All Questions
Tagged with image-processing image-processing
3,213 questions
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How to produce self-adjoint filters using Gaussian and motion blur in Matlab?
I am trying to write a Matlab code to produce motion and Gaussian blur. Here is my code:
...
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1
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0
answers
56
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What is the meaning of pixel 'value' when interpreting as inverse-fourier transform?
I’m working on a image signal project using C++ with DFT, IDEF.
I major in physics and have lots of experience dealing with 1d fourier transform..
HOWEVER, 2d dft is really not intuitive.
I studied a ...
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4
votes
2
answers
103
views
Fingerprint enhancement lighter version
I've been advised to ask here, I hope that it fits.
Original question:
I want to create a more straightforward and lighter version of this fantastic repo (which itself is based on Fingerprint Image ...
- 141
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votes
0
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59
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Apply fft on video as 4D array
I working on a project called " eulerian video magnification " and i want to apply FFT on video and get the frequency response from the video . I have gotten 4D array ( frames,width,high,...
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Using three data sets of different resolutions together for imaging
I am new in this community. I hope the question I want to ask suits the people here.
Here, we are dealing with two-ring Positron Emission Tomography (PET) scanner (figure 1), also called Compton-PET, ...
0
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1
answer
115
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Does the combined pointsample+bilinear upscaling algorithm have a name?
I have been performing digital image upscaling of pixel art in one of my hobby projects, and the two simplest upscaling algorithms are point sampling or bilinear upscaling.
Point sampling exhibits ...
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-1
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1
answer
541
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Problem with running BM3D implementation in Python
I found about one of the BM3D implementation in Python through this post and tried to use the same, however, I don't see any difference after using the algorithm.
Here is a small snippet of my code,
<...
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0
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2
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210
views
In Foreshortened Area - why we use cosine?
When calculating Foreshortened Area as in the image below, why are we using cosine(theta) to calculate the scaled length in the x-axis? I understand intuitively why no correction is needed in the y-...
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6
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1
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238
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Discrete Cosine Transform (DCT) as the Limit of Principal Component Analysis (PCA)
On the Wikipedia article about Discrete cosine transform it is said:
For strongly correlated Markov processes, the DCT can approach the compaction efficiency of the Karhunen-Loève transform (which is ...
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3
votes
1
answer
429
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Choosing sigma values for Gaussian blurring on an anisotropic image
I have an anisotropic image that is anisotropic both in terms of number of voxels and also in terms of voxel resolution.
...
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4
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1
answer
76
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How to Estimate a Multi Channels and Multi Kernels Convolution Kernel (Deep Learning Style) Given the Input and Output Images
Is it possible that can estimate convolutional kernel that have multi channels and multi filters ?
I saw answer from this to link to estimate kernel for one channel and one filter (Estimating ...
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1
answer
65
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preparing the ct scan data of a patient, using a visible feature in the mri image
A dataset of mri and ct scan images of patients has been prepared. There is a feature /damaged area/ in the mri image that is easily visible. But the injury of this area is not visible in the CT scan ...
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3
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162
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The Effect of the Finite Radius of Gaussian Kernel
Page 168 of Digital Image Processing, Global Edition says:
we know that the values of a Gaussian function at a
distance larger than 3𝜎 from the mean are small enough that they can be ignored.
If we ...
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1
vote
1
answer
56
views
Segment Image of Small Elements on Neutral Background
I have a 8 bit gray level image where if the value = 122 it means no information, value = 0 means highly negative, and value = 255 means highly positive.
I want to connect as many positive information ...
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1
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1
answer
175
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Segment Hand Image into Palm and Fingers
Here is my code, i want to extract only the fingers and save them as a new image
...
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1
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1
answer
68
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What are the purposes of color extraction using k-means clustering?
Using K-means clustering it is possible to reduce the amount of colors in an image. What are the purposes of using this method for extracting colors from an image?
user66064
5
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2
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134
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Analyzing 2 2D Kernels Which Approximates a Gaussian Kernel
I'm new to image processing and am working on mask operations.
I was given two kernels A and B, and performed convolutions respectively on an image.
