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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21 views

KL (Karhunen-Loève) transform of images

I know how to implement the Karhunen-Loève (KLT) for one 2D image. Which we first find the covariance matrix of the image vectors of length N along the column and the row dimension and etc. When we ...
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1answer
442 views

Difference between Generalized Hough Transform and Cross-correlation Feature Matching

I've been taking the Udacity Computer Vision Course, and one thing that has confused me so far is how the Generalized Hough Transform is any different from feature matching on an edge image using ...
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3answers
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What is energy in image processing?

There are several web articles on the topic, but, after having read them, I still don't know what "energy" is, in the context of computer vision (CV) and image processing (IP). It is related to ...
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Image Shadow Removal Using OpenCV and Python

How do I remove a shadow after MOG2 background subtraction using OpenCV Python? I used all morphological operations, gaussian and median blur, thresholding. it removes noises but deep shadow is ...
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I need the C++ implementation for Haralick feature extraction from images consistent with Mahotas library in Python [closed]

I need the C++ implementation for Haralick feature extraction from images, that is consistent with the python implementation in Mahotas library for haralick feature extraction.
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1answer
50 views

Finding Homography Matrix Using Lines

I have some Points and Lines from original image and the corresponding points and lines from top view image. -> I tried to find homography using points Used OpenCV function findHomography(...
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1answer
994 views

How can I detect pipeline cracks using OpenCV and Python?

I have developed a robot that captures images of the pipeline interior as it moves. The requirement was to be able to detect cracks inside. So far i tried several OpenCV codes that find the crack ...
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2answers
690 views

How to Create Image Editing Filters

I am trying to make filters for days but now I just want to know the experience of others rather than go on to wrong way and finally decided to put my query over ...
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2answers
52 views

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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2answers
4k views

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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0answers
16 views

Detect rotation of circle on its axis

A wheel is rotating on its axis. I want to find how many angles it is been rotate i.e. 90, 3340 etc. The wheel does not have any specific mark which can be tracked. I tried to use the Fourier-Mellin ...
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1answer
229 views

How to remove striped noise from this image. Which filter or algorithm use better?

I need to process a gray scale image. The task is to remove the stripes, which constitute some noise. I have next origin image: This image received many channels ADC(Y) in moment of time (Xn) from ...
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22 views

Combining Multiple Point Clouds

I have a car with 8 lidars, each with a field of view of 60 degrees. My car looks like this How can I merge all the lidar readings into 1 point cloud?
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1answer
26 views

Can Normalized Cut be used to find connected components in binary images?

I'm unsure whether Normalized Cut can or can't be used to find connected components in binary images. I would argue that it could, but could not validate this argument.
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2answers
2k views

blur detection using opencv

I'm writing a script to detect blur images using OpenCV by applying Laplacian filter and calculate the std but there is a problem the std for images that contain motion blur is very close to those ...
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0answers
19 views

Matching Coordinates between two images

I am using images and corresponding lidar values for depth estimation CNN. I have RGB images. Corresponding to each RGB images, there is another image representing a subsets of pixels and distances to ...
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14 views

Face image quality assessment

I'm trying to filter out bad face images (with artifacts) generated by StyleGAN. Is there a good image quality measurement mechanism in python for doing this? I've tried using BRISQUE but it is not ...
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1answer
53 views

How are line pairs and pixels related in image resolution?

I hope this is the correct place to ask this. If not, please refer me to a better place, thanks. Now to my question, I am learning about digital image processing, and the book I am reading is ...
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9answers
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Why do we use the HSV colour space so often in vision and image processing?

I see the HSV colour space used all over the place: for tracking, human detection, etc... I'm wondering, why? What is it about this colour space that makes it better than using RGB?
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1answer
42 views

Why reprojection error is minimized instead of triangulation error for bundle adjustment?

For bundle adjustment optmization why is reprojection error minimized instead of traingulation error or ray-to-3d point error? Disadvantage with reprojection error is: for perspective camera, its ...
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1answer
65 views

How is the Gaussian kernel related to the Euclidean distance of the neighbourhoods in the non-local means algorithm?

I am reading the paper A non-local algorithm for image denoising that describes the original non-local means algorithm. They define (p. 3 of the pdf) the distance between two square fixed ...
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1answer
66 views

What is the relation between time, frequency, spatial and spectral domains?

What is the relation between time, frequency, spatial and spectral domains? I think that time and spatial domains are the "original" domains (e.g. if the signal is a greyscale image, then the domain ...
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2answers
699 views

Calibration (intrinsic) parameters of a virtual camera with some known information

I need the calibration matrix of my simulated camera, I am trying to fully comprehend and follow the steps from Step by Step Camera Pose Estimation for Visual Tracking and Planar Markers as well as ...
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13 views

Camera Pose Estimation from Vanishing Points

I want to estimate the pose of camera (Location and Orientation). Can I use Vanishing Points to get the location and orientation of the camera? There is object in the image which I also know his size,...
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1answer
590 views

3D point cloud to 2.5D graycale image (metric) [Halcon?]

I have a problem ragarding transferring a point cloud to a 2.5D metric grayscale image (gray value gives depth information). I start with a three channel image of 32bit floats with each pixel ...
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1answer
2k views

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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21 views

What is scale ambiguity in computer vision?

