# Questions tagged [computer-vision]

Computer vision includes methods of processing, analyzing, images and high-dimensional data to form high level understanding and recognition of the scene or images.

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### Corner detection using Chris Harris & Mike Stephens [duplicate]

I am not able to understand the formula, What is $W$ (window) and intensity in the formula mean, I found this formula in opencv doc http://docs.opencv.org/trunk/doc/py_tutorials/py_feature2d/...
95 views

### How do I detect the sharp edges in the following image?

I am looking to count the sharp pointy triangular things in the image. However I was unable to do so. One approach I did try was take a convex hull of the contour and then find convex defects but it ...
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 ...
2k views

### Pose from Homography matrix - Zhang method

This post also contributes to the post at Step by Step Camera Pose Estimation for Visual Tracking and Planar Markers by Jav_Rock (since I cannot add any comment there and I don't know why) It can be ...
12 views

### Is there a difference in SNR between using 2x2 pixel binning in the camera and shrinking the full resolution image in software?

Is there a difference in SNR (or any other measure of image quality) between using 2x2 pixel binning in the camera and shrinking the full resolution image in software (cv::INTER_AREA) to the same size ...
68 views

### Why are 8 points needed to compute a fundamental matrix?

Homograpies have 8 degrees of freedom. Fundamental matrices have 7. Essential matrices have 5. To the best I could find, all those matrices are obtained by using the 8 point algorithm. I don't see ...
26 views

### What is the difference between an image plane and a virtual image?

I have the following diagram that describes a camera model (I believe it is the pinhole camera model). Wikipedia has an article about the image plane and virtual image, but these articles do not ...
395 views

### Laplacian of Gaussian Approximation and Gaussian Blur as the Solution of Heat Equation

While I was reading SIFT paper(Lowe, 2004), I came across the method that he apply "heat diffusion equation" to Gaussian function to derive that $$\frac{∂G}{∂σ} = σ∇^2G$$ I searched Wikipedia and ...
266 views

### Automatic Image Enhancement of Images of Scanned Documents (Auto Whitening)

Dropbox have make a blog post about there automatic enhancement method for scanned document image - Fast Document Rectification and Enhancement. I followed the post and they mention a formula to make ...
30 views

### Low samples numbers machine vision training for object detection

I'm trying to set-up a machine vision application in which I have to detect the position of a printing nozzle (in the red sqaure in the image) in a field of view in order to prcisely position a ganty ...
17k views

### Good Language for Implementing Computer Vision System / Algorithm / Application?

I am trying to implement a content based image retrieval system but before I do so I would like to get an overview of some programming languages suitable for this task (having good libs and such). ...
14 views

### Flat Field Correction - When images are taken at different exposures

The light source I am using is known to have a Gaussian intensity distribution along the height. I took the raw images at "x" seconds of exposure. However, while taking the bright field image, the ...
59 views

### Projecting a vector to another to detect the sparse values of such vector

Assuming we have sparse vector of length $N$ such as $X = [0,1,0,-1,0,1,1,0]$ which has some non-zeros values. The vector $x = iFFT(X)$ is convoluted with another vector $h$ resluting $y = h*x$. ...
2k views

### Jacobian of affine warp in Lucas-Kanade image alignment

I hate this kind of questions, but I'm really stuck. I'm trying to implement Lucas-Kanade algorithm as described in this paper (see pages 4 and 5). Unlike most explanations I've seen they don't assume ...
27 views

### How the Grayscale images are converted back to RGB?

In case of RGB to grayscale conversion we take the average of R,G,B channels and convert them to Grayscale which has songle channel. How to convert back the Grayscale to RGB ??
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### What is Magnitude and Phase actually represents in Fast Fourier Transform?

When we reconstruct the image from its magnitude only using Inverse Fast Fourier Transform, then why the resulting image looks nothing like but the original image? Can someone please explain me in ...
33 views

### What's the purpose of augmenting an image with a random “gradient”?

I have the following Python code ...
104 views

### Finding Homography Matrix Using Lines

I have some Points and Lines from original image and the corresponding points and lines from top view image. -> I tried to find homography using points Used OpenCV function findHomography(...
1k views

### How can I detect pipeline cracks using OpenCV and Python?

I have developed a robot that captures images of the pipeline interior as it moves. The requirement was to be able to detect cracks inside. So far i tried several OpenCV codes that find the crack ...
6k 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 ...
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. ...
19 views

### Use sparse optical tracking to track a Bounding Box object

I need some help on solving this issue. Any tips are appreciated. The goal of the project is to try to track a Bounding Box object, chosen arbitrarily in an image, throughout many frames of a ...
30 views

### Fast Document Enhancement

I followed Dropbox's blog - Fast Document Rectification and Enhancement To enhancement image, I need solve this formula J(x,y) = gain(x,y) * I(x,y) + offset(x,y) Where J is image after ...
16 views

### Parameters for inverse image distortion

I'm trying to simulate camera (barrel/radial) distortion, and to reverse it. I.e. a process that would do: Image --> Distorted Image --> ~ Image In ...
34 views

### Harris Corners Detector squared derivatives

I have trouble understanding something (small) regarding the math behind Harris Corners Detector. (for example I looked at this explanation - https://aishack.in/tutorials/harris-corner-detector/) In ...
96 views

### 3D model from high speed videos?

Is there a way to convert or somewhat replicate RADAR data from a set of given high speed videos taken from multiple angles. The problem is quite ill defined but the task I have in hand is to ...
78 views

### Computationally Efficient Ways of Determining If Pixels Are Clumped

I'm working on an application where I get a video frame that's already segmented into good and bad pixels (as in -- the hardware either coughs up a pixel value or a flag that says "bad"). I want to ...
158 views

### How Is the Gaussian Kernel Related to the Euclidean Distance of the Neighborhoods in the Non Local Means Denoising Algorithm?

