PImage obrazek;
float q = 0;
int value=0;
int step=5;
boolean inc=true;

void setup() {
    size(750, 500);
      background(0);
      obrazek = loadImage ("smutnypan.jpg");
}
void draw() {

  background(0);
  //imageMode (CENTER);
  image (obrazek, (375), (250), 325, 250);


  if(mouseX > 375 & mouseX < 375+325 & mouseY >250 & mouseY < 250+250 ) {
    fill(value,0,0);
      if(inc)value+=step;
      else value-=step;
      if(value>250)
      {
        inc=false;
        value=250;
      }
      if(value<0){
        inc=true;
        value=0;
      }
  } else {
    fill(0,127,0);
  }

  ellipse(mouseX, mouseY, 30, 30);

}