Questions tagged [edge-detection]

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

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411 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 ...
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1answer
816 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 ...
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42 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? ...
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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 ...
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2answers
37 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 ...
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2answers
1k views

Why is zero padding required for Sobel edge detection?

Why do we leave two rows and two columns of an image (or) padding zeros to an image for detect edges while using Sobel operator and Prewitt operator?
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1answer
412 views

ICY feature detector and edge detector in opencv

I need to trace the internal feature boundaries of blobs (blood cells) in OpenCV to train a classifier. As a good reference from ICY in java, the following sequence of operations gives good, ...
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1answer
115 views

Intuition behind image derivative using Fourier Transform for edges detection

This equation can be shown mathematically: $\frac{\partial f}{\partial x}=\frac{2\pi i}{N} \mathcal F^{-1}\left(u\cdot \mathcal F(f(x,y)\right)$ I am struggling to understand the intuition behind it ...
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15 views

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 ...
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1answer
138 views

How to find Performance Ratio (PR)?

If we have one image from BSD (The Berkeley Segmentation Dataset and Benchmark) and for this images Ground truth, how to calculate PR? PR is the ratio of true to false edges and can be calculated by ...
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1answer
70 views

Does flat surface detection and orientation require special hardware to compute?

Modern augmented reality platforms such as Google's ARCore and Apple's ARKit seem to only operate on mobile devices, I'm guessing, because their underlying algorithms require specialized hardware that ...
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1answer
233 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- ...
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34 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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4answers
17k views

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 ...
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2answers
9k views

Rectangle detection in “real life” images

I have seen a lot of posts here and on SO and on various websites, using Matlab, OpenCV, name it, on how to detect rectangles in an image. I have done it myself too, using Matlab. My usual steps were: ...
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3answers
252 views

Are 2nd Order Edge Detectors More Susceptible to Noise?

I am reading about edge detection and I read that 2nd order detectors are more susceptible to noise. Is there a mathematical proof to this ?
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81 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 ...
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1answer
29 views

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 ...
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2answers
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Laplacian Operator with and without Diagonal Direction Elements in the Kernel

This is a general question on the laplacian operator, which has two different versions. The first version is : \begin{matrix} 0 & 1 & 0 \\ 1 & -4 & 1 \\ 0 & 1 & 0 \end{...
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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 ...
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1answer
26 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 ...
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0answers
21 views

Detecting enclosed regions in an image

I am having a difficult time searching for this, and I am not sure if it has a general solution, but I thought I would ask. Basically, I am looking to detect the inside of a bounded region, but ...
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13 views

Measures of edge image continuity and connectivity

Suppose I have a scalar image $I:\mathbb{Z}_{1,m} \times \mathbb{Z}_{1,n}\rightarrow [0,1]\subset \mathbb{R}$, where $\mathbb{Z}_{1,m} = \{1,\ldots, m\}$. (For instance, computed as the (scaled) ...
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2answers
76 views

Finding the edge pixels on only one side of the object

For my work on lung images, I get a binary image mostly resembling the pattern shown below. I need to find the pixels on the borders shown by yellow arrows. The edges on the other end are shown in ...
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1answer
569 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 ...
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87 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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2answers
60 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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27 views

Edge detection for bio-film filaments

I have this image of bio-film filaments growing in a matrix and would like to extract just the filaments from the image to calculate the angle at which they are growing. What techniques would be best ...
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1answer
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 ...
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4answers
11k views

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 ...
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2answers
1k views

Is the Sobel filter a high pass filter, and if not, what is the difference between them?

I am an artist with an interest in signal processing. I realize that maybe this question very basic, but the web banner on the frontpage says "anyone can ask", so I assume that means beginners too. ...
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1answer
306 views

How to segment multiple overlapping coins (ellipses)

I am doing a program that counts coins (and tells their value by their size) with OpenCV (C++). Let's say we have an image of some coins. If there is an overlap of two coins at the same time, it is ...
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2answers
207 views

Beginner Question: Extracting Features for Image Classification

I'm a Python programmer, but a beginner to image processing :) Apologies if this isn't a suitable question for the forum, happy to rewrite or move. I want to create a supervised classifier to ...
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248 views

edge detection of 1-D signals

Would you please introduce me to some methods (or references) to do edge detection on some pulses (rectangular pulses embedded in noise). At first I apply some filters to smooth the signals, then I ...
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2answers
435 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 ...
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1answer
835 views
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1answer
427 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 ...
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1answer
6k views

An alternative algorithm for blob detection

Here's a sample image of my experiment which is to be processed for finding the information of all the blobs (centre, dimension etc.). Basically the image contains some noise, few bold lines, and of ...
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1answer
243 views

Automatically detect an image collage

I'm trying to automatically detect if an image is a collage vs a single photograph. I'm not too concerned with difficult cases of artistic collages. What I'm trying to solve is rectangular collages ...
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0answers
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. ...
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2answers
955 views

What's the best technique to determine if the contents of two images are the same?

I need to run comparisons on the output of hundreds of frames of simple 3D-rendered characters. Perceptually, many of the frames are exact duplicates. Based on this, I assumed something like a ...
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1answer
1k 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, ...
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3answers
190 views

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 ...
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1answer
241 views

Designing an efficient curve-matching algorithm

I'm currently designing a curve-matching algorithm and as I already explored many ideas I'm requesting your help. So, if you got some advices about how to handle this problem, feel free to answer! ...
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2answers
606 views

Why edge sharpening produces high frequency?

I have a low-resolution image in which the high frequencies are missing. When I apply an edge sharpening filter some of the missed high frequency is recovered. I am wondering why this edge sharpening ...
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2answers
12k views

Straight lines with an edge detection algorithm

I've been thinking of an algorithm for object recognition but it would relies heavily on straight non-noisy lines and as far as I know this is hard to obtain with edge detection algorithms. What's the ...
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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 ...
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2answers
12k views

In opecv function Hough circles how does parameter 1 and 2 affect circle detection and how can I adjust them to increase accuracy?

I'm using opencv houghcircle function to detect circles. http://docs.opencv.org/doc/tutorials/imgproc/imgtrans/hough_circle/hough_circle.html Problem is if I set minimum radius to null it detects ...
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1answer
375 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 ...
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3answers
366 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 ...