// from http://www.jhlabs.com/ip/filters/download.html

/*
Copyright 2006 Jerry Huxtable

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/**
 * A filter which replcaes each pixel by the mimimum of itself and its eight neightbours.
 */
sclass MinimumFilter extends WholeImageFilter {
  int hRadius;
  int vRadius;

  *() { this(1); }
  *(int radius) { hRadius = vRadius = radius; }
  *(int *hRadius, int *vRadius) {}
  
  protected int[] filterPixels( int width, int height, int[] inPixels, Rectangle transformedSpace ) {
    int index = 0;
    int[] outPixels = new int[width * height];
    int y1 = -vRadius/2, y2 = y1+vRadius;
    int x1 = -hRadius/2, x2 = x1+hRadius;

    for (int y = 0; y < height; y++) {
      for (int x = 0; x < width; x++) {
        int pixel = 0xffffffff;
        for (int dy = y1; dy <= y2; dy++) {
          int iy = y+dy;
          int ioffset;
          if (0 <= iy && iy < height) {
            ioffset = iy*width;
            for (int dx = x1; dx <= x2; dx++) {
              int ix = x+dx;
              if (0 <= ix && ix < width) {
                pixel = PixelUtils.combinePixels(pixel, inPixels[ioffset+ix], PixelUtils.MIN);
              }
            }
          }
        }
        outPixels[index++] = pixel;
      }
    }
    ret outPixels;
  }
}

Began life as a copy of #1018734