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4
votes
2answers
154 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
25 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
141 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
48 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
46 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 ...
0
votes
0answers
134 views

Hough transform for transposed image (image rotate by 90 degrees)

For a given binary image, we can perform Hough transform very easily with the help Matlab or OpenCV. Suppose the given image's Hough transform is H, and its transposed image's (image rotated by 90 ...
1
vote
1answer
48 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
175 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
304 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 ...
9
votes
2answers
1k 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
695 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
738 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 ...