Questions tagged [optical-flow]

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Optical-flow visualizations explained

What do the arrows depict in the optical-flow visualizations such as the one below? (image source: learnopencv) Is it correct to say that the pixel at the tip of an arrow was at the origin of the ...
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Why are different methods used to optimize energy function for optical flow and stereo vision?

Optical flow and stereo vision both try to estimate dense correspondence from each pixel in one image to matching pixel in another image. For optical flow, the two images are taken from the same ...
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Use sparse optical tracking to track a Bounding Box object

I need some help on solving this issue. Any tips are appreciated. The goal of the project is to try to track a Bounding Box object, chosen arbitrarily in an image, throughout many frames of a ...
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How to calculate Walsh hadamard transform for image patches of odd sizes?

I was reading this paper on optical flow, which as apart of the algorithm makes use Walsh-Hadamard transform on image patches of size 2r+1. So far, where ever I have looked, I could only find that ...
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Lucas-Kanade-Algorithm in 1D

I am trying to get a simple implementation of Lucas-Kanade-Algorithm in 1D using a sigmoid function just as an arbitrary choice! In the following code i want to get the displacement $v$ of the two ...
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Simple question about HS algorithm's formul(Optical flow)

In the below pic, I can not understand what U vector is? It says flow field but I can not imagie what really is the flow field?
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Is it possible to calculate the optical flow magnitude for rigid motion?

For objects in 2D plane, it is pretty simple to calculate the displacement vectors using optical flow algorithms such as SLIC, LK, Färneback etc. But how it is possible to know the magnitude of the ...
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Are there paper about black box testing of optic flow algorithms?

Do papers exist about comparisons of the resulting optic flow and its precision compared to the used optic flow method? I would like to find paper that dealt with this topic in some way and had ...
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Nagel, 1987, On the estimation of optical flow - attributes of this method

I know Horn and Schunck and Lucas-Kanade (81) as optic flow methods. But Nagel is way to complex for me. Anyway I have an blackbox implementation of this method but would like to understand the ...
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Determining Optic Flow - Horn and Schunck - robust/insensitive to …

Can somebody explain to me why the Horn and Schunck algorithm (probably mostly the smoothness constraint) is robust to image sequences that are quantized rather coarsely in space and/or time. (Thought ...
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Video stabilization using Lucas-Kanade method

I got an assignment in a video processing course - to stabilize a video using the Lucas-Kanade method. Assuming the matlab code I wrote for performing LK on 2 images works (i.e, I can get the optical ...
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Position vector of Lukas-Kanade optical flow algorithm

The classical optical flow equation by Lukas-Kanade can be simplified as follow: $$ \frac{\delta I}{\delta x}\triangle x+\frac{\delta I}{\delta y}\triangle y + \frac{\delta I}{\delta t}\triangle t=0 $$...
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Optical Flow: Method to estimate a very small displacement

As I was searching for available resources( here, here, here and many more), I realize that many developed optical algorithm is to estimates LARGE displacement. However, there is very limited ...
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Difference between optical flow field and motion field?

I have been trying to understand the various confusing definitions of optical flow field and motion flow field but cannot wrap my head around it. Some authors use the term interchangeably other give ...
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2 answers
192 views

Motion detection one threshold over dataset

We're working on a project where we have to detect the moments where motions happen in a medical scene. I have a data set of 20 videos that are closely resemble (Same camera & configuration used, ...
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Accuracy of dense optical flow

Currently I am learning dense optical flow by myself. To understand it, I conduct one experiment. I produce one image using Matlab. One box with a given grays value is placed under one uniform ...
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701 views

Understanding Farneback Displacement Estimation

I am having some trouble in my attempt to understand some of the operations in the Farneback optical flow algorithm, and i would really appriciate if somebody could help me a bit along the way (and i ...
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Optical flow equation and real images

We know optical flow equation cannot be calculated without additional constraints. But what I cannot figure out is why it does not hold exactly for real images? This equation has gradient and so, it ...
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Image warping with subpixel accuracy

I am trying to test the sub-pixel accuracy of an optical flow method and need to generate some synthetic data to do so. I start with an image $I_0$, which is a Perlin noise image and a set of sub-...
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OpenCV Motion Analysis: Optical Flow vs Motion History

OpenCV Motion Analysis Documentation lists multiple techniques for motion tracking: Sparse Optical Flow | calcOpticalFlowPyrLK, Dense Optical Flow | calcOpticalFlowFarneback, and Motion History ...
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2 answers
5k views

Why optical flow ? why not tracking

I have a question that might be stupide ! Supposing that I try to detect object moving in a video or human action. Many works are based on optical flow computation. My question is why using OF is ...
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5 votes
1 answer
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Iterative Lucas-Kanade algorithm

How is iterative refinement is applied to the estimate obtained by Lucas-Kanade algorithm? I am familiar with the following steps: Estimate velocity at each pixel using one iteration of Lucas and ...
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Image Registration and optical flow

Image registration algorithms can be classified into intensity-based and feature-based algorithms, I want to know When and Why should i choose intensity or feature based algorithm? another question ...
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4 answers
1k views

Fast approximate optical flow / image shift

I need to detect how fast a camera is panning (either horizontal/vertical) to give a warning to the operator to slow down. The entire image is moving as a block, I don't need an actual direction (...
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4 votes
2 answers
3k views

What does the "smoothing optical flow" mean?

I have this algorithm for Correlation Based Pyramids of images: • Create two Gaussian pyramids from the two input images • Compute optical flow using “5×5” regions on smallest pyramid level. • ...
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