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

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Creating graph from edges, shape detection

I am writing a shape detection program (for example, I make a triangle with fingers and algorithm finds it). My idea was to detect edges, "straighten" them, create graph from all the segments and ...
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Laplacian Operator with and without diagonal direction

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 ...
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60 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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Image Processing - Identifing/locating Random Solid Blocks of Colour

I am not overly familiar with image processing. I know a little about it from University, but I have not really done any for a while and I have found myself with a problem that requires it. What I ...
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1answer
88 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 ...
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Extraction of a decision boundary (LDA) after a systematic querying of the feature space and convolution with Sobel filter (examples in numpy)

I am doing some experiments with LDA (Linear Discriminant Analysis), in python. Now I am at the point in which I would like to display the separation planes in the 3-dimensional feature space. I ...
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65 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 ...
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1answer
157 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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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 ...
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42 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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28 views

Implementation of 2D Prony's exponential modeling to detect cracks in pipeline scan

I want to use 2D Prony's exponential modeling in order to find cracks in pipeline images. I found interesting algorithm presented in the following scientific article: 2D Prony's method In this paper ...
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36 views

Optimal way for curve detection

I am totally new to image recognition and image analysis and have a project concerning detecting a smooth curve on a uniform background (white/black/any color) and then be able to follow this curve ...
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2answers
61 views

Edge detection on a color image

I understand the process of using a Sobel kernel for edge detection in greyscale images. The input is a greyscale image, and the output is a greyscale image. I'm having trouble, however, figuring out ...
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62 views

Detecting blades of a wind turbine

I have many close-range images of a single wind turbine blade (taken from different positions, same angle): I need to separate the blade image from background like this: The problem arises in ...
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1answer
48 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?
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1answer
239 views

Algorithm for finding length and end points of a curly human hair

I'm trying to do some analysis of a curly human hair on an iPhone app. I've been using the openCV library. Particularly I want to be able to estimate the length of the hair, and locate its end points ...
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1answer
465 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 ...
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2answers
98 views

detecting “deformed” lines

I have a project in which I have to recognize 2 lines in different "position", the lines are orthogonal but can be projected on different surfaces. I'm using opencv. I'm not asking for code, ...
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3answers
133 views

Which sigma to use for edge detection

I know that in many edge detection algorithm the first step is choosing a scale to work on. We actually operate on the chosen scale by applying a gaussian blur on the original image. I wanted to ...
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2answers
61 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 ...
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2answers
958 views

How do convolutions become matrix multiplications?

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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1answer
296 views

Keypoint orientation with the oFAST from Rublee's ORB

I've just read the papers from Rublee et al. (ORB: an efficient alternative to SIFT or SURF) and Rosten et al. (Machine learning for high-speed corner detection) (=fast-detector). Rublee tries to ...
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1answer
220 views

best robust feature detectors for detecting similarities among archeological signs

I would like to implement edge detectors for creating a feature vector for archeological signs. Which are best features, algorithms to retrieve? That could be loaded in a Support vector machine for ...
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66 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 ...
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2answers
308 views

Why is Prewitt filter High Pass

Prewitt filters are popular filters in image processing for edge detection http://en.wikipedia.org/wiki/Prewitt_operator Can anyone give a proof on why Perwitt and other edge detecting filters are ...
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501 views

Difference of Gaussians

I use the following formula for DoG: $$\frac{1}{\sigma} (\frac{x^2}{2\sigma^2}-1.0) e^{\frac{-x^2}{2\sigma^2}}$$ What is the relationship between this formula and the difference of two Gaussian ...
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Differences between OpenCV Canny and MatLab Canny?

does anyone know why the MatLab Canny (MLC) is so different compared to the OpenCV Canny (OCC)? ML-C delivers precise and more connected edges than the OCC, but how is that possible? The reason why I ...
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Image segmentation issue of different materials

Hi CV/Pattern Recognition Community, I've got a serious problem regarding the segmentation of an image. The scenario is an atmosphere within a furnace which makes my head go insane. And I need to ...
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1answer
3k views

