Questions tagged [computer-vision]

Questions about algorithms for processing and analyzing images and videos.

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Computing structure tensors

As far as I understand, the structure tensor is: $$ M = \sum_{(x,y) \in W} \begin{bmatrix} I_x^2 & I_xI_y \\ I_xI_y & I_y^2 \end{bmatrix} = \begin{bmatrix} \sum_{(x,y) \in W} I_x^2 & \...
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How are epipolar lines useful in computer vision?

Why do use epipolar lines and what are it's benefits in computer vision ?I am unable to find the uses of epiploar lines and how they are helpful although i am aware of epiploar geometry concepts. I ...
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3D reconstruction from multiple images

Sorry if it's a trivial question but I'am a beginner. I am working on 3D reconstruction from multi-images project. I am working with these datasets. There is a par.txt file including the camera ...
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3D Reconstruction from multiview calibrated camera

I have a calibrated camera whose intrinsics were calculated prior. Suppose I have multi images with the same camera. Using the first two views.I have the 1) initial reconstruction using 8 point ...
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1answer
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Face recognition system with a sparse dataset

I have a dataset of 100 ID's, each ID with only a single unique face image. How can I develop an effective face recognition system to recognise only these faces? I was thinking Deep Learning but the ...
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Performing semantic segmentation on images on word documents

At the moment, I'm making a comparative analysis between two different neural networks for a class. The problem they are both trying to solve is detecting tables on documents. Below is an example of ...
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confusion regarding mid level image processing task?

I am reading gonzalez chapter1 As shown highlighted in attached snapshot, what is meant by this mid level task: description of those objects to reduce them to a form suitable for computer processing, ...
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How can I compare two faces using facial landmarks?

I'm using first_order_model for an expression transfer between an video and a static image. Part of the algorithm makes a facial comparison to get the frame in the video where the face is best ...
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Pattern detection by stacking convolutions

CNN use convolutions to perform many tasks. In some architecture, the first layer(s) are basic filters such as Gabor's. Many CNN work by stacking a number of convolution layers to build detectors ...
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I don't understand formula meaning of computer vision Paper

I am master degree student at Computer Science Department. I started master degree at this year. Now I'm reading two papers about computer vision. Actually before time I didn't have experience about ...
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What is the best algorithm for detecting the texture of a person's clothes in real-time for a mobile robot?

I am working on the human following robot. the robot extracts a feature of clothes's texture and distinguishes between the people that they stand up in front of the robot. So, the robot needs that it ...
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27 views

Using a rotation matrix to transform/shift a pinhole camera

I have a pinhole camera model with the following extrinsic (in Earth Centered, Earth Fixed Coordinate, (ECEF) system) and intrinsic parameters. focal length (x,y) = 55000 px, optical center = (2400,...
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Contrast detection implementation for blur detection in microscopic image

I am currently doing a project where I have to detect if the the microscopic images given are blurry. I tried canny edge detection but they seem to perform not so good in detecting blur. I realised ...
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Laser Plane Estimation for Laser-Camera system?

I have to set up a system of a laser line/ plane projector and a web camera to localize the 3D position of the laser in the camera image. I've read / come across several resources but the idea is ...
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Image/Video deblurring

I am currently working on an algorithm that will help to improve shaken blurry images. I know there are plenty of them, such as deconvolution, that is pretty useful though I don't really know how to "...
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Using the fundamental matrix for triangulation process?

Given the projection matrices from two cameras ($P$,$P'$) and a pair of corresponding points $(x_i,x'_i)$, it is straight forward to compute the triangulation using $$x_i=PX,x'_i=P'X.$$ I understand ...
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Why HOG angular bins have values between 0 and 180 degrees?

I have learned that HOG angular bins have values from 0 to 180 since the algorithm uses unsigned gradients. I am failing to understand why. As far as I know gradient orientation is calculated as <...
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Relation between shape descriptors and featured connected component in matching problems

Hope I'm asking in the correct community, from the title, I need a clarification regarding the idea of dealing with 3d descriptor and featured connected components. I have this approach: model -> ...
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Using The Output Of Semantic Segmentation In Autonomous Driving

I have read a couple of papers on semantic segmentation and ran this github code (which was trained on Cityscapes) against a KITTI sample image and it did pretty well (as seen below). I get that ...
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38 views

Text detection in computer vision

I'm curious about the way text recognition works in machine learning(or more generally, the question of object vs not object) in computer vision. How are systems trained when the not-object data set ...
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1answer
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“higher intensity” and “high signal intensity” in images

I'm newbie in Computer Vision and image processing. I'm reading the article "Automated White Matter Hyperintensity Detection in Multiple Sclerosis Using 3D T2 FLAIR" and it said: 2.2.4. WMH ...
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Does white balance correction improve the performance of visual object detection?

Visual object detecion aims to locate and recognize objects of interest in images. I wonder, does white balance correction contribute to better performance of visual object detection? Are there any ...
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The rotation matrix of a stereo pair with the cameras are horizontally aligned

Please forgive my ignorance on this. It seems like very soon I will have a D'OH moment and it will click. In the meantime, I am having trouble thinking about the joint rotation-translation matrix of ...
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Determine intrinsic camera parameters using one picture and a known point-cloud of the scene

I have a point-cloud of a city, and a perspective image of the same city. Is it possible to determine the intrinsic camera parameters, namely, position w.r.t. world coordinates, rotation, and focus? ...
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Bi-quadratic Interpolation

If bilinear interpolation is faster (uses 4 data points) but less accurate than bicubic interpolation, which uses 16 data points, why is there no "bi-quadratic" interpolation, which would use 9 data ...
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Measuring distance in arbitrary scale point cloud

I have one point cloud(point cloud of human feet) of arbitrary scale. If I have another point cloud(of human feet) with dimensions known, can I get the dimensions of a first point cloud? How will ...
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Using stereo vision for obstacle avoidance on quadcopter?

