opencv/javacv: How to iterate over contours for shape identification?

Question

I\'m developing a shape identification project using JavaCV and I have found some OpenCV code to identify U shapes in a particular image. I have tried to convert it into JavaCV

Answer 1

EDIT: Here is the most interesting finding - I think you are not iterating correctly through the contours - you should do something like:

CvRect rect = cvBoundingRect(cvGetSeqElem(cvSeq, i),0); //python default?

Or:

// ... 
CvSeq contours = new CvSeq();
CvSeq ptr = new CvSeq();
CvRect rect = null;
// ...
cvFindContours(..., contours, ...);

for (ptr = contours; ptr != null; ptr = ptr.h_next()) {
    rect =  cvBoundingRect(ptr, 0);
    // ... Draw the box if meets criteria
}

First, I think pst is right regarding the calculation of the ratio - you have to cast the width to float.

Secondly, I see that when you are making the gray image in python you use COLOR_BGR2GRAY and in java you are using CV_RGB2GRAY that could lead to a totally different gray picture. I would add some debug steps on both programs to save the temp gray images and compare them as also print outs for the values of x,y,w and h when (10 < (w/h) || (w/h) < 0.1) is true.

Another thing is that in the java solution you use CV_RETR_CCOMP to get the contours and in the python solution you use CV_RETR_LIST according to the documentation:

CV_RETR_LIST retrieves all of the contours without establishing any hierarchical relationships CV_RETR_CCOMP retrieves all of the contours and organizes them into a two-level hierarchy: on the top level are the external boundaries of the components, on the second level are the boundaries of the holes. If inside a hole of a connected component there is another contour, it will still be put on the top level

So first I would double check that all cv's parameters in both programs are the same, then I would add debug steps to see that the intermediate variables contains the same data.