Questions tagged [image-processing]

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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32 views

2D Fourier transform over mask of an image

I have an image, which has an inherent mask built into it. The exact shape isn't super important, but it looks something like a circ multiplied by a rect. I would like to calculate the 2D Fourier ...
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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 ...
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Understanding the high-pass filters in image processing

I am new to signal processing and I see that high-pass filters in image processing always have negative and positive value. In the image processing concept, why do masks have negative and positive ...
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How to systematically ignore image features (from a spatial light modulator)

(I am unsure if this is the best Stack Exchange site for this question. If not, please point me to the right one.) I am generating light patterns with a device called a spatial light modulator (SLM). ...
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Detecting bounded regions in JavaScript

I have an image of a crossword (i.e https://i.stack.imgur.com/qqy4X.png), and I would like to find the x,y coordinates of every valid square and the number associated with it, then I would feed it ...
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How can I turn an image into a scatterplot?

I'm doing a research on how to do image classification for embedded systems with 64kB flash and 16 kB RAM and Deep Learning won't work here Therefore, I need to use simplier tools that still have a ...
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what is bi-spectrum of signal

anyone knows what is bi-spectrum and its usage in signal processing? how can I extract data from bi-spectrum of signal? I want to use bi-spectrum of signals to classify them and I want to knows the ...
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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 ...
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How to do stretching Image distortion transformation

I have an assignment to transform an image like this: I have done with twirling, fisheye, bulge, but I'm having a hard time finding the right formulas for those effects. here is my code for twirling: ...
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How to interpret a 1D-DFT of an image with a sinus grating/gradient compared to its 2D-DFT outcome?

For getting a better understanding on how the 2D-DFT works I was playing around with sinus gratings in grayscale. I tried to compute the 1D-FFT first and compare it with the 2D-DFT to get a better ...
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Why does the 2D-DFT of a sinus gradient not show energy along the diagonal straigh lines and only vertical/horizontal from the diagonal point?

I have been experimenting a little bit with simple examples of the 2D DFT to get a better sense for it's interpretation. For this purpose I have been using sinus gratings with the following code: <...
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Scaling of FFT2 magnitude in image-processing

I got the following code: ...
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1answer
63 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 ...
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1answer
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Ideas on detecting holofoil trading cards?

I'm relatively new to image processing but am working on a trading card sorting machine, and would like to detect holographic cards. I'm currently identifying cards using ORB matching (moved from p-...
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image processing - good algorithm for lung detection

I'm a beginner in image processing and I have to create a segmentation algorithm to detect lungs from an image . Image given : And after removing the noise from the image and applying a threshold the ...
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1answer
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How can I segment areas, each of which has nearly same colors of pixels in an image?

For clarity, Nearly same colors of pixels belong to a category. Another nearly same colors of pixels belong to another category. The distinction depends on nearly same RGB values of pixels.
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3answers
155 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 ...
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1answer
29 views

How to train a FCNN with Spectrogram images?

I'm working on a audio dereverberation deep learning model, based on the U-net architecture. The idea of my project came from image denoising with autoencoders. I feed the reverbered spectrogram to ...
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1answer
95 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 ...
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Spectrogram normalizaion to train a Fully Convolutional Model for Audio dereverberation

I'm trying to implement a deep learning based dereverberation algorithm. The network I am using is inspired by the U-net. The idea is to supply the reverberated spectrogram as input and 'clean' it ...
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Eliminating shadow-like noise from wafer map images

I'm trying to eliminate a shadow-like noise from the wafer images and only leave the most prominent defects as shown in Image1 below. I thought I could treat it like salt-and-pepper noise. Hence, I ...
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Octaves and the SIFT algorithm

My current understanding is that the full algorithm is applied for each octave and then we have four images (the original image and its downsampled version) each with their key points and ...
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50 views

Overall approach for building a footfall/age/gender counter using CCTV footage

I would like some advice to validate my approach for building a computer vision system. Design brief: Using existing CCTV cameras in a retail store, detect the footfall in the shop (count individual ...
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1answer
46 views

Noise from irregular sampling pattern

In this paper the author says By using an irregular sampling pattern and filtering the irregular samples to create the pixels, featureless noise is produced from such high frequencies rather than ...
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20 views

Best way to reach experts in the Synthetic Aperture Radar (SAR) Simulation field?

I'm looking for Synthetic Aperture Radar (SAR) Simulation experts and struggling to find them (context: synthetic data for geospatial applications). I've found a few users in this community who could ...
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18 views

Optimising homography matrix without keypoints

I have two images (frames) that are misaligned. One is reference and for second one I have a homography matrix (which was not calculated by me, I just have it). I warped second frame with homography ...
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40 views

Input data for compression algorithm

I want to implement the algorithm from this paper. However in section 3.1.1, it says that it needs a binary image as input. My question is, does it mean that the method only applies to binary data (...
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35 views

Color coherence vector - implementation

I'm trying to implement a color coherence vector for a small dataset. I understand what are the steps to do, but for example, the number of connected components is giving me always 1. I didn't know if ...
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What is the calibration method of this stereo camera?

