The Stack Overflow podcast is back! Listen to an interview with our new CEO.

Questions tagged [2d]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
0
votes
0answers
9 views

What are the Red-Black Wavelets transformation for color (RGB) images?

I am looking for Red-Black Wavelet transform implementation on internet but I am unable to find it. Or How wavelets can be used for Images. Please help if you know how wavelets can be used for images.
4
votes
1answer
195 views

Efficient implementation of 2-d circularly symmetric low-pass filter

How can a two-dimensional ideal circularly symmetric low-pass filter or its approximation be efficiently implemented on data sampled on a square grid? I'm referring to an ideal filter with a spatial ...
0
votes
0answers
9 views

2D Fourier Synthesis (IDFT) not yielding expected result

I am trying to recover a 2D signal using inverse DFT, to my understanding the IDFT outputs the coefficients of the fourier series of the original function up to the Nyquist frequency. So for example ...
1
vote
2answers
144 views

Zero padding and 2D Fourier transforms: how does zero-padding affect phase?

It's pretty clear that zero-padding an image before performing Fourier transform simply enlarges the magnitude image (stretching it to the new, padded size). What I can't understand is how it affects ...
0
votes
0answers
22 views

Overlap-Add for 2-dimensional windows

I understand how overlap-add works for 1-dimensional signals, but I need to do something similar in 2 dimensions. The paper at this link covers the 1D case pretty well (see p29): http://edoc.mpg.de/...
0
votes
0answers
91 views

Adaptive Clip Limit on CLAHE

I am working on CLAHE algorithm in order to contrast enhancement. I try to find best clip value to get best result image. However, each input image desires different clip value. Therefore, I need an ...
1
vote
1answer
79 views

Compute the two-dimensional DFT

Compute the two-dimensional DFT [4x4] for the following 4x4 image $ \begin{matrix} 0.5 & 0.5 & 0.5 & 0.5 \\ 0.5 & 0.5 & 0.5 & 0.5\\ 0.5 & 0.5 & 0.5 & 0.5\\ ...
0
votes
0answers
168 views

Use 2D FFT to replace 2D Discrete Fourier Transform (MATLAB)

I met a problem. I ran a code to implement the 2D discrete Fourier Transform, here is the code: ...
0
votes
1answer
266 views

Scale Image by using FFT

Can we change the scale of image by using FFT? I mean, how should i do process on frequency domain of image to upscale or downscale the orginal image? The other question of mine is that how can ...
1
vote
1answer
243 views

How to represent impulse function in 2D?

To be more specific I want to show that impulse function in 2D can be represented as $β(r)=δ(r)/πr$. Also I want to show that each projection of a two dimensional impulse function at the origin is a ...
0
votes
0answers
97 views

Resampling or interpolating non-uniform 2D measurements

I am not sure what I should call what I am looking for, but I have some measurements that have 2 independent variables and I would like to get an interpolated value at a specified x,y coordinate. My ...
1
vote
1answer
976 views

How does MATLAB recover picture from magnitude spectrum alone?

This is the transformation I did. The code fft2() the Lena picture than ifft2() it back to the original. Add some ...
1
vote
1answer
50 views

On the symmetry of a $2$-dimensional discrete-time signal

Can we distribute the minus sign as follows? $$-h[n_1,n_2] = h[-n_1,-n_2]$$
4
votes
1answer
403 views

2D Convolution in MATLAB Causes Artifacts (Boundary Issues)

I`m trying to do a 2D fast convolution in Matlab of large matrices. If I use FFT version based on convolution theorem ( https://en.wikipedia.org/wiki/Convolution_theorem ), there are some artefacts in ...
1
vote
0answers
102 views

Choice of axes in 1D cross-correlation of a signal in a 2D space

I am working on a research project in which we present an observer with a target moving in a random walk in a plane in front of them, and record the eye movements they make to track it. We cross-...
1
vote
0answers
30 views

Efficient format for 2D signal?

