How to classify Chain codes?

asked 2016-02-24 21:08:36 -0600

bob409
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I have already extracted the shape descriptor chain code which is in the format CvChain* now I have to feed that into SVM for training. I need to convert CvChain* into Mat. Any idea on how to do this? Anyone who has used chain code as a feature extraction method can you tell me the approach you have used?

answered 2016-02-25 02:03:59 -0600

berak
32993 ●7 ●81 ●312

updated 2016-02-25 02:08:47 -0600

i don't think, there's a straightforward way to do this at all.

first, you can't simply put a CvChain into a cv::Mat. even if you manage to extract the contents via c-api macros (shudder), this chain consists of a cvPoint, and freeman-chain bytes, so 2 totally different datatypes, which can't go into a single Mat.

then, each of your contours will have a different length, which is not acceptable input for machine learning.

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I have noticed that some people use PCA as an intermediate step between chain code and classification. Do you think this may be the correct way to do this?

bob409 ( 2016-02-25 02:48:16 -0600 )edit

PCA expects same-length rows, too.

berak ( 2016-02-25 03:20:03 -0600 )edit

maybe you can fill the shorter arrays with zeros, until you reach the length of the largest contour, stack them to a matrix, then pca-compress it back to somewhere between the shortest and largest, some sort of procrustes

berak ( 2016-02-25 03:25:05 -0600 )edit

hmm, maybe you'd even skip the location point from the data, to make it translation-invariant

berak ( 2016-02-25 03:31:04 -0600 )edit

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