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Questions tagged [interpolation]

Interpolation is a method of constructing new data points within the range of a discrete set of known data points.

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58 views

Drawbacks of upsampling using polynomial interpolation

I've come across an upsampler that uses polynomial interpolation and no filter. What are the drawbacks to this? I looks more efficient than filtering.
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Different images between MATLAB and ImageMagick

I'm using ImageMagick 7.0.8-64 Q16 for Windows and MATLAB R2019. I'm doing the same operation (resizing with bicubic interpolation method) in both programs. ImageMagick code: ...
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O-MOMS3 interpolating function?

I've been reading the following paper on a B-spline based interpolation technique: https://pdfs.semanticscholar.org/fd55/61d561fa2bf1124959cba0d4abfd5d81a784.pdf The paper derives the so-called O-...
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Why zero padding the 2-d DFT interpolates images in spatial domain?

I was applying different image interpolation techniques and I came know to about interpolation in frequency domain. In this technique we first take 2d DFT of an image, padd it with zeros and take the ...
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51 views

Purely theoretical question about idelal filters and infinite oscillations

I am asking perhaps a naive question, but still, it would be nice to have this formally stated one time: in theory, if we could do it (of course, we cannot, but imagine we could), if we could ...
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31 views

Interpolation FIR filter Remez design criteria

I want to upsample an audio signal by a factor of 8. The technique I was going to use was to upsample by zero stuffing and then interopolate using a low pass anti-aliasing FIR filter designed using ...
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1answer
59 views

Why does my sinusoid look “AM” in shape?

My code is : Fs=200e6; Ts=1/Fs; NFFT=2^14; Runtime=(NFFT-1)*Ts; t=0:Ts:Runtime; f_in=90*1e6; y_in=sin(2*pi *f_in *t); plot(t,y_in) ylim([-1.5 1.5]) Then why does ...
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1answer
26 views

Linear interpolation formula

In the following lecture: http://www.ece.mcmaster.ca/~xwu/interp_1.pdf the model (formula) for solving the linear interpolation problem (1D) given at p.5 is: $f(x)= a_1x_1 + a_0x_0$ solve for $a1,...
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122 views

Sinc interpolation in spatial domain

I have tried to perform sinc interpolation (in 1D) with the following Matlab code: ...
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1answer
43 views

Estimation / Reconstruction of an Image from Its Missing Data 2D DFT

Given the 2D DFT of an image i.e. a NxM matrix of complex numbers, with some missing lines (or even partial lines), considering we have zeros in the missing positions. Any suggestions for an ...
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1answer
57 views

Why would FFT interpolation using zero-padding undershoot the true frequency of a single tone sinusoid?

Why would FFT interpolation by zero-padding or using the Chirp Z-Transform produce a maximum at a bin that corresponds to a frequency less than the input frequency of a single tone sinusoid? I am ...
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The annihilating filter-based low-rank Hankel matrix approach (ALOHA) for conpressed sensing

Can someone give an intuition about the annihilating filter-based low-rank Hankel matrix approach (ALOHA) for compressed sensing approaches ? It is for an MRI problem of k-space interpolation, i.e., "...
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1answer
59 views

Design of efficient digital interpolation filter

I came across this paper entitled "Design of Efficient Digital Interpolation Filters and Sigma-Delta Modulator for Audio DAC" where the author oversamples an input frequency, fsig = 1kHz with ratio L =...
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51 views

Multi-stage interpolation [closed]

So I've read here Multi-Stage digital FIR filter vs Single stage FIR filter. Which is better? if you want to interpolate by a great number, it's always better to do so in multi-stage interpolations so ...
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How to draw a smooth spectrum from a discrete array of measurements at selected frequencies?

I have a AS7265x triad spectroscopy sensor from SparkFun (link) which gives me measurements at 18 individual light wavelengths between 410nm and 940nm. The datasheet says that the FWHM of each sensor ...
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3answers
129 views

Resampling and removing high frequency noise?

I am currently working on a simple sampler that will allow me to load in a wav file and use my MIDI keyboard to play the loaded wav sample at the frequency according to the note played. Now I need ...
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1answer
17 views

Given local responses by a bank of equally spaced (log-)Gabor filters, how can we estimate the response of an intermediate-scale filter?

