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Questions tagged [image-processing]

In general, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame.

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186 votes
5 answers
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"River" detection in text

Over on the TeX stackexchange, we have been discussing how to detect "rivers" in paragraphs in this question. In this context, rivers are bands of white space that result from accidental alignment ...
Lev Bishop's user avatar
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131 votes
5 answers
88k views

What does frequency domain denote in case of images?

I was just learning about the frequency domain in images. I can understand the frequency spectrum in case of waves. It denotes what frequencies are present in a wave. If we draw the frequency ...
Abid Rahman K's user avatar
78 votes
9 answers
109k views

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?
porridge's user avatar
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78 votes
4 answers
61k views

What are some free alternatives to SIFT/ SURF that can be used in commercial applications?

As far as I understand, both SURF and SIFT are patent protected. Are there any alternative methods that can be used in a commercial application freely? For more info on the patent check out: http://...
Andrey Rubshtein's user avatar
70 votes
12 answers
22k views

Is deep learning killing image processing/computer vision?

I'm looking forward to enroll in an MSc in Signal and Image processing, or maybe Computer Vision (I have not decided yet), and this question emerged. My concern is, since deep learning doesn't need ...
Tony's user avatar
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58 votes
5 answers
28k views

Analogous Library to OpenCV for Audio Processing / Analysis

I understand OpenCV is the de facto library for programming image processing in C/C++; I'm wondering if there is a C or C++ library like that for audio processing. I basically want to filter raw waves ...
Tae-Sung Shin's user avatar
57 votes
8 answers
8k views

What are some good signal and image processing blogs worth following?

Are there some good sites or blogs where I can keep myself updated on the latest news and papers about image and signal processing research, or I should just check out "classical" providers like IEEE ...
54 votes
6 answers
25k views

Best way of segmenting veins in leaves?

I have done a lot of research and found out methods like adaptive thresholding , watershed etc that can be used of detecting veins in leaves . However thresholding isn't good as it introduces a lot of ...
vini's user avatar
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49 votes
3 answers
22k views

What algorithm does Google use for its "Search By Image" site?

What is your best guess how Google Image Search works? I can upload a photo and can search for similar images. What algorithm does it use to identify similar images?
Cory's user avatar
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48 votes
5 answers
11k views

Point Pattern Recognition

Having two different size of sets of points (2D for simplicity) dispersed within two different size squares the question are that: 1- how to find any occurrence of the the small one through the ...
Developer's user avatar
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45 votes
1 answer
18k views

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 ...
mahboudz's user avatar
  • 553
43 votes
6 answers
6k views

What properties make certain wavelets "better" than others in image compression?

I am trying to teach myself more about image compression using the wavelet transform method. What is it about certain wavelets that make them preferable when compressing images? Are they easier to ...
user807566's user avatar
40 votes
2 answers
21k views

What's the difference between the Hough and Radon transforms?

I'm familiar with the Radon transform from learning about CT scans, but not the Hough transform. Wikipedia says The (r,θ) plane is sometimes referred to as Hough space for the set of straight ...
endolith's user avatar
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40 votes
3 answers
53k views

What are the most common algorithms for adaptive thresholding?

Adaptive thresholding has been discussed in a few questions earlier: Adaptive Thresholding for liver segmentation using Matlab What are the best algorithms for document image thresholding in this ...
Dipan Mehta's user avatar
  • 5,597
38 votes
5 answers
48k views

Why are Gaussian filters used as low pass filters in image processing?

In 1d signal processing, many types of low pass filters are used. Gaussian filters are almost never used, though. Why are they so popular in image processing applications? Are these filters a result ...
nimrodm's user avatar
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35 votes
5 answers
6k views

What factors should I consider in choosing an edge detection algorithm?

I've learned about a number of edge detection algorithms, including algorithms like Sobel, Laplacian, and Canny methods. It seems to me the most popular edge detector is a Canny edge detector, but is ...
PearsonArtPhoto's user avatar
35 votes
7 answers
27k views

Finding squares in Image

I need to find the squares in an image using OpenCV (no problem in matlab or any other, generally what i expect are some ideas). Consider the test image below : I need to find those coloured squares ...
Abid Rahman K's user avatar
34 votes
5 answers
21k views

What Are the Best Algorithms for Document Image Thresholding (Example Inside)?

