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POPerformance comparison of OpenCV-Python interfaces, cv and cv2
 

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  1. POPerformance comparison of OpenCV-Python interfaces, cv and cv2
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    <p>A few days back, I started using new OpenCV-Python interface, <code>cv2</code>.</p> <p>My question is regarding the comparison of <code>cv</code> and <code>cv2</code> interface.</p> <p>Regarding the ease of use, new <code>cv2</code> interface has improved far greater, and it is really easy and fun to work with <code>cv2</code>.</p> <p>But what about speed?</p> <p>I made two small code snipplets, one in <code>cv</code> and another in <code>cv2</code>, to check the performances. Both does the same function, access pixels of an image, test it, make some modifications, etc.</p> <p>Below is the code:</p> <hr> <p><em><code>cv2 interface</code></em>:</p> <pre><code>import time import numpy as np import cv2 gray = cv2.imread('sir.jpg',0) width = gray.shape[0] height = gray.shape[1] h = np.empty([width,height,3]) t = time.time() for i in xrange(width): for j in xrange(height): if gray[i,j]==127: h[i,j]=[255,255,255] elif gray[i,j]&gt;127: h[i,j]=[0,0,255-gray[i,j]] else: h[i,j]=[gray[i,j],0,0] t2 = time.time()-t print "time taken = ",t2 </code></pre> <p>=====================================================</p> <p>And result is:</p> <p>time taken = 14.4029130936</p> <p>======================================================</p> <p><em><strong>cv interface:</em></strong></p> <pre><code>import cv,time gray = cv.LoadImage('sir.jpg',0) h = cv.CreateImage(cv.GetSize(gray),8,3) t=time.time() for i in xrange(gray.width): for j in xrange(gray.height): k = cv.Get2D(gray,j,i)[0] if k==127: cv.Set2D(h,j,i,(255,255,255)) elif k&gt;127: cv.Set2D(h,j,i,(0,0,255-k)) else: cv.Set2D(h,j,i,(k,0,0)) t2 = time.time()-t print "time taken = ",t2 cv.ShowImage('img',h) cv.WaitKey(0) </code></pre> <p>======================================================</p> <p>The result is:</p> <p>time taken = 1.16368889809</p> <p>=======================================================</p> <p>See, here old <code>cv</code> is about <code>12 times faster</code> than <code>cv2</code>. And resulting images are same. (input image is of size 720x540)</p> <p>Why does this happen?</p> <p>Is cv2 slower compared to cv?</p> <p>Or am I making any mistake here? Is there a faster method in cv2 for the above code?</p>
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