I'm trying to solve the following problem. I got a "low frequency" input 2D signal over a square region. I'll collect a few samples, somewhere around 10-30 maybe, the exact sample count will be ...
2
votes
1answer
380 views

Understanding 2D FFT result of an image having a pattern

I have created Fast Fourier Transform (FFT 2D) of the following image (without pattern angle markers) using ejectamenta online tool. Input (Original image is here) Output I got is the following As ...
0
votes
4answers
1k views

MATLAB phase of 2D rectangular pulse's Fourier transform

I'm trying to plot the graph of the phase of the Fourier transform of a 2D rectangular pulse. I've been able to evaluate the FFT but I'm not sure if the phase is correct because there are some tilts I ...
0
votes
1answer
45 views

A PID that can handle 2 inputs for my application

I am currently working on a Drone that navigates to different points that it detects on the ground. To go from one point to another in a smooth manner, I am employing a PID looks at the error between ...
0
votes
1answer
312 views

Linearity and shift-invariance of 2-D system on lattice

I know how to check a 1-D system for these conditions, but am confused about translating this to a 2-D system over a lattice. The system $H$ is define as: $$w[\mathbf x] = H\left\{u[\mathbf x]\right\}...
1
vote
2answers
42 views

Why does this plot correspond to this function?

I have a function: $$ u_1(\mathbf{x})= \begin{cases} 1, & \text{if} \;\;|x_1|\le r_1, |x_2| \le r_2 \\ 0, & \text{otherwise} \end{cases} ,\mathbf{x}=[x_1,x_2]^T \in \mathbb{R}^2 $$ And I'm ...
2
votes
0answers
4k views

Calculate 1D Power Spectrum from 2D Images

Imagine satellite images, these are irregular sampled in X and Y direction and the shapes are of course are oddly off. We now want to estimate a 1D power spectrum from the whole image to estimate the ...
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, ...
1
vote
2answers
236 views

Easy way to get rid of noise in a hand drawing

I would like to take a user's hand drawn input, and filter out "noise", aka small sketches or blobs, where the user might have screwed up and accidentally touched his hand to the drawing device, or ...
2
votes
2answers
1k views

Finding an Image's Orientation With DFT Frequency Amplitudes

I'm looking to get some general idea of an image's orientation so that I can then rotate it to the nearest 90 degree angle. My idea on how to do this is to take the DFT on the image, then do a "radar ...
0
votes
1answer
143 views

How to show Image FFT with origin as DC?

The page Here explains how to do the discrete fourier transform on a 2d image. It mentions this: In most implementations the Fourier image is shifted in such a way that the DC-value (i.e. the ...
-1
votes
1answer
3k views

Deconvolution in Python in 2D

Referring to this topic, I am interested in a deconvolution using Python. However, unlike the linked topic above, I want to deconvolve a 2D image. The scipy.signal.deconvolve function unfortunately ...
-1
votes
1answer
137 views

Is the system $L\{f[m,n]\}= c[m,n] f[m,n]$ shift invariant?

$c[m,n]$ is the spatially varying gain. My prof says that its not shift invariant. However if we put $m=m-k$ and $n=n-l$ we get $c[m-k,n-l] f[m-k,n-l]$ which is how a shift invariant system should ...
0
votes
1answer
181 views

Is a cubic Lagrange interpolation tensor product the same as bicubic interpolation?

I just implemented some interpolated texture sampling by sampling the 4x4 nearest pixels then doing Lagrange interpolation across the x axis to get four values to use Lagrange interpolation on across ...
1
vote
0answers
172 views

Singularity Detection from 2D Wavelet Modulus Plot

I was wondering if I could get some tips/resources on how to pick out the singularity from my 2D Continuous Wavelet Transform Coefficient Plot (scalogram) using the Gaussian Derivative as the mother-...
0
votes
2answers
132 views

Has this 2D filter for enhancing circular dots in images a name?

I came across this 2D filter for enhancing circular dots in images, for example to enhance a dot with a diameter of 5 pixel, the filter is: $\frac{1}{336}\left( \begin{array}{ccccccc} 0 & 0 &...
0
votes
0answers
49 views

Inferring space domain signal from 2D DFT

By just looking at the 2D Fourier Transform of a signal, can it every be known precisely which values in the space domain are zero?
0
votes
0answers
62 views

What is the 2D Fourier Transform of this function?

