Short Answer cvCanny is used to detect Edges, as well as increase contrast and remove image noise. HoughLines which uses the Hough Transform is used to determine whether those edges are lines or not. Hough Transform requires edges to be detected well in order to be efficient and provide meaning results. Long Answer The Limitations … Read more
It’s pretty easy, you just need to convolve your image with a Sobel filter. A Sobel filter has two kernels, x-direction kernel and y-direction kernel. The x-direction kernel detects horizontal edges, and y-direction kernels detects vertical edges. x-direction kernel (the size is 3×3) float kernelx[3][3] = {{-1, 0, 1}, {-2, 0, 2}, {-1, 0, 1}}; … Read more
I would try to use a skeleton representation of the image. The problem with your canny, here, is that it basically results in two lines because of the width of the line. Then I would apply the Hough transform on it.
Very nice work on boundary detection. I used to work on similar segmentation problems. Theory: Once you obtained your edge map where e(i,j) indicates the “edge-iness” degree of pixel i,j you would like a segmentation of the image that would respect the edge map as possible. In order to formulate this “respect the edge map” … Read more
In computer vision, there’s very often no perfect, universal way of doing something. Most often, we just try an operator, see its results and check whether they fit our needs. It’s true for gradient computation too: Sobel operator is one of many ways of computing an image gradient, which has proved its usefulness in many … Read more
Color information is often handled by conversion to HSV color space which handles “color” directly instead of dividing color into R/G/B components which makes it easier to handle same colors with different brightness etc. if you convert your image to HSV you’ll get this: cv::Mat hsv; cv::cvtColor(input,hsv,CV_BGR2HSV); std::vector<cv::Mat> channels; cv::split(hsv, channels); cv::Mat H = channels[0]; … Read more
You could create an invisible constraint, to cause the red node to appear to the left of all other nodes. redNode -> leftmostNode [style=invis]; Before: After:
Complete solution for arbitrary Sobel kernel sizes and angles tl;dr: skip down to section ‘Examples’ To add another solution, expanding on this document (it’s not particularly high quality, but it shows some usable graphics and matrices starting at the bottom of page 2). Goal What we’re trying to do is estimate the local gradient of … Read more
I’m Martin’s friend who was working on this earlier this year. This was my first ever coding project, and kinda ended in a bit of a rush, so the code needs some errr…decoding… I’ll give a few tips from what I’ve seen you doing already, and then sort my code on my day off tomorrow. … Read more