All Questions
468 questions
1
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29
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Is there a relation between Low-pass filter cutt-off frequency and 2d DCT coefficients?
I'am trying to make a low pass butterworth filter for an image. I try to find a relation between dct coefficients and cutoff frequency.
I know that the low frequencies are top left side in dct, high ...
- 11
2
votes
1
answer
55
views
Recreating the `dwt` function from Matlab
I am trying to implement DWT (Discrete Wavelet Transform) on a given signal, without using the dwt function in Matlab. My approach was to get the synthesis filter coefficients using,
...
- 23
4
votes
1
answer
124
views
How does MATLAB's edgetaper function work?
MATLAB has a function edgetaper that does something I haven't seen before:
J = edgetaper(I,PSF) blurs the edges of the input ...
- 2,760
2
votes
2
answers
128
views
Use DFT (`fft()`) to Replicate 2D Convolution (`conv()`)
In MATLAB, I tried to convert the fft2-based multiplication using conv2.
...
- 21
1
vote
1
answer
126
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Properties of DFT of Circularly Symmetric 2-D Matrices
I'm very new in image processing and trying to get a grasp in the basic concepts in 2-D DFT.
As far as I understood, DFT of a circulant matrix should also be a circulant matrix. But when I define a ...
1
vote
2
answers
643
views
Inverse fft does not give back the same image
I tried to Fourier decompose my image using FFT and reconstruct it back using IFFT. While I did this, I noticed something peculiar:
The first image is the regular one, and the second is the image I ...
- 113
0
votes
2
answers
172
views
How to produce self-adjoint filters using Gaussian and motion blur in Matlab?
I am trying to write a Matlab code to produce motion and Gaussian blur. Here is my code:
...
- 5
5
votes
2
answers
134
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Analyzing 2 2D Kernels Which Approximates a Gaussian Kernel
I'm new to image processing and am working on mask operations.
I was given two kernels A and B, and performed convolutions respectively on an image.
Then, I have to get the difference of output image ...
- 53
2
votes
1
answer
664
views
Before the fft2, why need fftshift for the kernel?
When I study some paper, I have some questions about usase of convolution theorem.
...
- 23
0
votes
2
answers
163
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How can I use the FFT in MATLAB to get the time domain equation representation of an image? [duplicate]
My goal is to take any image and break it down to obtain its time-varying equations so it can be redrawn and store the picture as two equations. One for $x$ and one for $y$.
As I understand, MATLAB's ...
4
votes
4
answers
150
views
What Measure to Compare the Color Depth (Distribution of Colors) of Images
I am looking to compare the color depth of multiple images, in order to see which one has the best color depth. I was wondering what is the best way to compute color depth computationally?
I've seen ...
- 53
1
vote
1
answer
887
views
What does hue, saturation and intensity means in image processing?
I ran some code in matlab to show what is hue, saturation and intensity to get an intuition of what they mean.
But the result of the code does not match the explanation i got from here
Hue is a color ...
- 111
7
votes
3
answers
95
views
How to exclude diffuse moving features in a stack of images
I have some stack of grayscale reconstructed images represented as a 3-dimensional matrix DPC with dimensions [Nz,Nx,Nt]. A ...
- 173
1
vote
2
answers
447
views
How can we compute power spectral density ($P_n$) in Weiner filter?
I have an image which I corrupted with white gaussian noise in order to have SNR (Signal to noise - ratio) 10 dB . I want to apply Weiner filter to image which has noise . If I want to compute Pf I ...
3
votes
1
answer
222
views
Color Image Watermarking with a Grayscale Watermark
I'm currently working on a project on digital watermarking in a color image. The host image is a color image, and the watermark image that will be embedded is a gray.
Is it necessary that the ...
- 41
1
vote
1
answer
271
views
Why does upsampling and interpolation by convolution introduce a shift compared to imresize?
For purposes of understanding the process - not for any practical purpose for which I could use imresize - I wanted to show that 2x upsampling followed by convolution with an appropriate kernel (...
- 683
2
votes
0
answers
39
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Additional artefacts in limited angle Radon transform reconstruction using the Fourier Slice Theorem
I want to simulate the limited angle Radon transform reconstruction problem by employing the Fourier-Slice Theorem which states that
$$ \mathbf{F}\left(\mathbf{R} f\right) (\theta, \sigma) = \mathbf{F}...
