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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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Border effects / artifacts for spectral filtering of images

I am working on a spectral filtering problem as follows: I'm given an image with a periodic distortion pattern (see below), and I want to remove the distortion pattern while preserving the main ...
normanius's user avatar
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What is the type of blurring in such an image?

I can't figure out what type of blur such an image has and how I would be able to generate it in python. I would be grateful for any help. I tried Gaussian blur, bokeh blur, Wolf and Born out of focus ...
empirefloo's user avatar
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Pixel Shift when using Fourier Downsampling

I am working on a Super-Resolution network, and want to try to use Fourier downsampling, different from the normally used bicubic downsampling as it relates to MRI imaging. I have tried using this ...
Christoffer Overgaard's user avatar
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What is Roboflow doing for its "exposure augmentation"?

I was able to find a small blurb here that describes what Roboflows exposure augmentation does. I'll reproduce the text here for convenience: Adjust the gamma exposure of an image to be brighter or ...
user20672's user avatar
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FFT2 to RFFT2 Fourier plane and similarities

I'm trying to understand how Python's fft2 is different from irfft2. Basically, I have some continuous Fourier 2D samples that I need to put in a (n,n) grid (this can be done by a simply count-in-cell ...
Miguel Cárcamo's user avatar
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Suggestions for image region separation

I have some SEM images that I need to process,all those images have extra information in the bottom of the images as can be seen in the red bounding box. I need to remove those portion before doing ...
mohammad's user avatar
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Detecting a large horizontal band in the center of an image

I have a small (228x228) grayscale image that I have created by segmenting the original image and converting it to grayscale after applying colors to the segment. I want to know possible approaches I ...
requiemman's user avatar
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Derive white balance matrix operator in YUV space

Assume that the white balance matrix operator in RGB space is $$W=\begin{bmatrix} \alpha &0 &0 \\ 0 & \beta & 0 \\ 0&0&\gamma \end{bmatrix}$$ where the constants ...
In the blind's user avatar
1 vote
2 answers
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Why in 2D Fourier Transform phase seems to be more "useful" than magnitude?

In 1D signals f(t) (e.g. a sound signal - independent variable t-->time) when we want to use informations from the Fourier transform F(ω) in order to reconstruct the signal, using the magnitude |F(...
user1198483's user avatar
1 vote
1 answer
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How am I supposed to acquire/measure vertical and horizontal effective resolution from my images?

I apologize first for some questions that might be dumb. Unfortunately, I am only a bachelor student (writing my bachelor thesis in physics) and have almost zero image processing experience. And I ...
Anothernewbie's user avatar
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Combining Two Grayscale Images Without Overlapping Using OpenCV and Matplotlib in Python

I am working on a project where I have two grayscale images of different sizes, named part1 and part2. Each image has some ...
Estiven's user avatar
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Generating new random phases for DFT of 2d uniform distributed noise image changes image distribution

My goal is to produce a new random noise image from two already existing noise images. For that I take the absolute values of one image and the angles (phases) from another image in Fourier Space and ...
Jaksl's user avatar
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Combining Three Images into One Output Image Python

I have to combine three images that are inside one single image into one output image in Python. This has to be done using Gamma corrections, Histogram equalization, filters convolutions (gradient, ...
Estiven's user avatar
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Removing dense grid lines & convert into clear image - opencv - python

I want to extract the text from this image. I'm a newbie in opencv. I've tried various opencv codes across various questions, but none is working for me. How can I extract text from this? Or maybe ...
Pankaj Singhal's user avatar
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Distance Transform & Chamfer Matching -- find actual edges

I have had good success using the Distance Transform and Chamfer Matching to locate a template in an edge image. Is there a recommended technique to then find the actual edges that match the template? ...
Andrew's user avatar
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Decoding images from sounds in Voyager golden records

I'm interested in a side learning project in decoding the images recorded as sounds in Voyager's golden discs (https://voyager.jpl.nasa.gov/golden-record/). The instructions to be able to decode these ...
rluque's user avatar
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real time streaming image encoding options

I'm interested in streaming video real time. There is an issue of deciding how to properly encoder the images and the format they should be. Since the data will be streamed over UDP, it needs to be ...
FourierFlux's user avatar
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I need help finding the PSF and characterizations of the following

My professor explained this to me in a super convoluted way, so hopefully someone can explain this to me better. I'm trying to find the PSF of the following signals. I also need to check if it's FIR ...
FafaDog's user avatar
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How did law enforcement recover fingerprints from the "blue cheese encrochat picture"

