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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36 views

Which is more powerful Laplace transform or Fourier transform?

In undergraduate, in some books, we study the first Laplace after Fourier and vice versa. there is the type of signal for which we found the first Laplace and we put jw in place of s and find Fourier ...
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18 views

what is the maximum value of mutual information for two images?

consider I have an image (I) with a filtered version (If). If I calculate mutual information between these two images, I get a ...
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17 views

Pixel Shuffle Layer

I was reading multiple sources to get an explanation for the Pixel Shuffle Layer. While I understand how the layer works, I do not get the intuition about why it would be helpful for the case of super-...
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3answers
28 views

Efficient algorithm to impose boundary conditions while applying a 2d filter

It is possible to filter an image by using a 2d DFT. This will result in periodic boundary conditions. Now, is it possible to use the DFT to filter an image, while maintaining predefined boundary ...
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1answer
22 views

Edge Detection Convolution Intuition

I was learning about convolution and how filtering helps us to detect an edge in an image;however I still cannot not understand how the convolution process in the image below does this. I understand ...
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0answers
15 views

Alternatives to Meyer Windows as Curvelets?

I am looking for alternative to Meyer window functions (Section 4.1) from which one can define a curvelet system. Are there any similar window functions which would be as easy to implement?
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1answer
47 views

Converting Hadamard Product into Matrix Multiplication in Image Deconvolution with Total Variation (TV) Using ADMM

I would like to solve the following Image Deconvolution equation by ADMM. $$\mathbf { \min\frac{1}{2}\Vert{Cx-b}\Vert_2^2+\Vert w\circ (D x)\Vert_1 \tag 1}$$ Where, $x$ is a vector of unknown pixel ...
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12 views

Average Power Spectral Density (1D and 2D) of multiple images of different sizes in python

I am trying to calculate avg 1D and 2D PSD of multiple image with different sizes. Any idea how can I do this? Current I'm calculating 1D psd using this function. The problem here is that each image ...
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1answer
31 views

How to Remove Temporal and Fixed Pattern Noise and Apply Tone Mapping?

I have a video, whose frames I have extracted and require to work with. 16 bits and grayscale images. My task is to improve the quality of the images, by removing the noise + adding tone mapping and ...
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19 views

Podcasts or video channels on applied signal processing

There is already a good list of text media on signal and image processing here. I'm curious if anyone is making audio or video media about new techniques or interesting applications across ...
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20 views

What image augmentations can help a neural network identify the lowest-value pixels within an image?

I am training a CNN to identify objects, and I believe the network will learn much faster if it can learn to focus on the pixels with the lowest value. One way to go about this would be to augment the ...
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20 views

Find vertical/horizontal lines

I tried everything including the Hough Transform with different inputs; Laplacian and Sobel and Canny edge detector were run on filtered image but cv2.HoughLinesP and cv2.HoughLines both give me wrong ...
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1answer
24 views

What is the condition under which the length of shortest 4-path equal to $D_4$ distance?

The following is a problem of "Digital image processing" book. Consider two points $p$ and $q$. State the condition(s) under which the $D_4$ distance between $p$ and $q$ is equal to the ...
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1answer
51 views

ringing artifacts using FFT-based gaussian blurring

I'm trying to do an FFT-based gaussian blur on a grayscale image, and it works, however it seems to introduce ringing artifacts to the result when compared to the expected direct filter. What can I do ...
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4answers
160 views

Algorithm for Scale Invariant Template Matching

I am using opencv for finding template images in a video stream. The elements I am trying to find are UI elements of android apps. Classic template matching is working quite well. But only as long as ...
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15 views

How can we interpret Spatial Cross Correlation between two images in case of compressed sensing based reconstruction of images?

I am reconstructing images using compressed sensing. The images are used from sipi database. One particular image, named Female Bell Lab, which is giving better result with high PSNR around 42 dB and ...
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1answer
49 views

Appropriate Gaussian filter parameters when resizing image

When scaling an image down it is common to first convolve the image with a Gaussian filter. Given a scale factor $0 < s < 1,$ what is an appropriate $\sigma$ to use? For example, if $s = 0.5$ (...
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13 views

What are some good references that define images from a statistical point of view?