- 59
2
votes
0
answers
64
views
Geometric Transformation of Distorted Grid Lines Using Image Processing
If the grid-lines in the image (attached: distort1.jpeg) are distorted and squares in image appears distorted a bit. What would be the best and easy approach to convert them to perfect squares (as ...
- 21
4
votes
1
answer
90
views
Image Standardization for Image Classification (Machine / Deep Learning)
I am trying to write a program to standardize an image which I need to better perform image classification. I found the definition of standardisation which is obtained simply by subtracting the mean ...
- 141
5
votes
6
answers
2k
views
Number of dimensions? Color image vs gray scale image? Colour video vs gray scale video? Especially in the context of MATLAB
I am very confused as I had a debate with my buddy regarding color (RGB) images. He insisted that color images are two-dimensional, but when I personally try myself to read a color image into MATLAB, ...
- 1,952
4
votes
1
answer
295
views
Arithmetic Coding for Blocks of Images
I try to understand that how to use arithmetic coding on images. For this, I code on MATLAB. I tell my understanding for arithmetic coding. If I misunderstood to this algorithm, please correct me. ...
- 174
5
votes
2
answers
399
views
The Effect of Spatial or Temporal Averaging on Noise Properties
I generate two noise images using MATLAB's function imnoise().
If I average the two noise images, the resultant image looks like the original noise
image but only ...
- 425
6
votes
1
answer
243
views
Building a Pipeline for Image Classification / Clustering Tasks with Features Extractor and Dimensionality Reduction (Example on MNIST Data)
In MNIST, there are 28x28 images of hand written digits.
What features would one extract in order to classify then without any Deep Learning involved?
How does Dimensionality Reduction get in the ...
- 417
5
votes
1
answer
679
views
Image Clustering Using Linear Discriminant Analysis (LDA) Compared to t-SNE / UMAP
This is a a continuation of the discussion from Unsupervised Clustering of Images.
Image that we have MNIST database and we want to separate all the images like this. But we want to use Linear ...
- 417
2
votes
3
answers
853
views
Understanding FFT output in Matlab
I'm very new to Fourier transform and I want to plot the Fourier transform of an image in Matlab. I've seen many examples and in all of them, the fft() of the image is a black picture with some white ...
- 121
3
votes
1
answer
567
views
Unsupervised Clustering of Images: Which Algorithms?
Given a set of images $ \left\{ \boldsymbol{x}_{i} \right\}_{i = 1}^{N} $ how could one cluster them in an unsupervised manner? What are the useful features / tools to do so?
For instance, will ...
- 417
0
votes
0
answers
176
views
Why psnr function in matlab returns a negative value for an image corrupted with Cauchy noise?
I have written the following matlab code for producing a noisy image corrupted by Cauchy noise but when I compute the psnr value of the noisy image using psnr function in matlab, it returns a negative ...
1
vote
1
answer
670
views
How to interpret fft2() plots for images in MATLAB? What are represented by axes?
I got the frequency spectrum of a grayscale image using
...
- 21
3
votes
1
answer
524
views
Comparing distribution of vectors with different length?
I have two vectors of different length, each vector contains similarity scores. I need to plot the probabilty density function of the scores in both vectors to compare their distribution using Matlab. ...
- 33
5
votes
1
answer
841
views
How to Use Convolution Theorem to Apply a 2D Convolution on an Image
How do I actually apply the convolution theorem? I have my fourier transformed image matrix, and a Fourier transformed kernel, but how do I actually multiply these together to achieve the intended ...
- 71
4
votes
2
answers
1k
views
Understanding the Bilateral Filter (Image Filtering)
I asked this question already on StackOverflow and was told to ask it here instead, so I will just copy the content of my question.
I do understand the general concept of bilateral filtering and I did ...
4
votes
1
answer
189
views
How to Solve the Image Dehazing Problem Using ADMM?
I want to solve the image dehazing problem using ADMM.
I want to use the proximal algorithm to optimize each element.
I refer to this treatise: Efficient image dehazing with boundary constraint and ...
0
votes
1
answer
328
views
How to Solve Blind Image Deblurring with Total Variation (TV) Prior Using ADMM?
As a continuation of the question How to Solve Non Blind Image Deblurring with Total Variation Prior Using ADMM? I would like to understand how could one solve the Blind Deblurring (Deconvolution) ...
- 387
4
votes
1
answer
662
views
How to Solve an Image Deblurring Problem by Variational Methods Using ADMM?
Following up on a previous question, I wanted to understand how to solve an image deblurring problem using Variational methods in matlab or julia.
