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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Understanding the Bilateral Filter - Neighbors and Sigma

I have been reading about the Bilateral Filter in - Fast Bilateral Filtering for the Display of High Dynamic- Range Images and have felt crippled and confused while understanding its working and the ...
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1answer
74 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 ...
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Eigen Value and Eigen Vectors in Image Processing

I have been reading about eigen values and eigen vectors but i haven't be able to find any decent explanation relating their application in image processing/computer Vision for example say face ...
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1answer
130 views

Fourier Transform Computer Vision Textbook

I am required extremely fast to fill the gap and learn Fourier Transform with application in Computer Vision. It was easy to find mathematical aspects of Fourier Transform, but I am more interested ...
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How are the scaling parameters included (extracted from) an essential matrix?

An essential matrix relates corresponding points between two images assuming that a camera satisfies the pinhole camera model, and can be expressed as: $$E=K'^TFK$$ where K is the calibration and F ...
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Face Detection + Cropping

Project: Face Detection Description: I want to detect and crop a face in an image. The image is captured through webcam and only one face per image.I used OpenCV face detector, but I was not ...
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1answer
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Implement the 3D Structure Tensor in C/C++?

I am trying to figure out the details on how to implement the 3D structure tensor in C/C++ in an easy but efficient way and need some advice! For a discrete function $ I(x_i,y_j,z_k)$ the 3D ...
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214 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 ...
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1answer
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What is a good distance measure for matching SIFT descriptors depending on the distribution of their noise?

I have read some papers about distance measures like Euclidean, Manhattan or Chi-Square for matching gradient based image descriptors like those computed from the SIFT Algorithm (128-D vectors). Most ...
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What is phase congruency?

I am beginner in Image processing.I am studying the importance of phase in signal.Can anybody explain what is phase congruency ?
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473 views

How to calculate particles sizes for spheric particles with overlapping and superposition? (Example image included)

I'm trying to automatically calculate particles sizes histogram for images like this one: Common threshold and segmentation doesn't seem to work. What filters and algorithms do you suggest to be used?...
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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 ...
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How Much Zero Padding Do We Need to Perform Filtering in the Fourier Domain?

Consider an $M\times N$ image $f$ and an $G \times K$ filter $h$. Given that convolution in the spatial domain corresponds to multiplication in the Fourier domain, then we can perform a convolution of ...
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1answer
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Wavelength filter with OpenCV

I am new to OpenCV and DSP. I want to code a filter which act like a real optical filter. When you filter the image, the output looks like shotted with a $550nm$ optical filter lens. Like a Bandpass ...
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1answer
7k views

When is a network called end-to-end training?

In machine learning, we often see the expression "end-to-end" learning (or training). However, I do not know that it means. When is a network called end-to-end training? How to recognize a network is ...
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928 views

Segmentation of overlapping noisy parallelograms in a binary image

Edited. Previously this question was named "Segmentation of overlapping pulses in a binary spectrogram" and it was stated in slightly different way. I'm apologise to those users, who were affected by ...
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ORB Algorithm: What Is Intensity Centroid?

So, I am reading a paper about ORB: An Efficient Alternative to SIFT or SURF and it happens to calculate the direction of corner from it center . According to Rosin the author of the paper;moments of ...
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1answer
463 views

What does an image of Fourier Transformation of an image tell us?

First time studying image processing... I just don't understand what does fourier transformed image of an image describe? For example consider given following pictures, The first one is the image, and ...
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Barcode localization in difficult environments

I'm creating a program for localizing types of barcodes. (I know plenty exist, that's not the question :) ) I'm focusing for the time being on 1D barcodes. The difficulty I have is that the barcodes ...
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1answer
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How to detect whether the object has triangular shape?

The task is to detect arrow from medical images. After segmenting, arrow-like objects can be connected with other connected components (noise). In this context, detecting a part of the object that ...
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1answer
126 views

Dynamic Textures

i know that texture refers to surface characteristics and appearance of an object given by the size, shape, density, arrangement, proportion of its elementary parts. But i am more interested in ...
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1answer
9k views

EmguCV: Detect a ball in the frame

I am having a VERY hard time capturing when the ball comes into frame in this video http://www.youtube.com/watch?v=x1V6_OHrXIo I have no idea what to set the parameters too, and trying random values ...
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Losslessness of Laplacian Pyramid

I was just reading up on the Gaussian pyramid and the Laplacian pyramid, used in compression applications of image. The source is here - Carnegie Mellon 16-385 Computer Vision - Spring 2019, Lecture 3 ...
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739 views

How to reliably detect the state (opened or closed) of sliding doors from a statically-positioned video stream

I have a mounted (static) camera that has a view of a set of sliding doors. Since doors are rectangular in nature, and they don't have many degrees of freedom, this seems like a problem that should ...
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1answer
848 views

Multi-scale in Object detection?

