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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Filter for Reducing Background Noise in Image

I have images where there is a lot of "black" background (few shades of black). (In many images at least half the pixels are background). I need to get interest points from the image, but because the ...
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42 views

Looking for algorithm to extract line network from binary images [duplicate]

Possible Duplicate: Looking for algorithm to extract line network from binary images within LabView I would like to create a LabView VI that receives an input image and the RGB-color codes of the ...
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199 views

How to categorize the images based on Illumination / shadow?

Input: Cropped face or Non Cropped face images. Detailed explanation: My project is face authentication. I am using OpenCV face detector to crop face from images. I am using OpenCV implementation of ...
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116 views

Sample keypoint found in multi-scale to one scale (scale space with O octaves)

For a multi-scale keypoints detector, local extremas are found between the scales at EACH octave. The scale-space is implemented as follows: Each octave is downsampled by half from the first image in ...
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1answer
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Difference between optical flow field and motion field?

I have been trying to understand the various confusing definitions of optical flow field and motion flow field but cannot wrap my head around it. Some authors use the term interchangeably other give ...
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Ship/Boat Detection

I want to do boat detection in almost real time around 2-3 frames/sec and my computation power is not very high. I want to keep the computations as low as possible. Which is the best method to do it? ...
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1answer
146 views

Calculate the entropy of Turkish alphabet and compare with the entropy of English alphabet with using Matlab? [closed]

Calculate the entropy of Turkish alphabet and compare with the entropy of English alphabet with using Matlab? How can ı do this question anybody help please?..
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22 views

Why does the Y component in YCbCr represent luma/intensity?

As far as I know, the RGB to YCbCr conversion is just a linear transformation, yet the Y channel successfully captures the intensity value of each pixel. How? In other words, where do the following ...
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1answer
161 views

Multiple-image dense point cloud reconstruction with camera extrinsics/intrinsics

I have the following data available: Images from different angles X, Y, Z, pitch, yaw, and roll for each camera/image, together with the timestamp Lens distortion parameters and intrinsic camera ...
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176 views

Selecting gradient orientation for Generalized Hough Transform while scaling and rotation is present

I am using this link to study Generalized Hough Transform. I will explain it briefly. In order to detect a shape, an R-table is created for the shape with $\phi$ indicating gradient orientation for ...
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1answer
404 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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The difference of downsampling an image and smoothing an image?

I am, at the moment, trying to read up on some simple computer vision elements, in which i have become a bit comfused on the terms downsampling and smoothing, and whether there is a difference between ...
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117 views

Video: Detecting a digital timer and when it ticks

Input: A video with a digital timer, possibly several hours long, such as this video. The timer might use any font or color, and might be located anywhere on the video, but it probably won't fill the ...
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1answer
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what is the possible solution for the Intra-class variations poblems?

my poblem is that i have a database for human dorsal hand veins ,but with intra-class variations , so this problem have a large effect on my results when i need to do matching between my samples for ...
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1answer
31 views

Why exactly is the Guassian filter a low-pass filter?

In image processing, a Guassian filter is used to blur an image. A low-pass filter is a filter that attenuates the high frequencies, preserving only smooth variations in the provided image. Is a ...
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1answer
24 views

Lighting for computer vision automisation

Currently I am working on a computer vision project where we want to gather data from a composite material production environment. I have an example picture here: What I learned so far that my ...
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What happens when we reconstruct a signal after its Fourier transform is done and some frequencies are altered? [closed]

Since we loose time information when we take a Fourier transform, what happens if we alter a few frequencies from the transform and then reconstruct the signal, do we get the altered frequency at the ...
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1answer
125 views

Pinhole camera model from houdini parameters

From a simulation with Houdini software I retrieved these parameters: Camera position: -0.675839, 33.5945, 0.0318854 Camera Rotation: 0.0318854, 92.4693, 0.1 Focal Length: 52.5172 mm Image size: 1920 ...
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462 views

Backgammon checkers and dice detection

first of all thanks for reading, and sorry for such a generic question. If it is off topic for your forum i would be thankful if someone could point me to a place where i can find an answer. I am ...
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108 views

Generate 3D image from Multiple 2D Images

If we're to capture an image of a body using four (4) WebCam with a 16 megapixel (1 in the front, 1 in the back and 2 sides(left and right)). Is it possible to make a 3D out of it using image ...
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1answer
6k views

What is different between gradient and imgradient functions in MATLAB

I would like to compute the gradient of an image I. I have the following two options : [Gx, Gy] = gradient(I); g = sqrt(Gx.^2+Gy.^2); or ...
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1answer
962 views

Converting from RGB to Lab to reduce colors

In many papers I see the following: First we have to convert image from RGB to Lab color space to reduce colors then ...
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2answers
426 views

Magnitude of Sobel filter result, vector or scalar?

I have a question about image gradient magnitude, given an image $I$. The horizontal and vertical derivatives resulting from Sobel filters are defined as: $$K_x= \begin{bmatrix} -1 &...
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2answers
65 views

How to represent a given equation more clear, profressional and short form?

I have a image $U_{m \times n}:\Omega \to \mathbb R^2$, the output $P$ can be define as $$P=\mu J_{m \times n} - U$$ where $\mu = \max \{ u_{ij} : 1 \leq i \leq m, 1 \leq j \leq n\}$, $J_{m \times n}$...
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Projecting a 3D point into new camera coordinates

Given I have: a camera with estimated rigid motion 3x4 matrix $P = [R|t]$ that starts from the origin of the reference coordinate system an intrinsics 3x4 projection matrix $K$ a 3D point $X$ How ...
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2answers
180 views

How can I go forward with this image processing task?

