Questions tagged [image]
This tag covers signal processing where input is an image, such as a photograph or video frame and the output could be an improved or altered image, parameters related to the image or information about features within the image.
487
questions
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0answers
23 views
Image downscaling methods
I am researching downscaling methods for image downscaling. I've both read and found area-averaging to work well in Python using CV2, but the settings in MATLAB allow for it's bicubic interpolation ...
0
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1answer
33 views
What exactly is a connected componnent in an image?
The following is a paragraph from "Digital image processing, 4th edition, Gonzalez and Woods".
Let S represent a subset of pixels in an image. Two pixels p and q are said to be
connected in ...
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0answers
18 views
Image convolution using FFT
I just can't get my head around Fourier transform and convolution in 2D. I am trying to implement image convolution using fast Fourier transform (in julia). So the first thing I need to do is to pad ...
1
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1answer
26 views
T1 Mapping in Python?
I'm trying to write a simple program to perform T1 mapping of a few MRI Images.
My understanding is that all I need is to plot the pixel intensity values by inversion time then fit a curve. The output ...
0
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3answers
43 views
Beginner Educational Resources
New member here. Recently got hired into a mid level EE position. Have a BSEE but performed more radar performance analysis at a higher system level previously. In my new group we're doing a lot of ...
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0answers
12 views
How to calculate the magnitude while calculating Blur in an image using using OpenCv based on Fast Fourier Transformation
I am working on image blur detection and found 3 methods for it. One is Laplacian Method but it works good with Gaussian, average, median and other distribution ...
0
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1answer
42 views
How is non-integer upres downres (1080p game on a 1440p screen etc) calculated
Please redirect me if this is not the right place to ask.
I was unable to find a straightforward answer to this question. What I am wondering is, if I am playing a 1080p game on a 1440p display, what ...
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0answers
11 views
Correlated signal components from uncorrelated and incoherent source after reflection
To this point, it has been assumed that the point sources
composing the source are uncorrelated, generating fully
incoherent signals. Thus, capturing the reflected signals and after sufficient time ...
0
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1answer
26 views
How to come true the convolution with a 2-D array in frequency domain with python
I use the pretty simple example used in many books to understand the convolution in the frequency domain. But I cannot find the real results.
...
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0answers
13 views
How to obtain height above ground, angle the pixel’s local surface normal makes with the inferred gravity direction from depth map of image?
For extraction of the HHA features from the image depth map we need to calculate the height above ground, angle the pixel’s local surface normal makes with the inferred gravity direction. How to ...
0
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1answer
29 views
SAR spotlight raw signal database
For practicing spotlight processing, i am looking for I/Q baseband signal from a SAR airborne or spaceborne system. In my research I have only found processed image from :
eoweb geoportal https://...
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0answers
123 views
How to make a contour smooth in OpenCV
I am using OpenCV(4.5.1) and trying to extract a smooth contour of an object on my image.
Firstly I got the contour by:
...
-1
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1answer
54 views
How to find a pixel's image coordinates by its rgb value in MATLAB? [closed]
How would one find the pixels that match an RGB value in a matrix in MATLAB?
Let's suppose that I want to find the image coordinates of pixels whose value is $RGB=(144,127,11)$ for a given image in a ...
0
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1answer
78 views
kernel to calculate second order partial derivative of digital image
im working on image stacks, and I need to calculate second order partial derivatiatives of it.
I already know how to calculate derivative on x and y axis, using coefficients calculator: https://web....
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0answers
28 views
What is the between spatial frequency of an image and pixel size of the sensor?
In my lecture notes about the sampling of an image I've written that:
Since pixels have a finite dimension the spatial frequency response is attenuated before the "ideal" Nyquist frequency
...
1
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0answers
27 views
Multivariate Histogram Matching for Image Color Matching
Suppose X is random variable that is spatial position in finite range, which its Cumulative Distribution Function (CDF) could be calculated easily, then if I have two random variable X and Y spatial ...
2
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1answer
37 views
Where 2-D DFT is necessary in image processing applications instead of 2-D DCT?
