code: public void undim(int duration) {
          if (mDimView != null && mDimView.isShown() && mDimView.getAlpha() != 0) {
              mDimView.animate().cancel();
              mDimView.animate().alpha(0.0f)
                  .setListener(mDimAnimatorListener)
                  .setDuration(duration)
                  .start();
          }
      }
docs: Start the undim animation.
  
  @param duration