# Questions tagged [edge-detection]

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

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### How to Clean Black and White Images Which Are Results of Edge Detection

I want to extract text from some images with messy backgrounds. First step was switching to gray scale, applying an edge detection algorithm, and then cleaning up a little bit. Here's an example of ...
715 views

### Edge map based on a Haar Wavelet Transform

I have been implementing the paper Blur Detection for Digital Images Using Wavelet Transform and was asking myself how the following formula could reconstruct the edges given a Haar Wavelet ...
44 views

### How do I scale Gaussians for Edge detection

Say I have an $m\times n$ image and I want to use DOG for edge detection. I can see in this answer he is using: ...
2k views

### Ridge finding in noisy 2D image

I'm using MATLAB, and have experience with it but not with this kind of problem. I'm trying to identify white lines in noisy 2D images such as the one below. I can separate the brighter ones just by ...
3k views

### Sobel Vs Gaussian Derivative

What would be the most significant difference when using either a sobel filter or a gaussian-derivative filter, apart from the obvious difference of the size of the 2 filters?
220 views

### Why are 2nd order edge detectors such as Laplacian more susceptible to noise?

I've been told that they are influenced by noise considerably more than that of a first order edge detector such as a Gaussian. But why?
312 views

### Find best fitting rectangles after applying edge detection

I am trying to implement a box detection algorithm. In my pipeline, I start with image warping to simulate a frontal view of the shelf containing the boxes (assuming boxes are straight in that ...
1k views

### Edge linking using local processing - why is this criterion imposed

I'm reading Digital Image Processing by R. Woods and R. Gonzalez. In it, a section on edge linking using local processing in an image details a simplified algorithm, that imposes a criterion on the ...
2k views

### How to trace the edges on matlab

I am doing my Bachelor's project on Road extraction. I have detected the line segments(edges) in the image using hough transform. I need to detect the curved lines in the road and link them(edge ...
80 views

### Is it feasible to try and classify an enclosed space as being a. Very crowded b. Less crowded & c. Sparsely crowded using image processing?

The idea is to get three classifications for crowd: High, low and medium based on an image captured inside a train compartment. Something like this: This gets classified in the 'High' category http:/...
114 views

### Finding optimal detectors by numerical optimization (Canny)

In "A Computational Approach to Edge Detection", John Canny explains that the optimal "detector" for finding step edges profiles in an image via convolution is a non-closed-form function closely ...
407 views

### edge detection evaluation methods [closed]

I'm working on some edge detection algorithms that I want to evaluate them. I want to know what are standard ways to evaluate them that check does them work better that old ones or no. thank you for ...
2k views

### How to detach overlapping contours but not to remove small ones. Alternative to erosion-dilation cycle

Background: I'm trying to detect trees on a sequence of aerial images by calculating a stereo disparity for consequent pairs of images. This is how disparity looks like. White spots are trees: Next, ...
102 views

### Is it appropriate to use Sobel operators to find the derivatives of an image?

Strictly speaking, the $x$ direction derivative should be the difference between the left and right pixel of each pixel. So, then I should be using a $1\times 3$ filter: \begin{bmatrix}-1&0&1\...
970 views

### What's the state-of-the-art algorithms in image edge detection?

There are several state-of-the-art algorithms in image denoising including Non-Local Means, BM3D and so on. I am wondering whether there is some well-known state-of-the-art algorithms in image edge ...
496 views

### Why are edges in spatial images represented as edges in their Fourier transform image?

Here is a well-known image and its Fourier Transform (magnitude). If I understand correctly the theory behind the FFT, each pixel in the FFT image represents a certain 2D sine wave with frequency ...
861 views

### how sobel edge detector as a first order derivative is turned to a 2 dim filter?

I want to know theorem behind sobel operator. basically a first order derivative is -1/2 0 1/2 . its a vector. the question is how this vector is turned to a matrix below and what was theory and ...
43 views

### How Last Edge Image Can Be Achieved from Law Masks

as we know thechnique of law edge detection has 25 2d masks that is obtained form 5 different 1d filters. we can use each of those masks on image with convolution but how can we obtain final result? ...
415 views

### Difference of Gaussian filter but using Gaussian CDFs not PDFs

A very common filter in signal / image processing is the Laplacian of Gaussian filter, and its approximation, the difference of gaussians filter. The DoG filter is the difference of 2 Gaussian PDFs ...
571 views

### edge detection evaluation medical test images MATLAB

I programmed an algorithm for edge detection, i want to compare it with other algorithms but with a criteria (Pratt's figure of merit, GMC1) not only a a visual comparaison. the thing is PFOM needs ...
420 views

### Convolution theorem for “weighted” convolution?

Consider what I call a "weighted" convolution of a two-dimensional signal (image) with itself: $f({\bf r}) = \int d {\bf r}' \, g({\bf r}') s({\bf r},{\bf r}') g({\bf r}-{\bf r}')$ where $s$ is a ...
44 views

### Tracking a Predefined Curve in a Series of Images

I have a series of images. I want to be able to draw a curve on the image and track the curve in the series. For example, in the figure below, the left image illustrates the original image at time <...
353 views

