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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When computing mAP for object detection, how many detections should one consider?

I am trying to write some code to evaluate the MS COCO style mAP (mean average precision, average computed at the category level) at different IOU levels in the context of object detection with a ...
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Improving Vanishing Point Accuracy

I've been working for a while on 3D building reconstruction from old photos (c. 1904). In all of these cases, the cameras and buildings are long gone, making standard camera calibration impossible. ...
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Forums for Discussing 3D Reconstruction from Images [migrated]

While this and other StackExchange sites are extremely useful, as I understand it, they're for specific questions & answers, not discussions. Some of my questions aren't really well enough ...
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In pulse code modulation what is pulse word represent?

we study lot of things in PCM we do sampling quantization encoding etc but we never come across pulse so what is pulse word represent in PCM
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Numerical computation of the derivative of a curve valued in $\operatorname{Diff}(\mathbb{R}^2)$

Assume we have a (discretized) sufficiently smooth curve $\alpha : [0, 1] \to \operatorname{Diff}(\mathbb{R}^2)$. Further assume that this curve is generated via a large deformation diffeomorphic ...
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Easiest Pattern to Recognize with Machine Vision

I need to detect the exact position of some kitchen tools using machine vision. I've the possibility to label the tools with a pattern, to make the detection (more specifically the image segmentation) ...
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Normalizing directed graphs from image space to compute joint differences

My question is how to transform a 'skeleton' (directed graph) from image space so that I can compare it joint-wise against another 'template' or reference skeleton that may be differently sized/...
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What is the difference between full octave and half octave pyramid?

I couldn't find a good source to explain the diffrence between the Full octave and Half Octave pyramid in Computer-Vision. I saw the Gaussian-Pyramid, and the Laplacian Pyramid, but I didn't see ...
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Help or suggestions with Line detection in microscopy images

I'm doing a personal project in which I want to select some very specific lines in a microscopy image. The first picture is the raw image, the second picture is the image for the lines (in yellow) I ...
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Implementing Felzenszwalb's segmentation for 3D images

Is there an implementation available for unsupervised 3D segmentation using the Felzenszwalb's Graph Cut algorithm? If implemented what do you think are the bottlenecks of such an algorithm? In ...
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Problem definition in KLT tracking

I am studying about the KLT tracker algorithm. In the KLT tracker, we can try to estimate the optical flow for corner points (because these are good features to track) between frames and the computed ...
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Kalman Filtering with measurement latency

The timing involved in this problem is a little hard to explain, so I'll start with my specifics: I'm developing a program that visualizes output (a bounding box) from a computer vision model on top ...
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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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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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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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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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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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102 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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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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61 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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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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111 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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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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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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85 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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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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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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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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39 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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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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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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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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