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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Camera Pose Estimation from Vanishing Points

I want to estimate the pose of camera (Location and Orientation). Can I use Vanishing Points to get the location and orientation of the camera? There is object in the image which I also know his size,...
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34 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(...
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What is scale ambiguity in computer vision?

When you compute relative pose between cameras, translation is only accurate upto a scale. Need some help in understanding the scale ambiguity and what exactly does it mean translation is accurate ...
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Understanding 2D alignment using least squares

In Computer Vision Algorithms and Applications book by Richard Szeliski, the author explains 2D alignment using least squares as follows: Given a set of matched feature points ${(x_i, x_i')}$ and a ...
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Measures of edge image continuity and connectivity

Suppose I have a scalar image $I:\mathbb{Z}_{1,m} \times \mathbb{Z}_{1,n}\rightarrow [0,1]\subset \mathbb{R}$, where $\mathbb{Z}_{1,m} = \{1,\ldots, m\}$. (For instance, computed as the (scaled) ...
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1answer
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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 ...
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Can the colors of an image be interpreted as “virtual” Doppler effect? [closed]

In astronomy, the Doppler effect is used to estimate approximate distances to stars and other celestial bodies. Using the same principle, lets say we divide an image (photograph) in pixels and that ...
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131 views

How would you interpret the pattern in this picture? (generated by re-sorting pixels based on their RGB value)

Was playing with some pictures and ran the ruby code below. The code reads an input image using the ImageMagick library, gets an array of pixels, re-sorts the pixels and then writes out an image with ...
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1answer
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Stereo triangulation similar triangle derivation

I understand that the similar triangles are the red and blue triangles. I'm trying to understand where $T + x_r - x_l$ comes from. I understand we are trying to compute the length of the base of the ...
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25 views

Fast and Slow motion video detection using Optical Flow

I'm trying to calculate a "video motion" value in a given video sequence, meaning how fast or slow motion the video is. For instance, if a video is about a car racing, the value is high. Whereas if ...
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The rank of Fundamental Matrix

This question is regarding two view geometry where a point lying in the image plane of the first frame/ position of the camera is mapped onto the image plane of the second frame/ position of the ...
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1answer
152 views

How to remove striped noise from this image. Which filter or algorithm use better?

I need to process a gray scale image. The task is to remove the stripes, which constitute some noise. I have next origin image: This image received many channels ADC(Y) in moment of time (Xn) from ...
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BRIEF feature vector random point sampling 3rd method

When using the BRIEF algorithm to generate a feature vector, 5 methods are provided for selecting 2 random points inside a feature point patch. The 3rd method is described as follows: Let consider ...
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Gender classification using Periocular Region [closed]

I have a dataset of the periocular region, I have images of the male and female periocular region but they are only labeled as left and right periocular region, Folder is a mixture of male and female ...
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What is the name and theory behind a basic motion filter with background update?

I am working on machine vision task. I am using openCV in Python. I need to detect motion. Best would be if I can calculate the difference between the new image and background. However, the ...
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Sparse to Dense Flow

I'm trying to upgrade a flow from sparse to dense and have been recommended this for my use-case https://uk.mathworks.com/matlabcentral/fileexchange/25634-smoothn . When I run the interpolation, ...
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46 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 ...
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28 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 ...
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Optical flow Horn & Schunck smoothness error

I was reading about the Horn & Schunck method and they define the smoothness error as (Robot Control 1988 (SYROCO'88): Selected Papers from the 2nd IFAC Symposium p. 348): $E_{sm} = \iint{\left(...
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47 views

Definition of difference between compression and filtering

I'd like to explain the motivation. It sounds like a neuroscience topic but I am after the strict Signal Processing POV. (I don't come from a Signal Processing background). Interested to learn ...
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What do the 1D filters represent when using imfilter?

I am reading the source code of an algorithm that is used to process an image. While reading this source code (and others), I've found lines of code of the form ...
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1answer
57 views

Can CV or DS be seriously considered DSP roles? [closed]

This is not a technical question but can have a yes/no answer, and a why statement. My understanding about digital signal processing (DSP) is that it allows to take real-world analog signals (1D, 2D, ...
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How does the “additive operator splitting” exactly work?

I am reading about the non-linear (or non-homogenous) diffusion method (aka anistropic diffusion method). There are several ways of implementing this method. In all cases, we first need to discretise ...
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How can I calculate homography from the room height and camera calibration matrix?

EDIT2: I've added an assumption that the camera calibration matrix is given. Other factors (rotation, camera pose) are still not given. I want to measure actual lengths of floor edges (blue lines in ...
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Pascal Voc 2012 Annotaions for 6D viewpoint(pose) estimation

Everyone, I am working on 6D pose estimation and I have to predict a rotation matrix (Euler angle) and translation. Now In Pascal Voc annotations are in the form of azimuth, elevation and distance ...
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2answers
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What Is the Relation Between Deblurring and Deconvolution in Computer Vision and Image Processing?

