Questions about computer vision -- please include example images to illustrate your problem.

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2answers
26 views

Is it correct to use the pinhole camera model to get the mapping of a 3D line to a line in an image?

I've been working on a computer vision project in which I'm using the pinhole camera model to map one line of the world to one line in an image. From previous research on the topic, I know that it is ...
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0answers
24 views

Belief Propagation in Computer Vision

I am working on dense matching using DSP algorithm. They have used belief propagation to optimize their energy function? How do we do it? I mean how do we assign prior belief? Link: Deformable Spatial ...
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2answers
30 views

Reconstruction of drawing sequence from video

I have a video that record the drawing sequence with a pencil by a painter. I want to reconstruction the sequence from the video. And I have google some keywords like "drawing sequence ...
4
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3answers
75 views

How can I sum pixel values over a rotated rectangle?

I have an optimization problem in which I need to sum pixel values in an image over a rectangular region. This is a core component of the optimization so it will be done often and the naive solution ...
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0answers
22 views

In determining shape from line, what is special about the lines I've shown in these drawings by Ken Reid? [closed]

I'm interested in the way artists use lines to indicate shape in drawings. Strictly speaking, my question is about human vision — how our brains interpret certain lines — but I'm asking it ...
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2answers
42 views

Segmenting a human body point cloud into limbs

I have a human body point cloud taken through a Kinect (v1). Now, I want to segment the point cloud into different parts, namely hands, lower arms, upper arms, torso, upper legs, lower legs, feet and ...
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0answers
57 views

Computer vision: Why do random filters perform similar to edge detectors?

I read here that "a randomly initialized filter acts very much like an edge detector!". I want to know if there are any papers describing and explaining this phenomenon.
4
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1answer
38 views

How to choose the number of HOG pyramid layers?

Reading Histograms of Oriented Gradients for Human Detection, I cannot see any discussion of how many layers there should be in the HOG pyramid. OpenCV offers a scaling factor of 1.05 which would mean ...
4
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1answer
25 views

Inverting radial distortion

I'm trying to understand the math behind correcting a radial distortion (caused by a lens), but I'm failing to have it explained in simple terms. I found several examples that proceed this way: a ...
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0answers
23 views

Implementation Details In SIFT

I have two questions about SIFT. To keep on the same page I would love to use this good tutorial as an example ( http://docs.opencv.org/master/da/df5/tutorial_py_sift_intro.html#gsc.tab=0 ). Given ...
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2answers
64 views

What is the difference between object detection, semantic segmentation and localization?

I've read those words in quite a lot of publications and I would like to have some nice definitions for those terms which make it clear what the difference between object detection vs semantic ...
3
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1answer
43 views

What is the difference between 'features' and 'descriptors' in computer vision / machine learning?

I've read multiple time sentences similar to Finally, for standard image classification bag-of-words features based on SIFT descriptors have been found critical for high performances. We first ...
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1answer
24 views

How are HOGs calculated?

Histograms of oriented gradients for human detection seems to be the paper from which all other papers cite when they use HOG features. However, this was the only description I could find in it: ...
3
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1answer
30 views

Finding a method to classify pixels according to how drastic their intensity change

I am looking for a method to classify pixels into three groups: (1) Pixels which does not change their intensity much in general (the slight changes may be due to noise only), (2) Pixels which change ...
0
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1answer
33 views

Terminology for Digitally Interpretting Environment

I am looking into coding a program that can Analyse an image and identify objects in that environment (incl their depth and contours/shape). What is the term for this? Is there a term or area of ...
1
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1answer
24 views

What are the vertical and horizontal focal lengths?

In this paper, http://www.vision.caltech.edu/malaa/publications/aly08realtime.pdf the author mentioned "the vertical and horizontal focal lengths" but didn't have any clear definition. My ...
2
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0answers
31 views

Removing common background in image processing phase for classification

I'm trying to build a machine learning classifier that can detect which object is in an image. I have a labled training set of images and am currently in the image processing phase. Each of these ...
1
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1answer
15 views

Are there any articles or software which can infer original shapes from overlapping shapes?

