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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17 views

Remove noise from VGA image

I have 2 color images generated from same X-ray machines, but one of the image is obtained using VGA cable. Therefore the RGB intensities differ in the 2 images. I am using Object detection to detect ...
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1answer
25 views

Equal probability quantizer in Python

I am trying to apply Haralick textures to a SAR image (float32). As far as I know, the image first needs to be quantized to a reasonable bit depth prior to calculate the co-ocurrence matrix. In the ...
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1answer
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Terminology: Camera Tracking, Camera Relocalization

I am reading the paper RGBD Datasets: Past, Present and Future available here, and two terms that I am not familiar with are presented. On page three, middle left side of the page, the author refers ...
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1answer
98 views

Fundamental matrix rank

Is there any way one can prove that $\text{rank}\big(F+F^{T}\big)=3$? where F is a fundamental matrix. If you have any idea, do let me know. I am trying to solve this problem. I am just trying to ...
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45 views

Detecting corners using structure tensor matrix

How does eigenvalues of structure tensor matrix help in detecting corners? For eg, in Harris corner detection, we consider the matrix $$M = \sum_{w} w \cdot \begin{bmatrix} I_x^2 & I_x I_y \\ I_x ...
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11 views

Understanding R-FCN

I am reading the paper R-FCN: Object Detection via Region-based Fully Convolutional Networks available here, a fully convolutional network for object detection. The backbone architecture describes : ...
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1answer
33 views

Find camera pose by knowing triangle coordinates

I have this concrete problem where I know the 3 coordinates of a triangle $ABC$ in a $xyz$ frame reference and I need to estimate the position $P$ and direction $\vec{n_{p}}$ of a stationary camera ...
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1answer
65 views

Math for projecting 3d world point to VR image coordinates

Suppose, I've a 3d world point $P$ and I want to project it onto the image plane of camera, I can do it as follows $$M = \begin{bmatrix} R & t \\ 0 & 1 \\ \end{bmatrix}$$ $$p = K \cdot M \cdot ...
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1answer
26 views

How does filter works in noise reduction?

On page 22 of the slide, the 1D array is [1, 1, 1, 1, 1], but the dots are uneven. Then why their values are the same? What's the value of the point that the arrow is pointing at? Though it gives ...
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1answer
21 views

How does Correlation for 1D Signals work?

On page 2 of the slide, I don't understand the example. Like $j$ and $s$ are both on the x-axis, what does j+s mean? The filter is $(f(−1), f(0), f(1)) = (−0.5, 0, 0.5)$. How can we use it? Could ...
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32 views

Removing the effects of camera motion in a video

I have frames of a video consisting of both a moving camera(translation, rotation, zooming in and out) as well as moving objects. I need to recover only the trajectory of objects which means I need to ...
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1answer
19 views

Different type of padding in image?

I want to implement a gradient operator on an image in Matlab. Should I have to pad the image before its implementation? How do I decide which padding to use e.g. whether to use zero-padding or ...
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1answer
28 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{\...
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Dataset suggestion: video dataset with accurate depth and pose info

Please suggest some datasets (can be synthetic, like rendered in blender or so) which have video frames (30fps preferred) with accurate ground truth depth maps and pose (rotation and translation for ...
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10 views

Where to place origin when warping an image using 3D rotation and translation?

Suppose, I've two images taken by a camera at two different locations. The two locations are related by a Rotation and Translation. So, points $X1$ in first frame will be at $M \cdot X1$ where $$ M = \...
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1answer
30 views

CT Slices to Planar XRay

I have axial slices of chest CT scans. Now, I want to use all these slices to construct a planar structure like an X-ray with a coronal view (Posterior to Anterior or Anterior to Posterior view). I ...
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3answers
74 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 ...
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1answer
27 views

Intuition about tag pose estimation accuracy

I have some difficulties to have a correct intuition about expected pose accuracy when dealing with planar pose estimation (e.g. pose estimation from AprilTag detection) and perspective camera model. ...
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1answer
20 views

Feature detector vs dense detector

What is the difference between a feature detector and a dense detector in computer vision? Are they the same or a subset of one another? For the following algorithms (implemented in OpenCV), which of ...
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15 views

Intuition behind cost aggregation functions in stereo correspondence problem?

I don't seem to understand the concept of a cost aggregation function like a Fixed window or an Adaptive window, etc. Why do we need this additional step, and why can't we just calculate the disparity ...
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1answer
28 views

Understanding rho and theta in hough

I understood the concept behind Hough transform. One thing i am still unsure is the rho and theta range of hough transform. The range is given below. If theta is in the range [0,pi), then rho values ...
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1answer
22 views

What is Bottom-Hat transformation?