The deblurring problem can be modelled as follows $$ f = \phi u + \epsilon, \; \epsilon \sim N(0, \sigma) $$ where $\phi$ is a filter (e.g. a low-pass filter) and $\epsilon$ is a Gaussian noise. In ...
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Converting from 2D coordinates in image plane to 3D, use of focal length in gnomonic projection

I'm currently using libgnomonic to perform a gnonominc projection. I cannot find a derivation of the used formulas. But they don't seem to be particularly involved and there's a specific bit I'd like ...
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4answers
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After advice about detecting focus quality of objects in a photo detected using YoloV3

I've spent the last couple of days playing with YoloV3, and have had very good results. My use case is sports photography, and the object detection for people/bikes etc is very very good, I'm very ...
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21 views

Understanding SURF point-of-interest localization

I've recently read Herbert Bay's paper of SURF. From which I understand: SURF calculates a table from each image pixel's Hessian matrix's determinant, instead of SIFT's Difference-of-Gaussian table. ...
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KLT tracker, reject tracked occluded points

I want to use KLT tracker for a visual odometry application. Thus, I only want to track object features. Currently I'm using OpenCV's implementation ...
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77 views

What are the meanings of Fx, Fy, Sx and Sy in Image Processing?

I am currently reading a book titled "Learning OpenCV 3 Computer Vision in C++ with the OpenCV Library", and I come across these two equations: ...
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1answer
61 views

How to Combine / Cascade two `3 x 3` Filters into One `5 x 5` Filter

If you have a uniform 3x3 box filter T which is: 1 1 1 1 1 1 1 1 1 And an 3x3 laplacian filter W which is: 1 -2 1 -2 4 -2 1 -2 1 Can these 2 filters be combined into one 5x5 filter, the ...
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Implementing Edge Preserving Diffusion (Anisotropic Diffusion)

I am trying to implement edge preserving diffusion. Recall the general diffusion equation to be: $$\DeclareMathOperator{\Div}{div}\delta_t u = \Div(g \nabla u)$$ Where $g$ is the speed of the ...
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Auto Detection of Rotation Angle on Arbitrary Image with Orthogonal Features

I have a task at hand where I need to detect angle of an image like the following sample (part of microchip photograph). The image does contain orthogonal features, but they could have different size, ...
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Why does the Y component in YCbCr represent luma/intensity?

As far as I know, the RGB to YCbCr conversion is just a linear transformation, yet the Y channel successfully captures the intensity value of each pixel. How? In other words, where do the following ...
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26 views

Why does KLT rely on translation model for tracking when an affine model has to be computed iteratively to check the residue?

I am researching KLT tracking algorithm and I came across this paper. It says: However, smaller windows are in general preferable for tracking because they are less likely to straddle a depth ...
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36 views

Understanding performance of Lucas Kanade Iterative Image Registration Technique

I am reading the paper: Lucas, B. D., & Kanade, T. (1981). An iterative image registration technique with an application to stereo vision. I am having some trouble understanding section 4.3 ...
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33 views

Disabled parking sign detection

I would like to ask you, if you could recommend some algorithm for detection of handicapped or disabled parking sign painted on the road or on the traffic sign. I am thinking about image morphology (...
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1answer
76 views

How to extract a smooth contour from a set of points in 3D?

I am trying to segment a 3D volume. The outcome of all my volume segmentation algorithms is a set of candidate points in 3D space. Now I need to smooth this point cloud and fit a closed surface it. My ...
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Sigma Value change after down-sampling

I am I have an image with a specific sigma(say 2). I downsample the image. Will thr be any change in the sigma for the downsampled image?
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1answer
56 views

How is the Gaussian kernel related to the Euclidean distance of the neighbourhoods in the non-local means 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 ...
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2answers
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Why can convolution only be applied to compute the output of a linear filter?

We apparently cannot compute the output of a bilateral filter (BF) using convolution (with the image) because the BF is a non-linear filter. In general, why can convolution only be applied to compute ...
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106 views

What is energy in image processing?

There are several web articles on the topic, but, after having read them, I still don't know what "energy" is, in the context of computer vision (CV) and image processing (IP). It is related to ...
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Why isn't bilateral filtering shift-invariant?

I have a source (that I can't share) that states that bilateral filtering isn't shift-invariant (that is, it depends on the input signal), hence we cannot use convolution and the Fourier convolution ...
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63 views

Use FOV or camera deprojection to find position of pixel in world coordinates relative to my camera?

A teammate and I were discussing how best to get a 3D coordinate point (X, Y, Z) in world units from an RGB-D depth image. I'm using an intel real sense D435. From how I have researched it using the ...
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1answer
26 views

Deriving vector paths from pen strokes

I want to calculate vector paths that approximate pen strokes from handwritten documents. My tool needs to run in batch mode, unlike hand tracing or Illustrator's "Image Trace" feature. The potrace ...
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1answer
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What is the difference between domain and range filtering?

In the context of image processing, I have heard the expressions "domain filtering" and "range filtering". What do these terms refer to? What is the difference between them?
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What is a periodic signal in image processing?

In the context of image processing (and computer vision), the concept of convolution comes up a lot. Convolution is quite related to the concept of Fourier transform and DFT. In the context of image ...
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How Much Zero Padding Do We Need to Perform Filtering in the Fourier Domain?

Consider an $M\times N$ image $f$ and an $G \times K$ filter $h$. Given that convolution in the spatial domain corresponds to multiplication in the Fourier domain, then we can perform a convolution of ...
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35 views

What are the parameters of a calibrated spherical camera?

I'm aware if we have a pinhole camera model several parameters describe the specific camera (such as aspect-ratio, focal length, principal point, distortion parameters etc). There're standard ...