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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Filter for female/women appearing in images on websites?

This question is not against women/female But if a talented engineer/programmer is going through a severe heartbreak , it is better that he is exposed less to female So are there any such filters ...
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image preprocessing(filtering) : before or after undistortion and stereo rectification

I'm currently working on a stereo visual-slam program (using OpenCV). After I get the images, there are 2 preprocessing steps to be done : A) Undistort the images + stereo rectification B) Some ...
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Distinguishing between intensity image plots

I have a series of intensity images generated by varying different scatterer geometries. An example of variation observed by varying the aspect ratio of these geometries is shown below in the three ...
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how to understand the gradient vector flow formula

Currently, I am learning gradient vector flow. I have one question about the calculation. After Euler equations, the GVF can be found by solving the following formula: Then, the paper said: "...
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Any ImageJ like platform that can leverage Python backend?

It is kind of a follow-up question of Any good alternatives of ImageJ (Fiji)? I love ImageJ in the way that it is able to easily create Python plugins. However, it seems that there is no way to ...
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The difference between convolution and cross-correlation from image processing point of view

The difference between convolution and cross-correlation from a signal-analysis point of view The above question gives very good information from signal processing point of view. But what about images?...
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Any good alternatives of ImageJ (Fiji)?

I worked on some medical image processing research two decades ago and I used ImageJ then. I started to pick up some medical image processing projects again (some registration and segmentation). I ...
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Signal/image processing using python?Additional IDE must required or default pyhton IDLE is sufficent?

Can we perform signal processing and image processing using default pyhton IDLE(that is downloaded from pyhton website) for scenarios where we may also need plotting etc? or is it necesssary to ...
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Wider sharpening filter

The kernel of a sharpening filter of size 3x3 may look like $$ \frac{1}{4}\begin{bmatrix} 0 & 1 - \alpha & 0\\ 1 - \alpha & 4\alpha& 1 - \alpha\\ 0 & 1 - \alpha & 0 \end{...
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Get The DCT Middle band

I want to get the middle-band frequencies in my DCT matrix of image wdct = cv.dct(wm) How can I extract it ? is there any equation to extract it ?
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Guided bilinear interpolation: is it a known algorithm?

I have a function that's sampled relatively coarsely along one direction, $x$, and much more finely along another, $y$. Sampling grid is regular. I need to interpolate between all these samples, with ...
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Which Blur is being used in this effect

I'm trying to recreate an effect used on photoshop called satin effect, which has an option that control the size of the satin, which I think it's just a special blur applied to the satin pattern So ...
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Why are real-world digital images not bandlimited?

In the materials about image resampling, it always mentions that real-world digital images not bandlimited. However no explanation is provided. For example, Sinc resampling in theory provides the ...
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Bring two Fourier transforms to same range to add them

I have Fourier transforms of two images which I wish to add (Basically I have an input Fourier transform which I mask, reconstruct the underlying image using an algorithm, and then try to replace the ...
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Why resizing an image smoothed by Gaussian by factor of 2 also increase sigma by factor of 2

In the paper about SIFT algorithm (Distinctive Image Features from Scale-Invariant Keypoints) it says at the end of section 3.3: We double the size of the input image using linear interpolation prior ...
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Improving the intuition for the 2d fourier transform

As far as I understand, the 2d fourier transform is calculated as following: ...
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Metric for image sharpness?

Suppose I have a blurry image: a photo convolved with a gaussian blur kernel of unknown sigma. I would want to deconvolve the blurry image using several gaussian kernels (with different sigmas). Is ...
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Image warping with heat map that "pulls" on pixels

I am looking for an efficient image warping function $$f: (\text{image}\in \mathbb R ^{M\times N\times3}, \text{heatMap} \in \mathbb R ^{M\times N}) \to \text{warpedImage} \in \mathbb R ^{M\times N\...
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What does hue, saturation and intensity means in image processing?

I ran some code in matlab to show what is hue, saturation and intensity to get an intuition of what they mean. But the result of the code does not match the explanation i got from here Hue is a color ...
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Noise Reduction - noisy lines

I'm trying to reduce the noise in this photo. What type of filters/techniques should I use to cancel out the noise? I've tried using box filter and Gaussian filter to blur out some of the noise, but i ...
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What's the difference between SIFT and general stereo matching algorithm (eg, sgbm)?

I am working on an open source project s2p which creates digital height model from satellite stereo imagery. The procedure of how s2p works can be roughly summarized with the following steps. Split a ...
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Interpreting results of Sobel Edge Detection

I am implementing A No-Reference Perceptual Blur Metric paper. Somewhere in the prep steps they mention the use of vertical Sobel filter for finding vertical edges. The algorithm is summarized in Fig....
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Copy an object (along with bounding box) from one image and paste on different image (only background)

I have a dataset of images with bounding boxes. I also have another dataset of images with different backgrounds. I want to copy the images from one dataset (with their ground truth boxes) and paste ...
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How to achieve uniform gaussian profile? Beam profile has grainy/multimode pattern

Hi apologies in advance if this (optics & image-process) is not where I should post this question. Thanks for the help! I'm required to make a jig that measures the divergence angle of a ...
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Why doesn't JPEG file format follow indexed color technique?