I am reading the Digital Image Processing book by Gonzalez and i can't seem to understand Bottom-hat transformation. Can anyone explain it to me in easy terms?
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14 views

Faster R-CNN and 4-step Alternating Training

I am reading the paper Faster R-CNN available here. In section 3.2, page 6 bottom left, the authors describe what they refer to as a 4-step Alternating Training between the Region Proposal Network, ...
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1answer
74 views

Understanding the relationship between the convolutional feature map and the region proposals in Fast R-CNN

In the paper Fast R-CNN available here, I am trying to understand the relationship between the region proposals and the convolutional feature map. So from what I understand, Fast R-CNN takes in an ...
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1answer
14 views

Comparision between SSIM and MAD Image Quality Assessment Algorithms

I have been working with Most Apparent Distortion(MAD) tool to evaluate the quality of images. I have read a paper that compares SSIM, PSNR, FSIM, etc. with MAD. I am uncertain about some calculations ...
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1answer
38 views

Guassian Derivatives with orientations

I am reading the paper Selective Search for Object Recognition here. In Section 3.2, they give a similarity measure between two regions of an image based on the texture of the regions with what they ...
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1answer
43 views

What helped you in reading and implementing papers and coming up with original ideas in computer vision/graphics?

I'm trying to get into academic research at the intersection of vision and graphics, and was wondering how researchers in the field went about this: Was it useful to do a lot of fundamental math ...
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17 views

Smoothing jagged lines in an image?

I have an image like this - I would like to smoothen the lines in this (as you can see they lines are a little jaggy.) How can I do this? I obtained the lines by isolating them from another image ...
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25 views

How can I stitch bottom of some image to topside of another image by erasing as much overlapped image as possible?

I have 2 images of size 1920*1080 and I want to try image-stitching on them. These are images (images are from wind turbine blade.) This is the first image And the second image. I already have ...
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16 views

How does Lowe's ratio test work when you compute more than 2 nearest neighbours?

Lowe's ratio test can be used to discard matches that are possibly irrelevant or noisy. However, it isn't clear to me how the ratio test should be performed when you retrieve more than 2 nearest ...
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21 views

What is the difference between template matching and object detection?

What is the difference between template matching and object detection? Is the only difference that the template is typically rectangular while the objects can be of any form (including rectangular)? ...
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1answer
50 views

What function to apply a Metamorphopsia (grid warp) translation?

How would I go about finding or creating a function to warp images dependent on grid lines surrounding an origin (I don't wish for a grid on my actual images): It should work in practically the same ...
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23 views

How to know what kind of noise?

Im working with friends on a computer vision project for university. For the preprocessing part we are going to use a Gaussian filter. One of my project partner said I have to justify the use of a ...
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33 views

How to calculate the plane at infinity? either in Matlab or Python

I tried to implement this function to compute the plane at infinity $n_\Pi$ from the equation: where $w^{-1}$ is the image of the absolute conic IAC, $M_j$ is the Projection Matrix of image $j$, but ...
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1answer
46 views

Understanding legacy code: Algorithm to remove radial lens distortion

The method below to remove lens distortion from a camera was written more than ten years ago and I am trying to understand how the approximation works. ...
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1answer
24 views

How can I infer the cost function from Kruppa's simplified equations

The following equations are Kruppa's simplified equations used in camera autocalibration. My objective here is to infer the cost function(Error Function) from this equations, So I can minimize the ...
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7 views

How to implement a single shot object detector with only “one” anchor box per feature-map cell

I am newbie to SSD model, I have some images of products on a shelf , I trying to detecting that products using SSD with one anchor box per feature map, please help me out, how to prepare the data and ...
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5 views

Learn the relationship between the pixels in a chunk of an image and then search for more chunks like this one

I've just started to learn computer vision and I have a doubt about if I can do the following and how can I do it. If a 4x4 square of the image is like this one: Here I want to detect another chunk ...
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2answers
48 views

Gonzales Digital Image Processing and the Laplacian Operator

In Gonzalez' book Digital Image Processing, third edition, he writes on page 182 that It can be shown that the simplest isotropic derivative operator is the laplacian operator where the ...
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8 views

Spectrogram vs MelSpectrogram

I am a university student in computer science and during a project, I run into the Mel Spectrogram. Doing some research, I found that the MelSpectogram is essentially a spectrogram where the distance ...
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1answer
47 views

Erosion compotition rule $\left ( f \ominus g \right ) \ominus h = f \ominus \left (g \oplus h \right ) $

I want to prove that erosion of a signal by a function $g$ followed by erosion with another function $h$ is equivalent to erosion of the signal by the dilation of the two functions (Erosion property): ...
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12 views

How would one obtain 3D coordinates from 2D coordinates as well as the roll, pitch and yaw values of the observing camera?

I am trying to decipher the ParkNet DNN introduced by Nvidia. With no research paper released, this is proving quite a hassle. Right at the end of the blog post, it is mentioned that, using the roll ...
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1answer
20 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 ...
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1answer
34 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 ...
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16 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 ...
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1answer
72 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 ...
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1answer
68 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 $y = h*x$. ...
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1answer
29 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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2answers
123 views

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 ...
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1answer
35 views

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

I have the following Python code ...

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