Consider a grayscale image convolved with a bank of 2D wavelet quadrature pairs – in my case, log-Gabor filters. I have eight filters. For simplicity, let's say they are all vertically oriented, and ...
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130 views

Optimal trade-off between oversampling and filter length

For some sampling-frequency-preserving operations on Nyquist–Shannon sampled signals, such as: a shift a.k.a. translation, and differentiation by applying a derivative filter a.k.a. gradient filter, ...
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1answer
27 views

Method to rescale signals to mean length

I have a set of signals of varying lengths. I have provided an example of the same below - Their lengths vary between 186 to 202, with a mean length of 197. I am looking to rescale them to the mean ...
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1answer
67 views

Side Lobes in the Magnitude Response of a Low Pass FIR Filter

I have the impulse response (from the filter coefficients) of an FIR filter obtained from MATLAB's "interp" function using the command: [y, b] = interp(x, 5); % where b contains the interpolation ...
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20 views

How can single low-resolution have multiple high-resolution versions?

I'm trying to prove the fact that the super-resolution problem is an ill-posed problem. Having a single low-resolution image, we can generate multiple high-resolution images. Which also known by ...
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1answer
83 views

Frequency Domain Interpolation: Convolution with Sinc Function

I am reading a paper, and I came across the following definition of sinc interpolation. Warning. I don't have a strong background in signal processing. Also, I have no clue what that bar on $\bar{F}$ ...
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Sparse to Dense Flow

I'm trying to upgrade a flow from sparse to dense and have been recommended this for my use-case https://uk.mathworks.com/matlabcentral/fileexchange/25634-smoothn . When I run the interpolation, ...
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2answers
97 views

Sinc interpolation of pure sine wave sampled just at Nyquist frequency

Following this question: Shannon-Nyquist theorem reconstruct 1Hz sine wave from 2 samples could you explain the algorithm to apply for sinc interpolation to avoid the "sawtooth" effect due to linear ...
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389 views

Absolute convergence of periodic sinc interpolation

An $N$-periodic complex discrete-time sequence $[x_0, \dots, x_{N-1}]$ can be resampled to an $M$-periodic sequence $[y_0, \dots, y_{M-1}]$ with $M>N$, using sinc interpolation: $$\begin{align}y_m ...
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1answer
83 views

Why does downsampling stretch a signals frequency response and upsampling shrink and create images of a signals frequency response?

I am learning some basic DSP and I have a pretty good intuition as to why sampling creates spectral images of the frequency response at intervals of the sampling frequency (convolution with pulse ...
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20 views

How to calculate splines of different order under MATLAB?

I am trying to compare spline interpolation of different order to show that Cubic is working better. Is there any toolbox or so to spline interpolate points between knots?
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1answer
188 views

Omega-K algorithm implementation for synthetic aperture radar

I have been trying to develop Omega-k algorithm for SAR image formation. I am using the equations from chapter 8 in digital processing of Synthetic Aperture Radar data by Cumming and Wong. The steps I ...
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0answers
63 views

How to get an interpolation weight from a mathematical definition

It was recently explained to me that a "Nearest neighbor" kernel for 1D interpolation can be implemented like this using NumPy ...
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1answer
25 views

Estimate gap between two adjacent images

I have two images of a panoramic view but there is a small gap (<24 pixels) in the horizontal dimension between them. I would like to do interpolation/inpainting to fill the gap, but the exact size ...
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2answers
94 views

Interpolation and harmonics

A real valued causal sequence $x1[n]$ exists with length of the sequence being $N$. Valid indices of x conform to $0 \le n \le N-1 $ The DFT of x[n] is: $$ X1[k] = \sum_{n=0}^{N-1} x1[n].e^{-j.2.\...
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5answers
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Multi-channel audio upsampling interpolation

I have a four-channel audio signal from a microphone tetrahedral array. I wish to upsample it from 48 kHz to 240 kHz. Is there a preferred interpolation method for audio? Does cubic ...
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25 views

delayed result in sinc upsampled signal

I have implemented an infinite kernel sinc interpolation. For some signals I notice an artifact, visible at the right end of the plot. I am wondering: is it a bug in my code or a phenomenon usual for ...
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2answers
335 views

What Does 'Zero Order Hold' and 'First Order Hold' Mean?

