Questions tagged [computer-vision]

Questions about algorithms for processing and analyzing images and videos.

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9 views

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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land-cover classification (matlab) (maximum likelihood) Gaussian models [closed]

Remotely sensed data are provided as 6 images showing an urban area, with the ground-truth information. These images have already been registered. You are required to implement the Maximum Likelihood (...
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16 views

Automatically detect Object points and Image points from a Single Grid for Camera Calibration?

What is the best generalised algorithm suited for detecting Object points and image points automatically from a single grid image with different line thickness and luminance intensity? Link defining ...
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34 views

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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12 views

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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14 views

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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23 views

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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1answer
35 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
13 views

“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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15 views

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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16 views

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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16 views

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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10 views

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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28 views

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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51 views

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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30 views

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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1answer
160 views

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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30 views

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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16 views

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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39 views

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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1answer
68 views

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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22 views

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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10 views

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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1answer
37 views

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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24 views

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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1answer
34 views

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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15 views

maximum tensor rank for computer vision tasks

Most computer vision tasks do not require 4+ ranked tensors. Are there any use cases for tensors with ranks more than 4 in computer vision? Are there any use cases for deep learning in general?
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42 views

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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57 views

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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16 views

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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1answer
68 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
201 views

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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16 views

Confused between different Structure from Motion pipelines

What is the difference between Global SfM, Incremental SfM, Sequential SfM, Progressive SfM and VSLAM (Visual Simultaneous Localization and Mapping). Is sequential SfM the same as VSLAM ? I have tried ...
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1answer
80 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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49 views

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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42 views

identify abrupt frame changes in a video

The frames of live streams or videos, in general, do not flow smoothly. A sports game would have multiple cameras recording the game and hence, there will be camera switches in the stream. I am ...
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29 views

Finding the linear mapping between homogeneous coordinates of affine camera

If I have an affine camera with a projection relationship governed by: \begin{equation} \begin{bmatrix} x & y \end{bmatrix}^T = A \begin{bmatrix} X & Y & Z \end{bmatrix}^T + b \end{...
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1answer
99 views

Camera calibration without grid

Ususally a grid pattern (circles or squares) is used for camera calibration. Features (circles or corners) are detected in a function (e.g. findCirclesGrid in OpenCV) and passed to the a camera ...
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1answer
79 views

what the mean and median filters with an n x n kernel (neighborhood) do to the grey-levels of the image? [closed]

sorry i haven't found a good title for these three questions i'm wondering if someone could give me explaination with proof (if possible ) of these three questions : Given a grey-level image stored ...
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1answer
33 views

How do we fix area of detectors in object detection?

I have gone through various articles on medium and also some from other sites trying to understand SSD. I am able to figure out most of the things from articles except this one. They always say that ...
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21 views

3D registration for reconstructed surface

I use Meshroom (based on the framework AliceVision) to reconstruct a scene based on photographs (e.g. a bottle on a table in a room). The software captures the bottle, but also the table and the whole ...
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47 views

Algorithm to determine paths that define shape of connected rectangles

Say you have a bunch of rectangles like these: They get organized into 3 distinct final shapes like this: As you can see, there are a few "complete contours", as in here: The way you figure out the ...
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111 views

What is the practical limit to how many object classes you can detect with Faster RCNN?

I am trying to follow this tutorial where the Faster-RCNN-Inception-V2-COCO model from TensorFlow's model zoo is used to detect playing cards. I was wondering what is the practical limit to the number ...
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195 views

When estimating camera motion from the fundamental matrix, why can translation only be recovered up to scale using epipolar geometry?

I was wondering once you have recovered the fundamental matrix F such that xFx' = 0. If you try to recover translation and rotation from F, I am told that this is possible only up to scale? Why so?

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