/*
 * 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 to the full grayscale.
 */

// Can either load an image stored locally, as follows:
// PImage slu = loadImage("campus4.jpg");

// Or can load an image from a URL
PImage slu = loadImage("http://business.slu.edu/uploads/2012/11/08/slu-homepage-campus4.jpg");

int w = slu.width;
int 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
size(w,h);
image(slu,0,0);