While studying the Image Magnification in spatial domain, I have come across this definition of Image Magnification by Replication: Replication is a zero order hold where each pixel along a scan ...
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79 views

Alignment of 2 Set of Samples from Different Sensors

If we measure the heart rate of a subject with two different devices, which have big different sampling rates then how we can compare their outcomes. For instance, one of the devices has the sampling ...
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131 views

signal interpolation (upsampling) by factor 2

The task is to interpolate the signal by increasing the sampling rate by factor 2. Matlab has a dsp.FIRHalfbandInterpolator function. Let's try using it. ...
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1answer
197 views

Extrapolate a 2D array using Fourier Transform

I need to extrapolate a given 2D array to a larger domain, keeping the spatial frequency. This is the original field: (the data file in numpy npz format and a Jupyter notebook to plot it can be found ...
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40 views

Zero padding frequency domain data for improving time domain resolution before inverse FFT

I am working in MATLAB with measured data from a VNA. The bandwidth is 1 GHz from 5-6 GHz with 801 samples in the frequency domain. Everywhere I have read that I need to split the data into 2 parts at ...
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1answer
54 views

What's wrong with this Whittaker-Shannon-Kotel’nikov interpolation implementation?

I tried to implement Whittaker-Shannon-Kotel’nikov interpolation formula but I get unexpected results: the reconstructed signal lags with respect to the original. I know that I can not expect a ...
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1answer
131 views

difficulties implementing windowed sinc interpolation (C++)

I'm currently trying to implement a windowed sinc interpolation. I've already written some code for that, but it only seems to work for cases where phaseInc <= 1.0 (phaseInc = outSampleRate / ...
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2answers
131 views

Frequency response of numerical differentiation by polynomial interpolation / finite difference

One can use polynomial interpolation (or finite difference) to do numerical differentiation. However, there seems to be a surprising lack of interest in obtaining frequency response of this numerical ...
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1answer
105 views

Isosurfaces from three dimensional column data: methods

I have just been asked the following question, and I somehow felt short of smart answers. You are given a series of $N$ triplets of values ($P_1$, $P_2$, $P_3$), pertaining to physical measurements. ...
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2answers
107 views

Interpolation of audio for new frames

I am trying to upsample a video by existing frame interpolation techniques. In the process, I realize that I also need to interpolate the audio signal for the new frames so that the audio signal is in ...
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1answer
143 views

Upsampling signal using convolution-based interpolation filters

I am currently reading this paper which discusses several image interpolation methods, such as nearest neighbor and linear interpolation, using convolution filters. I first want to do this in 1D with ...
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1answer
66 views

Having Glitches trying to use a Sinc Function Interpolation on a Signal, by chunks of 1024 samples

I am trying to interpolate a signal using a third party lib that performs Sinc Function Interpolation on a signal. It works well if I input all the samples at once but introduce phase distortion if I ...
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1answer
131 views

Why is interpolation a time varying system

I was reading about interpolation (Interpolation and Decimation of Digital Signals - A tutorial Review, Ronald E. Crochiere) and found that Interpolation filter is a time varying system. Can someone ...
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1answer
48 views

Interpolation of missing audio signal in a video sequence

Suppose there is a video sequence and there are some frames for which the audio data is missing. I want to interpolate the missing audio data on the basis of the correlation of the audio signal with ...
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1answer
586 views

Bilinear interpolation implemented by convolution

I read the paper Deep Feature Flow for Video Recognition https://arxiv.org/abs/1611.07715. In Sec.3, the author implements bilinear interpolation like this: $$f_i^c(p)=\sum\limits_{q}G(q,p+\delta p)...
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285 views

Low pass filtering of an upsampled(zero inserted) signal

I have been working on interpolation in python from quite some time. The input signal is a sinusoid signal sampled at 933KHz. I am upsampling the signal by a factor of 5 and later using an FIR ...
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415 views

Implementation of a Variable Fractional Delay with Lagrange Interpolation using Farrow Structure

I am writing a C++ simulation software working in time domain. I generate regularly sampled data, and need them to be delayed, in "real-time", by a variable fractional delay. This is a pretty common ...