original.jpg", Highgui.CV_LOAD_IMAGE_COLOR);


         Mat destination = new Mat(source.rows(),source.cols(),source.type());

         // make the border with a size of 10px for each side 
         Imgproc.copyMakeBorder(source, destination, 10, 10, 
                                10, 10, Imgproc.BORDER_CONSTANT, new Scalar(255,0,0));

         // Save the image
         Highgui.imwrite("images\\borderWrap.jpg", destination);
         }
         catch (Exception e) {
            System.out.println("error: " + e.getMessage());
         }
   }
}

运行这段代码，我得到了一个漂亮的边框，每边都像预期的那样有 10px。

现在，如果我修改代码以首先裁剪图像，这将按预期停止工作。

public class main {
   public static void main( String[] args )
   {
      try{
         System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
         Mat isource = Highgui.imread("images\\original.jpg", Highgui.CV_LOAD_IMAGE_COLOR);

         // crop the image to half of its width
         Mat source = new Mat(isource, new Rect(0, 0, 480, 540)); 

         Mat destination = new Mat(source.rows(),source.cols(),source.type());

         // make the border with a size of 10px for each side 
         Imgproc.copyMakeBorder(source, destination, 10, 10, 
                                10, 10, Imgproc.BORDER_CONSTANT, new Scalar(255,0,0));

         // Save the image
         Highgui.imwrite("images\\borderWrap.jpg", destination);
         }
         catch (Exception e) {
            System.out.println("error: " + e.getMessage());
         }
   }
}

它不绘制边框的右侧。这是一个错误，还是我做错了什么？

现在，如果我再次调用 copyMakeBorder，但这次只有最右边的边框参数有一个值，它将正确地填充它。

 // First border pass (doesn't draw right size)
 Imgproc.copyMakeBorder(source, destination, 10, 10, 
                                                10, 10, Imgproc.BORDER_CONSTANT, 
                                                new Scalar(255,0,0));

 //Second border pass -- only rightmost param is supplied a size      
 Imgproc.copyMakeBorder(destination, destination, 0, 0, 
                                                        0, 10, Imgproc.BORDER_CONSTANT, 
                                                        new Scalar(255,0,0));

有人知道这里发生了什么吗？

Answer 1

来自 Imgproc.copyMakeBorder javadoc:

When the source image is a part (ROI) of a bigger image, the function will try to use the pixels outside of the ROI to form a border. To disable this feature and always do extrapolation, as if src was not a ROI, use borderType BORDER_ISOLATED.

因此，如果您切换到 Imgproc.BORDER_ISOLATED 常量，它应该可以正常工作(确实如此):

Imgproc.copyMakeBorder(source, destination, 10, 10, 10, 10,
        Imgproc.BORDER_ISOLATED, new Scalar(255,0,0));