$ f(x, y) = \begin{cases} 1,\hspace{30px} x > 0 \\ 0,\hspace{30px} else\\ \end{cases} $ i.e. $f(x,y)$ is a bi-variate function which is zero everywhere to the left of the y-axis and one ...
0
votes
1answer
94 views

2D IIR filter design (x-axis width proportional to y-axis)

I want to design a 2D IIR filter (that is, created line-by-line progressively, in this case from left-to-right). What is the best way to go about this? I would like the response to look something ...
0
votes
0answers
709 views

Distinguish between 2D and 3D objects according to depth

I'm trying to distinguish by code between a real 3D object and its picture - a 2D object, based on depth information. However the picture (= the 2D image) might be captured from noisy background, so I ...
0
votes
1answer
312 views

Fast/efficient way to compute Laplacian edge enhancement filter

I would like to implement a somewhat smarter Laplacian edge enhancement convolution. Right now it is implemented as (generic 3x3 convolution): ...
1
vote
2answers
1k views

Working with the DCT

I am having a very hard time to implement the DCT algorithm. I have quite a few requirements like it has to work with NxN matrix or at least power of 2, it has to be 2D, it has to produce same output ...
3
votes
2answers
1k views

Laplacian Operator with and without Diagonal Direction Elements in the Kernel

This is a general question on the laplacian operator, which has two different versions. The first version is : \begin{matrix} 0 & 1 & 0 \\ 1 & -4 & 1 \\ 0 & 1 & 0 \end{...
1
vote
3answers
3k views

[2D fourier transform]: Most people can't explain this

I am confused with 2d magnitude plot of frequency spectra. So we have 2 images, the first one is shown at the top, and the dilated or enlarged version of the white box is shown at the second row. ...
-1
votes
1answer
959 views

FFT on XY data points [closed]

Are there any algorithms out there that can do a FFT of 2D or XY data (not sure of the exact terminology here), I don't mean XY data like in a graph I mean XY/2D data points like a circle or a smiley ...
2
votes
1answer
761 views

Image 2D Real Cepstrum with DFT, Is `ifftshift` Needed?

This is my testing image,it is taken from this paper: I tried to transform it into its real cepstrum domain with this simple MATLAB code: ...
2
votes
2answers
8k views

2D Deconvolution in matlab

I am trying to solve the following equation for h (an [MxM matrix]): $$ k[\tau_1,\tau_2]=\sum_{i_1=0}^M \sum_{i_2=0}^M h[i_1,i_2]x[\tau_1-i_1]x[\tau_2-i_2] $$ I have k, which is a 2D [MxM] symmetric ...
0
votes
2answers
2k views

partial derivative of image

I have to find the partial derivative of an image with respect to its x dimension. I am using central difference method i.e $ \partial_x F(x) = \frac{F(x+1,y)-F(x-1,y)}{2} $ Here $F(x,y)$ ...
0
votes
2answers
174 views

How do I implement the CDF wavelet inverse?

I understand and have implemented a 2D discrete wavelet transform that uses a Haar wavelet to process images. Now I would like to implement a 2D Cohen-Daubechies-Feauveau wavelet transform, but I am ...
3
votes
2answers
4k views

How do you interpolate between points in an image (2D), e.g. using splines?

I can understand just fine how to use 1-dimensional interpolation on data points where one coordinate is a function of the other: y = f(x). However, when we have an ...
0
votes
1answer
96 views

Two-dimensional wavelet analysis

Could you tell me why wavelets without scaling functions can't be used for two-dimensional analysis? What is the role of scaling function?
2
votes
0answers
130 views

Upsampling Methods for Computed-Tomography

I have two sets of data of given Field of view, one of them only covers a subset of the FOV of the other. I therefore want to upsample the one with the larger FOV to combine it with the other one. So ...
5
votes
1answer
1k views

2D adaptive filters

Does anyone know about different adaptive filtering implementations (LMS, RLS ...) in 2D or even 3D ? I have sequences of 2D images and 3D volumes with repeating patterns but small differences. I was ...
6
votes
1answer
618 views

Data fusion using 2d discrete wavelet transform (DWT)

I am working on a project that employs a linear array sensor that provides data from the same object at two different energies. Collected in time, I end up with two images (16-bit sensor values, MxM ...
3
votes
2answers
713 views

2D FFT of Vector

I have a bunch of 8x8 images which have been vectorized and formed into a 64xN matrix, X. I'd like to take the 2D-FFT of each of these images without reshaping each column of X into an 8x8 image and ...