All Questions
119 questions
0
votes
0
answers
29
views
Detecting a large horizontal band in the center of an image
I have a small (228x228) grayscale image that I have created by segmenting the original image and converting it to grayscale after applying colors to the segment. I want to know possible approaches I ...
- 19
4
votes
1
answer
326
views
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 ...
- 43
4
votes
1
answer
991
views
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.
...
- 41
4
votes
2
answers
129
views
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.
...
1
vote
1
answer
56
views
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 ...
- 13
0
votes
2
answers
79
views
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 ...
1
vote
1
answer
216
views
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 ...
- 111
1
vote
1
answer
252
views
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 ...
- 113
4
votes
1
answer
177
views
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....
- 41
1
vote
1
answer
496
views
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 ...
- 500
2
votes
1
answer
273
views
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. ...
- 51
1
vote
1
answer
170
views
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 ...
- 51
2
votes
0
answers
70
views
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). ...
- 51
2
votes
1
answer
54
views
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 ...
- 21
2
votes
1
answer
49
views
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 ...
- 293
0
votes
0
answers
129
views
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 ...
- 103
2
votes
1
answer
670
views
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 ...
- 121
4
votes
1
answer
602
views
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 ...
- 145
3
votes
1
answer
554
views
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 &...
- 31
2
votes
1
answer
197
views
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 ...
- 141
5
votes
2
answers
681
views
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.
- 73
3
votes
2
answers
232
views
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 ...
- 167
0
votes
2
answers
418
views
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 ...
- 103
6
votes
2
answers
1k
views
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 $[1,0,-1]$ ...
- 293
2
votes
1
answer
173
views
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{\...
- 294
5
votes
3
answers
171
views
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 ...
- 53
5
votes
1
answer
923
views
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 ...
- 241
2
votes
1
answer
147
views
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 ...
- 127
0
votes
0
answers
365
views
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 ...
- 127
5
votes
2
answers
1k
views
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)
- 1,952
1
vote
1
answer
252
views
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 ...
- 127
1
vote
1
answer
413
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 ...
- 167
5
votes
1
answer
202
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.
...
- 53
1
vote
1
answer
124
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 ...
- 111
1
vote
0
answers
44
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 ...
- 11
1
vote
2
answers
1k
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 ...
- 13
5
votes
1
answer
637
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 ...
- 165
2
votes
2
answers
1k
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 ...
- 123
0
votes
1
answer
110
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 ...
- 11
1
vote
1
answer
424
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 ...
- 111
0
votes
1
answer
53
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 ...
- 111
7
votes
2
answers
6k
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.
...
- 171
2
votes
1
answer
116
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 ...
- 131
1
vote
1
answer
3k
views
How can I trace a path around an image consisting of only black and white lines?
I'm looking for a way to trace a closed curve (i.e. a long list of pixel values all connected by lines in between) that approximates a bitmap image of black and white lines.
The image starts out as an ...
- 203
1
vote
2
answers
3k
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 ...
- 163
5
votes
1
answer
1k
views
What's Logic Behind the Construction of Sobel's Filter in Image Processing?
I am basically very new to this image processing field. I am presently working on edge detection on colour images. While learning the basics of edges and edge detection in images, I encountered image ...
- 213
0
votes
1
answer
1k
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 ...
- 3
3
votes
2
answers
102
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.
Basically ...
- 435
1
vote
1
answer
5k
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, ...
- 133
3
votes
1
answer
262
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 ...
- 76