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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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MIMO FMCW radar - back-projection

any suggestion how to start implementing the back-projection algorithm in a FMCW MIMO radar? Currently I'm using 2D FFT to get radar image, I would try time-domain algorithms to improve the overall ...
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Peak Signal to Noise Ratio (PSNR) in Python for an Image

How do I calculate the maximum signal to noise ratio (PSNR) in Python? Is there any library that can calculate PSNR for Image?
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Response function for digital camera pixel

To help me with doing some signal processing on an image, I'd like to model how a digital camera works. The camera has a bunch of pixels. What is the relationship between the value of that pixel in ...
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What principles to use, in order to create field that will be read by OCR?

I currently have an invoice, where some numbers are written by hand, and I would need to read them automatically. My past experience is that people who write numbers will them write in so many ...
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Local noise intensity in an image

Noise can be assessed in uniform regions of an image, by subtracting a lowpass-filtered version of it. Then from the histogram of intensities, a global measure can be obtained (such as the average ...
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Active contours (cvSnakeImage) in OPencv 4, legacy module

I want to use active contours (SnakeImage), but i can't find them in Opencv 4.1.0, i know that cvSnakeImage existed in modules in the older versions of Opencv, i can't find an answer to question in ...
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Losslessness of Laplacian Pyramid

I was just reading up on the Gaussian pyramid and the Laplacian pyramid, used in compression applications of image. The source is here - Carnegie Mellon 16-385 Computer Vision - Spring 2019, Lecture 3 ...
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CLAHE - Redistributing excess pixels among histogram bins

In order to clip an image's histogram to a maximum value, according to the CLAHE algorithm, the excess pixels (above the clip limit) will be distributed equally among all the histogram bins (While ...
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2answers
333 views

Interpretation of Histogram in Statistical Image Processing

I am learning statistical image processing by myself. In papers and books, it always show the histogram of original images and gradients as the following image shows. The histograms of images vary ...
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1answer
123 views

What Is the Difference Between MRF and Total Variation in Noise Removal?

I have a general question in image processing. I have a noisy image. I would like to classify the noisy image into some regions. Two famous approaches I can use are: MRF/Gibbs MRF: Model the spatial ...
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1k views

Magnitude of the Gradient in Frequency Domain

I'm learning some basics of image processing. Recently I've read about image filtering and two-dimensional Fourier transform, because I'm preparing for exam. And I have one question I don't know ...
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1answer
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How to Clean Black and White Images Which Are Results of Edge Detection

I want to extract text from some images with messy backgrounds. First step was switching to gray scale, applying an edge detection algorithm, and then cleaning up a little bit. Here's an example of ...
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ORB Algorithm: What Is Intensity Centroid?

So, I am reading a paper about ORB: An Efficient Alternative to SIFT or SURF and it happens to calculate the direction of corner from it center . According to Rosin the author of the paper;moments of ...
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1answer
349 views

Use Scale Space Representation to Filter Single Image

Currently I hope to use scale space representation to filter one image. Features in one image can be filtered using an Gaussian smooth filter with one optimal sigma. It means different features in one ...
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What Is the Algorithm Behind Photoshop's “Black and White” Adjustment Layer?

Can someone explain the algorithm behind the "Black and White" adjustment layer in photoshop? I have to reproduce it using C++ for an application that emphasizes non-red/magenta(ish) pixels from an ...
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Laplacian Operator with and without Diagonal Direction Elements in the Kernel

This is a general question on the laplacian operator, which has two different versions. The first version is : \begin{matrix} 0 & 1 & 0 \\ 1 & -4 & 1 \\ 0 & 1 & 0 \end{...
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Applying Lowpass (LPF) and Highpass (HPF) Filters to an Image in Frequency Domain in MATLAB

What I want is simply to apply low pass and highpass filters to an image in the frequency domain. Does MATLAB image processing toolbox have any commands for this?
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How to synchronize audio and video streaming for not fixed FPS streaming?

It's a 3-stage process. In the first stage, a video (with audio) is recorded at a fixed 25 FPS rate. In the second stage, it's demuxed in two different channels and the video is processed. In the ...
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Estimate Variance of Additive White Gaussian Noise (AWGN) Given Multiple Realizations with Different Mean

Given $ N $ images of the same scene, where each image is corrupted by additive white Gaussian noise of the same variance $ {\sigma}^{2} $. How can $ {\sigma}^{2} $ be estimated? So we have an Image $...
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Trying to make magic color filter for scanned document, but not getting perfect output

I am trying to make a magic color filter for the scanned document but not getting the desired output. In some documents text is distorted in some document, images colors get lost. In some document, ...
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How to produce color image using edge detected images?

Hi I am trying to produce an image which is a combination of multiple images such as in focus stacking. Now I have 6 photos and I want to produce a final image such that the final image uses blocks of ...
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1answer
57 views

Determining Parameters of S Function for Image Global Contrast Enhancement

I know that S-function (membership function from fuzzy set theory) is a commonly used function for image enhancement. I am reading a paper titled - A Novel Fuzzy Image Enhancement Using S-Shaped ...
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Is it necessary to have a reference plane when doing structured-light scanning for depth calculation?

I'd like to create a point cloud of an object using the structured-light approach with either fringe-projection or dot markers but the object I plan on "scanning" won't be in front of a flat ...
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212 views

How to remove striped noise from this image. Which filter or algorithm use better?

I need to process a gray scale image. The task is to remove the stripes, which constitute some noise. I have next origin image: This image received many channels ADC(Y) in moment of time (Xn) from ...
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How to simulate Zoom, Pan, Tilt transformations?

