# Questions tagged [edge-detection]

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

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### Detecting a large horizontal band in the center of an image

I have a small (228x228) grayscale image that I have created by segmenting the original image and converting it to grayscale after applying colors to the segment. I want to know possible approaches I ...
264 views

### Detect Longest Vertical Lines (Edges) in an Image

I have a task in image processing, which need to detect vertical lines from matrix. For example, there is a pair of white and black vertical lines segmenting the picture below. I need to find it. So I ...
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1 vote
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Looking at the basic characteristics of a Chebyshev Filter, I was wondering if there were any analogous type filters in Computer Vision? The way that it can minimize the error between the idealized ...
769 views

### OpenCV 2 Connect Incomplete Contours edges

I have to connect the unfinished edges of the contours in the red color bounding box. I used distance transform, watershed, and morphology, but still, edges are not connecting. ...
125 views

### Separating dominoes pieces from one another and counting them

I Have a picture of Dominoes on a table, which is noisy. I am trying to do the following: removing the background. counting how many dominoes pieces are there. identifying what each piece represent. ...
1 vote
38 views

### A mathematical justification of discontinuity detection using STFT

I'm trying to detect rapid changes in a one-dimensional signal say $[0,1]\ni t \mapsto f(t) \in [-1,1]$. By rapid changes, I mean corner points, edges, or sharp transitions at a point for example the ...
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1 vote
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### Segment Image of Small Elements on Neutral Background

I have a 8 bit gray level image where if the value = 122 it means no information, value = 0 means highly negative, and value = 255 means highly positive. I want to connect as many positive information ...
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### Removing tessellating interference patterns from images

The microscopy image below is corrupted by an irregular checkerboard-like grid. I attempted running 2D-FFT on the image, but was unable to isolate the frequencies which cause the pattern. How would I ...
144 views

### Segmenting dark spots from a light background?

I need to perform automatic segmentation of dark blue spots on light yellow paper. Here's a very simple example: In this case, a simple threshold based on hue or brightness works well. But here are ...
• 101
1 vote
194 views

### How many directions are there in the Non Maximum Suppression part of the Canny Edge Detector

In the Non-maximum suppression algorithm, each pixel has a total of 4 directions since there are 8 neighboring pixels. But why there is not 8 directions instead, please? I see below there are 8 ...
• 113
1 vote
133 views

### Why is Envelope noisy even after filtering and achievement of SNR gain (-6dB SNR to 14dB snr)?

A noisy signal with 500 MHz bandwidth, with negative SNR, when filtered to 6 MHz bandwidth, should attain a theoretical SNR gain of 20 dB. So if the original signal has -6 dB SNR, after filtering we ...
137 views

### Interpreting results of Sobel Edge Detection

I am implementing A No-Reference Perceptual Blur Metric paper. Somewhere in the prep steps they mention the use of vertical Sobel filter for finding vertical edges. The algorithm is summarized in Fig....
1 vote
407 views

### Removing dark borders in Image Stitching for Panorama

I am working on a Matlab code for panoramic image stitching for multiple image frames and getting satisfactory results however there are always dark regions surrounding the stitched images as ...
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### Implementation of Deriche filter

The Canny edge detector is expressed by the derivative of the Gaussian. Its practical implementation involves the Gaussian filter, then the Sobel filter to calculate the gradient in both directions. ...
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1 vote
161 views

### Finite/Infinite Impulse Response filters

Most image filters are of finite extension (which correspond to Finite Impulse Response in 1 dimension), like Laplacian, Canny, Gaussian... Instead of being of infinite extension (IIR in 1D). Why is ...
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67 views

### Numerical optimization method for optimal edge detector

John Canny, in his paper "A Computational Approach to Edge Detection" (PDF), finds the expression of an optimal edge detector by first using an analytical approach (Euler-Lagrange equation). ...
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46 views

