// This program shows how to you can access pixels 
// and separate out the rgb values. You can then 
// modify these rgb values if desired.

// The original image
PImage orig;
orig = loadImage("tree.png");

size(orig.width, orig.height);

loadPixels(); 
for (int i = 0; i < height*width; i++) {

  // The functions red(), green(), and blue() pull out the 3 color components from a pixel.
  // The values of r,g,b are in the range 0 to 255
  float r = red(orig.pixels[i]);
  float g = green(orig.pixels[i]);
  float b = blue(orig.pixels[i]);

  pixels[i] =  color(r, g, b);
}

updatePixels();