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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23 views

Intuition about tag pose estimation accuracy

I have some difficulties to have a correct intuition about expected pose accuracy when dealing with planar pose estimation (e.g. pose estimation from AprilTag detection) and perspective camera model. ...
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Comparision between SSIM and MAD Image Quality Assessment Algorithms

I have been working with Most Apparent Distortion(MAD) tool to evaluate the quality of images. I have read a paper that compares SSIM, PSNR, FSIM, etc. with MAD. I am uncertain about some calculations ...
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How do I answer this computer vision theory question? [closed]

Suppose there is an image containing multiple objects of different types. The objective of the problem is to recognize objects using primary features of objects (colour, texture, shape). Explain your ...
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Feature detector vs dense detector

What is the difference between a feature detector and a dense detector in computer vision? Are they the same or a subset of one another? For the following algorithms (implemented in OpenCV), which of ...
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Intuition behind cost aggregation functions in stereo correspondence problem?

I don't seem to understand the concept of a cost aggregation function like a Fixed window or an Adaptive window, etc. Why do we need this additional step, and why can't we just calculate the disparity ...
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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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What function to apply a Metamorphopsia (grid warp) translation?

How would I go about finding or creating a function to warp images dependent on grid lines surrounding an origin (I don't wish for a grid on my actual images): It should work in practically the same ...
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1answer
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Understanding rho and theta in hough

I understood the concept behind Hough transform. One thing i am still unsure is the rho and theta range of hough transform. The range is given below. If theta is in the range [0,pi), then rho values ...
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1answer
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What is Bottom-Hat transformation?

I am reading the Digital Image Processing book by Gonzalez and i can't seem to understand Bottom-hat transformation. Can anyone explain it to me in easy terms?
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Understanding the relationship between the convolutional feature map and the region proposals in Fast R-CNN

In the paper Fast R-CNN available here, I am trying to understand the relationship between the region proposals and the convolutional feature map. So from what I understand, Fast R-CNN takes in an ...
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Understanding legacy code: Algorithm to remove radial lens distortion

The method below to remove lens distortion from a camera was written more than ten years ago and I am trying to understand how the approximation works. ...
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Faster R-CNN and 4-step Alternating Training

I am reading the paper Faster R-CNN available here. In section 3.2, page 6 bottom left, the authors describe what they refer to as a 4-step Alternating Training between the Region Proposal Network, ...
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844 views

Generate a nonuniform illumination (bias field) 2D image

I am creating a nonuniform illumination in MATLAB R2015. The nonuniform illumination (known as bias field) is defined as Nonuniform Illumination (intensity inhomogeneity) which manifests itself as ...
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How Is the Gaussian Kernel Related to the Euclidean Distance of the Neighborhoods in the Non Local Means Denoising 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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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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35 views

Guassian Derivatives with orientations

I am reading the paper Selective Search for Object Recognition here. In Section 3.2, they give a similarity measure between two regions of an image based on the texture of the regions with what they ...
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How to calculate the plane at infinity? either in Matlab or Python

I tried to implement this function to compute the plane at infinity $n_\Pi$ from the equation: where $w^{-1}$ is the image of the absolute conic IAC, $M_j$ is the Projection Matrix of image $j$, but ...
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1answer
43 views

What helped you in reading and implementing papers and coming up with original ideas in computer vision/graphics?

I'm trying to get into academic research at the intersection of vision and graphics, and was wondering how researchers in the field went about this: Was it useful to do a lot of fundamental math ...
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Smoothing jagged lines in an image?

I have an image like this - I would like to smoothen the lines in this (as you can see they lines are a little jaggy.) How can I do this? I obtained the lines by isolating them from another image ...
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1answer
59 views

Licence plate enhancement

Is it possible to enhance the image below and make it more readable? I have tried apply binarization but there is some kind of shadow. So I have tried to convert image to gray scale and then ...
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How can I stitch bottom of some image to topside of another image by erasing as much overlapped image as possible?