0 down vote favorite I am totally new to Image processing. I just started my Master thesis in the area of Computer vision and Machine learning. My background is Informatics. Now, my first task is to ...
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2answers
678 views

Ho 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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1answer
106 views

Queries on Kalman Filter

I am trying to apply kalman filter for video processing , i am studying about it from different sources but it take me towards question that if i don't know that where my object come in frame mean i ...
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1answer
359 views

Is “early vision” chronological or process

This might sound silly, but I have a language barrier type of question, and I was hoping someone could clear up this misunderstanding: I've seen the term "early vision" several times in papers I've ...
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2answers
248 views

Automatical skyline alignment on image

I need for an algorithm which do steps, displayed on image below. Are solutions for doing this exist? (Preferably on C# or JavaScript).
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1answer
174 views

trainCascadeObjectDetector seems to be missing from MATLAB R2012b

I wish to use trainCascadeObjectDetector to train on new objects (other than faces); I have the Computer Vision Toolkit installed; but this function trainCascadeObjectDetector seems to be missing from ...
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2answers
215 views

What is the procedure to obtain a 3D face dataset? Can anyone suggest a good 3D face dataset?

Project Description: Input: Frontal Face Image Expression Angle Size Details: I have to convert the input frontal face image into 3D face and simulate the ...
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1answer
180 views

Can anyone suggest good algorithms for CBIR?

Project: Content Based Image Retrieval - Semi-supervised (manual tagging is done on images while training) Description I have 1000000 images in the database. The training is manual (supervised) - ...
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1answer
30 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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1answer
18 views

Gender classification using Periocular Region [closed]

I have a dataset of the periocular region, I have images of the male and female periocular region but they are only labeled as left and right periocular region, Folder is a mixture of male and female ...
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2answers
45 views

What do the 1D filters represent when using imfilter?

I am reading the source code of an algorithm that is used to process an image. While reading this source code (and others), I've found lines of code of the form ...
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1answer
60 views

How to Combine / Cascade two `3 x 3` Filters into One `5 x 5` Filter

If you have a uniform 3x3 box filter T which is: 1 1 1 1 1 1 1 1 1 And an 3x3 laplacian filter W which is: 1 -2 1 -2 4 -2 1 -2 1 Can these 2 filters be combined into one 5x5 filter, the ...
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1answer
76 views

How to extract a smooth contour from a set of points in 3D?

I am trying to segment a 3D volume. The outcome of all my volume segmentation algorithms is a set of candidate points in 3D space. Now I need to smooth this point cloud and fit a closed surface it. My ...
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1answer
40 views

What is the difference between domain and range filtering?

In the context of image processing, I have heard the expressions "domain filtering" and "range filtering". What do these terms refer to? What is the difference between them?
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1answer
482 views

python: how to compute the gray level histogram features as mentioned in the paper, and

Hi I am extracting the grey level features of image mentioned in this paper (part 4.5 low level features). "We describe two low level features that are particu- larly important for photo quality ...
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1answer
154 views

Hough Transform not working to recognize a line

I have an image composed of small white dots that should stay on the same line. I wanted to recognize this line using the Hough Transform. To do that I binarized the image, calculated the centroid of ...
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1answer
108 views

Computer Vision - Does implementation of Hough Transform for lines require a loop for angle parameter?

I am trying to understand how Hough Transform is implemented in real world applications. Consider a line with equation: $y = mx + b$ In parametric form, this line can be represented using (d, $\...
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1answer
152 views

Correlation peformed by convolution

Background: The question here is related to images in particular and not signal/waveforms. I have been reading a lot of answers about the difference between convolution and correlation but I am stuck ...
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1answer
1k views

Scale invariant template matching

For my application I am looking for a free, fast and scale-invariant template matching algorithm. The templates can only be scaled within the scene (no skew or rotation) and the scale is unknown. ...
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1answer
159 views

How Can PCA Be Used in Image Analysis [closed]

I am still a not how PCA can be used in image analysis and where is it is mostly used. For example how can PCA be used in order to differentiate between different faces? Can you please mention other ...
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1answer
86 views

Good Metric for Spatial Resolution

I am trying to filter crawled images with their image quality. By 'high quality' I mean high resolution, not aesthetic score or perceptual score. However I found that some images have very high pixel ...
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2answers
643 views

Camera measurement of heart rate - frequency bias towards 50 bpm (0.83 Hz)?

I am trying to develop a RGB camera-based non-contact measurement of heart rate using principles of remote photoplethysmography. I want to be able to measure a range of heart rates I have been looking ...
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1answer
647 views

Block normalization of histogram of oriented gradient

I am a beginner in image processing. I have some questions regarding HOG. https://www.learnopencv.com/histogram-of-oriented-gradients/ From this website, it mentioned that each element inside the ...
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1answer
3k views

Line Detection with OpenCV and Python [closed]

Why do we get less amount of lines then desired in line detection using HoughLines tranformation from OpenCV? How could we improve this method and get all the lines appearing in the image? I would ...
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1answer
2k views

Calculating distance between two blobs in a binary image in microns

I have a monochrome CCD camera with resolution 960 X 1280 and can give up-to 15 fps I am working on python opencv. I want to track the distance between two rectangular blobs in binary images in real ...