PImage    Simg; //Source image
 
void setup(){
  Simg = loadImage("./img/color.jpg");
  surface.setResizable(true);  //image size window
  surface.setSize(Simg.width, Simg.height);
  noLoop();
}
 
void draw(){
  background(128);  //Set bacground color
  PImage Dimg = createImage( Simg.width, Simg.height, RGB );
  Simg.loadPixels();
  for ( int y = 0; y < Simg.height; y++) {
    for ( int x = 0; x < Simg.width; x++) {
      int pos = x + y*Simg.width;
      color c = Simg.pixels[pos];
      float r = red( c );
      Dimg.pixels[pos] = color(r, 0, 0);
    }
  }
  Dimg.updatePixels();
  image( Dimg, 0, 0);  //Display
}