light_sort.pde

final int threshold = 38;
final color black = color(0);
final color white = color(255);

PImage img;
boolean isSorted = false;

void setup() {
  img = loadImage("IMG_0010.jpg");
  size(1, 1);
  img.loadPixels();
}

void draw() {
  if (isSorted) return;
  
  PImage filtered = filter(img, threshold);
  filtered.loadPixels();
  for (int x = 0; x < img.width; x++) {
    sortColumn(x, 0, getEnd(x, filtered));
  }
  isSorted = true;
  img.updatePixels();
  img.save("landscape-reverse-sorted.jpg");
  exit();
}

PImage filter(PImage source, color threshold) {
  PImage filtered = createImage(source.width, source.height, RGB);
  for (int x = 0; x < source.width; x++) {
    for (int y = 0; y < source.height; y++ ) {
      int i = x + y * source.width;
      filtered.pixels[i] = brightness(source.pixels[i]) > threshold
                           ? white
                           : black;
    }
  }
  return filtered;
}

void sortColumn(int col, int start, int end) {
  int sortLength = end - start;
  color[] unsorted = new color[sortLength];
  for(int i = 0; i < sortLength; i++) {
    unsorted[i] = img.pixels[col + i * img.width];
  }
  color[] sorted = reverse(sort(unsorted));
  for(int i = 0; i < sortLength; i++) {
    img.pixels[col + i * img.width] = sorted[i];
  }
}

int getEnd(int col, PImage brightMap) {
  for (int i = 0; i < img.height; i++) {
    if (brightMap.pixels[col + i * img.width] == black) {
      return i;
    }
  }
  return img.height;
}