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POAffine transformation between contours in OpenCV
 

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  1. POAffine transformation between contours in OpenCV
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    <p>I have a historical time sequence of seafloor images scanned from film that need registration. </p> <pre><code>from pylab import * import cv2 import urllib urllib.urlretrieve('http://geoport.whoi.edu/images/frame014.png','frame014.png'); urllib.urlretrieve('http://geoport.whoi.edu/images/frame015.png','frame015.png'); gray1=cv2.imread('frame014.png',0) gray2=cv2.imread('frame015.png',0) figure(figsize=(14,6)) subplot(121);imshow(gray1,cmap=cm.gray); subplot(122);imshow(gray2,cmap=cm.gray); </code></pre> <p><img src="https://i.stack.imgur.com/XP2F3.png" alt="enter image description here"></p> <p>I want to use the black region on the left of each image to do the registration, since that region was inside the camera and should be fixed in time. So I just need to compute the affine transformation between the black regions.</p> <p>I determined these regions by thresholding and finding the largest contour:</p> <pre><code>def find_biggest_contour(gray,threshold=40): # threshold a grayscale image ret,thresh = cv2.threshold(gray,threshold,255,1) # find the contours contours,h = cv2.findContours(thresh,mode=cv2.RETR_LIST,method=cv2.CHAIN_APPROX_NONE) # measure the perimeter perim = [cv2.arcLength(cnt,True) for cnt in contours] # find contour with largest perimeter i=perim.index(max(perim)) return contours[i] c1=find_biggest_contour(gray1) c2=find_biggest_contour(gray2) x1=c1[:,0,0];y1=c1[:,0,1] x2=c2[:,0,0];y2=c2[:,0,1] figure(figsize=(8,8)) imshow(gray1,cmap=cm.gray, alpha=0.5);plot(x1,y1,'b-') imshow(gray2,cmap=cm.gray, alpha=0.5);plot(x2,y2,'g-') axis([0,1500,1000,0]); </code></pre> <p><img src="https://i.stack.imgur.com/yU88w.png" alt="enter image description here"></p> <p>The blue is the longest contour from the 1st frame, the green is the longest contour from the 2nd frame.</p> <p><strong>What is the best way to determine the rotation and offset between the blue and green contours?</strong></p> <p>I only want to use the right side of the contours in some region surrounding the step, something like the region between the arrows. </p> <p>Of course, if there is a better way to register these images, I'd love to hear it. I already tried a standard feature matching approach on the raw images, and it didn't work well enough.</p>
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    1. CODo you need only vector between green and blue contour or vector, angle of rotation and scale of scaling ?
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    2. COoffset and rotation only (no scaling)
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