java - 不使用 ConvolveOp 的高斯滤波器

Question

我正在尝试在不使用 ConvolveOp 的情况下创建高斯滤波器。 我在尝试让它工作时遇到了很多问题，我已经有了一个可以工作的灰度滤镜，但是对于这个，我在查找像素 8 邻居的位置时遇到了问题，所以我可以应用该滤镜。这是我到目前为止所拥有的。这是获取每个像素的正确方法吗？

public class Gaussian implements Filter {


   public void filter(PixelImage pi) {
    Pixel[][] data = pi.getData();
    Pixel[][] original = data;


    int kernel_rows = 3;
    int kernel_cols = 3;

    // define kernel here (double loop), these are the 1/16, 2/16, etc...
    // values that you're multiplying the image pixels by
    double[][] kernel = {{1,2,1},
      {2,4,2},
      {1,2,1}};

    // iterate over each pixel in the image
    for (int row = 0; row < pi.getHeight(); row ++) {
      for (int col = 0; col < pi.getWidth(); col++) {
        // iterate over each pixel in the kernel
        for (int row_offset = 0 ; row_offset < kernel_rows ; row_offset++ ) {
          for (int col_offset = 0 ; col_offset < kernel_cols ; col_offset++ ) {

            // subtract by half the kernel size to center the kernel
            // on the pixel in question
            // ** you'll have to modify to account for boundary conditions **
            int row_index = row + row_offset - kernel_rows/2;
            int col_index = col + col_offset - kernel_cols/2;

            int r =0;
            int g =0;
            int b =0;




            r += (data[row_index][col_index].red * kernel[row_offset][col_offset])/16;
            g += (data[row_index][col_index].green * kernel[row_offset][col_offset])/16;
            b += (data[row_index][col_index].blue * kernel[row_offset][col_offset])/16;
            Pixel temp =new Pixel( r, g, b );
            original[row][col] = temp;
          }
        }
        data = original;
        pi.setData(data);

      }
    }
   }
}

Answer 1

卷积本质上是一个四重嵌套循环:两个循环遍历图像中的像素，并且在每个像素处，两个循环遍历内核中的像素。

因此，您可以使用如下方式显着清理代码:

   int kernel_rows = 3;
   int kernel_cols = 3;

   // define kernel here (double loop), these are the 1/16, 2/16, etc...
   // values that you're multiplying the image pixels by
   double[][] kernel = ... 

   // iterate over each pixel in the image
   // leave a kernel_rows/2 sized gap around the edge of the image
   // so that we don't run into IndexOutOfBounds exceptions
   // when performing the convolution
   for (int row = kernel_rows/2; row < pi.getHeight() - kernel_rows/2; row ++) {
     for (int col = kernel_cols/2; col < pi.getWidth() - kernel_cols/2; col++) {

       int r = 0;
       int g = 0;
       int b = 0;

       // iterate over each pixel in the kernel
       for (int row_offset = 0 ; row_offset < kernel_rows ; row_offset++ ) {
         for (int col_offset = 0 ; col_offset < kernel_cols ; col_offset++ ) {

           // subtract by half the kernel size to center the kernel
           // on the pixel in question
           int row_index = row + row_offset - kernel_row/2;
           int col_index = col + col_offset - kernel_cols/2

           r += data[row_index][col_index].red * kernel[row_offset][col_offset];
           g += data[row_index][col_index].green * kernel[row_offset][col_offset];
           b += data[row_index][col_index].blue * kernel[row_offset][col_offset];

         }
       }

     data[row][col] = new Pixel( r, g, b );

     }
   }