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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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Implementation of PCA for hyper-spectral Image Processing

I have been studying the concept of PCA and its implementation for dimensionality reduction for more than 1 month. My goal is to classify a hyperspectral image using sparse representation by the ...
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11 views

How to receive v-chip signals from digital TV stream

I'm trying to retrieve and decode V-chip data from my TV streams (NTSC/ATSC digital streams). Apparently these data are embedded somewhere in the stream itself, but I have no clue how they are ...
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Co-prediction of signals

Is there any plausible method to estimate or predict one signal, on the basis of known value of another signal, provided the two signals bear a strong correlation? For instance, the audio amplitude ...
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1answer
16 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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Can We Measure Diameter and Length from Camera using MatLAB? [closed]

Can we measure a circle diameter or line length from camera using matlab? If we can, how can it works?
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1answer
23 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
24 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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28 views

On Human (Face) Detection

There are many face detection and recognition algorithms and APIs out there; however, most of them can produce same results for paintings and avatars as for human face. So, is there any specific ...
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Computer Vision - What are the possible values for indices in auto correlation function for Harris Corner Detector?

The auto correlation function for Harris Corner Detector is defined as $E(u, v) = \Sigma_{x, y} w(x, y) [I(x + u, y + v) - I(x, y)]^ 2$ The idea here is that we ...
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1answer
29 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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1answer
41 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 find corresponding points between two photos when there's a repeated pattern?

Suppose that I have two photos, I1 and I2 and I want to find a set of corresponding points between the two photos to define a homography between them. There are many algorithms for this purpose, ...
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Probabilistic color recognition of an object

I am trying to detect an object using a probabilistic approach. One the main attributes is its overall yellow color, apart from some portions than will reflect white-yellow, depending on ambient ...
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Measuring the Accuracy of Image Segmentation Algorithms (TP,TN,FP,FN)

I'm currently working on evaluating image segmentation algorithms applied or tested in $2D$ images of fish fingerlings. I'm hoping to evaluate different approaches in terms of how accurate the ...
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1answer
158 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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34 views

POV when merging camera and point cloud data

I am trying to merge camera data with colorless point cloud data obtained from a LIDAR device. I used the pinhole camera model and assign each 3D point to a pixel using external/internal matrix ...
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finding distance between object and camera

I am using the pinhole camera model to perform some calibration. At the moment, I can convert from image plane to world coordinates as follows: I pick a point whose position in the world coordinates ...
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1answer
61 views

How to segment multiple overlapping coins (ellipses)

I am doing a program that counts coins (and tells their value by their size) with OpenCV (C++). Let's say we have an image of some coins. If there is an overlap of two coins at the same time, it is ...
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1answer
25 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
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Image processing - Why is sum of values of a blurring filter = 1?

Usually, blurring filters have the sum of all the values in the filter matrix equal to $1$. Why is it so?
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converting digital length to physical length using reference object

I am trying to find actual length of an object, say X, from an image. For that I'm using a reference object , say Y, ( object of known dimensions ). From image while converting pixel length of X to ...
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58 views

Weird features mismatch using SURF

I'm trying to use SURF to detect an object (particularly a cur number plate) in another image. After unsuccessfully trying to use OpenCV i have moved to MATLAB. Everything works perfect on MATLAB's ...
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1answer
27 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
58 views

given an image and its fourier transform, find another image fft using fourier properties

I managed to solve few of those questions , but I'm not manage to answer 3 of them correctly, the question is: given an image and its fourier transform, find another image fourier transform ,using ...
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224 views

Determine when a constant signal changes to another constant value

As a novice to digital signal processing I have a scenario that probably seems trivial but I dont know the answer to. I want to detect when a signal changes but ignore noise. 255 255 255 255 255 ...
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97 views

Perspective Transform using depth and scale information

I want to transform perspective on an input image and output image from the new perspective. I have depth map and scale information. The picture roughly demonstrates what I want to do. I have a single ...
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139 views

How to apply a homography matrix after finding it via a common camera calibration technique

I am trying to find a matrix that maps four specific 2D-points to another set of specific 2D-points. Specifically, I'm trying to find the matrix $H$, such that $x_i=HX_i$ achieves the following ...
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2answers
78 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
70 views

Morphology - Why does the concept of opening and closing images exist when we already have erosion and dilation?

