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 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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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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28 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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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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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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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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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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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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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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Is there a way to find edges of an image using eigenvalues without thresholding?

How could an edge be detected using eigenvalues and eigenvectors of a second moment matrix? Could it be done without thresholding? If so how? If no, how to find a suitable threshold?
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157 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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159 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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260 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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187 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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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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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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947 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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118 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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138 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
147 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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501 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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673 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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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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3answers
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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 ...
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266 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,...
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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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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 ...
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Why is the median filter called 'edge-preserving'?

I want to know about median filtering. Recently, I read that it is best for preserving edges. But how does it preserve edges? I need complete knowledge of median filters. Why it is non-linear filter ...
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1answer
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How to apply Prewitt Edge Detection algorithm on a given image?

I am trying to figure out the answer to the following question: As I understand it, I am supposed to apply the algorithm only on this part of the image ...
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1answer
161 views

Sobel filter weird output

I am trying to implement a sobel filter to locate horizontal edges in a 160x120 pixel image that is captured from a OV7725 CMOS camera module that outputs RGB565 data. I've done the RGB565 -> 8-bit ...
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283 views

Detect almost circular shapes in RGB image

I want to extract circular trees from this rgb image, I've tried circular hough and segmentation techniques but in vain. Any help?
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640 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 ...
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278 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 ...
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229 views

detecting edge direction using Julia-language

Let say we have following image: made with following Julia-code: ...
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490 views

Discard circular/blob like structures from image

I have a binary image that looks like this: And I would like to get rid off all the small structures and just keep what's on red: Image erosion is an option that works well to remove the very small ...
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226 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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457 views

Segmentation and edge linking

I am trying to implement segmentation on an image. after a difference of Gaussians Process and applying weights to my edges I want to go through edge linking by local processing. I have seen this ...
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43 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: ...
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945 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's operator and Prewitt's operator?
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469 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?
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Which is faster: image segmentation or line detection?

Some papers use image segmentation techniques and others use edge detection. I need to know which one is faster. update: I need to do semantic segmentation for outdoor sense and the data is optical ...
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51 views

How would I go about detecting and following edges in time lapse data?

I have a time lapse movie from a specimen and would like to trace the cell wall movements, but I'm not sure how to. By eye, following the cell wall is fairly easy but it seems computationally quite ...
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400 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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383 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 ...
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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 ...
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592 views

Average gradient of pixels and sum of absolute diference

Studying the research paper Multidirectional Scratch Detection and Restoration in Digitized Old Images, E. Ardizzone et al., 2011: I have several questions regarding this section (5. Restoration), ...
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96 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\...
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1answer
537 views

Poster detection in OpenCV?

I'm really new in image processing, so please sorry I'm a newbie. I tried to use the squares.cpp for detecting posters (since they usually are rectangles) without using expensive feature detectors (...
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550 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 ...