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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Understanding Implementation of ULA Array Response and Beamforming Techniques in MATLAB [closed]
I am currently working on a MATLAB project where I aim to replicate the functionality of certain Phased Array System Toolbox functions (phased.ULA() and ...
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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 ...
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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.
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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 ...
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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 ...
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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 $\frac{1}{2 \pi \sigma^2} e^{-\frac{(x - x_0)^2 + (y - y_0)^2}{2 \sigma^2}}$ ...
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Use DFT (`fft()`) to Replicate 2D Convolution (`conv()`)
In MATLAB, I tried to convert the fft2-based multiplication using conv2.
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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 ...
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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 ...
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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...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 \...
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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 ...
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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-...
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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 ...
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How would the correlation coefficient between 2 images change if we rotated 1 image?
Suppose we have a image which is represented by a matrix
$
\begin{bmatrix}
a & b & c \\
d & e & f \\
g & h & i \\
\end{bmatrix}
$
and we want to find its correlation with ...
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Image resolution vs. dimensions
Doing a machine learning computer vision project, and I am a bit unsure of the difference between image resolution and dimensions is, and how I should refer to them in writing. The images in my ...
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How to reconstruct MMW image using electrical field in each direction at Receiver points using Back projection algorithm
I have used a structure including 109 Receivers and 4 transmitters in order to do MMW imaging(multistatic imaging). Imaging was done in 3 different frequencies. So, now I have electrical field in each ...
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Applying DCT two times in perceptual hashing
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-...
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1
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How to use DCT to compare images?
I want to compare 2 images X and Y, and I have the DCT results dct(X), ...
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Converting cutoff_frequency_ratio to Cycles/Pixel in Butterworth Filtering with skimage
I am working on my thesis where I'm employing Butterworth filtering on images using the function butterworth from scikit-image's skimage.filters module. The code/formula I'm referring to is available ...
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modulation transfer function and ground resolved distance
I am trying to understand something in remote sensing but lack a background in science and technology so it is difficult. Hopefully this is a reasonable question to ask.
In sensing there are different ...
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Template Matching non-rectangular template in non-linear order
Question
Is there an existing algorithm that does cross correlation with two images, including a weight image?
In template matching, when should I prefer the sum of absolute errors vs cross ...
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How can I find an error measure based on the horizontal shift of vertical lines?
I have a grayscale image consisting of MxN 1 byte pixels.
The image shows K vertical lines. Each vertical line has the same thickness.
Due to a systematic error each line is imaged in a different ...
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Detecting camera raw image saturation/clipping level
I'm looking for a fast but robust algorithm to detect whether a camera raw image has clipped/saturated highlights and, if so, compute the level at which saturation occurs. This saturation/clipping ...
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Periodicity problem with FFT for generating "starburst" from aperture
I am following a paper on computationally modeling optical phenomena within a lens. (https://resources.mpi-inf.mpg.de/lensflareRendering/)
At some point they use the Fourier power spectrum of an ...
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Sampling a pulse train with a controllable square wave
I have an issue regarding a sampling process of a pulse train in an image sensor based on events. Basically, these are a family of image sensors in which each pixel outputs a train of pulses, and the ...
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systematic approach to enhance brightness and contrast of a panchromatic image
I have panchromatic images taken from a remote senescing device, and it is downloaded as a raw which is dark/ underexposed (as 1st pic), hence it needs enhancement in brightness and contrast to be ...
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Using an experimental PSF to perform a deconvolution
I have an experimental PSF (point spread function) of an optical system for remote sensing images.
However, it is asymmetrical and has some sidelobes as below.
And I want to perform deconvolution to ...
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How to measure quality of sharpening in images
have a distorted (blurred image) and I perform several deconvolution algorithms on it to sharpen it (Richardson lucy, regularized inverse filter, tikhonov miller). And i want to measure each ...
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Separate two images using a statistical approach
So I have a fundamental question (for which I can't find a good answer anywhere). Say we have two images (A and B) and their mixed image (C) as follows:
Now say that I've been given Image (A) and ...
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Can the FFT be employed to make a dataset as Multivariate Normal distributed?
I have dataset composed of a large number of images with a large size (i.e., 32x32px), and I'm trying to adapt a feature extraction framework which assumes that the input dataset is Multivariate ...
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Robust method to detect pinpricks in an image?
I expose films in a jig with pin pricks as reference markers. I use these references to register the scanned images of the film to other data.
I've been using mouse click coordinates to date, but I ...
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What does the $H$ operator exactly do in the deconvolution process and why is it needed?
According to Deblurring Dynamic Scenes via Spatially Varying Recurrent Neural Networks, given a 2D sharp image $x(m, n)$ and a blur kernel $h(k, l)$, the blurred image is obtained as
$$
y(m, n) = (x*h)...
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sinusoidal waves for texture similarity
I created an algorithm that approximates the tiny image texture by a series of sinusoids. It is NOT Fourier or discrete cosine because the boundary is highly irregular.
I have each wave's frequency, ...
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Understanding difference in rotation and translation
Hi I am a newbie to the field so please don't mind a rookie question. I have read multiple articles and want to ensure my understanding is correct.
I have following two images. In the second image, ...
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Compare sharpness at subpixel level
I'm working on algorithms for a camera system (which go down to sub-pixel precision). Until now, I just worked on a recorded dataset, but I'm now moving to real cameras.
My question is how to find the ...
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Video Alpha Matting
I'm looking to composite an opaque object (e.g. 3D art) into video footage of semitransparent fog/clouds before a landscape background so that the object seems immersed in the clouds but occludes the ...
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How do I remove the aurora from an image to enhance the background stars?
Most auroral pictures are post-processed and enhance the aurora to such an extent that you don't see the background stars. Suppose I have a photo of the night sky with an aurora, taken with my phone ...
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The Second Derivative of an Image Using the Sobel Filter
For computing the Harris corner detector, I want to calculate $I_{xy}$ and $I_{xy}$. Obtaining $I_x$ and $I_y$ are clear for me. But what about the second order derivatives?
This and this and this one ...
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Detect Longest Vertical Lines (Edges) in an Image
I have a task in image processing, which need to detect vertical lines from matrix. For example, there is a pair of white and black vertical lines segmenting the picture below. I need to find it. So I ...
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Robust encoding of data into visual image
I have an app which lets users download presets as ~10kB of data and share them. There's no web-service or anything, it's just posting files and stuff.
Bandwidth and storage space aren't so tight in ...
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When computing the phash value for an image, why compare against the median?
The pHash algorithm for computing perceptual hashes of images is as follows:
Convert the image to greyscale and scale to 32x32.
Compute the discrete cosine transform of this scaled image.
Discard all ...
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