All Questions
112 questions
1
vote
1
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42
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Intensity uncertainties in 2D image
I am trying to detect patterns in a raw image file where each pixel has an intensity. I can imagine fitting a 2D surface to the image (or to a portion of it) using a chi2, but for that, I need the ...
- 111
-2
votes
2
answers
137
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 ...
- 107
-3
votes
1
answer
185
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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 ...
- 107
1
vote
2
answers
203
views
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 ...
- 73
0
votes
3
answers
379
views
How do I know if an Image contains Noise?
I am working on a set of Images captured by an Industrial camera. However, I am not sure if I need to apply any Denoising (e.g. Gaussian or Laplacian etc) on it ?
Is there any metric that I can used ...
- 101
-1
votes
1
answer
126
views
Can FFT2 be used as a randomness test for image encryption?
Based on this link
Is it possible to consider a model to introduce FFT2 as a parameter to determine how random the image is? (randomness test like Entropy)
consider Lena's image and its FFT2:
If we ...
- 51
4
votes
3
answers
439
views
Any Relationship Between the Entropy of an Image and Its Spectrum?
Is there a relationship between the Shannon entropy of image and the output of the 2D Fourier transform (DFT) of the image?
- 51
1
vote
2
answers
570
views
What's the FFT2 of white noise image?
I try to compute the FFT2 of the white noise image.
I use this image
with Entropy 7.995 and
pixel scatter plot:
based on this python code:
...
- 51
0
votes
1
answer
122
views
Measurement of blocking artifacts in images
I want to define a threshold for maximal blocking artifacts in an image.
What is a good key value to measure blocking artifacts?
I have no reference image
non natural image
Example:
I looked into ...
2
votes
1
answer
585
views
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 ...
- 39
0
votes
1
answer
71
views
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:
...
- 101
0
votes
0
answers
49
views
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 ...
- 101
5
votes
2
answers
399
views
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 ...
- 425
1
vote
1
answer
433
views
Help generating non-Gaussian noise
I'm trying to add non-Gaussian noise to an image. The purpose is to synthesize realistic camera noise. I am doing the following:
Obtain a noisy image sample by subtracting a low ISO photo from a high ...
- 13
4
votes
1
answer
363
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 ...
- 41
4
votes
2
answers
2k
views
periodic noise detection in image's frequency domain
Since I'm learning frequency domain and I'm really curios about this topic, I'm trying to solve a problem (that I have already solved it using morphology [detecting lines by their thickness]) in ...
- 43
2
votes
1
answer
197
views
Extracting ridges in automatically in image
I am trying to extract ridges from an image, calculated using the eigenvalues of the Hessian matrix (see answer in Best way of segmenting veins in leaves?). In this image I have zeroed out the ...
- 141
0
votes
0
answers
84
views
standard deviation of two constant noised signals related through interpolation
Let us say say we have a noised constant signal and want to evaluate the standard deviation (std) of the noise. We calculate the std of the said noised signal and call it $\sigma_1$. Now we process ...
- 9
2
votes
1
answer
120
views
Thresholding Algorithm for Separating Skin from Clothes
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 ...
0
votes
2
answers
418
views
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 ...
- 103
4
votes
3
answers
437
views
How to denoise a video stream 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 ...
- 41
0
votes
0
answers
228
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?
- 27
1
vote
1
answer
798
views
How to calculate variance of noise on a noisy image (Noise+Signal)
I have a long exposure image captured at 70ms. (I1) (As attached)
I also have another image captured at 0.7ms with Gain24. (I2) (As attached)
This image has both noise and signal together.
I would ...
- 11
0
votes
1
answer
70
views
Regarding the nature of white noise in images
I have just started learning the very basics of noise.
I have come to understand what white noise is in sound samples, but I do not understand the meaning of white noise in images.
In sound samples, ...
0
votes
2
answers
2k
views
confusion regarding correlation in noise?
I am reading online article about image processing at following link
https://www.electronicsforu.com/electronics-projects/software-projects-ideas/image-processing-using-matlab-basic-operations-part-2-...
- 1,952
0
votes
1
answer
157
views
Measure how Straight/Smooth the Borders are Rendered in an Image
I have two images:
I want to measure how straight/smooth the text borders are rendered.
First image is rendered perfectly straight, so it deserves a quality measure ...
- 127
0
votes
0
answers
45
views
Dirty Image Quality Assesment Measure
I was looking for a way to measure how dirty is the document in image processing. Example images below:
a. Dirty Backgrounds
b. Dirty Backgrounds with Text
Can someone give me an initial idea to ...
- 127
1
vote
0
answers
210
views
Randomly Generate Synthetic Noise in an Image Text Document
I'm working on denoising dirty image document. I want to create a dataset wherein synthetic noise will be added to simulate real-world, messy artifacts. Simulated dirt may include coffee stains, faded ...
- 127
2
votes
1
answer
91
views
Estimate Local Noise Intensity in an Image
Noise can be assessed in uniform regions of an image, by subtracting a lowpass-filtered version of it. Then from the histogram of intensities, a global measure can be obtained (such as the average ...
user7657
4
votes
1
answer
1k
views
Estimate Variance of Additive White Gaussian Noise (AWGN) Given Multiple Realizations with Different Mean
Given $ N $ images of the same scene, where each image is corrupted by additive white Gaussian noise of the same variance $ {\sigma}^{2} $. How can $ {\sigma}^{2} $ be estimated?