As we know the 2-D DCT is a real-valued kernel and less computational complexity and it used in several image processing applications like image compression etc. 2-D DFT is a complex kernel and high ...
3
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1answer
99 views
Is the Laplacian Filter an High Pass Filter (HPF)?
Is this kernel name as mean difference kernel or Laplacian filter?
Is mean difference just a method?
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0answers
20 views
Feature extraction for IRIS recognition
What are types for feature extraction in iris recognition? How can I divide it on types which detect phase, edge, etc.?
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0answers
22 views
LPF and HPF filters in ENVI
Since we know about convolution filter in image processing, it is basically a matrix applied to an image and a mathematical operation comprised of integers and it works by determining the value of a ...
0
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0answers
23 views
feature extraction techniques for iris recognition
I want to ask how I can divide feature extraction techniques to feature detectors and feature descriptors. I have big problem how to understand it. For example I can use Gabor filters (feature ...
1
vote
1answer
28 views
Where do you recommend getting “standard” images for testing algorithms?
I've noticed that there are a LOT of websites which claim to have a standardized repository of images (for image processing algorithms). However, I don't know which ones are actually trusted by the ...
0
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1answer
47 views
Edge detection in spatial or in frequency domain?
I want to ask why everywhere is used to do edge detection in spatial domain and not in frequency domain with FFT of image and apply HP filter. Thank you.
0
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0answers
23 views
How can I compute the result of the magnitude of edges of an image?
I have a random image with 11x11 pixels. In the center of the image is a square of 5x5 pixels. The gray level of the background is 0 and the gray level of the square is 50. How can I compute the ...
1
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1answer
141 views
Defining the SNR or PSNR for color images (3 channel RGB files)
In image compression applications, I know that for an $8$-bit $0$ to $255$ level grayscale image the PSNR (peak signal to noise ratio) can be defined as:
$$
\text{PSNR} = 10 \log_{10} \frac{\sum_{m,n} ...
1
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0answers
23 views
Thresholding algorithm for separating skin from clothes in python
I have an several images that look like the following:
I would like to separate the skin from the trousers here without specifically training a segmentation model. Can anyone suggest any such ...
0
votes
1answer
79 views
Cropping binary images based on pixel counts in python
I have a numpy binary masked image that looks like the following:
I want to automatically crop this image like the following:
Can I achieve this using some sort of image processing rather than ...
0
votes
1answer
50 views
What are the 'phases' in this 2D scaler filter
I am pretty new to DSP and have been looking at how image scaling is done in hardware. I and came across a 2D scaler core for an FPGA here. I have read up a bit about polyphase filters, but am ...
0
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0answers
11 views
How to accurately pinpoint multiple overlapping circles in image?
I have binary bitmap images (medical annotation overlays) where sometimes multiple circle perimeters are present which are overlapping.
I need to extract the individual center and radius for each ...
1
vote
0answers
25 views
Red Color selection in Python and Skimage
I'm trying to load an image from the disk and then to extract just the red channel of it and display it in grayscale with grey colormap but I don't know what I'm doing wrong.. The image should be ...
1
vote
1answer
140 views
Noise Power Spectrum calculation
I want to compute the 1-D noise power spectrum (NPS) for a uniform CT image. The equation of the 2D NPS is as following:
$$
NPS(f_x, f_y) =\frac{1}{N}\sum_{i=1}^N|DFT_{2D}[I_i(x,y)-\bar{I}_i]^2\frac{\...
2
votes
1answer
274 views
2D Frequency Domain Convolution Using FFT (Convolution Theorem)
In the time domain I have an image matrix ($256x256$) and a gaussian blur kernel ($5x5$). I've used FFT within Matlab to convert both the image and kernel to the frequency domain as zero padded $...
2
votes
2answers
187 views
Coordinate system in digital image processing
I am trying to understand image coordinate system where I read that it is reversed.
So if $f(x,y)$ is actually $f(y,x)$ where $f(\cdot, \cdot)$ is the image. I am a bit confused and would appreciate ...
