Signal Processing

Questions tagged [image-processing]

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In general, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame.

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9 views

Thresholding algorithm for separating skin from clothes in python

I have an several images that look like the following: I would like to separate the skin from the trousers here without specifically training a segmentation model. Can anyone suggest any such ...
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24 views

Cropping binary images based on pixel counts in python

I have a numpy binary masked image that looks like the following: I want to automatically crop this image like the following: Can I achieve this using some sort of image processing rather than ...
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32 views

Taylor series expansion in mean shift tracking

I am trying to understand the first order Taylor series expansion when deriving the math behind mean shift tracking. Given the Battacharya coefficient between the target descriptor and candidate ...
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Why the circular cross correlation values between two different images is higher than its values between an image and the same image?

I tried to perform circular cross correlation between two images using cxcorr_fft.m downloaded from https://www.mathworks.com/matlabcentral/fileexchange/43967-circular-cross-correlation-using-fft ...
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36 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 ...
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10 views

Calculate perimeter and area of Head CT from DICOM

I’m trying to calculate the perimeter and area of the outer lining of the skull from head computed tomography scans. I have these scans as a DICOM, and single slices can be exported as image files. ...
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23 views

Circular cross correlation

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 ...
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20 views

Impulse response of the system image processing

In case of the signal, when we plot an impulse response we have our x-axis - samples (or time), y-axis - amplitude, but in case I work with image processing? x-axis is pixels? and y is still amplitude?...
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How can I calculate the circular cross correlation between two images with matlab?

I found a Matlab function that calculates the circular cross correlation between two sequences How can I calculate the circular cross correlation between two images? https://www.mathworks.com/...
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Find points that are mapped to the original grid with image rotation by a non multiple of 90 degrees

I would like to find the point that are "not interpolated" when I rotate an image with e.g. Matlab's imrotate() by an angle which require interpolation e.g. 6 degrees, i.e. not a multiple of ...
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fft calculations for spectral amplitude and spectral phase to resolve the eigen modes

I am using Jupyter notebook for micromagnetic simulations. The output formats are in .ovf and .npy and a table.txt file which contains average magnetization components (t, m_x, m_y, m_z). I am a ...
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45 views

What are the 'phases' in this 2D scaler filter

I am pretty new to DSP and have been looking at how image scaling is done in hardware. I and came across a 2D scaler core for an FPGA here. I have read up a bit about polyphase filters, but am ...
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45 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 (...
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26 views

Help or suggestions with Line detection in microscopy images

I'm doing a personal project in which I want to select some very specific lines in a microscopy image. The first picture is the raw image, the second picture is the image for the lines (in yellow) I ...
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Implementing Felzenszwalb's segmentation for 3D images

Is there an implementation available for unsupervised 3D segmentation using the Felzenszwalb's Graph Cut algorithm? If implemented what do you think are the bottlenecks of such an algorithm? In ...
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Find camera tilt

If I have a camera that captures tilted images what is the way to find the tilt of the camera? Is there a pattern that I can photograph or something similar. I want to reduce the tilt as precisely as ...
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1answer
25 views

Finding the equivalent filter H(u,v) in the frequency domain of a 3x3 spatial mask

I'm trying to find the equivalent frequency domain filter, $H(u,v)$, of a 3x3 spatial mask that averages all neighbours of a point $(x,y)$ in said 3x3 neighbourhood excluding the point itself. So far, ...
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21 views

Adapting Richardson Lucy (RL) Deconvolution for Shot Noise Limited Coherent Imaging

I am an experimental physicist who is collecting a series of coherent imaging of trapped gas. If you are familiar with phase contrast imaging, you may understand what I mean by coherent imaging. The ...
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Registration of segemented medical images

I’m looking to register images based on probability maps (or possibly the binary images) resulting from segmentation of medical images of blood vessels with a circular FOV using python. Are there any ...
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Problem definition in KLT tracking

I am studying about the KLT tracker algorithm. In the KLT tracker, we can try to estimate the optical flow for corner points (because these are good features to track) between frames and the computed ...
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1answer
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Should we use all $N$ correspondence points to compute Homography or just $4$ points?

Given correspondences of $(x,x')$, we want to find a Homography matrix $H$ that maps $x' = Hx$. If we use 4 corresponding non - collinear points and the matrix $H$ has rank $n-1$, then the homogenous ...
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1answer
29 views

Why do we need to construct Gaussian pyramid using SIFT detector

I am learning about SIFT detection and descriptor. I am slightly unsure about why a Gaussian pyramid is built for the image. I do understand that within each octave, we are applying the Difference of ...
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17 views

Normalisation of CWT coefficients

I am trying to train a Convolutional Neural Network (CNN) model on an EEG measurement dataset consisting of 32 channels (i.e. 32 non-stationary signals at each time frame/window). In terms of ...
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Difference between images

I am using a template matching algorithm to find a region in an image. Now there is something strange about the templates I am using. Some of them work and some others don't. And I can't find out the ...
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1answer
26 views

Enhancement by adaptive wavelet shrinkage denoising

I was wondering does anyone know any programming library or a way that can help me implement this algorithm.
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What is the current “state of the art” in future audio sample prediction, given recent developments in “image inpainting” using deep learning?