Then, I have to get the difference of output image ...
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1
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1
answer
260
views
Calculating satellite position from images taken by the satellite of the earth surface
I'm currently a little stuck with a problem, that sounds easier than it is (at least for me):
Let's say you have satellite images taken from LEO that show an approximately 1000 km wide area (the image ...
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1
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0
answers
144
views
Algorithm for Hue correction behind HSL sliders in image processing software
I have a project where i need to recreate hue specific hue adjustment sliders like in Lightroom/Capture One/DxO photolab.
Initial image.
Image after hue adjustment (Orange hue range) in DxO Photolab....
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3
votes
1
answer
204
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Estimating the Most Likely Harmonic Signal in a Spectrogram
Experimental data description: below image is from spectrogram of doppler radar return as I walk toward sensor. Bright sinusoid shape modulated with frequency F is from motion of small retroreflector ...
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1
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615
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2D Cross-Correlation on different sized images
As per this post the cross-correlation between 2 images is obtained as it follows:
...
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4
votes
1
answer
105
views
Extract the Frequency from the Index of the Bin in 2D DFT
How can I find the distance from DC term (center) to the peak point of the frequency in the image Fourier transform?
In the figure below, we know that the distance of the peak point goes to the edge ...
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1
vote
1
answer
158
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main idea of Adaptive histogram equalization (AHE)
I want to understand the main idea behind AHE and the way for applying it manually with my hands.
Wikipedia says:
In its simplest form, each pixel is transformed based on the histogram of a square ...
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3
votes
1
answer
260
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Mathematically show the problem of Histogram Equalization
Wikipedia - Adaptive Histogram Equalization says about classic Histogram Equalization:
This works well when the distribution of pixel values is similar throughout the image. However, when the image ...
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2
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329
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purpose of histogram equalization
What is the main purpose of histogram equalization on image? Is it used to enhance contrast of image or is its goal finding a transformation which gets a more
uniformly histogram?
Although Wikipedia ...
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1
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148
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What are the results of the two-dimensional Fourier transform of the image?
What are the results of the two-dimensional Fourier transform of the image?
For an intuitive interpretation of the Fourier transform, refer to the link below.
enter link description here
The link ...
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6
votes
2
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181
views
Best parameter to estimate image reconstruction quality?
Context: I am a PhD student in physics and right now I am studying phase retrieval with low illumination
With two different parameters I obtain these two images:
With hight illumination (less noise) ...
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5
votes
3
answers
2k
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2D Cross-Correlation using 1D FFT
I need to calculate cross correlation between 2 images which I read in 2 vectors, both of them uni-dimensional.
As per my understanding I need to do the following operations:
FFT(1D) on vector 1 and ...
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4
votes
1
answer
75
views
Calculate magnitude of the gradient using higher order statistics
I am making a model for detecting blurred part of an image. I'm using features described in the paper Blurred Image Region Detection And Segmentation by Hyukzae Lee and Changick Kim, and I have a ...
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6
answers
2k
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Why color is coded with two numbers rather than one?
I was thinking why color spaces use two numbers to represent color: Lab, HSV, HSL? Is it possible to use one number and have the same or very similar properties when comparing colors as we have for ...
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1
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92
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Based on the eigen structure, What applications of discrete sine/cosine transformations can be found?
I am a PH.D in mathematics. I am interested in finding some applications of discrete Sine/Cosine transformations (DTTs) that are based on the eigenvectors.
I have found some results concerning ...
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4
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78
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How can I analyse the motion of plasma
I am currently attempting a project of plasma analysis. One of the aspects of this project is to determine the stability of the plasma, when a plasma is unstable it loses its shape partially or starts ...
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0
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67
views
2d fourier based filter on odd image sizes
I am trying to use
$$
f(x, y) (-1)^{x + y} \Leftrightarrow F(u - M/2, v - N/2)
$$
to post-process the result of a Fourier-based filter operation, like so
...
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1
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0
answers
83
views
Replicating Hysteresis based Thresholding Technique to an Image from a Paper
I was reading a paper where they applied a hysteresis thresholding to help with segmentation of vessels in an image. It provided a formula to determine how to select a hard threshold (Th), which ...
