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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1answer
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How Can Convolution and Deconvolution be Defined for 3D Images?

I am trying to understand how convolution and deconvolution can be represented for 3D images/ stacks of data. I would prefer it, if you built the these concepts from 1D vectors to 3D matrices in terms ...
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3answers
5k views

An Intuitive Way to Understand the Sharpen Convolution Filter in Image Processing

Can someone explain sharpen in a non-technical way. So, I don't mean that you need to multiply every pixel with 5 and subtract it with the pixel left, under, above and right.
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4answers
17k views

How Does a Convolution Can Be Expressed as a Matrix Multiplication (Matrix Form)?

I know this question may not be very relevant to programming, but if I don't understand the theory behind image processing I'll never be able to implement something in practice. If I got it right ...
4
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1answer
99 views

2D Multi Scale Dot Enhancement Filter based on Gaussian Filter and Hessian Matrix

I'm trying to implement an algorithm that enhance dot and line like structures based on Hessian matrix, the algorithm uses Gaussian filter with different scales before calculating the hessian matrix ...
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2answers
20k views

Detection of a Circle in Noisy Image Data

I have an image that looks like the one below: I'm trying to find the radius (or diameter) of the circle. I have tried using circular Hough transform (via matlab's ...
3
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1answer
159 views

Multi Scale Shape and Detail Enhancement from Multi Light Image Collections

I have been working on a practical implementation in Matlab of the algorithm Raanan Fattal suggested in the following paper. I couldn't understand the meaning of eq. 11 on page 5: \begin{equation}\...
4
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1answer
6k views

Where to get a proper dataset collection for bikes and cars

I am doing a project on image classification and I don't know where to get the data-set collection for cars and bikes.Any suggestions to sites for this purpose is welcome.Also please suggest the ...
3
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2answers
856 views

What Is the Best Color Space to Work with for Hand Detection: RGB, HSV, or YCrCb?

I'm working on hand gesture recognition using C#. I'm using OPENCV for skin detection but its performance is not optimal. So I decided to do some filtering based on color space, but I do not know what ...
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4answers
22k views

How do I get the most accurate camera calibration?

First off, I hope this is the correct Stack Exchange board. My apologies if it is not. I am working on something that requires me to calibrate the camera. I have successfully implemented the code to ...
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1answer
204 views

Running the BM3D Denoising Algorithm in Python

I am looking for a strong baseline in image denoising and therefore wanted to have the BM3D algorithm in my benchmark. These 2 python implementations: https://github.com/ericmjonas/pybm3d https://...
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0answers
11 views

Texture Synthesis using Heeger siggraph paper

i am implementing texture synthesis using steerable pyramid using Heeger Siggraph et. Al. paper, link for the paper is here https://www.cns.nyu.edu/heegerlab/content/publications/Heeger-siggraph95.pdf ...
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1answer
25 views

Applying a 2D band pass filter (Butterworth ?) to an array with NaNs

I am trying to filter out the low frequencies of an array looking like this : For now, I am taking transects of this array and applying a 1D - butterworth band pass filter : ...
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1answer
3k views

How to Estimate the Noise of an Image / Estimation of the Noise in an Image?

I want to know how to estimate the noise of an image? Also is this represent the camera's noise? Does anyone know how to estimate the noise of an image or camera? Update: Especially, I want to ...
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1answer
37 views

Similarity or Relation between Walsh Hadamard Transform and Slant Transform

Is there any relation between Walsh Hadamard Transform and Slant Transform? Or is there any common property or similarity?
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0answers
182 views

Skewed rectified aerial images

I have a series of aerial images from which I would like to get disparity maps for every consequent pair. In order to do that I do a stereo rectification. The problem is that sometimes rectified ...
2
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1answer
425 views

What Are the Differences in Four Different Types of Third Order Image Moments (Skewness)?

I am attempting to analyze images using the third order image moment (aka skewness), but I am having trouble figuring out how to do so. As it turns out, there are four different types of third order ...
2
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1answer
474 views

How to Use Maximum a Posteriori Probability (MAP) in Classification Task

I have a 2D image defined on a region $\Omega$. Let $I: \Omega \to R$ be a gray image. Assume that the region can be separated into $N$ sub-regions $\Omega_i$ such that $$\forall i,j=1,\ldots ,N:\...
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4answers
886 views

Apply Principal Component Analysis for RGB Images

I've implemented a method to compute PCA on grayscale images. I haven't seen PCA on RGB images yet, which left me wondering if it is possible to perform it. With RGB images, is PCA done for each ...
6
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1answer
260 views

Analytical Expression for Convolution of Two 2D DFTs

I am trying to do an image analysis problem on some images, and I want to calculate some things in the frequency domain which are giving me problems. Say I have an (discrete) image $I(x,y)$ of size $...
2
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1answer
52 views

What impact have different types of border-handling on high pass or low pass filtering?

When high or low pass filters are being applied to an (grayscale) image, the borders need to be handled separately. They could be filled with 0's or 255's (b/w), repeat the nearest pixel value, or ...
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0answers
20 views

Randomly Generate Synthetic Noise in an Image Text Document

I'm working on denoising dirty image document. I want to create a dataset wherein synthetic noise will be added to simulate real-world, messy artifacts. Simulated dirt may include coffee stains, faded ...
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4answers
79 views

Understanding correlation in image processing using examples

I have been trying to understand the intuition behind the correlation. I understand from this guide that correlation is a way to detect a known waveform in a noisy background. I have seen from this SO ...
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2answers
3k views

Why Should the Sum of Masks / Kernel / Filter in Image Processing be One?

