Questions tagged [edge-detection]

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

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33 views

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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1answer
49 views

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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35 views

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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25 views

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
48 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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1answer
142 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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2answers
98 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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24 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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18 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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1answer
44 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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114 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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1answer
32 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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2answers
69 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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1answer
91 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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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
34 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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1answer
370 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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1answer
289 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
561 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
1k views
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1answer
287 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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34 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
81 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
2k 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
161 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
228 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
295 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
649 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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1answer
912 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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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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3answers
431 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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269 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
43 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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118 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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4k views

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
423 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
3k 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
191 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
355 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
747 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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318 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
276 views

detecting edge direction using Julia-language

Let say we have following image: made with following Julia-code: ...
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1answer
624 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
245 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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483 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
44 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
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
600 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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75 views

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 ...