code: public static String roundCorner(int radiusInner, int radiusOuter, int color) {
      if (radiusInner < 1) {
        throw new IllegalArgumentException("Radius must be greater than zero.");
      }
      if (radiusOuter < 0) {
        throw new IllegalArgumentException("Outer radius must be greater than or equal to zero.");
      }
      StringBuilder builder = new StringBuilder(FILTER_ROUND_CORNER).append("(").append(radiusInner);
      if (radiusOuter > 0) {
        builder.append("|").append(radiusOuter);
      }
      final int r = (color & 0xFF0000) >>> 16;
      final int g = (color & 0xFF00) >>> 8;
      final int b = color & 0xFF;
      return builder.append(",") //
          .append(r).append(",") //
          .append(g).append(",") //
          .append(b).append(")") //
          .toString();
    }
docs: This filter adds rounded corners to the image using the specified color as the background.
  
  @param radiusInner amount of pixels to use as radius.
  @param radiusOuter specifies the second value for the ellipse used for the radius. Use 0 for
  no value.
  @param color fill color for clipped region.