Update usv_software_perception.rst

source/usv/usv_software_perception.rst

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 Perception
 ==========
+
+Start using OpenCV with Python
+--------------------------------------------------
+
+Authors:
+
+* Alejandro Hernández
+* Eduardo 
+* Alberto
+* Pequeño
+* Alexa Arreola
+
+First practice: Canny
+------------
+
+Canny() is used to detect edges in an image.
+
+.. code-block:: python
+
+  import numpy as np
+  import cv2 #importamos opencv2
+  import sys
+
+
+  #imread loads an image from a path, supports .jpg, .jpeg, .png, .tiff, .exr, etc... : https://docs.opencv.org/3.4/d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56
+  image = cv2.imread('C:\\Users\\oscar\\Downloads\\img1.jpeg',0) # 0 is used to read in grayscale mode
+  #Comment: the path's format can change
+  #Ex.: image = cv2.imread('C:/Users/oscar/Downloads/img1.jpeg', 0) 
+
+
+  #canny = cv2.Canny(image, 20, 170)
+  canny = cv2.Canny(image, 50, 120) #v2.Canny(image, T_lower, T_upper)..T_lower/T_upper: threshold value in Hysteresis Thresholding
+  #https://www.geeksforgeeks.org/python-opencv-canny-function/#:~:text=Canny()%20Function%20in%20OpenCV,the%20edges%20in%20an%20image.
+
+  #imshow is used to display an image, it fits into image's size 
+  cv2.imshow('Canny', canny) # cv2.imshow(window_name, image)
+
+  #displays window for x miliseconds or until key is pressed
+  cv2.waitKey(0) #close window until any key is pressed
+  #Ex. for 5 seconds: cv2.waitKey(5000)
+
+  cv2.destroyAllWindows() #Destroy all windows created
+