I am studying pyramids (expanding and reducing) and I am a newbie. Why should the sum of the convolution mask be one when we are using gaussian distribution? According to When should the sum of all ...
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3answers
253 views

Are 2nd Order Edge Detectors More Susceptible to Noise?

I am reading about edge detection and I read that 2nd order detectors are more susceptible to noise. Is there a mathematical proof to this ?
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2answers
148 views

Wavelet Filter Coefficients from Scaling Filter Coefficients

I am trying to develop a new type of wavelets and I found out a function that following a particular two scale relation. The function at a scale $t$ say $x(t)$ can be related in a finer scale $x(2t)$ ...
2
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1answer
263 views

How to Get Rid of Ripples from a Gradient Image of a Smoothed Image?

I have a gray scale UINT8 image. When I smooth it with a Gaussian filter and then compute the gradient image with a Sobel filter in OpenCV, ripples would appear. ...
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2answers
85 views

Understanding the Bilateral Filter - Neighbors and Sigma

I have been reading about the Bilateral Filter in - Fast Bilateral Filtering for the Display of High Dynamic- Range Images and have felt crippled and confused while understanding its working and the ...
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2answers
14k views

Gaussian Blur In MATLAB and Connection to Image Resolution

I am calling fspecial() in MATLAB to create a Guassian blur of an image. For example, ...
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1answer
283 views

Should I Use a High Pass Filter (HPF) or Low Pass Filter (LPF) to Enhance the Features for Image Splicing Detection?

I'm recently learning image splicing detection. I've already known image splicing can bring some abrupt changes to an image,which generate the sharp edges.And sharp edges correspond to high frequency. ...
2
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1answer
416 views

Amplitude of an Image

If I take a two dimensional image and conduct a fourier transform on it, I would get a two dimensional matrix of complex values. If I want to find the amplitude of each value, is that the same as ...
2
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2answers
82 views

why do directional derivatives work better with a gaussian filter?

I've been working on image segmentation and computing the directional derivatives of a grey-scaled image, with the objective of detecting contours and edges. I have realised that if I apply a gaussian ...
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0answers
15 views
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1answer
62 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 ...
2
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1answer
531 views

Gaussian weighted distance between pixel amplitudes: motivations and sources?

In several image processing papers, and for instance in Random Walks for Image Segmentation (2006) by Leo Grady, changes in image intensities are turned into edge weights. In some fields, it is called ...
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1answer
44 views

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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2answers
11k views

Measuring the contrast of an image

For a project, I want to measure the contrast of a global image. I want to compare different images to get the image with the best contrast. I know about the Weber contrast, but I need a normalized ...
2
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2answers
42 views

What are the measurable factors of image sharpness?

I need a way to present data on an essay written about image sharpening algorithm. So I've thought that if I measure a factor of sharpness from image or relative sharpness (between test img and ...
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3answers
200 views

Are There Good Methods for Converting Color Image to Gray Scale Image?

Converting color image to gray-scale image is often the first step of many image processing tasks. There exists many gray-scale image conversion methods. Most them, however, is to give R G B bands a ...
0
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1answer
89 views

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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0answers
15 views

Signal similarity analysis after cross correlation

I have a time series signal and using this as reference, from the main data set extracted possible matching sections using cross correlation technique.(xcorr matlab).Based on with the threshold xcorr ...
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0answers
17 views

Power spectral density of surface roughness

I am currently working on understanding how visually and intuitively the power spectral density is the fourier transform of the autocorrelation of a signal. I was wondering if anyone had a good ...
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0answers
14 views

Looking for a way to fill holes in objects, and break bridges between them

I am trying to extract building footprints from satellite images. Using a series of morphological operations i.e erosion and opening by reconstruction, I'm able to obtain the footprints, albeit with a ...
1
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1answer
30 views

Sharpening Using Laplacian Kernel - How to Handle the Output (Specifically Negative Values)?

In order to sharpen an image using Laplacian kernel, it should be convolved with the original image. It is evident that the result might have negative values. I am not sure what to do with these ...
5
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3answers
310 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 ...
3
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2answers
146 views

What Is the Correct Way to Apply Richarson Lucy Deconvolution to Luminance Data?

My question concerns the Richardson–Lucy deconvolution algorithm, which is described in Richardson's original paper. I am interested in applying it in the context of a raw image converter for digital ...
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1answer
25 views

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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0answers
25 views

What does total variation norm mean in an image?

What is the notion of total variation and how is total variation norm calculated in an image? More exactly, I want to calculate and understand the meaning of $ \left \|X \right \|_{TV} $ if $X$ is an ...
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2answers
10k views

Image Shadow Removal Using OpenCV and Python

How do I remove a shadow after MOG2 background subtraction using OpenCV Python? I used all morphological operations, gaussian and median blur, thresholding. it removes noises but deep shadow is ...
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0answers
33 views

SIFT between 1 image and dataset (2 images)

I use SIFT, and I want to find the angle of inclination of an image compared to two reference images, in short: I have 3 images : Image x: input image Two images 1 and 2, reference images that are ...
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4answers
2k views

Implementation of Fourier Domain Denoising with Hard Threshold

I just tried the Fourier denoising method with a hard threshold and my code is as follow: ...