If we consider the closing operation of an image, we first dilate the image and then erode it. So, first we expand the foreground (white pixels) and and then we take away some part of the foreground. ...
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1answer
507 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
16 views

Anisotropic filter implementation wrong?

I've this implementation of the anisotropic filter: ...
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0answers
26 views

Chapter 4, section 4.2.1. in Szelisky computer vision, is there a mistake?

I've already asked a similar question in mathematics exchange without getting an answer, I read a bit more and I think the question might be more suitable for the signal processing exchange. ...
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0answers
33 views

Output of a bank of gabor filters, derive ellipses like regions

I'm trying to implement an algorithm that show how to detect wrinkles in clothes, without going to much into details this is the step that is confusing me. Assuming we have an image $I$ and a set of ...
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1answer
148 views

Laplacian of Gaussian Approximation and Gaussian Blur as the Solution of Heat Equation

While I was reading SIFT paper(Lowe, 2004), I came across the method that he apply "heat diffusion equation" to Gaussian function to derive that $$ \frac{∂G}{∂σ} = σ∇^2G $$ I searched Wikipedia and ...
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1answer
120 views

The Differences between Super Resolution and Denoising and Deblurring

In the field of computer vision/image processing, what are the differences between super-resolution and de-noising/de-blurring? Thanks.
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1answer
68 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
93 views

Automatic Image Enhancement of Images of Scanned Documents (Auto Whitening)

Dropbox have make a blog post about there automatic enhancement method for scanned document image - Fast Document Rectification and Enhancement. I followed the post and they mention a formula to make ...
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1answer
20 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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1answer
353 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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50 views

How to extract text from scene images?

I tried many methods for segmenting images like the example below ; but i obtained no efficient result can someone suggest me a good method for extracting text from complicated images like this ...
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91 views

A question about visualizing “Lucas-Kanade(optical flow)” algorithm

I am reading O'Reilly's OpenCV 3 book. In keypoints section(for tracking objects), there is an algorithm named "Lucas-Kanade". in the below image it tries to give a visualization of it but I can not ...
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Detection of calibration (dummy) stickers

I was looking for some commonly used approaches in computer vision to find the following calibration stickers and I was pretty surprised that I have not found any. I am not sure if I am just googling ...
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1answer
274 views

Is there a penis detection demo similar to face detection?

Tutorial for face detection: Is there a script / tutorial / demo for penis detection? These guys ran into some issues: Fairly serious question, future of internet memes is at stake. Breast / ...
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1answer
40 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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2answers
59 views

What are some current algorithm(s) for finding if two images are copies of each other?

Could anyone enlighten me on what are the current best ways to detect if two images are the same (i.e. a copy or edited copy of each other)? What feature detection method do they use (SIFT, DWT, pixel ...
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1answer
44 views

Best way to fill an image placed into a larger box without creating artificial edges?

If you are training a neural net for a bunch of images of different size, and you have to put them all in a same-size enclosing box for input to the neural net, what's the best way to fill the ...
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52 views

Estimating the deformation of a printed label in an image

For a university honours project, I am developing an algorithm to read the text on nutrition labels. One difficulty I have encountered is how to 'flatten' the text in images of labels that are very ...
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1answer
139 views

How to detach overlapping contours but not to remove small ones. Alternative to erosion-dilation cycle

Background: I'm trying to detect trees on a sequence of aerial images by calculating a stereo disparity for consequent pairs of images. This is how disparity looks like. White spots are trees: Next, ...
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1answer
44 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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1answer
164 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 ...