Signal Processing Stack Exchange
Signal Processing Stack Exchange

Questions tagged [edge-detection]

Edge detection is the process of identifying points in an image, where image brightness changes sharply.

Edge detection is a fundamental tool in image processing and computer vision, particularly in the areas of feature detection and feature extraction, which aim at identifying points in a digital image at which the image brightness changes sharply or, more formally, has discontinuities. The same problem of finding discontinuities in 1D signals is known as step detection.

Source: Wikipedia.

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What factors should I consider in choosing an edge detection algorithm?

I've learned about a number of edge detection algorithms, including algorithms like Sobel, Laplacian, and Canny methods. It seems to me the most popular edge detector is a Canny edge detector, but is there cases where this isn't the optimal…
PearsonArtPhoto
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How do I detect distinct objects when their edges touch each other?

I need to find all the contours in an image retrieved from the camera. So I first use the canny edge detector to find the edges and then find the contours. Pretty simple. However, my contours get "merged". For example, in the image below, I clearly…
user650
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What Are the Limitations of a Canny Edge Detector?

Broadly a majority of the literature on edge detection algorithms and applications that uses edge detection, references Canny's edge detector. So much so that it looks like almost "the solution" to edge detection. Certainly, it would do the best…
Dipan Mehta
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Connecting edges detected by an edge detector

I have a binary image obtained from a canny edge detector. The edges are not nicely detected in the center and I need to join them. The connection of edges is orientation and neighborhood dependent. I need to connect the vertices if they are below a…
Naresh
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Image segmentation issue of different materials

Hi CV/Pattern Recognition Community, I've got a serious problem regarding the segmentation of an image. The scenario is an atmosphere within a furnace which makes my head go insane. And I need to detect object contours of different materials (glass,…
mchlfchr
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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 computing-friendly method to find circles (or ellipses in advanced version). The intuitive idea is to use Brute-Force Search on all possible points (as…
Developer
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Estimating onset time of a tone burst in noise?

What techniques might one use to estimate the onset time of a sinusoidal tone burst in a noisy signal? Assume the tone burst has a known fixed frequency (but unknown phase) and a very sharp rise time, and that the goal is to estimate the onset time…
hotpaw2
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How Does a Convolution Can Be Expressed as a Matrix Multiplication (Matrix Form)?

I know this question may not be very relevant to programming, but if I don't understand the theory behind image processing I'll never be able to implement something in practice. If I got it right Gaussian filters are convolved with an image for…
Matteo
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Identify the correct spot to place a label

In the image shown below, I have a 2D data set where I have identified four clusters labeled [0,1,2,3]. I'm looking for an algorithm to place the labels in a natural* way for each shape. My first guess was to place them in the "center-of-mass" of…
Hooked
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Can edge detection be done in the frequency domain?

Can we take advantage of the fact that high frequency components in the FFT of an image generally correspond to edges, to implement an edge detection algorithm in the fourier domain? I did try multiplying a high pass filter with the FFT of an…
rounak
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Roberts Edge Detector how to use?

I am trying to use Roberts edge detection to process an image. Do I just apply both of the masks to the image and perform convolution as normal? Could someone give me the breakdown of how to use this edge detection method, as I am trying to program…
adamjmarkham
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Explanation on Haarlets

Would someone be able to give me some info or a link etc ... regarding haarlets aka Haar wavelet-like features. I'm reading several papers for my master dissertation and several of these papers briefly mention haarlets. I can't seem to really get…
Olivier_s_j
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How to implement a gradient based Hough transform

I am trying to use the Hough transform for edge detection, and would like to use gradient images as the basis. What I have done so far, given the image I of size [M,N] and its partial derivatives gx, gy, is to calculate the gradient angle in each…
Jonas Due Vesterheden
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Could you describe the effects for varying different parameters of a canny edge detector?

Last couple of questions touched upon Canny edge detector What are the limitations of a Canny edge detector? and Best way of segmenting veins in leaves? The basic outline of the algorithm is as follows: a. Apply Gaussian Convolution. (Choice of…
Dipan Mehta
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How can I detect elements of GUI using opencv?

Given a screenshot of an application, is there any way of finding GUI elements of that application using only opencv? (something like in the image) I tried to play with blending the image and other effects from the coherence.py sample in the opencv…
Radu Enea
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