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4
votes
2answers
185 views

Why is the Canny edge detection used instead of Sobel/ Prewitt edge detection before Hough transformation?

I know that for the Hough Transform to work on an image, it needs to be a binary image. To convert from a grayscale image, an edge detection algorithm should be employed. I notice that people always ...
2
votes
0answers
26 views

How to quickly calculate all the line segments when their coordinate in the Hough transform is given

Hough transform is a very powerful tool to find dominant straight lines in a black-and-white image. A very common practice of analyzing Hough transform result is to find some local maximum points in ...
1
vote
3answers
168 views

Hough lines and Convex Hull methods give jagged lines

I need to do a perspective transformation on an image section from newspaper, here the girl's image. The section's coordinates are given as rough estimates. I need to find the boundary of the section ...
0
votes
0answers
53 views

Hough Transform - sign of rho and theta- Matlab

I understood that origin of the picture space (x,y) will be upper left corner. Origin of the parameter space (rho, theta) will be center point. I understood basic idea of the hough transform. I am ...
0
votes
1answer
51 views

Edge following using Hough transform

Im trying to improve an edge following algorithm developed by some students who did a projekt at my work. The algorithm is supposed to make an robot follow a line with use of an camera. Their approch ...
1
vote
2answers
2k views

Detecting lines with houghlines in matlab

I have This image which is basically made of sloped lines (almost horizontal and parallel) I tried exactly the code in matlab documentation to detect those lines (except the rotation part) but I ...
1
vote
1answer
49 views

Confusion about hough transformation for ellipse

I saw the following sentence from Feature Extraction & Image Processing, 2nd Edition $$ x = a_0 + a_x\cos(\theta)+b_x\sin(\theta) $$ $$ y = b_0 + a_y\cos(\theta)+b_y\sin(\theta) $$ This ...
2
votes
1answer
1k views

Influence of image size to edge detection in OpenCV

I need to scan an image in OpenCV and obtain the lines. For this I use the canny edge detector and then the propabilistic Hough transform, with which I actually get the lines. The problem now is that ...
2
votes
1answer
186 views

Improving the performance of the Hough transform

I have just started doing image processing, and I am currently working on line detection. I am using Hough transform on the image below. I'm wondering how I can improve the efficiency of the Hough ...
1
vote
2answers
312 views

hough voting, turning transformation into a vote

I need help understanding how/what does it mean to "turn" a transformation parameters into a vote. I know how to recover the transformation parameters (in my case: 6 DOF), but how this turns into a ...
11
votes
2answers
2k views

Alternatives to Hough transform for detecting a grid-like structure

I have an image which is composed of multiple 'angles' which form a grid shape: After some searching, Hough seemed like a good fit, because it isn't troubled by breaks in lines. However, the ...
4
votes
2answers
2k views

find the gradient direction at a point in a shape

I am trying to implement the generalized Hough transform in matlab. The algorithm requires the gradient direction at each point in the shape. How can I measure $ \phi $ as shown in the figure below? ...
12
votes
3answers
4k views

help understanding hough transform

I'm trying to get a Hough transform to work in MATLAB, but I'm having problems. I have a really bad way of detecting peaks that needs to be fixed, but before that I need to be able to reverse the ...
8
votes
4answers
720 views

How to do De-Houghing of a Hough transform'ed Image?

I'm working with code found at Rosetta Code for creating a Hough transform. I now want to find all the lines in an image. To do so I need the ρ and θ values of each of the peaks in the Hough space. A ...
11
votes
1answer
768 views

Detection of circles (ellipses) in 2D point cloud

Given a set of points (2D) i.e., point cloud (PC), the question is about a robust, accurate and ...