code: function saveImage(rect) {
          if (DEBUG && rect && !rect.bottom) inspectArgs("saveImage: ", rect);
  
          if (rect && typeof rect.bottom === "number") {
              phPage.property("clipRect", rect);
          }
  
          // Set a timeout to give the page a chance to render.
          setTimeout(function () {
              phPage.render(option.output)
                    .then(function () {
                        phInstance.exit();
                        // process.removeListener("uncaughtException", onUncaughtException);
                        process.nextTick(callback);
                    });
          }, option.renderdelay || 250);
      }
docs: Output the saved image to the specified file.