When you compute relative pose between cameras, translation is only accurate upto a scale. Need some help in understanding the scale ambiguity and what exactly does it mean translation is accurate ...
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1answer
117 views

camera calibration change orientation of axis

I want to solve for the extrinsics by using direct linear transformation on corresponding 3D LIDAR points and 2D camera points. I already have the intrinsics. Problem is, points behind the camera ...
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3answers
724 views

How to select the specific frame with object

I am detecting the object from the live camera through feature detection with svm , and it read every frame from camera while predicting which affect its speed , i just want that it should select the ...
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3answers
16k views

Object detection versus object recognition

I have a slight confusion differentiating between object recognition and object detection. Some people say object detection is a sub-topic of object recognition? Can someone clarify the the difference ...
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1answer
936 views

What are the various techniques for detecting Walls in the Building(Architectural) floor plan Images?

I have to process building floor plan images to extract Walls from the structure. It is trivial in case of binary images; but the images in our case are colored, and each have different color of walls....
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1answer
38 views

Understanding 2D alignment using least squares

In Computer Vision Algorithms and Applications book by Richard Szeliski, the author explains 2D alignment using least squares as follows: Given a set of matched feature points ${(x_i, x_i')}$ and a ...
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2answers
1k views

Segmentation of warped text lines

I am trying to segment warped text lines found in photos taken from a page of a book (from the camera of a smartphone). This is meant as a preprocessing step before running OCR on them. I have found ...
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1answer
123 views

What do we mean by spectrum?

Consider the context of image processing and computer vision, and, in particular, discrete Fourier transform. For example, in the sentence In the Discrete Time Fourier Transform the forward ...
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1answer
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
2k views

What is the difference between a range image and a depth map?

https://en.wikipedia.org/wiki/Depth_map https://en.wikipedia.org/wiki/Range_imaging To me, it sounds like they are the same thing, except depth map implies only having the z coordinate info. But ...
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Measures of edge image continuity and connectivity

Suppose I have a scalar image $I:\mathbb{Z}_{1,m} \times \mathbb{Z}_{1,n}\rightarrow [0,1]\subset \mathbb{R}$, where $\mathbb{Z}_{1,m} = \{1,\ldots, m\}$. (For instance, computed as the (scaled) ...
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2answers
10k views

Understanding SURF Features Calculation Process

So, I was reading the paper on SURF (Bay, Ess, Tuytelaars, Van Gool: Speeded-Up Robust Features (SURF)) and I can not comprehend this paragraph below: Due to the use of box filters and integral ...
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1answer
612 views

How Do Steerable Pyramids Work?

I'm reading a paper about texture synthesis using pyramids, and the very first section mention two methods for constructing pyramids, one is the Laplacian Pyramid (which I'm quite familiar with), the ...
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1answer
806 views

What's the Difference Between UQI and SSIM Measures for Image Similarity / Quality?

I'm studying image quality assessment (IQA) problem and I'm currently learning about quality measures UQI and SSIM, I know UQI is a predecessor of SSIM, but they look exactly the same for me...
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1answer
728 views

How to warp a pixel patch to another camera

I have two cameras with rotation and translation starting from the world origin and a patch in the first camera's reference coordinate system. I want to warp this patch into the second camera's ...
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3answers
68 views

Can the colors of an image be interpreted as “virtual” Doppler effect? [closed]

In astronomy, the Doppler effect is used to estimate approximate distances to stars and other celestial bodies. Using the same principle, lets say we divide an image (photograph) in pixels and that ...
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1answer
125 views

Removing lines of certain length from an image in MATLAB

I want to remove the portion of the line (highlighted by the yellow circles) where pixels form a straight vertical line segment. If I use the strel ...
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2answers
141 views

How would you interpret the pattern in this picture? (generated by re-sorting pixels based on their RGB value)

Was playing with some pictures and ran the ruby code below. The code reads an input image using the ImageMagick library, gets an array of pixels, re-sorts the pixels and then writes out an image with ...
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1answer
471 views

In Plain English, What Are the Within and Between Class Variances in Otsu's Thresholding?

For the past week I've been through numerous research papers and tutorials on Otsu's thresholding. Even wrote to the authors, but every single one of the explanations are in terms of "Class" and "...
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1answer
240 views

Can I segment characters from this image with CSV?

I am trying to segment my characters on this image with using column sum vector. This method actually works on the paper I've read about license plate recognition. it looks useful for my images ...
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0answers
32 views

Fast and Slow motion video detection using Optical Flow

I'm trying to calculate a "video motion" value in a given video sequence, meaning how fast or slow motion the video is. For instance, if a video is about a car racing, the value is high. Whereas if ...
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1answer
30 views

Stereo triangulation similar triangle derivation

I understand that the similar triangles are the red and blue triangles. I'm trying to understand where $T + x_r - x_l$ comes from. I understand we are trying to compute the length of the base of the ...
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2answers
162 views

Scratch Detection On Noisy Textured Surface

I wish to extract long thin scratches from the noisy background image.I have tried several ways such as stacking smoothed image with input image to remove some of the noisy background patch before ...
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1answer
111 views

Image reconstruction using Irradiation

I am a bit confused as to how to go about this. I have a surface [x,y,z] given by: ...