Given that some shapes overlap in an image, are there any papers or articles or code which can infer the original shapes from the overlapping? I am thinking to apply some machine learning to this ...
2
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0answers
23 views

Learning Image Processing/Computer Vision

What do I need to learn dense correspondence? I am a newbie in Image processing/CV. Please help me by suggesting a kind of syllabus or show me a way to learn about Dense Matching. What are the things ...
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0answers
28 views

How to train a Conditional Random Field/Markov Random Field Model for Object Classification in images given the features?

I want to classify superpixels in a image using a Markov Random Field/ Conditional Random Field model but have found no place that can help me with this (references don't even show how the network is ...
2
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1answer
37 views

Image Comparison tuned to Human Perception

Say I have two systems that take the same drawing commands and starts drawing on their respective platforms (i.e. HTML Canvas). After this is done, I want to save and compare these two images to ...
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0answers
62 views

What happen to the Zero Mean Normalized Cross Correlation (ZNCC) if one of the vectors is a Zero Vector?

I am studying the Zero Mean Normalized Cross Correlation (ZNCC) method for pattern matching. I would like to match the pattern of a square region of size $N \times N$ from two different images. Hence ...
2
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1answer
35 views

Alignment of RGBD with a thermal camera

I have a thermal camera that I would like to overlay, automatically, to the output of a RGB-D camera (e.g. Kinect). I have retrieved the intrinsic and extrinsics parameters of both cameras. My ...
2
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1answer
35 views

Looking for Methods in Computer Vision for Distinguishing Disappearing and Fading Objects

Suppose I have a video in which there are two objects $A$ and $B$. Object $A$ appears suddenly at time $Ta1$, and then disappears suddenly at time $Ta2$. Object $B$ appears suddenly at time $Tb1$, and ...
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0answers
36 views

How to select a good window size in the Running Gaussian Average method for Selective Background Updating?

I have been studying the Selective Background Updating in Running Gaussian Average Method, as discussed in the Wikipedia (the Variant method). The details of the algorithm, as I understand, is as ...
3
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1answer
56 views

Register images containing objects with varying distance to the cameras

I'm learning about using image registration to align two images, e.g., two photographs of the same scene taken from a slightly different location. What factors influence how well we can align the ...
0
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1answer
61 views

Clustering a set of images using keypoint descriptors

I'm trying to cluster around 16000 images into ~200 clusters, using kmeans with metric as euclidean distance or cosine distance. I understand that i need to extract keypoint descriptors to compute ...
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1answer
52 views

Algorithm for Filling Regions with Small Gaps

I am looking for an algorithm that fills a region with one color, but the edge of the region is not completely closed (i.e. one or more gaps are being left). The result is like the use of the Paint ...
2
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1answer
41 views

Selective Background Updating in Running Gaussian Average Method for Background Subtraction

I am studying the Running Gaussian Average Method for background subtraction. One alternative, as described in Wikipedia, also known as Selective Background Updating, is to only update the ...
3
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1answer
42 views

Multi object image segmentation methods

I want to survey the state-of-the-art in image segmentation. Is there a paper on how to segment multiple objects in an image? The segmentation papers I read, normally identify one of the many objects ...
1
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1answer
71 views

Intrinsic matrices in stereo camera calibration

Suppose I have two cameras, c1 and c2, observing the same scene. I can now Calibrate each camera independently (e.g., with MATLAB's Camera Calibration App) Calibrate both cameras simultaneously ...
1
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1answer
25 views

Is the Projection Matrix estimated using least-squares pose specific?

I am calibrating a camera and estimating the projection matrix using the least-squares technique described here. So far, I thought that the projection matrix that I got with this method was ...
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0answers
34 views

Any applications that need fast insert or delete for quadtrees?

