All Questions

1
vote
1answer
46 views

Mathematical description of the ACF using fft2

I computed the acf of an image with the following code: ...
1
vote
1answer
50 views

Histogram of Gradient

I was calculating which would be faster in computation, Inverse Fast Fourier Transform or Histogram Of Gradient but I am unable to calculate its running time. What would be the running time of ...
7
votes
1answer
2k views

Scanning from Book - Gradient Removal

This sample image: is warped on the left side. I don't want to dewarp, but just to remove shadow gradient (caused by book's spine). I guess gradient can be calculated from upper part of the image ...
0
votes
1answer
3 views

The Gradient of 2D Image Convolution

Given the objective function: $$ \frac{1}{2} {\left\| h \ast x - y \right\|}_{2}^{2} $$ Where $ h $ is the 2D convolution kernel and $ x $ is the 2D convolution image and $ y $ is a given 2D image. ...
0
votes
0answers
2 views

How many ways are generally used for Image segmentation using Image processing?

I want to segment an image and extract very small specific area using image processing without using machine learning. Most of the time I used color based segmentation using thresholding. but it is ...
0
votes
1answer
167 views

Convolution in Image Processing

Does anyone know how to write arg min code in matlab with explanation? I am referring to a paper for my research. I am not sure whether I can paste the paper link here. At first, I try to do feature ...
2
votes
1answer
138 views

Wiener Filters - Obtaining /Estimating Image and Noise Spectrum

We all know the famous Wiener Filter, $$G(\omega_1 , \omega_2)=\dfrac{H^*(\omega_1 , \omega_2)}{|H(\omega_1 , \omega_2)|^2 + \dfrac{N(\omega_1 , \omega_2)}{S(\omega_1 , \omega_2)}}$$ How to we use ...
6
votes
1answer
230 views

Analytical Expression for Convolution of Two 2D DFTs

I am trying to do an image analysis problem on some images, and I want to calculate some things in the frequency domain which are giving me problems. Say I have an (discrete) image $I(x,y)$ of size $...
0
votes
2answers
39 views

Image Brightness on 2D Fourier Transformation

What effect does the brightness have on the frequency spectrum of 2D Fourier Transformation? Example. Suppose we have a gray image and calculate 2D Fourier Transformation. Then we increase the ...
2
votes
1answer
1k views

Convolution Based Image Interpolation

From a book, I learned that image interpolation (or upsampling) can be written as a convolution like this: $$g(i,j) = \sum_{(x,y)}f(x,y)h(i-rx,j-ry)$$ while $r$ is the upsampling rate. But I have a ...
1
vote
1answer
2k views

Convolution in Image Processing?

I got the concept of Convolution in signal processing from a video lecture that it is method to get the area overlapped between two signals when one signal is flipped over and traversed over another ...
2
votes
1answer
239 views

Algo Name: Detecting Elongated Shape in 2D Image by Convolution with Directed Lines

I am detecting a shape with roughly known orientation (obtained by using Hough line transform) in thresholded binary image by convolving the image with line with that orientation, and counting the ...
1
vote
1answer
463 views

How to Do Convolution a 2D Signal (Image) and Result of Convolution of Two 1D Filters?

Assume a 2-D signal (i.e., some image). Load image and assume it to be signal x. Next assume that instead of having a 2-D filter you have two one D filters $$f_1[n] =\begin{bmatrix}0.25 && 0....
1
vote
1answer
131 views

Detection Algorithm in 2D Images

Suppose there is a two-deimensional image which consists of pixels. In every pixel, there are 0 to n apples with different colors, which can be digitalized(e.g.[0,10000]). So we can plot a histogram ...
0
votes
2answers
105 views

Generate 3D image from Multiple 2D Images

If we're to capture an image of a body using four (4) WebCam with a 16 megapixel (1 in the front, 1 in the back and 2 sides(left and right)). Is it possible to make a 3D out of it using image ...
17
votes
3answers
7k 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 ...
2
votes
1answer
164 views

Morphological Gradient Versus Linear Gradient in Image Processing

To obtain the gradient from an image, one can use a linear filter that for example is derrived from the derrivative of a gaussian. Then convolving the image with this linear filter gives you the ...
0
votes
1answer
465 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 ...
1
vote
1answer
2k views

What Does It Mean by Gradient / Divergence / Curl of a 2D Image $ g \left( x, y \right) $?

