# 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.

631 questions
105 views

### Background averaging not working

I'm working on a problem where I'm trying to use background averaging to see what the frame looks like in a beehive behind the bees. I've been trying to use standard averaging (I take an image every 1 ...
2k views

### Rotated object detection by Viola jones Algorithm

In my project I need to detect rotated and non-rotated faces in real time. I read original articles and try to use common implementation in matlab and openCV. And as I understood Haar features are not ...
411 views

77 views

### How to prove $\int_{\Omega} \sum_{i=1}^{N} f_i(x)dx$ is equivilant with $\sum_{i=1}^{N} \int_{\Omega} f_i(x)u_i(x)dx$

I have a 2D image defined on a region $\Omega$. Assume that the region can be separated into $N$ sub-regions $\Omega_i$ such that $$\forall i,j=1... N:\Omega_i \cap\Omega_j=\emptyset$$ and \bigcup_{...
90 views

### Understanding Eigenface Face Recognition Algorithm Notations

I have been reading the paper from Matthew A. Tusk and Alex Pentland https://www.cs.ucsb.edu/~mturk/Papers/mturk-CVPR91.pdf I got stuck in this part. I have a couple of questions. Assume my images ...
162 views

### How to calculate binocular overlap

I have two cameras of which I know focal length, principal point, rotation and position. The cameras are in an ideal parallel stereo system. I want to know with as few calculations as possible how ...
1k views

### How to extract text from a scanned document?

The task I am facing is extraction of rotated text (any angle) from a scanned image(attached Image). The image contains a blue sticker on it and need means in extracting the text (printed text) from ...
72 views

### How to calculate performance of your object recognition algorithm and compare results with others?

I am working on a novel object recognition algorithm with BoF implementation for my MSc project and it performs fairly well. I am using it on Caltech101 dataset. I want to compare the results with ...
79 views

### How to gather similar objects in an image?

I am working in a traffic tracking app, I am using a background subtraction approach to obtain information about the moving vehicles. After some morphological operations I obtain blobs of the moving ...
60 views

### Image processing using conv-neural net

Okay I am starting to understand the idea of neural networks but I still haven't been able to understand the use/benefits/implementation of convolutional neural networks especially for image ...
676 views

### How to use ImageNet Database in Matlab [closed]

How to use ImageNet Database in Matlab for object classification or recognition? I didn't find any tutorial which could practically tell me how to train images on ImageNet database and classify the ...
2k views

### why the sum of masks should be one?

I am studying pyramids (expanding and reducing) and I am a newbie. Why sum of the convolution mask should be one when we are using Gaussian distribution? According to When should the sum of all ...
60 views

### neural network for 3D pictures

I'm wondering if they are some state-of-art algorithms to apply the convolutional neural network approach to 3D pictures, eg. input is no longer a grid of pixels, but voxels. My objective is to ...
7k views

### Difference between cv::subtract and operator - in cv::Mat OpenCV

What's the difference between cv::subtract and operator - in OpenCV? Mat original = imread...; Mat smoothed, difference, result; smoothed - original image ...
85 views

### Which anatomical model to use as “ground truth” for validating an MRI segmentation method?

I am research in brain segmentation task that classify a brain in to 3 classes : White Matter, Gray Matter and CSF. To validate my method, I used Dice Coefficient that compare my result and ground ...
195 views

### Image Segmentation - Comparing GrabCut Method vs. Level Set Method

Checking the literature about image segmentation, if I am not wrong, there are two main approaches: Variational approach e.g. level-set optimization in Chan-Vese Combinatorial approach e.g. using ...
134 views

### Invariances in Neural Networks

I have a question about invariances in neural networks. In general, neural nets with enough layers can learn arbitrarily complicated nonlinear functions. Therefore, it's not hard to understand how a ...
3k views

299 views

### Convex Optimization in Signal and Image Processing

In signal processing, convex optimization plays a useful role in problems such as sparse signal recovery and filter design. What other places does convex optimization appear? For example, in ...
224 views

### why the ultasound image is noisy by speckle noise?

My first question : I want to know why an image is noisy ?. why the ultrasound, SAR and Laser... images are noisy by a multiplicative noise not an additive noise? Another question : So the ...
4k views

### camera calibration: why chessboards?

Chessboards are very frequently used for camera calibration, this website also talks a bit about why: wiki. One of the reasons is, that chessboards define many natural interest points. Now my (very ...
2k views

### How to estimate radial distortion from lens characteristics?

Is there a way to estimate the radial distortion coefficients without calibration, given the lens characteristics, such as its diameter and its focal length? Typically for camera calibration a ...
2k views

### How to find the actual size of an existing object from the pixels of an image?

I am quite new to vision and OpenCV, so forgive me if this is a stupid question but I have got really confused. My aim is to detect an object in an image and estimate its actual size. Assume for now ...
141 views

### Difference between video mosaicing and video stitching

What is the difference between video mosaicing and video stitching ,is this both are similar or is there any methodology difference?
60 views

### Understand about registration between spatial prior and original image

I am working in level set/active contour method using spatial prior information . The main papers that I am focusing:"Automatic segmentation of neonatal images using convex optimization and coupled ...
5k views

### Using SURF algorithm to match objects on MATLAB

I am trying to find the difference between two images, using Matlab. The classic built in function that Matlab provides for this is because the two images don't have the same dimensions (The objects ...
5k views

### Question about Difference of Gaussian (DoG) algorithm

I am recently learning about Computer Vision and I am having a trouble understanding Difference of Gaussian (DoG) algorithm. I get how the algorithm works in high level idea, but I am trying to ...
3k views

### Camera calibration using multiple images

I am trying to get the hang of camera calibration. For this purpose, I have mainly watched this lecture on youtube: Lecture 12: Camera Model by UCF CRCV. I believe that I understood the main ideas: ...
12k views

### difference between feature detector and descriptor?

I am new to feature detection and tracking. can anybody please explain in detail the difference between detector and descriptors. which among these are detectors and which are descriptors : Harris, ...
382 views

### relation between luminance and eigen values of an image

There are some research papers in the literature which apply Singular Value Decomposition (SVD) on an image to decompose the image matrix into U, ...
119 views

### Machine Vision - Infinity Focus effect

I am working on a research project that involves machine vision. The camera we are using implements infinite focus - I have been informed that this can affect the accuracy of computer vision ...