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2
answers
150
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Extract diagonal area from image
I have a gray scale image of fibres in different orientations. My goal is to mark the area where the fibres have a specific angle and neglect the rest. In the future it should be an automated process ...
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4
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1
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184
views
The Effect of the Order of Downsampling and Smoothing on the Output
How do I prove or disprove:
Smoothing an image with a 3x3 filter using full convolution and then downsampling an image by 2 produces the same result as downsampling an image by 2 and then applying ...
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2
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1
answer
664
views
Before the fft2, why need fftshift for the kernel?
When I study some paper, I have some questions about usase of convolution theorem.
...
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3
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1
answer
114
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Computer Vision: What is a good approach to find the similarity between 2 screenshots of a screen from a mobile application?
I am trying to find an algorithm to determine the similarity between 2 screenshots of the same screen of a mobile application. I have tried structural similarity index, Peak signal-to-noise ratio and ...
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2
votes
1
answer
3k
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Implementation of Wiener filter to deblur an image using Python and OpenCV
EDIT: I have debugged the runtime warning, and now I am able to get an output image. However, the output image is still blurry. Increasing the constant value heavily distorts the image. Setting ...
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0
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247
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What image similarity measure is best for measuring the structural similarity of two images?
I am looking for an image similarity measure that can measure the differences between the structural composition of two images. For example these two images have structural differences between them
...
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1
vote
0
answers
43
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Proof symmetry after 2D-convolution with $1/\lvert \mathbf x\rvert$ implies 2D-symmetry [closed]
Let be two 2D functions $f(x,y)\geq 0 \ \forall (x,y)\in \mathbb R^2$ and $g(x,y)=\frac{1}{\sqrt{x^2+y^2}}$.
I have, furthermore,
$$\int_{\mathbb R^2} f(t_1,t_2)g(x-t_1,y-t_2)dt_1dt_2=\int_{\mathbb R^...
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1
vote
1
answer
935
views
Diferrence between normalization of a histogram and equalization in image processing
So I know that the two methods aim to change the intensity of the pixels. My question is in which way do they differ?
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3
votes
1
answer
409
views
How is the inverse Fourier transform of a Hermitian-symmetric input efficiently calculated?
The np.fft.rfft2 function exploits the Hermitian symmetry of the transform of a real input to more efficiently calculate the transform by omitting the negative ...
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2
answers
79
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Removing tessellating interference patterns from images
The microscopy image below is corrupted by an irregular checkerboard-like grid. I attempted running 2D-FFT on the image, but was unable to isolate the frequencies which cause the pattern.
How would I ...
1
vote
1
answer
216
views
Segmenting dark spots from a light background?
I need to perform automatic segmentation of dark blue spots on light yellow paper. Here's a very simple example:
In this case, a simple threshold based on hue or brightness works well. But here are ...
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2
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163
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How can I use the FFT in MATLAB to get the time domain equation representation of an image? [duplicate]
My goal is to take any image and break it down to obtain its time-varying equations so it can be redrawn and store the picture as two equations. One for $x$ and one for $y$.
As I understand, MATLAB's ...
5
votes
1
answer
447
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Is there an analogue to the 2D DFT that is rotation equivariant?
I'd like to know if there is some general Fourier transform or other signal processing algorithm, such as a discrete wavelet transform, that is rotation equivariant.
Rotational equivariance of a ...
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1
vote
2
answers
207
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Spline interpolation of a binary mask
I have the following binary mask (If it helps you can assume that every it is always 1px wide).
I want to travel from one given point to another (from start to end in this case). You are given the ...
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0
answers
83
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Object detection only when a particular type of object is on the image
Apologies if this has been answered already.
I am very new to computer vision. I am kind of familiar with object detection and classification for many types of classes, which involves training data ...
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2
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244
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Downsample (aggregate) raster by a non-integer factor, using a Gaussian filter kernel
The task is to downsample (aggregate) a raster from 100m pixel size to 460m. The aggregation should be performed using a Gaussian filter. To better understand the task, I am following the paper ‘The ...
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