Update file sobel.py

L11/sobel.py

+import sys # for command line arguments
+import numpy as np # for matrix processing
+from PIL import Image, ImageOps # for image processing
+import time # to time part of the code
+
+# make sure command line arguments are provided
+if (len(sys.argv) < 4):
+    print ('command usage :',sys.argv[0],'infile','outfile','threshold')
+    exit(1)
+infile = sys.argv[1]
+outfile = sys.argv[2]
+threshold = int(sys.argv[3])
+
+# open the input image, convert to grayscale,
+# convert to a matrix, and determine the rows and cols
+input = Image.open(infile)
+gray = ImageOps.grayscale(input)
+carA = np.array(gray).astype(np.int32)
+rows,cols = carA.shape
+
+# pad the perimeter of the image matrix with zeros
+# and create the E matrix initialized to all zeros
+carA_pad = np.pad(carA,[1,1],'constant',constant_values = 0)
+E = np.zeros((rows,cols),dtype='uint8')
+
+# time just the Sobel edge detector
+start = time.process_time()
+
+# Sobel Edge Detector
+for i in range(1,rows+1):
+    for j in range(1,cols+1):
+        P1 = carA_pad[i-1][j-1]
+        P2 = carA_pad[i-1][j]
+        P3 = carA_pad[i-1][j+1]
+        P4 = carA_pad[i][j-1]
+        P6 = carA_pad[i][j+1]
+        P7 = carA_pad[i+1][j-1]
+        P8 = carA_pad[i+1][j]
+        P9 = carA_pad[i+1][j+1]
+        Gx = P3+2*P6+P9-P1-2*P4-P7
+        Gy = P1+2*P2+P3-P7-2*P8-P9
+        size = np.abs(Gx)+np.abs(Gy)
+        if (size > threshold):
+            E[i-1][j-1] = 255
+
+# record and print elapsed time
+elapsed = time.process_time()-start
+print ('Time to Run The Nested For Loop Sobel Edge Detector in Python =',
+        np.round(elapsed,4),'seconds')
+
+# create the edges image
+edges = Image.fromarray(E)
+edges.save(outfile)
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