I hope that my question suits well within the topics discussed in this SE website. It was reported some time ago how a man was identified after he shared the photo on the encrypted messaging service ...
user71107's user avatar
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Issue with cudafft library and fftshift on odd image dimensions

I'm facing with a code I'm implementing for an exam using the GPU. Specifically, the code I'm writing is in C++, and I'm using the CUFFT library to perform the Fast Fourier Transform (FFT). The ...
overflow''s user avatar
2 votes
3 answers
106 views

How to find PSNR from two images with different size in python

I have 2 images, one original and other is reconstructed from the original via some processing. I want to find the PSNR for the reconstructed image The original has a size of ...
QuantumOscillator's user avatar
1 vote
1 answer
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Trying to understand significant loss caused by OpenCV's inverse DFT

I'm quite a novice on computing Discrete Fourier Transforms with OpenCV, and I've been attempting to compute the DFT, and computing the inverse of the DFT using the latter as the input. Judging from ...
edition's user avatar
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-2 votes
2 answers
135 views

What is the event that repeats itself in sinusoidal signals

I am studying medical imaging and it has been stated that it is sufficient for Nyquist Theorem to hold for the signal to be Bandlimited. I am trying to understand what is the wave in a signal. What is ...
George Ntoulos's user avatar
-3 votes
1 answer
175 views

Assumptions of Nyquist sampling theorem [closed]

Hoping I can save the question and it doesn't get migrated to philosophy stackexchange as Hilmar said in any case I don't think it is a different question the question was always meant to be ...
George Ntoulos's user avatar
1 vote
1 answer
39 views

2D Fourier downsampling to even number of points gives incorrect modes in the last column

I would like to downsample an image in the frequency domain to an even shape, similar to what is described in this post. I have been able to do this successfully with a 1D signal to both an odd and ...
Jacob Helwig's user avatar
1 vote
0 answers
13 views

Aligning Ir images and RGB images

I was wondering if given a picture from a Raspberry Pi NoIr camera and a Raspberry Pi RGB camera, how can the two images be aligned. From what I understand the NoIR camera when used with the blue ...
mdansfo's user avatar
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1 vote
0 answers
51 views

Statistical technique for distinguishing between artefacts and no artefacts [closed]

I would like to know how to create an algorithm from the table below in order to distinguish between data that has artefacts and data that does not. I'm trying to leverage video attributes like ...
Coder's user avatar
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0 answers
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Correct low pass filter after applying discrete cosine transform

I am working on the compression of a bmp image using discrete cosine transform. First, I split the image into 4x4 blocks and then apply a DCT to each block. I know that low frequency coefficents (the ...
purecobalt's user avatar
1 vote
0 answers
77 views

Does ORB-Slam3 perform better than ORB-Slam2?

I was trying to compare ORB-Slam2 performace with ORB-Slam3 performance. Consider following comparison from ORB-Slam3 paper (columns with numbers correspond to different sequences from EuRoC dataset): ...
Mahesha999's user avatar
1 vote
1 answer
37 views

How can I estimate the number of rows and columns in a chess pattern?

I am working on some code for estimating the position and orientation of a camera. From an image taken by the camera I require that the user select lower left interior corner: green, the lower right ...
Andy's user avatar
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How to avoid the edge effects that may occur when applying the Hilbert transform (by mirroring)?

How to avoid the edge effects that may occur when applying the Hilbert transform (by mirroring) for image or image series signal? Code is appreciated (in python) please.
holder fo's user avatar
1 vote
2 answers
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Related to Additive white Gaussian noise (AWGN)

In my research work regarding wireless communication, I came across many research papers wherein AWGN is assumed to be modelled as "complex Gaussian with zero mean and unit variance". I ...
Heretolearn's user avatar
3 votes
0 answers
21 views

HSI formula inconsistency in Gonzalez & Woods

I'm confused about how the book Digital Image Processing by Gonzalez & Woods explains HSI model. It includes a double cone-shaped space for the model (like the figure below) and says every color ...
Mehrin's user avatar
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6 votes
2 answers
151 views

Discrete Fourier Transform of the Gaussian

Cross-posted from here I encountered the following question in a Digital Image Processing examination: Find the 2D DFT of $\frac{1}{2 \pi \sigma^2} e^{-\frac{(x - x_0)^2 + (y - y_0)^2}{2 \sigma^2}}$ ...
kaddy's user avatar
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2 votes
2 answers
115 views

