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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21 views

Requirement of time step in convolution output?

I am studying time domain analysis from book signals and systems labotary with matlab by alex palamides when i was studying convolution command topic on page 187, author discussed use of ...
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20 views

Concept of scales in Gabor filter

I've been reading about Gabor filters, and there is a concept of scale. While I understand that Gabor features help in analyzing both the frequency and orientations of an image, what is the idea of ...
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33 views

confused in difference between calculations of convolution and multiplication?

How are two signals multiplied? And how is it different from convolving two signals?? I have read the above question on dsp stack exchange and i also tried it in my matlab , code is as follow: ...
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84 views

Isotropic and Anisotropic in the Total Variation Framework

The isotropic TV is defined as the estimation of 2-norm of gradients $\sqrt{(y_{i+1,j}-y_{i,j})^2+(y_{i,j+1}-y_{i,j})^2}$, while the anisotropic TV is defined as the estimation of 1-norm of gradients $...
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19 views

Satellite imagery color normalization

Satellite images available from public sources (Google Maps, Bing, ArcGis, etc) have a common "flaw" with color balance abruptly changing in places where two different images were stitched (perhaps ...
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65 views

Sampling Theorem for images

A medical Image has a size of 8x8 inches. The sampling resolution is 5 cycles/mm. How many pixels are required? Will an image of size 256x256 be enough? I know sampling in 1D signal but cannot get ...
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53 views

Why am I not getting the intended coefficients in this 2D Fourier demonstration?

I am trying to demonstrate how the 2D Fourier decomposition of an image works with Matlab and a very, very simple example. I create a 4 x 4 pixel image with cosine basis vectors as such: ...
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42 views

How to Remove the Patch Artifacts of Neural Network Denoising Process?

I have written a python script which uses the Noise2Noise: Learning Image Restoration without Clean Data implementation of the Auto Encoder which is useful to remove noise from images. In the original ...
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34 views

Understanding performance of Lucas Kanade Iterative Image Registration Technique

I am reading the paper: Lucas, B. D., & Kanade, T. (1981). An iterative image registration technique with an application to stereo vision. I am having some trouble understanding section 4.3 ...
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27 views

Automatically crop out certain region around red objects

I have the image seen below and I would like be able to automatically crop out everything around each red section - not enough to overlap but enough that you can see how connected to the green parts ...
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2answers
103 views

Circular Convolution Matrix of $ {H}^{H} {H} $

We all know that Discrete Fourier Transform (DFT) corresponds to circular (not linear) convolution. That is to say, if $x(n),h(n)$ and $y(n)$ is the original signal, the filter and output signal in ...
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30 views

Disabled parking sign detection

I would like to ask you, if you could recommend some algorithm for detection of handicapped or disabled parking sign painted on the road or on the traffic sign. I am thinking about image morphology (...
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18 views

How to separate spliced(photoshopped) part from the rest of the spliced image?

I'm working on a project to detect spliced images and want 128x128 patches at the boundaries of the forged regions. I have the authentic background image and the spliced(photoshopped) one. If I ...
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18 views

Hisotgram equalisation error, help with my code

Iam working on implenting a histogram equalisation of an image without using inbuilt functions specifcally imhist and histeq, I have, for the most part understood what do during a histogram ...
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23 views

Elimination of image blurring using noise model restoration techniques

How can the blurring be eliminated from image using the noise model restoration process techniques? To my knowledge the answer must be filter.If yes,then which filter is used?
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1answer
49 views

How is the Gaussian kernel related to the Euclidean distance of the neighbourhoods in the non-local means algorithm?

I am reading the paper A non-local algorithm for image denoising that describes the original non-local means algorithm. They define (p. 3 of the pdf) the distance between two square fixed ...
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1answer
58 views

How do I denoise a microscope image?

I'm working in a computer vision project, where the goal is to detect some specific parasites, but now that I have the images, I noticed that they have a watermark that specifies the microscope ...
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2answers
83 views

Why can convolution only be applied to compute the output of a linear filter?

We apparently cannot compute the output of a bilateral filter (BF) using convolution (with the image) because the BF is a non-linear filter. In general, why can convolution only be applied to compute ...
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98 views

Extracting image metadata programatically

I hope this is the right location to post this, as my question isn't really stack-overflow material but involves images. I have hundreds of SEM-Images like this: and need to track changes in certain ...
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90 views

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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1answer
29 views

Fresnel transform over image

You can recommend the literature or tell you what the Fresnel Transform does to the image. I realized that this describes the passage of a light wave through an optical element, but I need to ...
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2answers
94 views

Why isn't bilateral filtering shift-invariant?

I have a source (that I can't share) that states that bilateral filtering isn't shift-invariant (that is, it depends on the input signal), hence we cannot use convolution and the Fourier convolution ...
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79 views

How to implement separable bilateral filter?

I’m trying to optimize my naively implemented O(n^2) bilateral filter for 2D images. I googled and found a lot of theoretical explanations about the separate one. However, it seems there are things ...
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1answer
59 views

Microscopy crystal particle object length detection

Hi I try to detect the particle length size from this image and I'd like to get the length size of the particle Like this below. and get the histogram of the size of the particle using centroid and ...
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53 views

Use FOV or camera deprojection to find position of pixel in world coordinates relative to my camera?

A teammate and I were discussing how best to get a 3D coordinate point (X, Y, Z) in world units from an RGB-D depth image. I'm using an intel real sense D435. From how I have researched it using the ...
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1answer
88 views

Sum of Squared Intensity Difference for block matching with ORB features, c++

I am trying to implement feature matching algorithm between image reference and image current. The pipeline is as follows: ...
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1answer
26 views

Deriving vector paths from pen strokes

I want to calculate vector paths that approximate pen strokes from handwritten documents. My tool needs to run in batch mode, unlike hand tracing or Illustrator's "Image Trace" feature. The potrace ...
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1answer
35 views

What is the difference between domain and range filtering?