I'm trying to implement various binarization algorithms to the image shown: Here's the code: clc; clear; x=imread('n2.jpg'); %load original image % Now ...
mark's user avatar
  • 475
33 votes
6 answers
3k views

Detecting Trail in Forest Images

Is anyone aware of any research/papers/software for identifying a trail (as a line or point-to-point curve) in an image of a forest scene (from the perspective of the camera standing somewhere along ...
Cerin's user avatar
  • 618
29 votes
5 answers
20k views

Good Language for Implementing Computer Vision System / Algorithm / Application?

I am trying to implement a content based image retrieval system but before I do so I would like to get an overview of some programming languages suitable for this task (having good libs and such). ...
Hans Sperker's user avatar
29 votes
4 answers
109k views

Gaussian Blur - Standard Deviation, Radius and Kernel Size

I've implemented a gaussian blur fragment shader in GLSL. I understand the main concepts behind all of it: convolution, separation of x and y using linearity, multiple passes to increase radius... I ...
LodeRunner's user avatar
28 votes
1 answer
5k views

Mathematics of Harris corner point detection

This is the mathematical expression for Harris corner detection: But I have the following doubts: What is the physical significance of $u$ and $v$? Many references say it is the magnitude by which ...
rotating_image's user avatar
28 votes
4 answers
2k views

Find the stomata in a plant microscopy image

Here is a question for image processing experts. I am working on a difficult computer vision problem. The task is to count the stomata (marked below) in DIC microscopy images. These images are ...
Matt M.'s user avatar
  • 1,088
26 votes
3 answers
12k views

Fastest Algorithm for Distance Transform

I am looking for the fastest available algorithm for distance transform. According to Image Processing Learning Resources - HIPR 2 (HYPERMEDIA IMAGE PROCESSING REFERENCE) - Morphology - Distance ...
Karl's user avatar
  • 837
26 votes
3 answers
18k views

How do I remove motion blur?

Is there a generically accepted method of removing motion blur from an image. For a simple case, we can assume that motion happens in a straight line. I assume that it's a two part process composed of ...
Phonon's user avatar
  • 5,236
26 votes
1 answer
11k views

What are the practically relevant differences between various image resampling methods?

Mathematica's ImageResize function supports many resampling methods. Not being familiar with this area, beyond nearest neighbour, bilinear, biquadratic and bicubic ...
Szabolcs's user avatar
  • 365
25 votes
6 answers
37k views

How do I get the most accurate camera calibration?

First off, I hope this is the correct Stack Exchange board. My apologies if it is not. I am working on something that requires me to calibrate the camera. I have successfully implemented the code to ...
Cheetah's user avatar
  • 453
24 votes
15 answers
7k views

DSP or signal/image/data processing jokes

Some other StackExchange/StackOverflow sites are entertained with a certain level of humor or fun. What is your favorite “data analysis” cartoon? is particularly worth mentioning (IMHO) this xkcd ...
Laurent Duval's user avatar
24 votes
3 answers
44k views

What Is the Difference between Difference of Gaussian, Laplace of Gaussian, and Mexican Hat Wavelet?

There are three techniques used in CV that seem very similar to each other, but with subtle differences: Laplacian of Gaussian: $\nabla^2\left[g(x,y,t)\ast f(x,y)\right]$ Difference of Gaussians: $ \...
DeusXMachina's user avatar
24 votes
6 answers
28k views

What Is the Walsh Hadamard Transform? How Could One Use It in Image Processing?

I am trying to teach myself about the WHT but there dont seem to be many good explanations of it online anywhere. I think I have figured out how to calculate the WHT, but I am really trying to ...
Spacey's user avatar
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24 votes
3 answers
3k views

How can I reconstruct a 3D structure from a set of images?

I have a set of contours (set of line segments) grouped in the following way: $S_i = \{I^0, I^\frac{\pi}{4}, I^\frac{2\pi}{4}, \ldots, I^\frac{7\pi}{4} \}$ where $S_i$ denote sequence of photos of ...
om-nom-nom's user avatar
22 votes
1 answer
45k views

Difference Between Correlation and Convolution in the Context of Image Processing

Could you please clearly explain what is the difference between correlation and convolution that is done by a filter on an image? I mean in terms of signal processing definition I know that ...
the_naive's user avatar
  • 363
22 votes
5 answers
3k views

What are the audio equivalents of images like "Lena", "Mandrill", and "Cameraman"?

I don't know what to call these images, but they're very often used in the image processing world as standard examples to show the output of a particular operation. Here's a link to the page ...
aardvarkk's user avatar
  • 321
22 votes
2 answers
25k views

Why do we use keypoint descriptors?