I want to ask about MultiScale Object Detection. For the multiscale, if we have an original image do I need to zoom-in at different scales in the image at a particular point or zoom-out at different ...
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1answer
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NORM_HAMMING2 vs NORM_HAMMING

I'm trying to use ORB features with a cv::BFMatcher. ORB is based on binary descriptors so HAMMING must be the choice, but I'm not sure I understand the difference ...
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2answers
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Minimum size for positive samples for HOG (Histogram of Gradient) detector training

I'm going to train a HOG detector for detect objects (pedestrian head) with SVMLight library. But my question is not about implementation. I'm wondering how to collect samples. I have to use some ...
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1answer
177 views

Recognizing hand-written archaeological signs

I have 75 images of handwritten signs from which I extracted 7 Hu moments and solidity features. How can I find similarities among them to train a classifier and predict the value? I thought SVM was a ...
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Why do we need 4 points for homography but 7/8 points for fundamental matrix calculation?

Sorry if this is a trivial question but I could not find a suitable answer elsewhere. I recently learned about homography and fundamental matrices in a CV class. I understand how these matrices are ...
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1answer
486 views

Detecting sloppy hand-drawn arrows in images

How can I easily and efficiently detect hand-drawn arrows and their directions from an image? They're probably drawn lightly, with something like a pencil, on a piece of paper. If I had ...
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2answers
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Can disparity range from negative to positive values for parallel cameras?

In my stereo-rectified camera pair (not physical, but two positions of the same camera), when I project some 3D points in both images to find a rough disparity range, I often get a range that goes ...
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1answer
169 views

Academic problem solving in Computer Vision

I am currently pursuing a Master degree of Engineering and I will have to write a thesis about solving a specific Machine Vision application. I have done some CV projects in the past but now I am ...
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1answer
1k views

What is the Difference between Texture and Image?

I am beginner in the image processing I want to know what is difference between Texture and Image? or whether they are same? can anyone explain it. Also,if i want to do texture segmentation,can i ...
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Trying to translate formula for blending mode

I am using OpenCV C++ for making the blending mode like in photoshop, I want to make overlay mode in it. I search its alternate in OpenCV in which I found this ...
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1answer
823 views

how could correlation-based image patches matching works?

In general, correlation-based image matching can be referred to as $$c(I_1,I_2) = \sum_{x \in patch} f(I_1(x), I_2(x))$$ , I do think normalized cross-correlation like $$ncc(I_1, I_2) = \sum_{x \in ...
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1answer
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Jacobian of affine warp in Lucas-Kanade image alignment

I hate this kind of questions, but I'm really stuck. I'm trying to implement Lucas-Kanade algorithm as described in this paper (see pages 4 and 5). Unlike most explanations I've seen they don't assume ...
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1answer
240 views

Incorporating Radial Distortion in Imaging Model

I'm currently developing a multi-view stereo system but I'm confused as to how all the standard equations in Structure from Motion are affected in the presence of radial and decentering distortion. ...
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1answer
138 views

scale invariant face similarity metric

I need some face similarity metric. I know about PCA,LDA approaches that uses raw pixels data, but they are not scale invariant(I know that I can resize image but I think that's not good solution). ...
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1answer
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what is the starting point of a contour as given by cvConvexityDefect() function in OpenCV

i have to distinguish between palm and elbow in my contour(I'm using cvconvexitydefect for that purpose). Here's the image: I'm taking contour of left image. the 2 topmost points in right image are ...
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1answer
311 views

Image Processing/ Computer Vision: How is separability of filters implemented?

I am trying to convince myself that a separable 2D filter can be implemented via two 1D filters. So, I took the example of following Sobel filter: $1/8\begin{bmatrix}-1&0&1\\-2&0&2\\-...
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How to choose the most appropriate color space for a computer vision application?

A lot of image processing techniques used in computer vision consist (among other things) in switching from RGB to another color space (HSV, YUV, LMS...) : color transfer, visual tracking... It seems ...
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1answer
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Obtain motion between image features by means of the homography matrix

I have been reading several really good answers about how to obtain camera pose (rotation, translation, etc), such as this one and this one, but I am not sure how this applies to my problem. My ...
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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 ...
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2answers
4k views

Metal Defect Detection

I am developing a machine vision project to find defects on metal surfaces. I want to learn and implement algorithms which commercial systems are use for metal surface defect. My sample object as ...
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1answer
83 views

Is there an OBJECT BASED Image Segmentation method, with pure non-segmented training images?

I wonder if there is a method works as follows: 1) The algorithm is trained with some images of a particular object (I train my Image with 1000 banana images) 2) I use the training data to segment a ...
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1answer
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Determining false positives in feature matching

I extracted features from an image using SIFT and SURF. Then I applied few transforms on the image and again calculated the features. While matching the features, I noticed that there are some ...
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1answer
179 views

Garment Cropping from mannequin

I have two images – mannequin with and without garment. Please refer sample images below. Ignore the jewels, footwear on the mannequin, imagine the second mannequin has only dress. I want to ...
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3answers
633 views

segmenting region of interest (ROI) from background

I am dealing with images from biological slides and want to segment out the ROI (cells) from the background. I have tried k-means clustering, otsu thresholding, adaptive thresholding, edge detection ...
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2answers
368 views

Document image vanishing point detection and evaluation

It is a natural idea to substitute our scanner with mobile phone, and perform OCR with the phone at the same time. If this can come true, two problems must be tackled: one is related to document image ...
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632 views

Correct Fish Eye camera Radial Distortion and blurry effect at the image edges

There are a lot of questions regarding this topic ,but I am trying to get a more clear picture from these questions. I am trying to calibrate a fish eye camera and I am using OpenCV omnidir class ...