In the context of image processing, I have heard the expressions "domain filtering" and "range filtering". What do these terms refer to? What is the difference between them?
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43 views

What is a periodic signal in image processing?

In the context of image processing (and computer vision), the concept of convolution comes up a lot. Convolution is quite related to the concept of Fourier transform and DFT. In the context of image ...
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245 views

How Much Zero Padding Do We Need to Perform Filtering in the Fourier Domain?

Consider an $M\times N$ image $f$ and an $G \times K$ filter $h$. Given that convolution in the spatial domain corresponds to multiplication in the Fourier domain, then we can perform a convolution of ...
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2answers
111 views

Understanding of Histogram-of-Oriented-Gradients

I am learning about HOG and I understand it from here. A well-explained page with an example. I am not understanding this concept that how it works A 16×16 block has 4 histograms which can be ...
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19 views

Is there any way to do 3D (Voxel Data) feature detection?

In the 2D image processing, there are ways to find and match features of the image (like corner of the edges). However, I could not find the equivalent of that in the 3D-voxel data (Here voxel means a ...
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28 views

How to calculate Walsh hadamard transform for image patches of odd sizes?

I was reading this paper on optical flow, which as apart of the algorithm makes use Walsh-Hadamard transform on image patches of size 2r+1. So far, where ever I have looked, I could only find that ...
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19 views

What is meant by peak value of gradient magnitude?

I am trying to write MATLAB code for the research paper entitled Echocardiography Image Enhancement Using Adaptive Fractional Order Derivatives. The two thresholds are given by a=(peak+min(Gmag))/2 ...
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26 views

What is the difference between a range filter and a low-pass filter?

A low-pass filter attenuates the high frequencies, preserving only smooth variations in the provided image. The result of an image which is low-pass filtered is an image with blurred edges (hence ...
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32 views

What is the relation between smoothing and blurring?

Is there any difference between smoothing and blurring? Are these two operations the same or do these terms refer to different operations?
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1answer
30 views

Why exactly is the Guassian filter a low-pass filter?

In image processing, a Guassian filter is used to blur an image. A low-pass filter is a filter that attenuates the high frequencies, preserving only smooth variations in the provided image. Is a ...
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8 views

Why is correlation involved? - Axis Rescaling for a 2D axes - brightfield illumination microscopy of blood cells

for 1D axis rescaling, you use a FOV calculation len_pixel=total_magnification * len_specimen_in_pixel len_specimen_in_pixel=len_pixel/total_magnification and then to get the axes rescaled, you do ...
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44 views

Intuitively, why is the comb function the sampling function?

The comb function can be used to sample a continuous signal. The comb function is defined as follows $$ C_T(t) = \sum_{k=-\infty}^{\infty} \delta(t - kT) $$ where $\delta$ is the Dirac function, ...
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12 views

What is intuitively a diffusion in the context of images?

I have heard the word "diffusion" in the context of image processing and computer vision. However, images are discrete and I associate the word "diffusion" with a continuous process. Intuitively, what ...
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18 views

PATMAX / Flexible ROI for matlab

I just googled for some hours if there is any toolbox / library for MATLAB with which you can realize something similar like PATMAX does for cognex cameras. I want to add flexible ROI for moving ...
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23 views

Extracting signal from data using Otsu thresholding in MATLAB?

I am very new to signal processing. I am trying to extract a signal from my data using otsu threholding but it's not fully accurate. In this case I know that there is going to be a single signal in ...
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1answer
45 views

What is the relation between time, frequency, spatial and spectral domains?

What is the relation between time, frequency, spatial and spectral domains? I think that time and spatial domains are the "original" domains (e.g. if the signal is a greyscale image, then the domain ...
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1answer
94 views

What do we mean by spectrum?

Consider the context of image processing and computer vision, and, in particular, discrete Fourier transform. For example, in the sentence In the Discrete Time Fourier Transform the forward ...
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1answer
38 views

Crop all written letters from single image

Above image has handwritten hindi / deavanagari letters all on a single image. Task is to Prepare a dataset from the given assignment.jpg image using image processing tools Idon't have clarity ...
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46 views

What is the difference between an impulse response and a kernel?

It seems to me they are two terms used to refer to the same concept, but, according to the Wikipedia page on Guassian filter a Gaussian filter is a filter whose impulse response is a Gaussian ...
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1answer
53 views

What does this notation $g(x) = S\{\delta(t) \}(x)$ mean?

What does this notation mean $g(x) = S\{\delta(t) \}(x)$ mean, where $S$ is a "system", $\delta(t)$ is the impulse function and $g(x)$ the output function of the system? I am really not familiar with ...
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1answer
24 views

Image Pixel Wise Transformations - Recommended Order

I'm new in image processing. Right now I know how to correct white balance and how to correct image contrast. But if I need to make this two tranformations. In which order should I do this?
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147 views

Why Does 2D FFT of Gaussian Looks More Sharper than Gaussian Itself?

I am trying to understand why 2D FFT is done on a Gaussian process in a particular code. From my understanding from these posts: https://www.researchgate.net/post/...
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129 views

What Does 'Zero Order Hold' and 'First Order Hold' Mean?

While studying the Image Magnification in spatial domain, I have come across this definition of Image Magnification by Replication: Replication is a zero order hold where each pixel along a scan ...