Given some original blurry image $f$, I would like to ...
- 257
2
votes
1
answer
370
views
How to Solve Non Blind Image Deblurring with Total Variation Prior Using ADMM?
How could one use the Total Variation frame work to solve the Deblurring problem?
Specifically using the ADMM as a solver.
One could assume the blurring operator is known, linear and shift invariant.
...
- 387
1
vote
1
answer
143
views
Different "zoom" after reconstruction from Radon transform using Fourier Slice Theorem
I have implemented the procedure to reconstruct an image from its Radon transform involving the Fourier Slice Theorem (FST). After application of the FST, the data is transformed from polar ...
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6
votes
2
answers
2k
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How to Solve Image Denoising with Total Variation Prior Using ADMM?
I was looking at some articles or Wikipedia on denoising images using the Total Variation norm. The setup is the Rudin Osher Fatemi (ROF) scheme, and the corresponding equation is:
$$
F(u)=\int_{\...
- 257
5
votes
1
answer
945
views
Replicate MATLAB's `conv2()` in Frequency Domain
When conv2d is on same mode, the image needs no padding, because the result is the same size as the image.
When ...
- 53
2
votes
2
answers
531
views
Simple Image Edge Preserving Filter
I am after a simple, yet effective, Image Edge Preserving Filter.
I need something which is faster than the Bilateral Filter with similar quality (The Guided Filter isn't good enough).
Are there such ...
- 144
5
votes
2
answers
1k
views
How to Calculate Local Spatial Variance of an Image?
For those who work often on image processing, I'm facing an algorithm of Non-Uniformity Correction (NUC) that requires the calculation of a parameter called "Local Spatial Variance". I can't ...
- 53
0
votes
1
answer
56
views
How up sampling of a signal is done in real world?
I know that up sampling by L means padding L-1 zeros between each samples. My question is how it is done practically? Do we use MATLAB or any other software, or there are hardware circuits to do so.
0
votes
2
answers
371
views
Filter for DC component in FFT2 of image
I am trying to get the main frequency of the Fourier Transform of the image below, which is the intereference pattern detected by a CMOS sensor.
When I apply fft2, I got the DC peak at 0 frequency, ...
- 3
0
votes
0
answers
53
views
Several Questions Regarding Color Space Representation
As part of my seminar, I have to make a full representation on the many color spaces. I took a deep dive in the internet and on YouTube and managed to gather a lot of information. BUT I have a few ...
- 9
4
votes
1
answer
409
views
Tile Laplacian Filter in MATLAB
I want to compute the output image by first dividing the image into 8*8 blocks and applying laplace filter separately and combine them but I am not getting the correct output
Here is the code:
...
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-1
votes
1
answer
248
views
How to find a pixel's image coordinates by its rgb value in MATLAB? [closed]
How would one find the pixels that match an RGB value in a matrix in MATLAB?
Let's suppose that I want to find the image coordinates of pixels whose value is $RGB=(144,127,11)$ for a given image in a ...
0
votes
1
answer
677
views
Generate an Ideal 2D Low Pass Filter in MATLAB
I've been tasked with creating a 32 x 32 half-band low-pass image filter in MATLAB. My thinking is to generate the ideal filter mask in the frequency domain and compute the corresponding convolution ...
- 912
0
votes
0
answers
48
views
N, N-Discrete fourier transform
What is $N$,N-point Discrete fourier transform? Is it different from 2D Fourier transform?
and how to compute $N$, N-point Discrete Fourier Transform of a given laplacian filter kernel? say for a ...
- 9
3
votes
2
answers
1k
views
Applying Circular Cross Correlation in MATLAB
I have searched Google for circular cross correlation using Matlab, and I have found it only for one dimensional signals.
Could you please help me implementing circular cross correlation between two ...
- 349
6
votes
1
answer
666
views
Image Restoration by Solving Constrained Least squares in Frequency Domain (Frequency Domain Filtering)
I am trying to implement the constrained least squares filtering as described in Rafael C. Gonzalez, Richard E. Woods - Digital Image Processing 3rd Edition Section 5.9. The equation (...
- 163
4
votes
1
answer
2k
views
Applying 2D Image Convolution in Frequency Domain with Replicate Border Conditions in MATLAB
I have created a function that filters an image (250x250) with a gaussian blur kernel (5x5) using FFT and IFFT. I am trying to get my filtered image to equal exactly the filtered image created by the '...
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