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Building an adjacency matrix from Harris CD output

asked 2019-05-01 18:36:13 -0500

Shaddox gravatar image

updated 2019-05-02 02:43:11 -0500

My final intention is to build something based off this :

And I'm stuck at part 3.2, with building the adjacency matrix for the corners. The figure below is to help vizualize what I'm trying to achieve.

Output so far

Say I take that image of A and apply Harris to it and then use this code

# define the criteria to stop and refine the corners
ret, labels, stats, centroids = cv2.connectedComponentsWithStats(dst)
criteria = (cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_MAX_ITER, 100, 0.001)
corners = cv2.cornerSubPix(gray,np.float32(centroids),(5,5),(-1,-1),criteria)

#print corners
for i in range(1, len(corners)):

I get a nice list of corner coordinates that looks like this :

[51.70207 62.5541 ]
[ 37.04742 100.78287]
[ 66.707726 100.73132 ]
[ 29.685337 119.28638 ]
[ 75.62286 119.49719]

For reference, the image is 106 x 189. But how can I figure out which is connected to which? I tried "walking" the image array from a corner until I run into another but this doesn't cover cases where there are multiple. I also thought about how I can iterate over each corner and see if I can connect to others, but since they're part of the same line they will always be able to connect.

Any advice is appreciated.

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I am curious, what will you do for curved letters like O or S?

Chris gravatar imageChris ( 2019-05-05 07:55:23 -0500 )edit

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answered 2019-05-05 08:04:33 -0500

Opencv has a cool tool called lineIterator

For each point, create a line (using line iterator) to all the other points. Step along the line and look at pixel values. If all the values are dark/black, then this is a potential edge. If 2 or more potential edges start at the same point and have the same direction (dot product), only add the shortest one (L2 norm) to the adj matrix.

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After experimenting and iterating I got something working thanks to your idea. So, thank you very much.

Shaddox gravatar imageShaddox ( 2019-07-08 03:20:16 -0500 )edit
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Asked: 2019-05-01 18:36:13 -0500

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Last updated: May 05 '19