Update app.py

app.py

@@ -8,6 +8,9 @@ def greet(image, in_contrast, in_brightness):
     # brightness [0-100]
     # https://docs.opencv.org/4.x/d3/dc1/tutorial_basic_linear_transform.html
     new_image = cv2.convertScaleAbs(image, alpha=in_contrast, beta=in_brightness)
+
+    cv2.imshow("Display window", new_image);
+    int k = waitKey(0); // Wait for a keystroke in the window
     return new_image