void nlfilter(image& img, std::size_t w, std::size_t h,
std::function<image::pixel_t(const ublas::matrix<image::pixel_t>&)> f)
{
auto iw = img.width();
auto ih = img.height();
// The number of rows above/aside the center element
auto top = static_cast<std::size_t>(std::floor(h / 2.0));
auto left = static_cast<std::size_t>(std::floor(w / 2.0));
// We must store the result and set the image to it after we have processed
// the image as subsequent regions may need to use the unchanged pixel at
// a location we have already modified.
ublas::matrix<image::pixel_t> result(iw, ih);
for(decltype(iw) x = 0; x < iw; ++x) {
for(decltype(ih) y = 0; y < ih; ++y) {
// img.region works from the top left of the region so we must
// offset it so that (x, y) is at the center.
result(x, y) = f(img.region(x - left, y - top, w, h));
}
}
img.set(0, 0, result);
}