Use DFT (`fft()`) to Replicate 2D Convolution (`conv()`)

In MATLAB, I tried to convert the fft2-based multiplication using conv2. ...
Ka Mirul's user avatar
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0 answers
10 views

problem with GSAFT (backprojection) algorithm for nearfield millimeter-wave image reconstruction on my simple planar array

I have a planar array containing 16 transmitters and 88 receivers located on the same plane with dimension 30cm-by-30cm. I have an object of size 6cm-by-6cm. Object and antenna array plane are in ...
mohammad rezza's user avatar
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0 answers
20 views

How to know which type of sensing matrix would do the job?

Compressed sensing refers to the recovery of a high-dimensional but sparse vector $x\in\mathbb{R}^n$ from its linear measurement $y = Ax+\eta$, where $A\in\mathbb{R}^{m\times n}$ $(m<<n)$ is a ...
shashank ranjan's user avatar
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0 answers
25 views

Python - CV, contour and measurements

I have small problem with cv in Python and rhombus. I can read frame from the camera and create contours... ...
Krzysztof's user avatar
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0 answers
13 views

Face Detection real-time with Local Binary Pattern

I'm writing for code to detect human face by Local Binary Pattern algorithm in webcam, but with my limited knowledge in optimization code, I having to struggle in detect in each frame , I want to say ...
Hau Chung's user avatar
1 vote
0 answers
45 views

Local Binary Pattern rotation

How does LBP work? To learn that, I decided to calculate by hand for the matrix but the problem is about the rotation pixel over the image based on the radius and neighbor of LBP. I do it clockwise ...
chews's user avatar
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1 vote
0 answers
35 views

is there a relation between video and audio

"I would like to extract 'n' frames and obtain the corresponding spectrogram for those frames. I'm unsure if there is a specific duration, such as 20 frames equating to 15 milliseconds or ...
Bala Sai Sigireddy's user avatar
2 votes
0 answers
30 views

Why DCT-III is not used as forward transform for image compression applications?

DCT-II is the most widely used type for image compression. This is due to its "Energy Compaction" property. According to this property, a good enough reconstruction of a natural image can be ...
Sahil Sharma's user avatar
1 vote
1 answer
57 views

byte order of P6 ppm image in C [closed]

this is the main function ...
Ishaan Vatus's user avatar
0 votes
0 answers
23 views

Identify variation patterns in image time series

I am working on time series of 12 remote sensing images obtained at irregular intervals. The pixels of all images are of exact same region. Pixels of some areas in these images vary in time with ...
sat_P's user avatar
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1 vote
1 answer
73 views

Properties of DFT of Circularly Symmetric 2-D Matrices

I'm very new in image processing and trying to get a grasp in the basic concepts in 2-D DFT. As far as I understood, DFT of a circulant matrix should also be a circulant matrix. But when I define a ...
Deniz Açıkgöz's user avatar
1 vote
0 answers
30 views

Algorithms for handling misaligned resolution values of images/videos

I know many algorithms to improve image quality. But now I am thinking about an apparently much simpler problem: how to display image when the pixels are not properly aligned with the screen's ...
Ma Joad's user avatar
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2 votes
0 answers
19 views

Defining the PSNR for images in CIE-LUV or CIE-XYZ or CIE-HCL spaces

In image compression applications, we know that for an 8-bit 0 to 255 level grayscale image the PSNR (peak signal to noise ratio) can be defined through the MSE as: $$MSE=\frac{1}{mn}{\displaystyle \...
user3236841's user avatar
1 vote
1 answer
33 views

Quantifying stitching effects

I have many images like this with high stitching, medium stitching, low stitching, and no stitching effects (the adjectives high, medium, low and no are purely subjective). How to quantify the amount ...
Kasthuri's user avatar
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0 votes
1 answer
155 views

Comparision of phash and Facebook PDQ

The phash algorithm is as follows: Convert the image to greyscale and scale to 32x32. Compute the discrete cosine transform of this scaled image. Discard all components of the DCT except the upper-...
Rma's user avatar
  • 105
1 vote
2 answers
410 views

Inverse fft does not give back the same image

I tried to Fourier decompose my image using FFT and reconstruct it back using IFFT. While I did this, I noticed something peculiar: The first image is the regular one, and the second is the image I ...
DatBoi's user avatar
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