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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Improving the intuition for the 2d fourier transform

As far as I understand, the 2d fourier transform is calculated as following: ...
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Metric for image sharpness?

Suppose I have a blurry image: a photo convolved with a gaussian blur kernel of unknown sigma. I would want to deconvolve the blurry image using several gaussian kernels (with different sigmas). Is ...
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Image warping with heat map that "pulls" on pixels

I am looking for an efficient image warping function $$f: (\text{image}\in \mathbb R ^{M\times N\times3}, \text{heatMap} \in \mathbb R ^{M\times N}) \to \text{warpedImage} \in \mathbb R ^{M\times N\...
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What does hue, saturation and intensity means in image processing?

I ran some code in matlab to show what is hue, saturation and intensity to get an intuition of what they mean. But the result of the code does not match the explanation i got from here Hue is a color ...
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Noise Reduction - noisy lines

I'm trying to reduce the noise in this photo. What type of filters/techniques should I use to cancel out the noise? I've tried using box filter and Gaussian filter to blur out some of the noise, but i ...
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What's the difference between SIFT and general stereo matching algorithm (eg, sgbm)?

I am working on an open source project s2p which creates digital height model from satellite stereo imagery. The procedure of how s2p works can be roughly summarized with the following steps. Split a ...
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Interpreting results of Sobel Edge Detection

I am implementing A No-Reference Perceptual Blur Metric paper. Somewhere in the prep steps they mention the use of vertical Sobel filter for finding vertical edges. The algorithm is summarized in Fig....
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Copy an object (along with bounding box) from one image and paste on different image (only background)

I have a dataset of images with bounding boxes. I also have another dataset of images with different backgrounds. I want to copy the images from one dataset (with their ground truth boxes) and paste ...
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How to achieve uniform gaussian profile? Beam profile has grainy/multimode pattern

Hi apologies in advance if this (optics & image-process) is not where I should post this question. Thanks for the help! I'm required to make a jig that measures the divergence angle of a ...
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Why doesn't JPEG file format follow indexed color technique?

This is table about "Image file formats supporting indexed color". I don't see JPEG file format in this table. Why doesn't JPEG file format follow indexed color technique?
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Does downsampling an image twice result in a "worse" (or different) image than downsampling once

I am working on a project where the input is a large high quality image (2560 x 1440 pixels), which is eventually scaled down a lot (256 x 256) and used as input to an ML model. For reasons that I won'...
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Fixing distortion in photographic reproductions

I am currently building a photographic setup which I intend to use to make reproductions of a large amount of transparencies(positive and negative film strips). As I will be using a fairly small (1&...
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Registration of point cloud based on feature matching method

I recently find myself an interesting problem to solve. Basically I got 2 partially overlapped point clouds (in real world) that I want automate the registration process. My naive approach currently ...
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3 answers
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How to exclude diffuse moving features in a stack of images

I have some stack of grayscale reconstructed images represented as a 3-dimensional matrix DPC with dimensions [Nz,Nx,Nt]. A ...
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How to build the measurement matrix used for compressive sensing

I have a sparse vector $x \in \mathbb{R}^{N \times 1}$, it's real and positive, the non-zeros values are maximum $N/2$ values. It means, I have at least $N/2$ zeros values in $x$. My question, is it ...
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Removing dark borders in Image Stitching for Panorama

I am working on a Matlab code for panoramic image stitching for multiple image frames and getting satisfactory results however there are always dark regions surrounding the stitched images as ...
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Implementation of Deriche filter

The Canny edge detector is expressed by the derivative of the Gaussian. Its practical implementation involves the Gaussian filter, then the Sobel filter to calculate the gradient in both directions. ...
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1 answer
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Finite/Infinite Impulse Response filters

Most image filters are of finite extension (which correspond to Finite Impulse Response in 1 dimension), like Laplacian, Canny, Gaussian... Instead of being of infinite extension (IIR in 1D). Why is ...
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Calculating connected component's central moments

I am learning about image's moments. As an exercise I got this: For x̄ value I get 5 from this formula: $$= \frac{\sum_{x=1}^{X} \sum_{y=1}^{Y} xf(x,y)}{\sum_{x=1}^{X} \sum_{y=1}^{Y} f(x,y)}$$ As ...
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Which type of noise can we see from the given image signal and its abs of 2D FFT?

1. Background: I get an 128*128 2D one-channel noisy image as follows: I get the shifted absolute values of 2D FFT result by the following Python code: ...
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Numerical optimization method for optimal edge detector

John Canny, in his paper "A Computational Approach to Edge Detection" (PDF), finds the expression of an optimal edge detector by first using an analytical approach (Euler-Lagrange equation). ...
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Stitching images with common "static" element using OpenCV

I need to stitch images from the camera attached to the robotic arm. OpenCV has a nice feature (Stitcher), though it's not working correctly, as there is one static element (in the same position on ...
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2 answers
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How can we compute power spectral density ($P_n$) in Weiner filter?

I have an image which I corrupted with white gaussian noise in order to have SNR (Signal to noise - ratio) 10 dB . I want to apply Weiner filter to image which has noise . If I want to compute Pf I ...
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Beginner question about MRI

I am used to process PET/CT scans currently I am starting working on magnetic resonance imaging and I have simple question that I can not find answer for. I have files in Dicom and multiple series. ...
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2 votes
1 answer
41 views

How many dimensions is a RGB image?

I first thought it would be 3 dimensions (one for R, one for G, one for B). However what about the width and height? More a physics/image processing question I think. So, I have a few possible answers ...
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2 answers
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Slicing an Image into Tiles According to Content

Given an image that contains an NxM grid of icons with text below them, somewhat like this: I'm wondering how to split it up into the individual icons with text. Some wrinkles: The image won't ...
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1 answer
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Color Image Watermarking with a Grayscale Watermark

I'm currently working on a project on digital watermarking in a color image. The host image is a color image, and the watermark image that will be embedded is a gray. Is it necessary that the ...
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6 votes
2 answers
196 views

Can the deconvolution Wiener filter reduce noise without having a blurred image?

