python: 'cv2.' -> 'cv.' via 'import cv2 as cv'

doc/py_tutorials/py_gui/py_trackbar/py_trackbar.markdown

@@ -5,7 +5,7 @@ Goal
 ----
 
 -   Learn to bind trackbar to OpenCV windows
--   You will learn these functions : **cv2.getTrackbarPos()**, **cv2.createTrackbar()** etc.
+-   You will learn these functions : **cv.getTrackbarPos()**, **cv.createTrackbar()** etc.
 
 Code Demo
 ---------
@@ -14,7 +14,7 @@ Here we will create a simple application which shows the color you specify. You
 shows the color and three trackbars to specify each of B,G,R colors. You slide the trackbar and
 correspondingly window color changes. By default, initial color will be set to Black.
 
-For cv2.getTrackbarPos() function, first argument is the trackbar name, second one is the window
+For cv.getTrackbarPos() function, first argument is the trackbar name, second one is the window
 name to which it is attached, third argument is the default value, fourth one is the maximum value
 and fifth one is the callback function which is executed everytime trackbar value changes. The
 callback function always has a default argument which is the trackbar position. In our case,
@@ -25,43 +25,43 @@ doesn't have button functionality. So you can use trackbar to get such functiona
 application, we have created one switch in which application works only if switch is ON, otherwise
 screen is always black.
 @code{.py}
-import cv2
 import numpy as np
+import cv2 as cv
 
 def nothing(x):
     pass
 
 # Create a black image, a window
 img = np.zeros((300,512,3), np.uint8)
-cv2.namedWindow('image')
+cv.namedWindow('image')
 
 # create trackbars for color change
-cv2.createTrackbar('R','image',0,255,nothing)
-cv2.createTrackbar('G','image',0,255,nothing)
-cv2.createTrackbar('B','image',0,255,nothing)
+cv.createTrackbar('R','image',0,255,nothing)
+cv.createTrackbar('G','image',0,255,nothing)
+cv.createTrackbar('B','image',0,255,nothing)
 
 # create switch for ON/OFF functionality
 switch = '0 : OFF \n1 : ON'
-cv2.createTrackbar(switch, 'image',0,1,nothing)
+cv.createTrackbar(switch, 'image',0,1,nothing)
 
 while(1):
-    cv2.imshow('image',img)
-    k = cv2.waitKey(1) & 0xFF
+    cv.imshow('image',img)
+    k = cv.waitKey(1) & 0xFF
     if k == 27:
         break
 
     # get current positions of four trackbars
-    r = cv2.getTrackbarPos('R','image')
-    g = cv2.getTrackbarPos('G','image')
-    b = cv2.getTrackbarPos('B','image')
-    s = cv2.getTrackbarPos(switch,'image')
+    r = cv.getTrackbarPos('R','image')
+    g = cv.getTrackbarPos('G','image')
+    b = cv.getTrackbarPos('B','image')
+    s = cv.getTrackbarPos(switch,'image')
 
     if s == 0:
         img[:] = 0
     else:
         img[:] = [b,g,r]
 
-cv2.destroyAllWindows()
+cv.destroyAllWindows()
 @endcode
 The screenshot of the application looks like below :