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 ...
BobbyChun's user avatar
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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.
holder fo's user avatar
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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 ...
Heretolearn's user avatar
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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. ...
Ka Mirul's user avatar
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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 ...
mohammad rezza's user avatar
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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 ...
shashank ranjan's user avatar
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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 ...
Hau Chung's user avatar
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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 ...
Bala Sai Sigireddy's user avatar
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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 ...
Sahil Sharma's user avatar
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byte order of P6 ppm image in C

this is the main function ...
Ishaan Vatus's user avatar
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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 ...
sat_P's user avatar
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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 ...
Deniz Açıkgöz's user avatar
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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 \...
user3236841's user avatar
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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-...
Rma's user avatar
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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 ...
Cerise's user avatar
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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 ...
BenjaminLi's user avatar
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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 ...
mohammad rezza's user avatar
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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-...
Rma's user avatar
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1 answer
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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), ...
beantowel's user avatar
2 votes
1 answer
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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 ...
napoleon4269's user avatar
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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 ...
Jinyoung Choi's user avatar
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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 ...
Michael Allman's user avatar
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1 answer
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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 ...
geloescht's user avatar
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1 answer
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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 ...
Sergi's user avatar
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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 ...
gin's user avatar
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1 vote
1 answer
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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 ...
gin's user avatar
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1 answer
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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 ...
gin's user avatar
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1 answer
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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 ...
SpaceCadet2810's user avatar
2 votes
1 answer
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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 ...
Francesco Binucci's user avatar
1 vote
1 answer
109 views

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 ...
Tom W's user avatar
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3 votes
1 answer
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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)...
user153245's user avatar
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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, ...
Jakub Mitura's user avatar
1 vote
1 answer
66 views

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, ...
NoviceB's user avatar
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1 vote
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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 ...
Sandro's user avatar
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4 votes
1 answer
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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 ...
LogicBreaker's user avatar
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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 ...
requiemman's user avatar
2 votes
1 answer
101 views

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 ...
hasanghaforian's user avatar
4 votes
1 answer
196 views

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 ...
Jun Yang's user avatar
3 votes
1 answer
51 views

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 ...
cloudfeet's user avatar
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2 votes
1 answer
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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 ...
Mark's user avatar
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