I know that images can be studied and understood as 2 dimensional signals. However, I hope you can point me towards references that define and present images rigorously in terms of realisations of a ...
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1answer
21 views

OpenCV: Can't find large rectangle contour

I'm trying to re-create the dimensions of an object by setting it up on a grid and taking as close to a top-down photo I can which I will then get the contours of the largest bounding rectangle and ...
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1answer
116 views

How to Solve the Image Dehazing Problem Using ADMM?

I want to solve the image dehazing problem using ADMM. I want to use the proximal algorithm to optimize each element. I refer to this treatise: Efficient image dehazing with boundary constraint and ...
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1answer
56 views

Basic question about RGB planes

If a 3-bit, 2 × 2 RGB image has the following planes: how can we write each plane to a vector of size 3x1?
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1answer
28 views

Is there a way to find the contours of instances in a binary mask image by color?

I need to find the contours for each of the instances of microscopic cells in a binary image mask of dimensions 256 x 256 shown below. My approach involves thresholding the image to get a binary mask ...
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78 views

How to find the Wavelet measurement matrix in compressed sensing?

Assume that an image vector x = Ψs. s is a sparse vector in which the image vector x of length N x 1 is sparse in the wavelet Ψ basis. I have issue in finding the measurement matrix A= φ Ψ where φ is ...
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1answer
40 views

The Meaning of $ \mathbb{E} $ Operator in the Pix2Pix Loss Formula of a Neural Network / Convolutional Neural Network

I've been observing the Pix2Pix Paper - Image to Image Translation with Conditional Adversarial Networks and wondered on formulas. For example, the objective of the CGAN is: , where x - observed image,...
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1answer
101 views

Generate a Gradient Operator for a Fourier Transform

I came across this equation while trying to process an image $z$, $$ \mathcal{F}\left(\mathbf{D}^T \mathbf{D}\right) \mathcal{F}\left(z\right), $$ where $\mathcal{F}$ is the 2-D Fourier transform, and ...
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1answer
67 views

How to Solve Blind Image Deblurring with Total Variation (TV) Prior Using ADMM?

As a continuation of the question How to Solve Non Blind Image Deblurring with Total Variation Prior Using ADMM? I would like to understand how could one solve the Blind Deblurring (Deconvolution) ...
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2answers
54 views

A question about quantization and dequantization calculations

Suppose we have a 2x2 image as follows: What does each dequantised image look like after it has first been quantised to 7, 4 and 2 bits respectively? I solve this question by initially quantising as ...
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37 views

A basic question about bilinear interpolation

I have a basic question about "Bilinear Interpolation". How to derive the bilinear interpolation formula of 4 pixels arranged as follows: And if the bilinear interpolation is applied to ...
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28 views

Filter 3D volumetric image with a Butterworth filter in Python

I have been looking for a way to filter a 3D volumetric image in python with a Butterworth filter, but I haven't found any good solution. I have tried this: ...
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1answer
43 views

How to Solve an Image Deblurring Problem by Variational Methods Using ADMM?

Following up on a previous question, I wanted to understand how to solve an image deblurring problem using Variational methods in matlab or julia. Given some original blurry image $f$, I would like to ...
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2answers
102 views

Metrics to evaluate the accuracy of image binarization algorithms?

I am working on image binarization for my undergraduate project. The idea is to convert an RGB image to a binary image while retaining maximum features. I presented a comparison of the results of my ...
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2answers
151 views

Locate Non Homogenous Areas in an Image

I need to choose some points on an image. These points should be chosen more where there is lots of color changes, transitions and variations. Which techniques can I use for determining where most ...
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2answers
62 views

Constructing frequency domain filter from a 2d spatial kernel

Given a 2d spatial kernel $h$, I want to construct the corresponding frequency filter $H$. In theory, $H$ is simply obtained by calculating the DFT of $h$ using a FFT algorithm. But in practice, there ...
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6 views

Finding a better threshold in a more accurate manner in OpenCV

I have a grayscale image, the dominant colors in the background are shades of white and light gray, I have tried using otsu binarization but it gave no good results, so I decided according to the ...
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1answer
90 views

How to Solve Non Blind Image Deblurring with Total Variation Prior Using ADMM?