EmguCV: Detect a ball in the frame

I am having a VERY hard time capturing when the ball comes into frame in this video http://www.youtube.com/watch?v=x1V6_OHrXIo I have no idea what to set the parameters too, and trying random values ...
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1answer
95 views

learnable segmentation or learnable edge detection

Is there some learnable segmentation or learnable edge detection algorithm exist? For example I mark N fotos by hands and than program "learns" how to do it best way and can do it on similar images. ...
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2answers
4k 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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3answers
2k views

Can edge detection be done in the frequency domain?

Can we take advantage of the fact that high frequency components in the FFT of an image generally correspond to edges, to implement an edge detection algorithm in the fourier domain? I did try ...
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276 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 ...
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Connecting edges detected by an edge detector

I have a binary image obtained from a canny edge detector. The edges are not nicely detected in the center and I need to join them. The connection of edges is orientation and neighborhood dependent. I ...
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157 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 ...
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188 views

Identify the correct spot to place a label

In the image shown below, I have a 2D data set where I have identified four clusters labeled [0,1,2,3]. I'm looking for an algorithm to place the labels in a ...
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1answer
283 views

Could you describe the effects for varying different parameters of a canny edge detector?

Last couple of questions touched upon Canny edge detector What are the limitations of a Canny edge detector? and Best way of segmenting veins in leaves? The basic outline of the algorithm is as ...
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4answers
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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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1answer
864 views

How can I detect elements of GUI using opencv?

Given a screenshot of an application, is there any way of finding GUI elements of that application using only opencv? (something like in the image) I tried to play with blending the image and other ...
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1answer
790 views

Detection of circles (ellipses) in 2D point cloud

Given a set of points (2D) i.e., point cloud (PC), the question is about a robust, accurate and ...
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1answer
1k views

Get histogram of edge lengths/orientations in an image using OpenCV

In the process of trying to estimate whether a ROI contains [Japanese] text, I need to get a rough count of edges, hopefully binned by length and/or orientation... I think this would give me ...
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234 views

What kind of edge detection use paint.net?

What kind of edge detection is used Paint.NET program? It allows me to choose the angle of the edge not like the one used by opencv (Canny). Here an example:
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1k views

Do the DCT coefficients correspond to particular pixels?

Getting the DCT coefficient based on what I've read, is usually done through a matrix, usually 8x8 or 16x16 using these formulas: ...
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651 views

Roberts Edge Detector how to use?

I am trying to use Roberts edge detection to process an image. Do I just apply both of the masks to the image and perform convolution as normal? Could someone give me the breakdown of how to use this ...
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2answers
1k views

Detection of lines in a point cloud

What are the best solutions to detect line in a point cloud? Comparison being made with and between Hough Transform, Radon Transform, RANSAC (see wikipedia) and Brute-Force Search (see wikipedia). ...
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4answers
2k views

How do I detect distinct objects when their edges touch each other?

I need to find all the contours in an image retrieved from the camera. So I first use the canny edge detector to find the edges and then find the contours. Pretty simple. However, my contours get ...
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2answers
266 views

Explanation on Haarlets

Would someone be able to give me some info or a link etc ... regarding haarlets aka Haar wavelet-like features. I'm reading several papers for my master dissertation and several of these papers ...
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2answers
2k views

How to implement a gradient based Hough transform

I am trying to use the Hough transform for edge detection, and would like to use gradient images as the basis. What I have done so far, given the image I of size ...
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3answers
927 views

Bitmap border/stroke alogirthm?

I am looking for an algorithm that adds borders to a bitmap image(very much like the photoshop stroke effect) but one that will also have antialiasing to the borders(or one that copies alpha from the ...
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754 views

Estimating onset time of a tone burst in noise?

What techniques might one use to estimate the onset time of a sinusoidal tone burst in a noisy signal? Assume the tone burst has a known fixed frequency (but unknown phase) and a very sharp rise ...