I know that quadtree could be used in collision detection. But most articles I found are related with quadtree construction and retrieval. I wonder if there are some circumstances which involve both a ...
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0answers
54 views

Featurizing images of different dimensions

I'm building a non linear svm for images to solve a classification problem with domain {0, 1} and I'm currently doing featurization. What I want to do is create 3 features for each pixel representing ...
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1answer
41 views

Getting the essential from the fundamental matrix

Is it possible to get E from F? I suppose that can't work, because then I could calculate the the extrinsic (and maybe also intrinsic?) parameters of the cameras without a calibration object of known ...
2
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1answer
22 views

Fundamental and essential matrices, value of intrinsic parameters

I observe a scene with two cameras, c1 and c2, that produce two images i1 and i2, respectively. What I ultimately want to do is to use information of image i1 and image2 simultaneously, e.g., for ...
1
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1answer
67 views

Calibration and overlay of RGBD with a thermal camera

I have a thermal camera that I would like to overlay automatically to the output of a RGBD camera (e.g., Kinect). I can retrieve the intrinsic parameters of the thermal camera by using a special ...
0
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1answer
38 views

Bringing images into alignment

I observe a scene with two cameras, c1 and c2, that produce two images i1 and i2, respectively. What I now want is to bring i1 and i2 into alignment, that is I want to know where pixel (x,y) in i1 is ...
1
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1answer
32 views

What is the reason of using Gaussian model for Background Modeling?

I am a new learner to Background Subtraction (Background Modeling) and I am reading a few previous works on how it is performed. Starting with Wikipedia (by searching "Background Subtraction"), I ...
2
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2answers
225 views

find the actual size of an object from pixel coordinates

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 ...
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0answers
21 views

Feature detector that doesn't use corners

I'm trying to use computer vision to identify objects an image. I am currently using the SURF algorithm, but Harris and SURF both find virtually no points on our objects (a paper ball and a deodorant ...
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1answer
33 views

How to test image segmentation algorithms? [closed]

What would be an ideal environment/manner to judge the effectiveness of multiple segmentation algorithms? The goal is to determine which algorithms provide the best results for pre-clinical imaging. ...
5
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1answer
162 views

How to compare SURF points in two images

I know how to find SURF feature points and have code to find them, but I have no idea how to find the same point in 2 different images, I have laplacian, scale, orientation, descriptor, response and ...
0
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1answer
145 views

How do I detect and rotate a square?

I have recently written code for detecting path colors in a 2D grid and printing the corresponding path costs and it works fine for me. Here's my code; I am currently new to OpenCV and know only C++ ...
1
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1answer
30 views

What is the triangulation angle?

I start to work in the field of computer vision and read a paper in which the author states "When suitable correspondences between salient image structures have been established, the 3D uncerntainty ...
3
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1answer
69 views

What is the name of this problem in Computer Vision?

My google skills have failed me during research for a college project. Our task is write a program that describes an image in spacial terms, e.g. "Cat on the left of a chair", or for a simple image ...
1
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1answer
316 views

The Fundamental and Essential Matrix

Could someone, in plain english, explain the distinction between the fundamental matrix and the essential matrix in multi-view computer vision? How are they different, and how can each be used in ...
1
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0answers
54 views

Computer vision training procedures: SVM/AdaBoost vs Neural Networks

With SVM, adaboost or similar alogrithms, image training sets must be cropped with specific constraints (keep image cropping ratio the same, have object tightly cropped, same resolution) In general, ...
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0answers
31 views

Any good algorithms for 3d volume alignment by feature extraction, especially ones involve machine learning?

I am trying to align 3d mri brain images of different rat individuals. I have dozens of examples that have been aligned manually, which are good resources for machine learning. I am considering ...
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1answer
84 views

Can you determine rotation/camera calibration from series of images separated by pure rotation

I have a series of about 50 images, each separated by a small rotation and taken from the same camera. The images are feature-dense, and I can calculate a homography from image-to-image easily. My ...