I am trying to denoise many several noises with several filters for a research i have, i found a deconvolution Wiener filter made by "mr.tranleanh" on Github, as you can see here . what I ...
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removing stripy artifact from fMRI

I have fMRI images, some of which have a stripy artifact that looks like a Gabor filter. Removing this kind of noise is not, to my knowledge, a standard part of any fMRI processing pipeline. I am ...
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Why I don't have phenomena of aliasing after resize image in frequency domain?

I'm writing code in cuda/c++ languages to resize images. I used a box filter ( it response in spatial domain is sinc filter ) and I have applied the convolution theorem and I'm using the fourier ...
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21 views

Covariance of 2D cross correlation result

I am trying to align two 2D signals with one unique correct alignment. After applying 2D cross-correlation on the signals I get results such as these: bad/degenerate peaks: good peaks: decent peak: ...
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jpeg compression: necessity of dividing input image into 8x8 blocks

For jpeg compression, is it necessary to divide the input image into 8x8 blocks and perform a DCT on each of the 64 blocks? If your input image is mxn, could you just have 1 mxn DCT coefficient matrix?...
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How are the edges of an image obtained with anisotropic diffusion?

I already know how to implement the method and obtain a correctly diffused image, but in the papers related to the topic there is usually an edge map that's calculated after the diffusion is performed ...
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0 answers
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2D transformation over triangle?

I think about divide image to triangles instead of blocks. Is possible transform it over triangle? Note that frequency domain can be block, not triangle. I found similar "2D Fourier transform ...
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1 answer
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Expression for DFT of linear 2D ramp

One dimensional solution is in “Expression for discrete fourier transform of linear ramp“ I need two-dimensional for image processing. We have function f(x,y) = $a_1 \cdot x + a_2 \cdot y$, My ...
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Plot Power Spectrum of Noisy Image in Python

I've been asked to plot the power spectrum of an image where I added Gaussian noise to it. However, I am very new to Image Processing so I don't know exactly how to approach my problem. I calculated ...
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Removing sawtooth wave from DFT transform [duplicate]

We have samples $x_n$ and sawtooth wave $s_n$ with period N (especially if N=$2^k$) $s_n = c \cdot n$ for n=0...N-1 where c is constant. What is formula for coefficients of DFT this wave? I want ...
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How to binarize an image using the triangle method?

I'm a college student taking an image processing class. My homework is to apply the "triangle method" on a grayscale image and binarize the image using the result. The problem is that I ...
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How to achieve similar colour isolation effects to this music video?

I am looking at how I might be able to programmatically achieve colour isolation effects similar to this Polyphia music video , and whether i am heading in the right direction by purely looking at the ...
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0 votes
0 answers
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Calculate i. Sampling interval ii. Physical signal length ii)fundamental frequency of s iv. Maximum frequency tv. spatial distance (in mm)

Assume we have a 1D print pattern with a resolution (i.e., spatial sampling frequency) of 120 dots per cm, which equals approximately 300 dots per inch (dpi) and a total signal length of N= 1800 ...
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13 votes
4 answers
618 views

Universal bases (dictionary) for image compression

I am a physics graduate student working on a data compression problem. I have been reading Prof. Steven L. Brunton's book on data driven science and engineering. I am fascinated to the concept of ...
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3 votes
1 answer
152 views

Why image deblurring still is an open problem?

This question is not written in order to criticize people efforts in image deblurring, to be honest, I just don't know the difference between techniques. My question is in title, why deblurring image ...
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2 votes
0 answers
28 views

Additional artefacts in limited angle Radon transform reconstruction using the Fourier Slice Theorem

I want to simulate the limited angle Radon transform reconstruction problem by employing the Fourier-Slice Theorem which states that $$ \mathbf{F}\left(\mathbf{R} f\right) (\theta, \sigma) = \mathbf{F}...
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5 votes
1 answer
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How to perform Spatial derivative calculation?

I'm trying to solve the following question about "Harris Corner Detection". Consider the following image: As the first step of the "Harris Corner Detection", we should compute the ...
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1 answer
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The Matrix Form of a 2D Circular Convolution

I have 3 closely related questions regarding 2d convolutions and how they are represented in matrix form. 1. Miming what happens in 1d, I assume the product of a doubly block circulant matrix $A$ by a ...
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1 vote
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Geometric transformation of distorted grid lines using image processing toolbox

If the grid-lines in the image (attached: distort1.jpeg) are distorted and squares in image appears distorted a bit. What would be the best and easy approach to convert them to perfect squares (as ...
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5 votes
1 answer
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Denoising a Grayscale Image Using Random Matrix Theory (RMT)

I am applying RMT on grayscale images. Basically for any matrix, it consists of two parts: one is pure noise and other is information. Now, to distinguish noise from information, RMT comes handy. We ...
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5 votes
1 answer
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Image Standardization for Image Classification (Machine / Deep Learning)

I am trying to write a program to standardize an image which I need to better perform image classification. I found the definition of standardisation which is obtained simply by subtracting the mean ...
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5 votes
1 answer
102 views

Rectangle Segments of Image (Rectangle Super Pixels) per Pixel

I would like to divide an image into "rectangular" components that are similar according to some visual criterion: For example I found these algorithms : https://scikit-image.org/docs/dev/...
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1 vote
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Difference between frame and image?

This term'Frame' is often used in image processing for frame rate,but is there any difference between an image and a frame?
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