How could one use the Total Variation frame work to solve the Deblurring problem? Specifically using the ADMM as a solver. One could assume the blurring operator is known, linear and shift invariant. ...
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14 views

Directions on how to estimate the additive intensity bias

I have been reading this paper on how to estimate the additive intensity bias from an image, and I want to test it and write an algorithm for it. However, I can't seem to understand how to write the ...
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7 views

APT Satellite Image False Coloration?

I'm working in MATLAB to try to take pristine APT satellite images (two greyscale images of the earth taken at different wavelengths) and turn them into one false-color image. I also have a second ...
2
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1answer
61 views

Basic Wiener application

I'm trying to filter this $g(x,y)$ WGN added image My Wiener filter is: $$H(u,v) = \frac{P_{f}}{P_{f}+P_{n}}$$ Where the image power spectral density $P_{x}$ is estimated as $\frac{|X(u,v|^{2}}{N^{2}}$...
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14 views

Can we do image classification using bag of features and classifier other than SVM

I developed code for image classification using SURF features , bag of features as instructed in https://www.mathworks.com/help/vision/ug/image-category-classification-using-bag-of-features.html but ...
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51 views

How to enhance thermogram image in grayscale?

I'm trying to do some image processing to improve the image below but I'm having some trouble. I already tried to do histogram equalization followed by laplace sharpening, I tried to implement a ...
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1answer
51 views

If we take Z-transform of a signal & find its ROC. How to use this ROC? There are ∞ signals in ROC, suppose we choose any signal what to do with it?

If we take Z-transform of a signal & find its ROC. How to use this ROC? There are infinite signals in ROC, suppose we choose any signal from ROC, what to do with it?
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1answer
34 views

What is the meaning of spectral contamination in image processing?

I resize the Multispectral image to perform IHS-to-RGB transformation. I used the Nearest Neigbour Interpolation method when resizing. While researching this issue, I saw that this is the best option ...
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1answer
31 views

Different “zoom” after reconstruction from Radon transform using Fourier Slice Theorem

I have implemented the procedure to reconstruct an image from its Radon transform involving the Fourier Slice Theorem (FST). After application of the FST, the data is transformed from polar ...
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0answers
27 views

How would you process this image?

I got this image: I need to keep only the part in the center (I mean, the circle with texture inside). How would you do it in Python? I'm trying to use Hough Transform, but some times it detect wrong ...
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1answer
46 views

Calculating Haar features

I am confused on how to solve this problem, does anyone have any ideas? https://www.merl.com/publications/docs/TR2004-043.pdf For a Haar filter $H \in \mathbb{R}^{3 \times 5}$ defined as below: What ...
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2answers
131 views

How to Solve Image Denoising with Total Variation Prior Using ADMM?

I was looking at some articles or Wikipedia on denoising images using the Total Variation norm. The setup is the Rudin Osher Fatemi (ROF) scheme, and the corresponding equation is: $$ F(u)=\int_{\...
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1answer
28 views

What is Label Refinement in the Context of Image Segmentation

I have been reading the paper entitled Measures of Similarity by Unnikrishnan and Herbet, in which they discuss some metrics to evaluate image segmentation. They use the word refinement of labels/...
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1answer
38 views

Why Does the Rudin Osher Fatemi (ROF) Method Use Variational Methods for Image Denoising When Denoising Problems Are Not Boundary Value Problems?

I was reading the recent book Variational Methods in Image Processing by Vese and Guyader which is quite interesting. In the book the authors discuss different types of image processing problems, from ...
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1answer
138 views

How to Apply the SSIM Measure on RGB Images?

I want to compare the similarity of two images by looking at its structure and colors. I need a measure that takes both structural and color fidelity into account. When I checked the formulation of ...
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0answers
15 views

Blended use of DoH and LoG for blob detection, is there any paper I can cite for this?

tl;dr: For blob detection, I determine locally maximal DoH responses in image regions which correspond to negative LoG responses. Is there publication I can cite for such blended use? Two of the most ...

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