In the last few years, there have been many breakthroughs in the image processing world regarding repairing "damaged" images, images with corrupt pixels, or even reversing artefacts from ...
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Red Color selection in Python and Skimage

I'm trying to load an image from the disk and then to extract just the red channel of it and display it in grayscale with grey colormap but I don't know what I'm doing wrong.. The image should be ...
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How to detect defects at a contour?

I am detecting a contour of a smooth metal. I do binarization first then use openCV contour function. But sometimes the metal has defects such as dots or dusts at edge. This leads a unsmooth edge. Is ...
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21 views

multi-frame image restoration

Suppose we have a sequence of still images each of which has been contaminated by some particles(ex, dust/sand/smoke) making the images very poor in certain areas. What approach would be best to teach ...
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1answer
50 views

Is Unsharp Mask (USM) Equivalent to Applying Laplacian of Gaussian Filter Directly on the Image?

There are some educational materials, like Alex Pan - CS 194-26: Image Manipulation and Computational Photography - Fun With Frequencies and Gradients, which demonstrate the unsharp masking technique ...
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120 views

Noise Power Spectrum calculation

I want to compute the 1-D noise power spectrum (NPS) for a uniform CT image. The equation of the 2D NPS is as following: $$ NPS(f_x, f_y) =\frac{1}{N}\sum_{i=1}^N|DFT_{2D}[I_i(x,y)-\bar{I}_i]^2\frac{\...
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44 views

Seeking advice on how to denoise a video from poor CCTV lighting

I have grainy CCTV footage that will need some amount of clean up. I request for ideas on the best way to clean out the noise. I am attaching a frame extracted from the video here for hints on the ...
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1answer
44 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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How to detect slices with circular crops in volumetric mri data

Ive got some MRI volumetric data I am trying to do some image analysis on. Ive got an issue right now where the first and last 2-4 slices of the data are cropped circularly. Here is an example of what ...
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22 views

Removal of parallel-line like streaks

Just wondering what image processing techniques can remove some artifacts of parallel-line like streaks, which are shown in the red box in the above picture. I was thinking about removing it from ...
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1answer
29 views

Logarithmic vs Nth root transformation of Image

This is an image for the explanation of Logarithmic Transformation of an Image. I want to ask considering a input pixel value rk, Value of nth root of rk should be greater than corresponding value of ...
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1answer
75 views

2D Frequency Domain Convolution Using FFT (Convolution Theorem)

In the time domain I have an image matrix ($256x256$) and a gaussian blur kernel ($5x5$). I've used FFT within Matlab to convert both the image and kernel to the frequency domain as zero padded $...
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51 views

Target Plane Orientation Detection in a Distorted Image

Doing a camera calibration of an extremely distorted camera ( wide-angle ) the OpenCV gives us the rogdriguez and the transpose vectors of each image used in the calibration process. How do they do ...
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26 views

Mean shift algorithm formula

I am watching a lecture on mean shift clustering. In the video, the mean shift vector is first defined and then it's relation to the gradient of a kernel density estimate is shown. The mean shift ...
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How does SURF handle image boundaries in key point description?

I am stuck on the key point description stage of my SURF implementation, which is based on An Analysis of the SURF Method. The authors extend the image borders through a mirroring process that extends ...
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1answer
40 views

The Effect of the Standard Deviation ($ \sigma $) of a Gaussian Kernel when Smoothing a Gradients Image

I am trying to understand why smoothing an image with a gaussian kernel of different sigma values and then computing the gradients of the smoothed image leads to "thicker" trails. In the ...
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1answer
26 views

Invariances of FFT-based Image-Registration vs. SIFT-Features

TL;DR: I don't understand how invariant FFT-based image-registration techniques are to object alterations (scratches, marks etc.) in comparison to SIFT-features. I want to build kind of a feature-...
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28 views

Taylor series approximation in Harris corner detection

While watching through the computer vision lecture on interest point detection, computing $E(u,v)$ requires computing the quantity $$E(u,v) = \sum_{x,y}(I(x+u,y+v) - I(x,y))^2$$ In the lecture, $I(x+u,...
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1answer
24 views

Harris corner detection shape of $E(u,v)$

I am taking a computer vision class and I have just learnt about the Harris corner detection concept. A corner is detected when a small shift in a window function defined around the corner results in ...
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33 views

How can I add any kind of noise to image for a given SNR?

What is the best way to add any kind of noise (not only Gaussian noise) to 2D signal (image) for a given SNR?
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2answers
90 views

Coordinate system in digital image processing

I am trying to understand image coordinate system where I read that it is reversed. So if $f(x,y)$ is actually $f(y,x)$ where $f(\cdot, \cdot)$ is the image. I am a bit confused and would appreciate ...
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52 views

Is this statement correct from DSP aspect?

So, In my report I am comparing the related works, In most of the previous work, researchers have used spectrogram as input to vanilla CNN and classify. Where I am using different handcrafted features ...
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Which one is better method and why? Manually Handcrafted sound features vs spectrogram + convolution

I am working on classifying different sounds ( not speech or words exactly something like ambulance alarm, police alarm, cough sounds etc) I read few paper which suggested to extract dsp features such ...
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Pretrained networks with Adam optimizer?

I have tried different pretrained networks with Adam optimizer, and obtained high performance. However, when I tried it with Alex network, the performance was poor. Could you please help me ...
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1answer
59 views

How does an image rotation affect the magnitude of a DFT?

Note: This is being applied only to images of b/w text If we're given some image and plot the DFT spectra as and then we plot the rotated image's spectra Is there any way we could recover the angle ...

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