/*
 * In this sketch, we use the luminosity formula to compute grayscale, but
 * then we adjust the image to be a gradient that transitions from the
 * original color (left) to pure grayscale (right).
 */

PImage slu;
int w,h;

void setup() {
  size(408,300);  // take advantage of our knowledge of the size

// Can either load an image stored locally, as follows:
//  slu = loadImage("campus4.jpg");
// Or can load an image from a URL as follows:
  slu = loadImage("http://business.slu.edu/uploads/2012/11/08/slu-homepage-campus4.jpg");

  w = slu.width;
  h = slu.height;

  for (int x=0; x < w; x++) {
    float pct = float(x)/(w-1);
    for (int y=0; y < h; y++) {
      color c = slu.get(x, y);
      float gray = (0.21 * red(c) + 0.72 * green(c) + 0.07 * blue(c));
      float r = gray * pct + red(c)*(1-pct);
      float g = gray * pct + green(c)*(1-pct);
      float b = gray * pct + blue(c)*(1-pct);
      color replace = color(r, g, b);
      slu.set(x, y, replace);
    }
  }

  // time to display it
  image(slu, 0, 0);
}