I am reading the paper A non-local algorithm for image denoising that describes the original non-local means algorithm. They define (p. 3 of the pdf) the distance between two square fixed ...
32 views

### Can Normalized Cut be used to find connected components in binary images?

I'm unsure whether Normalized Cut can or can't be used to find connected components in binary images. I would argue that it could, but could not validate this argument.
124 views

### What Distance Measure Is Proper for Image Patches?

I have a bunch of image patches extracted from two images. I want to find a proper measure of similarity between each patch from first images to patches from second image. I have made vectors from ...
81 views

### How Is the Bandwidth of an Image Reduced by an Octave in Gaussian Pyramid Procedure?

Reference paper 1. For arguments sake, let's say that the maximum and minimum frequency in an image are 256Hz and 1024Hz. When I perform filtering using the gaussian function, the "bandlimit" reduces ...
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### Licence plate enhancement

Is it possible to enhance the image below and make it more readable? I have tried apply binarization but there is some kind of shadow. So I have tried to convert image to gray scale and then ...
88 views

### Remove brighter regions in an image on frequency domain

I'm newbie and maybe this is not the right place to ask this question, or this question has no sense. I'm very interested in working on filtering images on frequency domain. I have found a few ...
82 views

### Why reprojection error is minimized instead of triangulation error for bundle adjustment?

For bundle adjustment optmization why is reprojection error minimized instead of traingulation error or ray-to-3d point error? Disadvantage with reprojection error is: for perspective camera, its ...
57k views

### OpenCV/C++ connect nearby contours based on distance between them

I have to connect nearby contours in an image based on the distance between them which specifies if the contours are to be connected. Now there's a question already on the same problem here https://...
41 views

### Understanding outputs of image Fourier Transform in Numpy

I am trying to understand the meaning of FFT outputs with respect to images. Take a look at the following example: ...
17k views

### Is deep learning killing image processing/computer vision?

I'm looking forward to enroll in an MSc in Signal and Image processing, or maybe Computer Vision (I have not decided yet), and this question emerged. My concern is, since deep learning doesn't need ...
201 views

### Correlation Performed by Convolution

Background: The question here is related to images in particular and not signal/waveforms. I have been reading a lot of answers about the difference between convolution and correlation but I am stuck ...
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### Image extraction post processing to increase similarity

I’m trying to train an OCR model, but I need to get my extracted images to look more like the training images. However I’m not sure of how to go about it and what techniques I can use. For instance ...
794 views

### How is WSNR (weighted signal to noise ratio) defined?

I'm studying about comparison between images to determine quality. I've learned about MSE, SNR and PSNR, and now I'm trying to understand WSNR, which I assume is similar to SNR but with weights. I ...
222 views

### What is the relation between time, frequency, spatial and spectral domains?

What is the relation between time, frequency, spatial and spectral domains? I think that time and spatial domains are the "original" domains (e.g. if the signal is a greyscale image, then the domain ...
723 views

### Calibration (intrinsic) parameters of a virtual camera with some known information

I need the calibration matrix of my simulated camera, I am trying to fully comprehend and follow the steps from Step by Step Camera Pose Estimation for Visual Tracking and Planar Markers as well as ...
633 views

### 3D point cloud to 2.5D graycale image (metric) [Halcon?]

I have a problem ragarding transferring a point cloud to a 2.5D metric grayscale image (gray value gives depth information). I start with a three channel image of 32bit floats with each pixel ...
2k views

### What is a good distance measure for matching SIFT descriptors depending on the distribution of their noise?

I have read some papers about distance measures like Euclidean, Manhattan or Chi-Square for matching gradient based image descriptors like those computed from the SIFT Algorithm (128-D vectors). Most ...
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### Converting from RGB to LAB Color Space to Reduce Colors

In many papers I see the following: First we have to convert image from RGB to LAB color space to reduce colors then ...
47 views

### Getting Composition of a Mixture of Colors

I wanted to validate a thought on blending of colours digitally. Imagine I have two colours, $C_1$ $(R_1,G_1,B_1)$ and $C_2$ $(R_2,G_2,B_2)$. Now, I create colour $C3$ as follows: \$C_3 = \alpha C_1 + ...
122 views

### camera calibration change orientation of axis

I want to solve for the extrinsics by using direct linear transformation on corresponding 3D LIDAR points and 2D camera points. I already have the intrinsics. Problem is, points behind the camera ...
763 views

### How to select the specific frame with object

I am detecting the object from the live camera through feature detection with svm , and it read every frame from camera while predicting which affect its speed , i just want that it should select the ...