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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16 views

multi-frame image restoration

Suppose we have a sequence of still images each of which has been contaminated by some particles(ex, dust/sand/smoke) making the images very poor in certain areas. What approach would be best to teach ...
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Which one is better method and why? Manually Handcrafted sound features vs spectrogram + convolution

I am working on classifying different sounds ( not speech or words exactly something like ambulance alarm, police alarm, cough sounds etc) I read few paper which suggested to extract dsp features such ...
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Why not use synthetic datasets for training machine vision (deep learning) algorithms?

I am studying some examples of how to perform 3D instance segmentation in indoor scenes, and I have noticed many of the available datasets are from real environments. I was wondering with the ...
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Understanding the math used to generate a point cloud from a depth image

In reviewing various algorithms for converting a depth image to a point cloud where the camera has extrinsic parameters $c_x, c_y$ the center point of a camera $f_x = f*m_x$, where $f$ is the focal ...
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46 views

Interpreting the accuracy of solutions to the correspondence problem

I have two pictures of the same object, taken by a car travelling down the road like shown on the right side of the image below. I want to find pixels of the object in each frame that correspond to ...
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57 views

Camera Calibration of a Depth Camera

For a regular RGB camera, reading the wikipedia page for camera resectioning/calibration here, they divide the paramters into two categories: Intrinsic: - focal length, scale factors in x and y, and ...
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Obtaining a horizontal disparity image from a depth image

In the paper Learning Rich Features from RGB-D Images for Object Detection and Segmentation available here, the authors encode depth images using three features computed from the depth image, called ...
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3answers
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How is digital signal processing related to Computer Vision?

Keeping in reference this image, I want to build a concrete understanding of interconnection between Digital Signal Processing and Computer Vision. What would be the applications of this co-relation?
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Is there an algorithm in Matlab that could track moving objects that present change of color?

I'm studying the photomechanical behavior of photochromic thin films. They react to specific light wavelengths exhibiting bending movement. I use a yellow light, which turns the film from blue to ...
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18 views

Are location in BRIEF feature descriptor reused?

In the BRIEF feature descriptor ("BRIEF: Binary Robust IndependentElementary Features", Calonder et al., 2011) they investigate five different methods of choosing point pairs to compute the ...
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2D to 3D view conversion

I came across this demo by Fox sports: https://youtu.be/N9SxFf5WCb0 Where they show a player's view in a 360 space. Very smooth and nice. I was wondering how do they achieve it without any cameras ...
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How does transformation matrix and camera matrix change when indexing pixels from -1 to 1 instead of 0 to N-1

I'm trying to warp frames for view synthesis. Specifically, given a frame1 and poses of frame1 and frame2, I'm trying to warp frame1 to frame2's pose/view. For this, I'm indexing pixel locations as $[...
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How virtual ads work in stadiums?

I was looking at a technology which enables virtual advertisement on the perimeter ads in soccer. It's relatively an old technology for a few years back, but I'm surprised to see the quality of it. ...
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46 views

Detect non rectangular bounding box for objects

I have a short video where a TV is shown. I need to detect the TV there (let's assume it's all pure black or it's covered with a green screen), and overlay a video on top of it on the same area. But ...
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2d motion field

I have a theoretical question regarding motion field within a scenario and have searched the internet to get the answer though have been unsuccessful in doing so. If I have a camera in my hand and I ...
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1answer
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Is Mask R-CNN a good fit for what I want to do?

I'm looking at isolating the foreground from a set of photos, and I think I want to use instance segmentation so that I can try to gauge how well-focused the main subject of each photo is. I have ...
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Poor convergence/generalization with few-shot learning object detection with “efficientdet”

Tensorflow's 2x object detection library utilizes a toy example for few-shot transfer learning using a few rubber ducky images (which is not a class in the original trained dataset....nor are ducks in ...
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Image processing with .HPG files

I have files with extension .hpg and I want to perform image processing on those file as they are hp plotter file. I tried googling but no luck there. hence hope someone can help me tackle this with ...
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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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38 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
26 views

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
103 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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57 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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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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36 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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80 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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27 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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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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33 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
23 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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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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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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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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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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30 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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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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31 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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26 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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54 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
80 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
16 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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43 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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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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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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29 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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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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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
74 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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