So we have an Image $...
- 43
0
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0
answers
347
views
Determine Gaussian distribution parameters from the signal-to-noise ratio
Is there a straightforward formula for determining the mean and standard deviation of the gaussian distribution followed by noise applied on an image, knowing the signal-to-noise ratio between the ...
- 121
7
votes
1
answer
816
views
Which Noise Reduction Algorithms Are Used in Commercial RAW Image Processors?
I'm trying to guess what noise reduction algorithms are used in commercial processors for raw images from digital cameras. I find this fairly easy to do for the sharpening algorithms (most use unsharp ...
- 123
1
vote
1
answer
2k
views
How to interpret PSNR value?
Say, I have original image, noised and denoised. By PSNR value I want to find out how good does my denoising algorithm works.
For which pair of the images should I calculate it? I've tried it for ...
- 173
6
votes
1
answer
1k
views
Are There Common Values of Standard Deviation for Gaussian Noise of an Image?
For example, it occurs to me that there might be a standard deviation value of Gaussian noise in which the human eye could no longer distinguish an object because the standard deviation is very high ...
- 63
0
votes
1
answer
147
views
When a stochastic process would be a beneficial model in terms of noise
Let's say we have an image/signal with some noise in it. When would it be beneficial to model the signal as an outcome of a stochastic process?
More specifically:
How significant would noise have to ...
- 45
1
vote
0
answers
398
views
Calculating the Mean Square Error (MSE) in Wavelet Denoising
I´m currently reading the paper (to be more precise: it´s a chapter from the book "Shearlets, Multiscale Analysis of Multivariate Data" by Kutyniok and Labate) "Image Processing Using Shearlets" by G....
- 11
0
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1
answer
163
views
Why does White Noise in images imply noise in adjacent pixels are independent?
My professor said in the class that for "Additive White noise, the noise in pixels adjacent to each other are independent". How?
This is what I have got so far: White noise implies that PSD (Power ...
- 447
0
votes
1
answer
254
views
How to add additive noise to an image?
I have the following image I and I want to add additive noise using the array N below. Can you please give me a calculation example of how to achieve this?
Do I have to move from image space to ...
- 101
1
vote
0
answers
244
views
Detection of interesting structure in images?
I'm looking for methods of computing some measure of structure in an image. (I do not have a rigorous definition of "structure" though........) Consider the 15 image blocks below:
Suppose for each ...
- 121
0
votes
2
answers
336
views
improving pre-processing (noise removal) orange seven segment display for OCR reading
About this project: Older images have the date they where taken placed on the image, in the bottom left hand corner. The goal is to extract this date and put it in the EXIF data of the scanned photo.
...
1
vote
2
answers
2k
views
Why Do Most of The Papers Use the Frobenius Norm for Denoising?
I have an noisy image and I want to remove noise from it; suppose $y$ is noisy image and $A$ is linear mask which makes my image noisy and $x$ is original image, so we have
$$
Ax + \eta = y
$$
and $\...
- 31
0
votes
2
answers
1k
views
Uncorrelated and zero mean image noise
Consider a noisy image g(x,y) formed by the addition of noise n(x,y)
to an original image ...
3
votes
1
answer
2k
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What is the effect of noise on Shannon entropy?
Since entropy is a measure of uncertainty or randomness, intuitively we would suppose that adding noise to an image would increase its entropy since we are now more uncertain about the information of ...
- 67
2
votes
1
answer
585
views
What does it mean by DN in salt-pepper noise?
What is DN on page 245 of these notes shown in the slide below?
user23572
2
votes
1
answer
417
views
What does photon noise mean in digital image processing or computer vision?
From this link:
Photon noise, also known as Poisson noise, is a basic form of uncertainty associated with the measurement of light, inherent to the quantized nature of light and the independence of ...
user23572
11
votes
4
answers
67k
views
Peak Signal to Noise Ratio (PSNR) in Python for an Image
How do I calculate the maximum signal to noise ratio (PSNR) in Python? Is there any library that can calculate PSNR for Image?
- 211
1
vote
1
answer
1k
views
How to calculate autocorrelation function of an image noise
I am trying to calculate the autocorrelation function of an image noise. Specifically, I want to calculate the NCORR parameter in the function deconvwnr(). I have knowledge about the noise, which is ...
- 111
0
votes
1
answer
899
views
Discard circular/blob like structures from image
I have a binary image that looks like this:
And I would like to get rid off all the small structures and just keep what's on red:
Image erosion is an option that works well to remove the very small ...
- 103
1
vote
2
answers
778
views
gaussian noise in an image
according to
Estimating acquisition noise P. 2
Estimating the mean and the standard deviation for each pixel is calculated as below:
$$
\begin{equation*}
i, j = 0,\dots,N-1 \\
\...
- 145
1
vote
1
answer
305
views
Whether Poisson noise will be dominant source of noise in low light conditions? [closed]
I have one paper saying that that the Poisson noise will be dominant source of noise in low light conditions and the other one says the opposite way(Poisson noise will be dominant except in low light ...
- 700