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.
497
questions
0
votes
0answers
24 views
Image Z Coordinate Clarification
I'm trying to understand 3D image reconstruction, and want to clarify how we can find a z image coordinate.
Is the z coordinate for image coordinates (x,y,z) the focal length since that's the distance ...
2
votes
1answer
20 views
What exactly is "connectivity" between pixels in an image?
So, my professor says that two pixels are connected if:
they are neighbours; and
their intensities satisfy a specified criterion of similarity.
And depending on the type of neighbours they are, they ...
0
votes
0answers
12 views
Convert pictures from the same camera with different FOV to pictures with same FOV
I have a camera device that produce two pictures at the time:
depth picture with FOV: 87° × 58°
RGB picture with FOV: 90 × 65°
I expect that they "share" the same objective so their origin ...
0
votes
1answer
30 views
Image conversion - raw ultrasound data to convex image
As a project, I'm trying to decipher raw data coming from a medical ultrasound device.
The data contains a 128x1008 matrix. Each one of the 128 columns represents a sensor element. Each row in each ...
0
votes
0answers
14 views
how to identify the main segmentation step in a paper?
I am trying to summarize the segmentation methods submitted in the Cell Tracking Challenge. Currently, I'm having a problem in identifying the main segmentation step used in each paper. How to ...
4
votes
1answer
38 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 ...
0
votes
0answers
15 views
What are some good references that define images from a statistical point of view?
I know that images can be studied and understood as 2 dimensional signals. However, I hope you can point me towards references that define and present images rigorously in terms of realisations of a ...
0
votes
1answer
86 views
Is there a way to find the contours of instances in a binary mask image by color?
I need to find the contours for each of the instances of microscopic cells in a binary image mask of dimensions 256 x 256 shown below.
My approach involves thresholding the image to get a binary mask ...
6
votes
2answers
159 views
Locate Non Homogenous Areas in an Image
I need to choose some points on an image. These points should be chosen more where there is lots of color changes, transitions and variations. Which techniques can I use for determining where most ...
2
votes
1answer
65 views
Basic Wiener application
I'm trying to filter this $g(x,y)$ WGN added
image
My Wiener filter is:
$$H(u,v) = \frac{P_{f}}{P_{f}+P_{n}}$$
Where the image power spectral density $P_{x}$ is estimated as $\frac{|X(u,v|^{2}}{N^{2}}$...
0
votes
0answers
77 views
How to enhance thermogram image in grayscale?
I'm trying to do some image processing to improve the image below but I'm having some trouble. I already tried to do histogram equalization followed by laplace sharpening, I tried to implement a ...
0
votes
0answers
27 views
How would you process this image?
I got this image:
I need to keep only the part in the center (I mean, the circle with texture inside). How would you do it in Python? I'm trying to use Hough Transform, but some times it detect wrong ...
3
votes
1answer
31 views
What is Label Refinement in the Context of Image Segmentation
I have been reading the paper entitled Measures of Similarity by Unnikrishnan and Herbet, in which they discuss some metrics to evaluate image segmentation. They use the word refinement of labels/...
0
votes
0answers
52 views
Removing feature matched outliers within same image using RANSAC
I'm a student working on a copy move forgery detection algorithm.
I have a forged image. By far I have,
Found keypoints and descriptors from the image
Matched the descriptors using 3 Nearest ...
0
votes
0answers
16 views
How can i center the optical mark image?
I want to recognize optical mark using image processing algorithms. There is a wide variety of optical paper and i want to recognize all off them. For example; If i create a template I can superimpose ...
1
vote
0answers
36 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
votes
1answer
57 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 ...
0
votes
0answers
56 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
vote
1answer
33 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
votes
3answers
77 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 ...
0
votes
0answers
33 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
votes
1answer
51 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 ...
0
votes
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
votes
1answer
77 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.
...
0
votes
0answers
15 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
votes
1answer
40 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://...
1
vote
0answers
789 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
votes
1answer
68 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
votes
1answer
152 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....
0
votes
0answers
29 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
vote
0answers
36 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
votes
1answer
42 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
votes
1answer
453 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?
1
vote
0answers
22 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.?
0
votes
0answers
28 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 ...
1
vote
0answers
24 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
29 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 ...
3
votes
2answers
95 views
Should Edge Detection Be Applied 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
votes
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
vote
1answer
413 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:
$$
\text{PSNR} = 10 \log_{10} \frac{\sum_{m,n} ...
1
vote
0answers
25 views
Thresholding algorithm for separating skin from clothes in python
I have an several images that look like the following:
I would like to separate the skin from the trousers here without specifically training a segmentation model. Can anyone suggest any such ...
0
votes
1answer
295 views
Cropping binary images based on pixel counts in python
I have a numpy binary masked image that looks like the following:
I want to automatically crop this image like the following:
Can I achieve this using some sort of image processing rather than ...
0
votes
1answer
79 views
What are the 'phases' in this 2D scaler filter
I am pretty new to DSP and have been looking at how image scaling is done in hardware. I and came across a 2D scaler core for an FPGA here. I have read up a bit about polyphase filters, but am ...
0
votes
0answers
12 views
How to accurately pinpoint multiple overlapping circles in image?
I have binary bitmap images (medical annotation overlays) where sometimes multiple circle perimeters are present which are overlapping.
I need to extract the individual center and radius for each ...
1
vote
0answers
44 views
Red Color selection in Python and Skimage
I'm trying to load an image from the disk and then to extract just the red channel of it and display it in grayscale with grey colormap but I don't know what I'm doing wrong.. The image should be ...
1
vote
1answer
164 views
Noise Power Spectrum calculation
I want to compute the 1-D noise power spectrum (NPS) for a uniform CT image. The equation of the 2D NPS is as following:
$$
NPS(f_x, f_y) =\frac{1}{N}\sum_{i=1}^N|DFT_{2D}[I_i(x,y)-\bar{I}_i]^2\frac{\...
3
votes
1answer
490 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
394 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
votes
0answers
150 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
votes
0answers
36 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 ...
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