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Questions tagged [edge-detection]

Edge detection is a tool in computer vision used to find discontinuities (edges) in images or graphs. Use this tag when asking about finding and manipulating edges or edge interaction.

Edge detection is a part of computer vision where the goal is to find edges in images. This often involves computing derivatives of the image with respect to the coordinates, because intuitively if the difference between two neighboring pixels is high, it is likely that there is an edge in the image. A popular edge detection algorithm is the Canny edge detector. Other edge detection algorithm includes Laplace & Sobel.

Discontinuities in image are likely to correspond to

  • discontinuities in depth
  • discontinuities in surface orientation
  • changes in material properties and
  • variations in scene illumination
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Extracting an edge list with conditions from an igraph object in R

I am working with an undirected igraph object composed of nodes of different types (e.g. males M in yellow and females F in orange): g <- graph.atlas(711) V(g)$name <- 1:7 V(g)$gender <- c("M","F","M","M","M","F","F") V(g)$color <-…
Pauline
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How do you handle negative pixel values after filtering?

I have a 8-bit image and I want to filter it with a matrix for edge detection. My kernel matrix is 0 1 0 1 -4 1 0 1 0 For some indices it gives me a negative value. What am I supposed to with them?
Thunfische
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Python rising/falling edge oscilloscope-like trigger

I'm trying to detect rising and/or falling edges in a numpy vector, based on a trigger value. This is kinda like how oscilloscope triggering works. The numpy vector contains floating point values. The trigger itself is a floating point value. I…
Cris
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How can I detect edges on an image of a document, and cut sections into seperate images?

The task is to take an image of a document, and leverage straight lines surrounding different 'sections' in order to split up the image into different documents for further parsing. Size of the different 'sections' is completely variable from page…
migsvult
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Creation of edge detection based image in PHP

I'm curious - is it possible to ahieve in PHP: 1) Send image file to server 2) Process image = detect edges and create simple strokes basing on the edges 3) Save file on server / send it to user's browser / whatever Here is some "sample" file ;P (as…
Paul
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What is the difference between edge and ridge detection?

The title is tells already enough, but citing Wikipedia: The purpose of ridge detection is usually to capture the major axis of symmetry of an elongated object,[citation needed] whereas the purpose of edge detection is usually to capture the…
justHelloWorld
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How to create a 2D map of room by a few images/movie frames?

I'd like to create a simple 2D map of a room by getting pictures (ceiling) of all directions (360° - e.g. movie frames), recognize the walls by edge detection, delete other unwanted objects, concat the images at the right position (cf. walls,…
Nils
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Image segmentation for screenshots (Region of Interest)

I want to compare Screenshots of different versions (same site) of a web-application. Until now I tried following approaches: pixel based comparison pixel based fuzzy comparison with Delta E segmented based comparison For the latter I subdivided…
user3801009
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Edge Detection and transparency

Using images of articles of clothing taken against a consistent background, I would like to make all pixels in the image transparent except for the clothing. What is the best way to go about this? I have researched the algorithms that are common for…
Joe Cannatti
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Can't get clean output in my MATLAB implementation of Canny-Deriche

My code so far is: function imgg = derichefilter1(x, k, a, b, c) osize = size(x); x = double(x); a = double(a); b = double(b); c = double(c); k = double(k); y1 = zeros(osize(1),osize(2)); y2 = zeros(osize(1),osize(2)); y1(:,1) = a(1)*x(:,1); y1(:,2)…
Hameer Abbasi
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what is the relationship between image edges and gradient?

Is there anybody can help me interpret "Edge points may be located by the maxima of the module of the gradient, and the direction of edge contour is orthogonal to the direction of the gradient."
Gary Gauh
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openCV: Sobel edge detection gives me assertion error

I am using python-openCV. When using the Sobel edge detection I get the following assertion error: src.size() == dst.size() && src.channels() == dst.channels() && ((src.depth() == CV_8U && (dst.depth() == CV_16S || dst.depth() == CV_32F)) ||…
Xolve
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Contour detection in MATLAB

I am trying to understand this code: d=edge(d,'canny',.6); figure, imshow(d,[]) ds = bwareaopen(d,40); figure, imshow(ds,[]) iout = d1; BW=ds; iout(:,:,1) = iout; iout(:,:,2) = iout(:,:,1); iout(:,:,3) = iout(:,:,1); iout(:,:,2) = min(iout(:,:,2)…
user1234
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Sobel edge detector in R?

I am working on an R assignment about Sobel edge-detection. Unfortunately the video tutorial I was following uses R for every other task, but switches to python for image processing - I am guessing he did not find any useful R package for image…
Manojit
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Detect words and graphs in image and slice image into 1 image per word or graph

I'm building a web app to help students with learning Maths. The app needs to display Maths content that comes from LaTex files. These Latex files render (beautifully) to pdf that I can convert cleanly to svg thanks to pdf2svg. The (svg or png or…
lami
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