I am basically an electrical engineer. I plan to use stereo vision for obstacle avoidance (and possible further development of object recognition). Any efficient libraries for depth mapping from ...
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Partial derivatives of bilinear Sampling

I'm going over the paper Spatial Transformer Networks (link). On section 3.3 they introduce bilinear sampling kernel (Eq. 5) $$ V_{i}^{c}=\sum_{n}^{H} \sum_{m}^{W} U_{n m}^{c} \max \left(0,1-\left|x_{...
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How to detect number of specific object in an image and it's diameter(size)?

I have two images of IRON RODS (i.e only two images) and I want to detect how many rods are there in each image and get the diameter of each rod in a image? I don'...
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RGBD alignment without explicit transformation between RGB and depth

I have a set of RGB-D scans of the same scene, corresponding camera poses, intrinsics and extrinsics for both color and depth cameras. RGB's resolution is 1290x960, depth's is 640x480. Depth is ...
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Difference between Image Analysis and Computer Vision

I have searched the web and I have only found the differences between Image Processing and Computer Vison (also in this website too). In addition, sometimes Image Analysis is confused with Image ...
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Graph neural network

I'm trying to build GNN model that classify images , the first step is to model each image with graph , each node represents one pixel , now how can I define the edges in my case ? does the spatial ...
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Using colors in feature detection

Is there any feature detector or extractor that uses color information? Detectors like SURF and SIFT and many others work with grayscale. How do you think, may be transform can be sued to generate a ...
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Do image artefacts reveal the original image orientation?

An image is taken and then rotated by an arbitrary angle and cropped. Let us assume that the original image is rather meaningless and is not aligned in any way. Given the rotated image, is it ...
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Computer Vision Techniques to find Slope of beach in the 2D Images?

What I am planning to do is to calculate the height and estimate the slope of the segmented Object. The camera will be static and the Object of Interest is the slope of the beach. I am finding harder ...
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How to transform an arbitrary graph into a fixed vector representation?

Actuality I work in computer vision, specifically on a problem known as "scene graph modeling." This problem aims to convert an image $I$ in a graph $G=(V,E)$ where the nodes $V$ represent the objects ...
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Descriptors in key-features during mapping

This question is related to this question. In SLAM-type applications the feature detectors like SIFT are used for finding keypoints in the images to be matched. The candidate keypoints are matched by ...
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How are image processing and computer vision related to artificial intelligence.?

We have often heard both terms image processing and computer vision in AI sessions But i am confused, how they both are related to artificial intelligence?
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Where is the epipole if one camera center is not in view of the other?

In the book multiple view geometry, the epipole is defined as follows: The epipole is the point of intersection of the line joining the camera centres (the baseline) with the image plane. ...
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Using Particle Filters to find optimal 3D rotation

There exists a set of points in a 3D euklidean space. A camera views that point set and that camera is aligned with the world coordinate system. The center of gravity of the point cloud is in the ...
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Does the illumination color (red/blue/green) has any effect over the disparity map generated from a stereo image?

I have a working model that creates a disparity map using stereoscopic image processing using opencv. I am thinking of improving the disparity map by using illumination and stuck with different ...
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How to calculate point in 3D space from multiple perspective

I have multiple camera in different points. I have their position and rotation as $(x,y,z)$ , $(\alpha,\beta,\gamma)$ or $( roll, pitch, yaw)$ . And I have output like this : Feed from camera-1, I ...
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What is the common way to approximate contour with quad?

I'm trying to find quads on stream from my webcam. cv2.HoughLinesP sometimes returns more lines then needed. How can I approximate them to contour of exactly 4 points that fits returned result best? I'...
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How to detect facial landmarks - using haar and other way?

I have done some projects using haar cascade(Ex.- Face-detection,Eye inside face detection,shoe detection etc), I also have some knowledge about it. I have trained my own models learning from youtube, ...
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Calculating depth mask from different lighting

I have a object which is static, the camera is static and light source is moving. How can the depth mask be calculated ? Concept is to use - calculate height from shadow length Lets imagine a have ...
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impact of the single pixel in disparity

Disparity essentially means the distance of a corresponding pixel in another image ( in pixels). This is clear and understood. When I looked after how the depth is related to disparity, then I found ...
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91 views

Triangulation algorithm for an arbitary amount of points?

I have multiple cameras that records the 2D pixel coordinates of the features each camera sees. After some searching, I came across this paper with a method to calculate the 3D coordinates of the ...
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2answers
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Computer Vision algorithm to tell if camera is moving?

I'm looking for a computer vision algorithm or method that can tell if the camera is moving in a video. Or maybe an alternate way of telling if the background is moving. I have a lot of videos and ...
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1answer
106 views

Image registration using gradient descent

I have a target image $f(x,y)$ (where $x \in [0, 250]$ and $y \in [0,300]$), and a source image $g(x,y)$ I want to align $g$ to $f$ using the transformation : $$\Psi(x,y;t_x, t_y, \theta) = \begin{...
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Why is sparsity useful in dictionary learning?

What is the particular reason for which we use sparse matrix X in dictionary learning equation Y=DX where Y is the signal matrix, D is dictionary and X is the coefficient matrix?

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