I have a stereo camera setup from "QuantifiCare" Company that specifies for 3D reconstructing image of a human face just by 3 images. Everything is working well but I like to know the method ...
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37 views

Removing the Dot-Patterns Like Noise

I am dealing with an image restoration problem with noisy measurement. I use the classical total variation norm to remove the noise, specifically, the TV-$L_2$ problem. I used the famous Lena image ...
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18 views

Foreground extraction with zebra background

I am trying to classifiy grayscale images but I need to focus on a specific object on each image. I would like to segment the object but the targeted object has the same color than the background. And ...
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1answer
72 views

Image Segmentation Using Deep Learning

I see in many reviews on Autonomous Car how they segment the images with person, cars, etc... How is it achieved in Deep Learning? Could anyone give an example of that? How it is done?
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113 views

Image / Video Upscaling (Super Resolution) Algorithm Explanation (Image and Video Upscaling from Local Self Examples)

So, I'm trying to implement the classical algorithm described in this paper Image and Video Upscaling from Local Self-Examples and this presentation to serve as a baseline for comparison with AI/NN-...
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Rolling shutter time per row on downsampled images

When working with rolling shutter images, it is common that we want to know the timestamp of each row (for example for motion interpolation). Using $T$ as frame timestamp (mid-exposure, mid-row) $T_i$ ...
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1answer
35 views

What are some relevant feature descriptors for recognition of images of fruits/vegetables?

I dont know if this is the right place to ask this but lets go. I am a beginner in computer vision and I have a project of fruit recognition (with this dataset https://www.kaggle.com/moltean/fruits/...
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1answer
84 views

Applying a 2D Convolution Using 2D FFT

So I was following the article Victor Podlozhnyuk (nVidia) - FFT Based 2D Convolution (Page 7). I have expanded the kernel to the correct way they have done it. However when it comes to the part on ...
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1answer
35 views

bilateral filter for color images

Fast Bilateral Filter I came across the above code of the bilateral filter for grayscale images. I tried to implement it for color images by splitting the image ti BGR channels and applying it to each ...
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32 views

What are some good examples of applications of Circular Convolution in Signal Processing and Image Processing?

I have derived the circular convolution property for an affine Fractional Fourier Transform and I need to work on an application for my research. Any idea?
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1answer
41 views

Fourier Transform High Pass Circular Filter Intuition

The situation I need to apply a high pass filter to an image. The approach I'm following uses Fourier transform to apply a circular filter which would eliminate low frequencies. Say I have a frequency ...
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34 views

How can i generate training progress plot from saved trained model in matlab?

I would like to know is there any ways to generate back the training progress plot or verbose result from the saved trained model if i forgot screenshot/save both data manually? the code that i use to ...
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54 views

High pass filter with specific cut-off frequency

The situation I am trying to apply a high pass filter to a black&white image to enhance the texture by keeping the high frequencies. The goal is to filter from a specific frequency value obtained ...
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39 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 ...
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1answer
47 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 ...
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1answer
37 views

SURF normalisation and Haar wavelet

I am reading the SURF paper (Speeded-Up Robust Features (SURF)) but can't understand two things. In 3.2 it says: Furthermore, the filter responses are normalised with respect to their size. This ...
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1answer
41 views

Effect of downsizing on perceived sharpness

Suppose an $N\times M$ image of an object is downsized to a $N'\times M'$ image using a standard algorithm such as bilinear. How does that downsized image compare in sharpness to an image of the same ...
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1answer
38 views

IP Block and Integrated Circuit using Image Compression and Parameters

I have to research and compare IP cores for FPGA and ICs that use image compression algorithms. 1.) I couldn't find any IP Cores apart from a few IP Cores(JPEG IP Core KJN Series). At the same time, I ...
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0answers
47 views

How to find sharpness of an image?

I have a rather difficult image processing image. I would like to rank order a set of images I have by their sharpness. The issue is the images themselves are not of the exact same thing. Usual ...
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2answers
322 views

Where is truncated-SVD image compression actually used?

What are some instances of real-world sensors, cameras, filetypes, or datasets whose image compression method is (at least mostly-based on) the truncated-SVD?
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FFT filtering by hand in python - iffy issue - cannot get filtering right

I am trying to filter an image by hand (with no using the image processing libraries) to understand how fft.shift works in python. No luck. I take a png an image from MNIST, e.g.. Here is the code: <...

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