Say we are looking at a football field from a broadcast view. To give us another tool, we also have a transform of that view to a topdown view. So our two views are like so: How would one simulate ...
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1answer
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Discrete wavelet transform disadvantages

I read in a paper that the discrete wavelet transform (DWT) has two disadvantages The first one is the shift variance property due to the downsampling process. Could you please help me understanding ...
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Zone Plate Reconstruction

I am trying to reconstruct the Zone Plate image and am struggling to remove the last remaining aliasing. ShaderToy: https://www.shadertoy.com/view/wdGGWK In the shader above you can see that I am ...
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Generate the Matrix Form of 2D Convolution Kernel

We know that a convolution can be replaced by a multiplication with a toeplitz circulant matrix. Meaning, assume I have convolution kernel $h$ and matrix $I$ (of size $m \times m$ for example), then ...
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Detect circle using Hough transform

I am new to image processing and try to learn how to detect circles using the hough transform in Matlab. I have a shortcode that seems to contain no errors but when I run it I get the image but with ...
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1answer
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Detect valve position without colors

I can't find a solution for my problem and I need your help. I have to create an application to detect if a valve is open or close like this : https://www.youtube.com/watch?v=VY92fqmSdfA Some ...
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1answer
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Why zero padding the 2-d DFT interpolates images in spatial domain?

I was applying different image interpolation techniques and I came know to about interpolation in frequency domain. In this technique we first take 2d DFT of an image, padd it with zeros and take the ...
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What factors should I consider in choosing an edge detection algorithm?

I've learned about a number of edge detection algorithms, including algorithms like Sobel, Laplacian, and Canny methods. It seems to me the most popular edge detector is a Canny edge detector, but is ...
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Recommended Order of Performing Denoising, Deblurring and Super Resolution on an Image

In the normal workflow of image processing, there are multiple operations, increase image contrast, image denoising, image deblur and image super-resolution. What are the sequence/order of performing ...
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How to do colour map in MRI?

For this question, I assume if we do a colour map, it is based on the magnitude of the magnetic strength? After that how do we know where each coordinates belong to? Like for example at p= 0 degrees,...
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3answers
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Reduce the Number of Intensity Levels of a Grayscale Image in MATLAB

I have written a Matlab script to reduce the number of intensity levels of each pixel of a grayscale image from 256 to some power of 2. ...
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1answer
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Dynamic Range and Image Contrast

Please explain the terms: dynamic range, and image contrast, and the difference between these two. Also, how can these two be understood by seeing an image by naked eye for the sake of understanding. ...
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Approaches to Segmentation in images of water surface

this is my first question here. Therefore please help me inform me when I miss any good practice in asking questions here. Given a short video sequence of an water surface, I would like to detect if ...
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Determine Gaussian distribution parameters from the signal-to-noise ratio

Is there a straightforward formula for determining the mean and standard deviation of the gaussian distribution followed by noise applied on an image, knowing the signal-to-noise ratio between the ...
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2answers
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Understanding the Probability Distribution of Intensity Values

From "Digital Image Processing 4th ed. - Gonzalez, Woods" Let $p_r(r)$ and $p_s(s)$ denote the PDFs of intensity values $r$ and $s$ in two different images. A fundamental result from probability ...
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2answers
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Difference between 2D DFT's and 1D DFT's of Linearized Matrices

I have recently left the safe and easy MATLAB environment and begun to use CUDA-C/C++ for image processing. Since CUDA doesn't allow 2D arrays to be passed into kernels I am now used to linearizing ...
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1answer
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Can Normalized Cut be used to find connected components in binary images?

I'm unsure whether Normalized Cut can or can't be used to find connected components in binary images. I would argue that it could, but could not validate this argument.
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Fast morphological erosion/dilation with variable window sizes

I want to perform the following operation on an image: consider a square window around every pixel, find the maximum value in this window, and replace the central pixel value with this maximum value. ...
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Why Are There Two Different Common $ 3 \times 3 $ Kernels for the Laplacian?

I find both of these 3x3 Laplacian kernels to be commonly used: 0 -1 0 -1 4 -1 0 -1 0 and: -1 -1 -1 -1 8 -1 -1 -1 -1 ...
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What is energy in image processing?

There are several web articles on the topic, but, after having read them, I still don't know what "energy" is, in the context of computer vision (CV) and image processing (IP). It is related to ...
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Palmprint Identification - Why do we align the images before we use the Fourier Transform?

I have been reading the paper PALMPRINT IDENTIFICATION BY FOURIER TRANSFORM by WENXIN LI, DAVID ZHANG and ZHUOQUN XU about identifying persons based on an image of their palm, one version of the paper ...
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What Is the Bilateral Filter Category: LPF, HPF, BPF or BSF?

I`m reading about Bilateral filter with images, I knew that it uses Gaussian filter (which is a LPF) as a domain filter plus a range filter and it is used to preserve edges(high freq component). Can ...
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blur detection using opencv

I'm writing a script to detect blur images using OpenCV by applying Laplacian filter and calculate the std but there is a problem the std for images that contain motion blur is very close to those ...
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Estimating Convolution Kernel from Input and Output Images

Given an original image and a convolved version of it, I need to calculate the convolution kernel. For example, given: and I would like to calculate the convolution kernel that generated the second ...
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1answer
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Image Gradient: Light to Dark, Dark to Light

From link: Black-to-White transition is taken as Positive slope (it has a positive value) while White-to-Black transition is taken as a Negative slope (It has negative value). So when you ...
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1answer
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What Is “Description Vector” in Image Processing?

When we want to use classifiers like SVM, we first should extract descriptors using algorithms like SIFT. But I have a question which might call a silly one: Let's assume $$ \begin {equation} D_a=\{...