### How are the edges of an image obtained with anisotropic diffusion?

I already know how to implement the method and obtain a correctly diffused image, but in the papers related to the topic there is usually an edge map that's calculated after the diffusion is performed ...
44 views

### Edge Detection with a special algorithm

Studying for my finals in Image Processing. Trying to solve the following question: An image processing specialist recommended an algorithm for Edge Detection in a color image RGB. He argued that it ...
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### Detecting bounded regions in JavaScript

I have an image of a crossword , and I would like to find the x,y coordinates of every valid square and the number associated with it, then I would feed it into crossword.js. Here are some sample ...
136 views

### MATLAB code to detect the corners of an object without using the built in functions

I need to write a MATLAB code to detect the corners of an object in a black and white image without the built-in MATLAB vision toolbox or bwlabel, imrotate, imresize, corner, edge, reshape, imfilter,...
620 views

### Edge Detection Convolution Intuition

I was learning about convolution and how filtering helps us to detect an edge in an image;however I still cannot not understand how the convolution process in the image below does this. I understand ...
541 views

### How to Remove Double Lines Detected Along the Edges by Edge Detector?

I'm trying to take real time input for hand gestures with web cam, then processing the images to feed them to a neural network. I wrote this processing function to make the hand features look ...
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474 views

### 1st and 2nd Gaussian derivatives for edge detection

I have a project about edge detection, I made research on internet about filters and read many articles but there is an article talked about using Sobel and Gaussian derivatives then it mentioned &...
156 views

### Extracting ridges in automatically in image

I am trying to extract ridges from an image, calculated using the eigenvalues of the Hessian matrix (see answer in Best way of segmenting veins in leaves?). In this image I have zeroed out the ...
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### Should Edge Detection Be Applied in Spatial or in Frequency Domain?

I want to ask why everywhere is used to do edge detection in spatial domain and not in frequency domain with FFT of image and apply HP filter. Thank you.
• 73
220 views

### Help or suggestions with Line detection in microscopy images

I'm doing a personal project in which I want to select some very specific lines in a microscopy image. The first picture is the raw image, the second picture is the image for the lines (in yellow) I ...
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388 views

### How to detect defects at a contour?

I am detecting a contour of a smooth metal. I do binarization first then use openCV contour function. But sometimes the metal has defects such as dots or dusts at edge. This leads a unsmooth edge. Is ...
• 103
1k views

### How Come the Low Pass Filter in Sobel Operator Isn't Normalized?

I am relatively new to the field of computer vision and I have just learnt about the sobel operator. The sobel operator in the x direction is a convolution of the finite difference kernel $[1,0,-1]$ ...
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162 views

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### Help understand the results of hough transform

I'm trying to apply the Hough transform of the following image using MATLAB: The result is: How could I predict that there are 6 bright spots in the resulted image? I expected 8 spots since I ...
• 101
1k views

### why do directional derivatives work better with a gaussian filter?

I've been working on image segmentation and computing the directional derivatives of a grey-scaled image, with the objective of detecting contours and edges. I have realised that if I apply a gaussian ...
103 views

### Recommended approach for extracting specific edges from image?

I have several sets of images with a typical image being: and from each image, I would like to extract the top and bottom curves of the object, shown in red here: What are some possible tools I ...
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1 vote
405 views

### What are the limitations of Watershed Segmentation Algorithm?

I am developing an Android application using Opencv to detect objects from images. I used Canny edge detector to detect the edges and extract contours, and it's working good so far. But I need to ...
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50 views

### Estimate gap between two adjacent images

I have two images of a panoramic view but there is a small gap (<24 pixels) in the horizontal dimension between them. I would like to do interpolation/inpainting to fill the gap, but the exact size ...
1 vote
270 views

### How to discard deviating values from standard deviation and running average

I'm building a inductive vehicle loop detector. By measuring the frequency of a LC-oscillator where the cars will pass over the inductor of the LC-Oscillator. If the cars pass over the inductor the ...
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