hilbert_dither.pde

int order = 10;
int N = int(pow(2, order));
int total = N * N;

PVector[] path = new PVector[total];

PImage img;

void setup() {
  size(1024, 1024);
  background(0);

  for (int i = 0; i < total; i++) {
    path[i] = hilbert(i);
    float len = width / N;
    path[i].mult(len);
    path[i].add(len/2, len/2);
  }
  
  img = loadImage("cabana_square.jpg");
  img.loadPixels();
  assert(img.pixels.length == path.length);
  
  int error = 0;
  for (int i = 0; i < path.length; i++) {
    int index = int(path[i].x) + int(path[i].y) * width;
    int bOriginal = int(brightness(img.pixels[index]));
    int b = bOriginal;
    b += error;
    b /= 255;
    if (b == 1) {
      error = error - (255 - bOriginal);
    } else {
      error = error + bOriginal;
    }
    //b = 1 - b;
    b *= 255;
    img.pixels[index] = color(b, 255);
  }
  img.updatePixels();
  
  image(img, 0, 0);
  img.save("out.jpg");
  println("done");
  noLoop();
}

PVector hilbert(int i) {
  PVector[] points = {
    new PVector(0, 0), 
    new PVector(0, 1), 
    new PVector(1, 1), 
    new PVector(1, 0)
  };

  int index = i & 3;
  PVector v = points[index];

  for (int j = 1; j < order; j++) {
    i = i >>> 2;
    index = i & 3;
    float len = pow(2, j);
    if (index == 0) {
      float temp = v.x;
      v.x = v.y;
      v.y = temp;
    } else if (index == 1) {
      v.y += len;
    } else if (index == 2) {
      v.x += len;
      v.y += len;
    } else if (index == 3) {
      float temp = len - 1 - v.x;
      v.x = len - 1 - v.y;
      v.y = temp;
      v.x += len;
    }
  }
  return v;
}

hilbert_dither_rgb.pde

int order = 10;
int N = int(pow(2, order));
int total = N * N;

PVector[] path = new PVector[total];

PImage img;

void setup() {
  size(1024, 1024);
  background(0);

  for (int i = 0; i < total; i++) {
    path[i] = hilbert(i);
    float len = width / N;
    path[i].mult(len);
    path[i].add(len/2, len/2);
  }
  
  img = loadImage("cabana_square.jpg");
  img.loadPixels();
  assert(img.pixels.length == path.length);
  
  int error = 0;
  for (int i = 0; i < path.length; i++) {
    int index = int(path[i].x) + int(path[i].y) * width;
    int bOriginal = int(red(img.pixels[index]));
    int b = bOriginal;
    b += error;
    b /= 255;
    if (b == 1) {
      error = error - (255 - bOriginal);
    } else {
      error = error + bOriginal;
    }
    b *= 255;
    img.pixels[index] = color(b, green(img.pixels[index]), blue(img.pixels[index]), 255);
  }
  img.updatePixels();
  
  error = 0;
  for (int i = 0; i < path.length; i++) {
    int index = int(path[i].x) + int(path[i].y) * width;
    int bOriginal = int(green(img.pixels[index]));
    int b = bOriginal;
    b += error;
    b /= 255;
    if (b == 1) {
      error = error - (255 - bOriginal);
    } else {
      error = error + bOriginal;
    }
    b *= 255;
    img.pixels[index] = color(red(img.pixels[index]), b, blue(img.pixels[index]), 255);
  }
  img.updatePixels();
  
  error = 0;
  for (int i = 0; i < path.length; i++) {
    int index = int(path[i].x) + int(path[i].y) * width;
    int bOriginal = int(blue(img.pixels[index]));
    int b = bOriginal;
    b += error;
    b /= 255;
    if (b == 1) {
      error = error - (255 - bOriginal);
    } else {
      error = error + bOriginal;
    }
    b *= 255;
    img.pixels[index] = color(red(img.pixels[index]), green(img.pixels[index]), b, 255);
  }
  img.updatePixels();
  
  image(img, 0, 0);
  img.save("out.jpg");
  println("done");
  noLoop();
}

PVector hilbert(int i) {
  PVector[] points = {
    new PVector(0, 0), 
    new PVector(0, 1), 
    new PVector(1, 1), 
    new PVector(1, 0)
  };

  int index = i & 3;
  PVector v = points[index];

  for (int j = 1; j < order; j++) {
    i = i >>> 2;
    index = i & 3;
    float len = pow(2, j);
    if (index == 0) {
      float temp = v.x;
      v.x = v.y;
      v.y = temp;
    } else if (index == 1) {
      v.y += len;
    } else if (index == 2) {
      v.x += len;
      v.y += len;
    } else if (index == 3) {
      float temp = len - 1 - v.x;
      v.x = len - 1 - v.y;
      v.y = temp;
      v.x += len;
    }
  }
  return v;
}