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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 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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33 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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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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21 views

Detecting Separate Contours on Image's Edge-Map

I've implemented the Canny edge-detection algorithm, which produces a 2D binary-map of edge/non-edge pixels (in Java, is that's of any matter). It performs the ...
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59 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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25 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
47 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
114 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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1answer
47 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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3answers
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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 ...
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1answer
73 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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Given a image of white lines forming a grid, how to get masks of the interior shapes using opencv?

I am trying to determine if there are pills in different cells of a pillbox. I have a raspberry pi camera that takes pictures of a pillbox at regular intervals. I would like to use computer vision ...
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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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19 views

Search the neighbor pixels along a given vector

How to fast search the neighbor pixels along a given vector? As following figure shows, I have a target point indicated by the green, then I want to find out the four pixels on the both side the ...
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0answers
25 views

How can we search for the maximum number of filled triangles that have a nucleus vertex in common?

Hi everybody, I want to detect the maximal nerves in the image below, a maximal nerve is a group of the nerves that have the maximum number of filled triangles that have a nucleus vertex in common. ...
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42 views

quantitative comparison in edge detection algorithms

I have a grayscale image. I did edge detection on it with my algorithm and with known operator such as Sobel and LoG in MATLAB. How can I compare result of them quantitatively in MATLAB?
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187 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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24 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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32 views

Sync on minimum/falling edge

I have a signal that I want to process (with Java) and so far I'm making good progress. However, the devil is in the details. For reference, it's a sound file at 48000Hz, 16-bit, I'll refer to samples ...
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3answers
195 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 ...
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246 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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1answer
34 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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2answers
93 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 ...
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2answers
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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
738 views

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
110 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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1answer
198 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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1answer
444 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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246 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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1answer
158 views

detecting edge direction using Julia-language

Let say we have following image: made with following Julia-code: ...
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1answer
240 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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1answer
200 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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319 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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1answer
39 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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2answers
620 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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1answer
223 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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1answer
48 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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1answer
318 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
209 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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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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459 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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1answer
62 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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0answers
2k views

fitting curves to contours with OpenCV and Python

The above image is an example of a lightbox, with some vessels on top. Overall goal is: to find the middle points of the vessels to mark the area of the disk, enclosed by each vessel What I want ...
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1answer
389 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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0answers
175 views

Is there an optimal range for Pratt's Figure of merit?

I am working on a new edge detection method. However, when I tried to evaluate it based of FOM values, I got really small values, though my algorithm's performance is good comparatively. What I ...
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1answer
474 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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31 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 ...
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3answers
186 views

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 ?