Suppose, a 2D image is represented by g(x,y). Then, what does it mean by "Gradient of g(x,y)", "Divergence of ...
1
vote
2answers
12k views

How to Compute Image Gradients?

How to compute Image gradients? In X Direction - Kernel : -1 0 1 In Y Direction - Kernel : -1 0 1 Let's assume my input image is: unsigned char* imgImage; ...
4
votes
1answer
374 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 ...
0
votes
1answer
2k views

Convolution and Cross Correlation on 2D Image

I have read that convolution and cross-correlation are the same thing, but convolution flips 180 degrees (images), or time reverses (sequences) the kernel, before performing the elementwise ...
0
votes
0answers
8 views

Cross Correlation as Noise Reduction, is this possible?

If I have two sensor measuring the same signal but from two different locations from the source, and I get two different readings of the signal, each with slightly different noise. Is there a way to ...
0
votes
0answers
6 views

Optical flow Horn & Schunck smoothness error

I was reading about the Horn & Schunck method and they define the smoothness error as (Robot Control 1988 (SYROCO'88): Selected Papers from the 2nd IFAC Symposium p. 348): $E_{sm} = \iint{\left(...
0
votes
0answers
3 views

What are i-vectors and x-vectors in the context of Speech Recognition?

I have read that i-vectors and x-vectors are widely used in speaker recognition tasks but I don't get the difference between them and how exactly they work. Can someone explain it starting from the ...
0
votes
1answer
43 views

How to get Fourier coefficients to draw any shape using DFT?

I'm teaching myself about Fourier Series and the DFT and trying to draw a stylised $\pi$ symbol by fourier epicycles as detailed by Mathologer on youtube (from 18:39 onwards). The goal is to generate ...
0
votes
1answer
90 views

What is the meaning of inverse signal bandwidth?

I have been studying the two ray model in communication systems. The text I'm studying has two signals, $u(t)$, which is Line of Sight and $u(t-t')$, which is the reflected signal. It quotes, ...
1
vote
0answers
7 views

Role of Riccati Equations in Kalman Filter Design

I am working on a Kalman Filter (KF) design problem and I am struggling to understand the role of the Riccati equations in the design process of a KF. Some sources discuss the importance of Riccati ...
0
votes
0answers
5 views

Papers/ guidance on the practicality of converting quantization steps (pixel) into phase adjustment (frequency) for CMOS images

In this older question How does subpixel image shifting using DFT really work? 2013, there is a clear answer which explains that the ability to sub-pixel shift (frequency domain) depends on the ...
0
votes
1answer
56 views

Fourier like spectral analysis with uneven intervals and redesigned DFT matrix

I intended to use a discrete Fourier transform (DFT) on a time series sampled at uneven intervals. What I did was to calculate a DFT matrix where the elements are the values at the uneven locations ...
0
votes
1answer
29 views

Notch filters: why is R(0) = R(π)?

I'm studying for the final exams and many example exercises require to design fir notch filters of length 5, given some passband and some stopband frequencies. You'...
0
votes
0answers
11 views

How to find out that a wav file is edited or original in Python?

I want to verify that if a audio (.wav or any format) file is original or edited. How can it possible in python? For example, for an investigation purpose I get a audio file for an evidence. I want ...
2
votes
2answers
80 views

Is there a rule of thumb for zero padding in image processing?

I see there are a lot of answers on why zero padding is necessary and how it avoids wrapping around the sides of images. However is there a rule of thumb on how much padding will be good for the image ...
0
votes
0answers
15 views

Window function correction when using frequency domain likelihood

I was wondering if someone could tell me or point to resources which discuss what kind of of windowing corrections factors one should use when using a frequency domain Whittle likelihood for spectral ...
0
votes
0answers
13 views

Can we band pass filter QPSK signal?

