AlphaIsMaxRGB

background(255, 0, 0);
PImage img = loadImage("179033_486608097723_1903922_n.jpg");
img.loadPixels();
int n = img.width * img.height;
for (int i = 0; i < n; i++) {
  color c = img.pixels[i];
  float a = alpha(c);
  float r = red(c);
  float g = green(c);
  float b = blue(c);
  a = max(r, g, b);
  img.pixels[i] = color(r, g, b, a);
}
img.updatePixels();
image(img, 0, 0);