0
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0answers
89 views
Zero Padding in image reconstruction
I need to zero-pad the image for a better reconstruction but according to my project details, I will be given a Fourier-transformed image so can someone tell me how to pad the image in such a ...
0
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0answers
32 views
Fourier coefficients of images?
For a continuous function $f$, it is well-known that the decay of $f$'s Fourier coefficients $\hat f_n$ is related to the differentiability of $f$. Some examples:
for a smooth periodic function $f$, ...
0
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0answers
23 views
Python, Is there a way to find the properties of a subregion within a larger image region?
The goal: I have images with particles that I need to find the area of. Each particle also has four to five sub-regions that I need to know the area of. Think of a bunch of stripped shirts in a ...
0
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0answers
34 views
Solving for a convolved function inside an integral
I have an imaging system that produces a signal in a pixel, in part, by responding to incident radiance $L(\lambda)$ that passes through a filter with transmission $T(\lambda)$. Lumping all the other ...
0
votes
1answer
26 views
MATLAB: Prepare an RGB image for digit and letter recognition
I need a Matlab function that prepares an image for digit and letter recognition.
What I need now is to convert the original RGB image to a binary image that every pixel in it is white except the ...
1
vote
0answers
35 views
Spatial frequency and video frequency of an image
in my lecture notes about image sensors (CCD, precisely) I have read the following statement:
The transfer function $F(\omega)$ of the image sensor is related to its spatial resolution function $F(\...
1
vote
1answer
39 views
Is it okay to interpolate between overlapping areas obtained using a sliding window?
I am using a 50x50 pixel sliding window which moves left to right every pixel so that it covers a whole binary image which is about 2000x2000 pixels. In the window, the ratio value of black to white ...
1
vote
3answers
153 views
What does this paragraph mean?
I'm reading this paper about about an algorithm to measure image sharpness, and am confused by these sentences in the 6th paragraph:
It is well known that the attenuation of high-frequency content ...
0
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0answers
19 views
Standard Deviation of Character Gradients in a Document Image
I have the paper titled "CG-DIQA: No-reference Document Image Quality Assessment Based on Character Gradient". It is all about assessing the quality of the document image based on its blurriness. To ...
1
vote
0answers
21 views
What is Maximally Stable Extremal Regions (MSER)?
In the paper , MSER is being defined. Please help me understand what is MSER and how to implement it.
The paper says,
The regions are defined solely by an extremal property of the
intensity ...
1
vote
1answer
29 views
Comparision between SSIM and MAD Image Quality Assessment Algorithms
I have been working with Most Apparent Distortion(MAD) tool to evaluate the quality of images. I have read a paper that compares SSIM, PSNR, FSIM, etc. with MAD. I am uncertain about some calculations ...
0
votes
1answer
33 views
Image Processing [closed]
I have an image and I am trying to find its rows and columns.
A = imread('lena.jpg');
nrows = size(A,1)
ncols = size(A,2)
This is 3 dimensional matrix. Output ...
0
votes
1answer
26 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
2answers
47 views
Average image over $N$ frames with one frame buffer
Can you give some filter that is averaging an image over $N$ samples in a recursive way that only needs one frame buffer?
$\frac{1}{N} \sum_{k=1}^{N} y_{k}(m,n)$
I can only imagine filters that need ...
0
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0answers
56 views
How do you apply DCT steganography on an RGB image?
I am working on a DCT-based steganography program in Python and I found a working model in Github. The program, however, can only encode on one of the RGB channels. Resulting in a discolored image. ...
0
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0answers
106 views
Maximally Stable Extremal Regions (MSER) Implementation in Document Image Character Patch Identification
My task is to identify character patches within the document image. Consider the image below:
Based from the paper titled "CG-DIQA: No-reference Document Image Quality Assessment Based on ...
0
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0answers
64 views
Why is my Fourier descriptor not rotation invariant?
I am trying to implement a simple contour based Fourier descriptor to classify some MNIST images. Nothing fancy.
As expected, if I discard the first coefficient, I achieve translation invariance. ...