Consider we have QPSK signal with carrier frequency 10kHz. Generally, we demodulate or use matched filter on the the QPSK signal and recover the transmitted bit or the symbols. If the QPSk signal is ...
0
votes
1answer
20 views

Subtract audio to another audio

suppose I have a sample of a snare and that snare is used in a song,¿ there is an algorithm or tool that detects the sound of the snare and subtracts it, that is to say that cancels its phase or ...
1
vote
1answer
16 views

What impact have different types of border-handling on high pass or low pass filtering?

When high or low pass filters are being applied to an (grayscale) image, the borders need to be handled separately. They could be filled with 0's or 255's (b/w), repeat the nearest pixel value, or ...
0
votes
2answers
36 views

Nulling odd samples of the FFT of a signal

Given X is a N point time domain sequence, let F be the DFT of X. Let Z be a new sequence of length N formed by setting all odd samples to zero. The even samples of Z are equal to the even samples of ...
0
votes
0answers
10 views

Early estimate the sign of the drift in a generalized Wiener process

I posting here my problem, perhaps somebody can point me how to proceed further :) [The challenge] I have an electronic system that can be modeled as a Wiener process with a drift $\mu$: $ X_t = \...
1
vote
1answer
35 views

Find the noise settings to reproduce it

I work on images that contain shot noise (Poisson) acquired from a microscop. On few images, I have a "flat" zone that is supposed to have the exact same intensity, but it's not because of the noise. ...
-2
votes
0answers
22 views

How can I prove this properties of Auto correlation? [on hold]

Plz mention assumptions taken while prove separately. There are also few queries I have regarding this formula 1.I have read But shouldn't value of auto correlation at infinity be minimum , but ...
-1
votes
0answers
14 views

What is definition of cross correlation function?

I mean there are three different formulas for cross correlation that I have studied f and g are two functions whose correlation has to be found 1.For Energy signals 2.For Power signals 3.For ...
0
votes
1answer
29 views

What principles to use, in order to create field that will be read by OCR?

I currently have an invoice, where some numbers are written by hand, and I would need to read them automatically. My past experience is that people who write numbers will them write in so many ...
0
votes
0answers
13 views

Scalable/vectorizable way of thresholding a time series with a changing baseline value

I have a timeseries composed of many overlapping signals and a variable* baseline. My goal is to create a thresholded delineation of activity, essentially splitting between activity and baseline. The ...
0
votes
0answers
10 views

Not sure why I get errors of missing blocks when trying examples in Gnuradio Companion

I just started working with GNURadio without much of familiarity about this software. I found a couple examples online and I tried to run them but I get many Missing Block errors. Thats how it looks ...
0
votes
0answers
10 views

Differentiating high frequencies if a signal

I have a power signal (in dBm) which contains lots of peaks (around -80 dBm) and most of the time is around -110 dBm which we can call it noise level (obviously with fluctuations). As you know, both ...
0
votes
1answer
27 views

FFT command line application?

Are there any command line programs for Windows, preferably free and stand-alone, which can report the peak/strongest frequency within a given range of frequencies? I need something like this to ...
0
votes
1answer
44 views

Calculating phase of DFT sinewave?

I have been attempting to make a basic, slow, DFT in Matlab and have noticed peculiar behavior that I don't understand. I have been trying to plot the phase of a 100Hz sinewave captured at 250kHz ...
1
vote
1answer
21 views

Calculate the Standard Deviation of Fundamental Frequency (MFCC)

I'm implementing a gunshot detector following the article "Algorithm for Gunshot Detection Using Mel-Frequency Cepstrum Coefficients (MFCC)" (paywall). In the article, the authors uses 22 features ...
0
votes
0answers
10 views

Looking for next-step ideas/ IMU data

I'm in a bit of rut regarding how to get anything useful from a data set i've created. Typically i have the following features, from a few different journeys on my bike: timestamp temp_h temp_p ...

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