Questions tagged [edge-detection]
Edge detection is the process of identifying points in an image, where image brightness changes sharply.
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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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Chebyshev filter analog in computer vision?
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 ...
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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.
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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.
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How to Implement the Sub Pixel Refinement Phase in Scale Invariant Feature Transform (SIFT)
I'm trying implement SIFT(Scale-invariant feature transform) myself. I've read some documents and stuck at Sub-Pixel Refinement - left without knowing how to actually implement it in code. I do ...
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Detection of a specific ship with known ship 3d model
I want to detect a specific ship in sea from a low flying aerial vehicle, equipped with a camera (e.g., a drone). Suppose the ship is this. In general, the ship should remain "constant" in ...
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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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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 ...
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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 ...
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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 ...
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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 ...
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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....
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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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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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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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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 ...
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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 ...
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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,...
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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 ...
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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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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 &...
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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.
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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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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 ...
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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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Significance of outer product in structure tensor / second moment matrix
How does one interpret the outer product $\mathbf{M} = \nabla I \otimes \nabla I = \begin{bmatrix}\left(\frac{\partial I}{\partial x}(x)\right)^2 & \frac{\partial I}{\partial x}(x) \cdot \frac{\...
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Reversing the Order of Operators for Edge Detection?
Usually, for edge detection, we perform smoothing and then pass it through difference filter. What if application of difference filter happens first and then smoothing. How the math behind the same ...
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What Is an Oriented Gaussian Second Derivative Filter
In the paper: Detecting and Localizing Edges Composed of Steps, Peaks and Roofs, the authors refer to an image filter as an oriented second-derivative Gaussian filter. I'm trying to figure out what ...
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What is Maximally Stable Extremal Regions (MSER)?
In the paper Robust wide-baseline stereo from maximally stable extremal regions , MSER is being defined. Please help me understand what is MSER and how to implement it.
The paper says,
The regions ...
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Maximally Stable Extremal Regions (MSER) Implementation in Document Image Character Patch Identification
My task is to identify character patches within the document image. Consider the image below:
Based from the paper titled "CG-DIQA: No-reference Document Image Quality Assessment Based on ...
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Edge Detection vs. Contour Detection?
What is the difference between edge detection and contour detection?
Apparently both techniques are used to detect boundaries of close shapes(whether oval shape or r rectangular shape)
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Identify if a Specific Edge Pixel Belongs to Horizontal, Vertical or Diagonal Edge Line
I have a code below that identifies the edge of the text image. Input image is:
Output display is:
I want to select random points near the edge border of the text. I was thinking to identify if the ...
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Understanding the Threshold Process in Harris Corner and Edge Detector
I have read the paper Chris Harris , Mike Stephens - A Combined Corner and Edge Detector about the Harris Corner and Edge Detector, but I didn't understand the point that after low and high threshold ...
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Is HSV Color Space Sufficient for Rudimentary Color ID and Edge Detection
I want to, as part of a C++ school project (no OpenCV), work with an RGB image taken from a camera filming smarties (round colored pellets) from above and extract the number of candies in each color.
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Why we need Laplacian for edge detection?
I am studying some trivial computer vision processing techniques and I came across edge detection algorithms. IMO sharp changes in the gradient are enough indications to detect the edges in an image ...
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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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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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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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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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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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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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