I have 2 images of size 1920*1080 and I want to try image-stitching on them. These are images (images are from wind turbine blade.) This is the first image And the second image. I already have ...
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How does Lowe's ratio test work when you compute more than 2 nearest neighbours?

Lowe's ratio test can be used to discard matches that are possibly irrelevant or noisy. However, it isn't clear to me how the ratio test should be performed when you retrieve more than 2 nearest ...
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What is the difference between template matching and object detection?

What is the difference between template matching and object detection? Is the only difference that the template is typically rectangular while the objects can be of any form (including rectangular)? ...
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How to know what kind of noise?

Im working with friends on a computer vision project for university. For the preprocessing part we are going to use a Gaussian filter. One of my project partner said I have to justify the use of a ...
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2answers
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Gonzales Digital Image Processing and the Laplacian Operator

In Gonzalez' book Digital Image Processing, third edition, he writes on page 182 that It can be shown that the simplest isotropic derivative operator is the laplacian operator where the ...
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1answer
99 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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How can I infer the cost function from Kruppa's simplified equations

The following equations are Kruppa's simplified equations used in camera autocalibration. My objective here is to infer the cost function(Error Function) from this equations, So I can minimize the ...
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How to implement a single shot object detector with only “one” anchor box per feature-map cell

I am newbie to SSD model, I have some images of products on a shelf , I trying to detecting that products using SSD with one anchor box per feature map, please help me out, how to prepare the data and ...
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1answer
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What is the difference between feature detectors and feature descriptors?

What is the difference between feature detectors and feature descriptors? Which among these are detectors and which are descriptors: Harris, SURF, Min Eigen, FAST, SIFT, BRISK
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Learn the relationship between the pixels in a chunk of an image and then search for more chunks like this one

I've just started to learn computer vision and I have a doubt about if I can do the following and how can I do it. If a 4x4 square of the image is like this one: Here I want to detect another chunk ...
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How to flatten the image of a label on a food jar?

I'd like to take pictures of labels on a jar of food, and be able to transform them so the label is flat, with the right and left side resized to be even with the center of the image. Ideally, I'd ...
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Spectrogram vs MelSpectrogram

I am a university student in computer science and during a project, I run into the Mel Spectrogram. Doing some research, I found that the MelSpectogram is essentially a spectrogram where the distance ...
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1answer
380 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
746 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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1answer
657 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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1answer
123 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
785 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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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
16 views

Is there a difference in SNR between using 2x2 pixel binning in the camera and shrinking the full resolution image in software?

Is there a difference in SNR (or any other measure of image quality) between using 2x2 pixel binning in the camera and shrinking the full resolution image in software (cv::INTER_AREA) to the same size ...
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2answers
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Why are 8 points needed to compute a fundamental matrix?

Homograpies have 8 degrees of freedom. Fundamental matrices have 7. Essential matrices have 5. To the best I could find, all those matrices are obtained by using the 8 point algorithm. I don't see ...
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1answer
47 views

Erosion compotition rule $\left ( f \ominus g \right ) \ominus h = f \ominus \left (g \oplus h \right ) $

I want to prove that erosion of a signal by a function $g$ followed by erosion with another function $h$ is equivalent to erosion of the signal by the dilation of the two functions (Erosion property): ...
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3answers
326 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 Fourier ...
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1answer
60 views

What is the difference between an image plane and a virtual image?

I have the following diagram that describes a camera model (I believe it is the pinhole camera model). Wikipedia has an article about the image plane and virtual image, but these articles do not ...
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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
222 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
3k 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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1answer
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What is the difference between an impulse response and a kernel?

It seems to me they are two terms used to refer to the same concept, but, according to the Wikipedia page on Guassian filter a Gaussian filter is a filter whose impulse response is a Gaussian ...
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1answer
44 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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855 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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