Update app.py

app.py

@@ -40,7 +40,8 @@ def concate_image(img_input):
         img2 = cv2.imread(img_name_lst[1])
         im_v = cv2.vconcat([img1, img2])
         cv2.imwrite('merge_image.jpg', im_v)
-        return "merge_image.jpg"
+        cv2.cvtColor('merge_image.jpg', cv2.COLOR_RGB2GRAY)
+        return 'merge_image.jpg'
 
 def encode_image(image_path):
     file_path = concate_image(image_path)