I just studied about SURF and I'm going for its implementation, but I still didn't understand why we use descriptors. I understand what keypoints are and their purpose, but when we extract the ...
ARG's user avatar
  • 601
22 votes
1 answer
30k views

How to Extract High Frequency and Low Frequency Component Using Bilateral Filter?

What does High frequency and low frequency component signify in an image. How to separate out the high frequency as well as low frequency component of an image using Bilateral filter.
Deepak kumar Jha's user avatar
22 votes
4 answers
8k views

How do I detect distinct objects when their edges touch each other?

I need to find all the contours in an image retrieved from the camera. So I first use the canny edge detector to find the edges and then find the contours. Pretty simple. However, my contours get "...
user avatar
21 votes
5 answers
47k views

How to Remove a Glare / Clipped Brightness from an Image?

I have an image Is there any way of removing the bright white spots ? Please help thanks Edit: After operating with gaussian and then displaying using imagesc get the following output which ...
vini's user avatar
  • 2,182
21 votes
4 answers
52k views

Discrete Fourier Transform: What is the DC Term really?

I am currently toying around with the Discrete Fourier Transform (DFT) in Matlab to extract features from images. I like to fully understand the concepts that I use. I have read several explanations, ...
Domi's user avatar
  • 323
21 votes
3 answers
76k views

OpenCV/C++ connect nearby contours based on distance between them

I have to connect nearby contours in an image based on the distance between them which specifies if the contours are to be connected. Now there's a question already on the same problem here https://...
Roney Island's user avatar
20 votes
3 answers
48k views

What is the difference between linear and non-linear filters?

How a mean filter is called as linear filter and a median filter is called as non linear filter? I understand how a mean and median filter operates, but I was not able to relate with the term linear ...
preethi's user avatar
  • 923
20 votes
3 answers
12k views

What's wrong with this code for tomographic reconstruction by the Fourier method?

I've been playing around with tomographic reconstruction algorithms recently. I already have nice working implementations of FBP, ART, a SIRT/SART-like iterative scheme and even using straight linear ...
timday's user avatar
  • 538
20 votes
5 answers
4k views

How can I compare two pictures from the camera and tell if there are enough differences to detect movement?

I want to use my phone as a CCTV system to control a room in my house, and display an alert when something is moving. For now, what I have succeeded in doing is to grab a picture every minute and ...
Waza_Be's user avatar
  • 303
20 votes
3 answers
35k views

Difference between SNR and PSNR

I understood that SNR is the ratio of signal power to the noise power. In terms of images, how the original image is affected by the added noise. In PSNR, we take the square of the peak value in the ...
Premnath D's user avatar
  • 1,011
19 votes
4 answers
14k views

What Are the Limitations of a Canny Edge Detector?

Broadly a majority of the literature on edge detection algorithms and applications that uses edge detection, references Canny's edge detector. So much so that it looks like almost "the solution" to ...
Dipan Mehta's user avatar
  • 5,597
19 votes
4 answers
994 views

Applicability of compressed sensing / compressive sensing

From what I have heard, compressed sensing can only be utilized for a sparse signal. Is this correct? If that is the case, how can a sparse signal be distinguished from any bandlimited signal? Every ...
user2346's user avatar
  • 291
19 votes
1 answer
7k views

Who is Barbara?

In recent years, I have started doing work in image analysis and have used the Barbara and Lena images. Early on, I became aware of the interesting history surrounding the Lena image and that got me ...
Paul's user avatar
  • 291
18 votes
5 answers
7k views

what is smoothing in very basic terms

What is smoothing and how can I do it? I have an array in Matlab which is the magnitude spectrum of a speech signal (the magnitude of 128 points of FFT). How do I smooth this using a moving average? ...
user avatar
18 votes
2 answers
3k views

A (Clear) Line Between Computer Vision and Image Processing

I have been working in and learning about both Computer vision and Image processing for a few years now, and I believe that I am not a complete beginner any more. Still, after all these years, it is ...
penelope's user avatar
  • 3,676
18 votes
2 answers
20k views

Downsampling an image by an integer factor

When downsampling an image by an integer factor $n$, the obvious method is to set the pixels of the output image to the average of the corresponding $n \times n$ blocks in the input image. I remember ...
Styg Oldenbaum's user avatar
18 votes
3 answers
9k views

How to Detect Gradients and Edges in Images?

I want to be able to find points in images that are the centre of a radial gradient like the one shown in the left picture below. Any ideas on how I could use a Hough transform or some other computer ...
waspinator's user avatar

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