### Are all of the edge descriptors necessary to differentiate edges?

My question is about edge descriptors produced from an edge detection method applied on an object image. As we know, an edge has four descriptors edge normal, edge direction, edge position, and edge ...
65 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 ...
938 views

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### Detect the beginning of an increasing signal

After denoising and cleaning, I get amplitude signals like this (y-axis: dB): On bottom left of each of these 3 graphs, you can see a noise floor (nearly "horizontal line"). This noise floor ...
418 views

### how gabor filter is used on image texture edge detection

as I searched gabor filter is most used tool on texture analysis and edge detection in digital image. its said that it searches a certain frequency as a texure around a pixel or point to find the ...
579 views

### How do derivative masks work for finding edges in image?

As I know, masks like follow are derivative mask, but I don't get it why they can detect edges and which one of them can find vertical edges and which one can find harizontal edges?
164 views

### How to find a noisy line in a picture

Hi I would like to find a line in a noisy image as showed bellow. I tried gabor filter and cany edge detection, but it didn't produce anything usefull. I am looking for lines of specific orientation ...
429 views

### Edge Preserving Smoothing

I'm searching for a method that can smooth a 3D volume whilst preserving the edges in my volume. I researched anisotropic diffusion filtering and bilateral filtering but I'm having trouble to evaluate ...
25 views

### Finding defects in wall paint (finding difference in textures)

I have been experimenting with computer vision techniques to find defects in paintings, more specifically defective brush strokes. I have tried a handful of techniques such as different filters, One ...
44 views

### How to find position, scale and rotation of a known shape/contour in an image?

I have an image of an object. The image shows a high contrast outline of the object. It is guaranteed that the image shows exactly one object. The shape/contour of that outline is known. It is not ...
33 views

### Chapter 4, section 4.2.1. in Szelisky computer vision, is there a mistake?

I've already asked a similar question in mathematics exchange without getting an answer, I read a bit more and I think the question might be more suitable for the signal processing exchange. ...
45 views

### Texture detection

I am looking for good methods, preferably parameterless, to detect textured areas in an image. I mean random textures, not regular patterns. The final goal is to discriminate between significant edges ...
269 views

### What is a segmentation mask in the paper “Fast Edge Detection Using Structured Forests”

I've read the paper about edge detection, in this paper they treat edge detection as a learning problem which takes an image patch as input and output a label, a binary edge map or a segmentation mask,...
237 views

### How can I properly detect a ball moving in a film capture?

I have problem in detecting a ball moving in a flume (image below). since converting the frames into grayscale format didn't work I converted it into rgb and make it more saturated. problems are: 1- ...
1k views

### Line Detection with OpenCV

I'm trying to use the native functions of OpenCV HoughLines and HoughLinesP to detect the lines from an image. The Canny edge output of that image is the folllowing: The problem is that the OpenCV ...
40 views

### Analytical expression for salient Blob detection in scale space

I am working on exact mathematical expression which can be obtained in image processing tasks.(I do not know much about image processing but my work is more mathmatical) In Gaussian scale space, we ...
381 views

### Algorithm to extract polygones with holes [closed]

I have this picture and would like to extract the bones. First I thought of contour-Tracking, but as you can see in some bones there are holes (Like for example at the left finger, in the bone in the ...
870 views

### How to do edge detection using Curvelet transform?

I wanted to use Curvelet thresholding for edge detection, that is first take discrete curvelet transform then choose coefficient which are for curve and then reconstruct back to get an edge map. ...
62 views

### Methods for edge detection with non-equidistant samples

This posting describes two methods of edge detection for wave analysis in a water pipe. I am not sure about advantaged and disadvantages. Therefore I want to evaluate the best method for this ...
173 views

### Singularity Detection from 2D Wavelet Modulus Plot

I was wondering if I could get some tips/resources on how to pick out the singularity from my 2D Continuous Wavelet Transform Coefficient Plot (scalogram) using the Gaussian Derivative as the mother-...
204 views

### Sobel Filter Operatios

I have an image which has a vertical line which is 2 pixels wide and 4 pixels long and the remaining image is black. Now I want to find the edges in the vertical direction and for that I use the ...
771 views

### Visual regression test - Extract elements of GUI-Screenshot - MSER OpenCV

For a visual regression test I need to compare screenshots of webpages (different release-versions). I started with pixel by pixel compare. Actually I split the screenshot in different parts (maybe ...
27 views

### Need to batch detect, measure, calc DPI for a consistently placed ruler in large set of technical images

I have a large set of photographs of pieces of rocks. In each photo there is a 4 inch ruler bar placed next to the rock, consistently on the left near the edge, see example: Over 10 years the ...
428 views

### Edge detection gives pixel ids, why?

This questions is in conjugation with this one here! Canny edge detector gives ids of pixels in an image. Not the locations of the edges. To be specific, after all it should be an edge between two ...
115 views

### How to detect the fuzzy edge in this image?

I am trying to process a lot of images of bacteria. As you can see from this image, when several bacterias are very close, the boundary tends to be very fuzzy. I try to binary the image or detect the ...
6k views

I would like to compute the gradient of an image I. I have the following two options : [Gx, Gy] = gradient(I); g = sqrt(Gx.^2+Gy.^2); or ...