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.
228
questions
111
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6answers
63k 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 ...
38
votes
3answers
43k 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 ...
45
votes
3answers
20k 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?
4
votes
2answers
1k views
Image Processing and applicability of 2D Fourier Transform
As a newbie in the world of signal processing, I am having a hard time in appreciating image 2-D fourier transforms.
I am fully able to appreciate the concept of 1-D Fourier transform. Essentially, ...
52
votes
10answers
16k 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 ...
4
votes
3answers
2k views
Vein extraction from this image
I have this image:
What methods should I use to extract the veins from this image.
Thank you.
67
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4answers
49k 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://...
47
votes
6answers
19k 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 ...
34
votes
2answers
16k 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 ...
19
votes
6answers
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What is the Walsh-Hadamard Transform and what is it good for?
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 ...
15
votes
4answers
4k views
List of possible image features for content based image retrieval
I am trying to find a list of possible image features like color, oriented edges and so on for measuring their usability in case of finding same/similar objects in images. Does anyone know such a list ...
11
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2answers
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Image Reconstruction:Phase vs. Magnitude
Figure 1.(c) shows the Test image reconstructed from MAGNITUDE spectrum only. We can say that the intensity values of LOW frequency pixels are comparatively more than HIGH frequency pixels.
Figure 1.(...
3
votes
1answer
331 views
Filtering $ n \times n $ Images by Separable $ m \times m $ Filters. Computation Time for Filtering Using FFT, 2D Convolution and Two 1D Convolutions
Consider filtering square $n\times n$ images by square, separable $m\times m$ filters.
Give general equations for the computation time for the following approaches to this:
Filtering using FFT
2-D ...
65
votes
9answers
76k 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?
31
votes
5answers
20k views
What are the best algorithms for document image thresholding in this example?
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 ...
18
votes
1answer
38k views
Difference between correlation and convolution on an image?
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 ...
27
votes
4answers
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 ...
33
votes
5answers
3k 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 ...
31
votes
5answers
2k 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 ...
23
votes
1answer
4k 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 ...
12
votes
2answers
1k views
Auto-focus estimation?
What kind of analysis might be used on sets of 2D monochrome image matrices or bitmaps to estimate or compare their relative quality of being "in focus"? Is there an efficient way of computing a ...
16
votes
1answer
20k 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.
10
votes
2answers
15k 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: $ \...
7
votes
2answers
4k views
Which domain used for denoising additive and multiplicative noises
I want to know what is the difference between additive noise, multiplicative noise.. In what domain these noises are handled to remove?
I am interested particularly in image dataset
Does different ...
3
votes
3answers
3k views
recover image by only magnitude of image fourier transform
I have a image and I want calculate fft2 of it, after it I want recover image only by magnitude of it. how can I achieve this work?
...
1
vote
3answers
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What is the advantage of weighted median filter over median filter?
I could not find any proof or comparison of weighted median and median filters. Yes the more occurring pixel contributes much but what should be the criteria of choosing weight function. And any ...
4
votes
2answers
1k views
JPEG DCT padding
Since the JPEG DCT block used is 8x8, how does the method deal with images with dimensions that are not multiples of 8? What kind of padding does it use? How are the 8x8 blocks of the image chosen?
2
votes
1answer
2k views
what's gaussian noise look like?
I am using Matlab function imnoise to add gaussian noise to one image. However, it seems that adjacent samples of the noise is correlated. I am using matlab code below to add noise.
...
1
vote
1answer
191 views
2D DWT computation order
In 2D the discrete wavelet transform (DWT) of an image using lifting based 5/3 filter, if I perform a row-wise operation first then perform column-wise operation then I will get 4 sub-band LL, LH and ...
1
vote
1answer
254 views
Applying Image Filtering (Circular Convolution) in Frequency Domain
To filter an image we can:
Use a 3x3, 5x5, 7x7, etc. filter, that is convolve the image and the filter in the space domain.
Use a FFT on both the image and the filter, multiply them together in the ...
0
votes
1answer
247 views
compression algorithm
Steganography can hide one image inside another.
If we have a compression algorithm that allows us to fit the bits for two images into the size of one, can we think of a way to modify a run-length ...
0
votes
1answer
518 views
2D DWT Image Issue
In the literature, I see that a 2D signal can be transformed by first doing a 1D transformation on each row of the matrix followed by the same procedure on each column. It seems that $k^{th}$ level ...
176
votes
5answers
62k views
“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 ...
54
votes
8answers
7k 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 ...
50
votes
4answers
22k 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 ...
40
votes
1answer
13k 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 ...
34
votes
7answers
19k 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 ...
18
votes
4answers
11k 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 ...
18
votes
3answers
53k 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 ...
13
votes
3answers
4k views
Is sift a good way to extract features from an image?
I am trying to extract features from an image, but I have failed to get the points that I want to extract, and hence my image fails to match with the template.
Are there any checkpoints that I have ...
15
votes
4answers
7k views
How to extract traffic signs from a photograph?
What image analysis techniques can I use to extract the traffic signs from an image such as the one below?
Edit:
After Anisotropic diffusion: The background that i don't want gets cleared a little
...
11
votes
3answers
2k views
Most common modern day Image Segmentation techniques
I was doing some reading up on image segmentation techniques and I was wondering about modern day, state-of-the-art segmentation algorithms.
What current segmentation techniques that are a 'must-read'...
9
votes
2answers
5k views
Wavelet Transform
I want to perform 2D haar discrete wavelet transform and inverse DWT on an image.Will you please explain 2D haar discrete wavelet transform and inverse DWT in a simple language and an algorithm using ...
8
votes
2answers
17k views
Why images need to be padded before filtering in frequency domain
In image processing books , we are told that Images need to be padded while doing filtering in the frequency domain. Why we need that zero padding ?
16
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2answers
7k views
Alternatives to Hough transform for detecting a grid-like structure
I have an image which is composed of multiple 'angles' which form a grid shape:
After some searching, Hough seemed like a good fit, because it isn't troubled by breaks in lines. However, the problem ...
12
votes
3answers
987 views
Image processing coding
I was wondering which is the best language for image processing? I know MATLAB has a good library and user community for it. I havent checked it out, its there for python as well.
What is the most ...
12
votes
2answers
535 views
What methodology to use for discrimination of different (musical?) tones
I am trying to research and figure out how best to attack this problem. It straddles music processing, image processing, and signal processing, and so there are a myriad number of ways to look at it. ...
8
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3answers
7k views
Why normalize the data set before applying Direct Linear Transform
Direct Linear Transform (DLT for short) is a method of homography estimation, it solves the overdetermined linear system via SVD $$Ah=b$$to find a solution $h$ under constraint $\|h\|=1$. Actually it ...
7
votes
1answer
3k views
Why does the separable filter reduce the cost of computing the operator?
A separable filter in image processing can be written as product of two more simple filters. Typically a 2-dimensional convolution operation is separated into 2 onedimensional filters. This reduces ...
4
votes
1answer
4k views
How to get a top view using open cv?
I have a situation where i need to extract the top view of a road from the 'skewed' view I get from a cc camera located on some roadside tree. I would like to do this using OpenCV, but since I'm very ...