This is table about "Image file formats supporting indexed color". I don't see JPEG file format in this table. Why doesn't JPEG file format follow indexed color technique?
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Does downsampling an image twice result in a "worse" (or different) image than downsampling once

I am working on a project where the input is a large high quality image (2560 x 1440 pixels), which is eventually scaled down a lot (256 x 256) and used as input to an ML model. For reasons that I won'...
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Fixing distortion in photographic reproductions

I am currently building a photographic setup which I intend to use to make reproductions of a large amount of transparencies(positive and negative film strips). As I will be using a fairly small (1&...
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Registration of point cloud based on feature matching method

I recently find myself an interesting problem to solve. Basically I got 2 partially overlapped point clouds (in real world) that I want automate the registration process. My naive approach currently ...
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7 votes
3 answers
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How to exclude diffuse moving features in a stack of images

I have some stack of grayscale reconstructed images represented as a 3-dimensional matrix DPC with dimensions [Nz,Nx,Nt]. A ...
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How to build the measurement matrix used for compressive sensing

I have a sparse vector $x \in \mathbb{R}^{N \times 1}$, it's real and positive, the non-zeros values are maximum $N/2$ values. It means, I have at least $N/2$ zeros values in $x$. My question, is it ...
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Removing dark borders in Image Stitching for Panorama

I am working on a Matlab code for panoramic image stitching for multiple image frames and getting satisfactory results however there are always dark regions surrounding the stitched images as ...
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Implementation of Deriche filter

The Canny edge detector is expressed by the derivative of the Gaussian. Its practical implementation involves the Gaussian filter, then the Sobel filter to calculate the gradient in both directions. ...
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Finite/Infinite Impulse Response filters

Most image filters are of finite extension (which correspond to Finite Impulse Response in 1 dimension), like Laplacian, Canny, Gaussian... Instead of being of infinite extension (IIR in 1D). Why is ...
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Calculating connected component's central moments

I am learning about image's moments. As an exercise I got this: For x̄ value I get 5 from this formula: $$= \frac{\sum_{x=1}^{X} \sum_{y=1}^{Y} xf(x,y)}{\sum_{x=1}^{X} \sum_{y=1}^{Y} f(x,y)}$$ As ...
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Which type of noise can we see from the given image signal and its abs of 2D FFT?

1. Background: I get an 128*128 2D one-channel noisy image as follows: I get the shifted absolute values of 2D FFT result by the following Python code: ...
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Numerical optimization method for optimal edge detector

John Canny, in his paper "A Computational Approach to Edge Detection" (PDF), finds the expression of an optimal edge detector by first using an analytical approach (Euler-Lagrange equation). ...
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Stitching images with common "static" element using OpenCV

I need to stitch images from the camera attached to the robotic arm. OpenCV has a nice feature (Stitcher), though it's not working correctly, as there is one static element (in the same position on ...
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How can we compute power spectral density ($P_n$) in Weiner filter?

I have an image which I corrupted with white gaussian noise in order to have SNR (Signal to noise - ratio) 10 dB . I want to apply Weiner filter to image which has noise . If I want to compute Pf I ...
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Beginner question about MRI

I am used to process PET/CT scans currently I am starting working on magnetic resonance imaging and I have simple question that I can not find answer for. I have files in Dicom and multiple series. ...
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2 votes
1 answer
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How many dimensions is a RGB image?

I first thought it would be 3 dimensions (one for R, one for G, one for B). However what about the width and height? More a physics/image processing question I think. So, I have a few possible answers ...
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Slicing an Image into Tiles According to Content

Given an image that contains an NxM grid of icons with text below them, somewhat like this: I'm wondering how to split it up into the individual icons with text. Some wrinkles: The image won't ...
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Color Image Watermarking with a Grayscale Watermark

I'm currently working on a project on digital watermarking in a color image. The host image is a color image, and the watermark image that will be embedded is a gray. Is it necessary that the ...
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Can the deconvolution Wiener filter reduce noise without having a blurred image?

I am trying to denoise many several noises with several filters for a research i have, i found a deconvolution Wiener filter made by "mr.tranleanh" on Github, as you can see here . what I ...
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removing stripy artifact from fMRI

I have fMRI images, some of which have a stripy artifact that looks like a Gabor filter. Removing this kind of noise is not, to my knowledge, a standard part of any fMRI processing pipeline. I am ...
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Why I don't have phenomena of aliasing after resize image in frequency domain?

I'm writing code in cuda/c++ languages to resize images. I used a box filter ( it response in spatial domain is sinc filter ) and I have applied the convolution theorem and I'm using the fourier ...
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Covariance of 2D cross correlation result

I am trying to align two 2D signals with one unique correct alignment. After applying 2D cross-correlation on the signals I get results such as these: bad/degenerate peaks: good peaks: decent peak: ...
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jpeg compression: necessity of dividing input image into 8x8 blocks

For jpeg compression, is it necessary to divide the input image into 8x8 blocks and perform a DCT on each of the 64 blocks? If your input image is mxn, could you just have 1 mxn DCT coefficient matrix?...
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How are the edges of an image obtained with anisotropic diffusion?

I already know how to implement the method and obtain a correctly diffused image, but in the papers related to the topic there is usually an edge map that's calculated after the diffusion is performed ...
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2D transformation over triangle?

I think about divide image to triangles instead of blocks. Is possible transform it over triangle? Note that frequency domain can be block, not triangle. I found similar "2D Fourier transform ...
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Expression for DFT of linear 2D ramp

One dimensional solution is in “Expression for discrete fourier transform of linear ramp“ I need two-dimensional for image processing. We have function f(x,y) = $a_1 \cdot x + a_2 \cdot y$, My ...
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