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

Homography valid for patch within the image but not the entire image?

The homography I have is non-degenerate (det!=0), and generated from a valid planar pose. When I use it to warp the four corners of image, it returns something like the following: ...
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Calculate surface of objects (rocks) in an image with lots of noise

Is there a way to caculate the size/surface of every individual rock visible in this image? I have tried: Contours - this doesnt seem to work the contours touch, gets real messy. Watershed algorithm -...
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How to obtain height above ground, angle the pixel’s local surface normal makes with the inferred gravity direction from depth map of image?

For extraction of the HHA features from the image depth map we need to calculate the height above ground, angle the pixel’s local surface normal makes with the inferred gravity direction. How to ...
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Removing halo effect in image composition: Google Meet's solution

Wanted to understand how google meet is removing halo effect when composing their image. They describe their method briefly in their blog as: "The blur shader simulates a bokeh effect by ...
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Feature Based Methods for Quality Inspection Problem

I am currently working on an image classification problem to classify thermal images (can be interpreted as false-color images) of certain products as with or without defect. From an initial search in ...
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Suggestions for creating 3D Bounding Boxes of Books on a Shelf from RGB-D Images

I am new to image processing, so I beg your pardon if this is a trivial question. I am trying to use an RGB-D camera to detect 3D bounding boxes of books on a shelf. Here are some examples of possible ...
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Three Projective Cameras in the Same “Projective Frame” - What Can I Do With This Info?

[I originally posted this under Mathematics, but I didn't get any replies. I thought I'd try here.] In Hartley & Zisserman's Multiple View Geometry in Computer Vision, in the chapter on trifocal ...
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Importance of Phase in FFT of an image

While processing digital images in the Fourier domain, mostly we exploit the amplitude and not the phase. This could be because the amplitude is much more structured and the amplitude spectrum reveals ...
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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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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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1answer
30 views

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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1answer
24 views

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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1answer
61 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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4answers
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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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1answer
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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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1answer
49 views

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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1answer
139 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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49 views

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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39 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
79 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
28 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
118 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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117 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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1answer
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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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1answer
89 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
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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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1answer
22 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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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
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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1answer
39 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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