This tag covers signal processing where input is an image, such as a photograph or video frame and the output could be an improved or altered image, parameters related to the image or information about features within the image.

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5 views

Measuring sharpness/contrast

For the implementation of an auto-focus for the raspberry cam I need some measure of image sharpness. I used the following sample picture: The first approach was to compute the shannon entropy of ...
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1answer
28 views

Why can FFT only operate on images with specific properties?

Can FFT only operate on Grayscale images? If Yes, why? Can FFT only operate on images with dimensions of power of two? If Yes, why?
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0answers
45 views

What transformation (or similarity metric) is rotation, shift, and scale invariant?

I have an algorithm to to detect copy-move forgeries in images. I used block matching to detect regions of an image that were forged with copy-move forgery and highlighted the alleged areas. For block ...
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3answers
60 views

Where and how do an Image and a complex number meet?

I am trying to implement a Gabor Filter bank. Gabor Filter uses a complex function. How do the filters like Gabor Filter operate on an Image? Does a complex number represent an entire Image or only ...
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1answer
29 views

Poster detection in OpenCV?

I'm really new in image processing, so please sorry I'm a newbie. I tried to use the squares.cpp for detecting posters (since they usually are rectangles) without using expensive feature detectors (...
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1answer
24 views

Global vector descriptor

Usually, algorithms as SIFT, SURF and many others provides a set of $k$ keypoints and the associated descriptor in $d$ dimensions (for example, in SIFT each descriptor has $d$=128 dimensions). So, in ...
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2answers
39 views

Estimate/Compute parameters of image dataset

I have a dataset of images taken by Kinect (RGB and D) How can I extract the following information only from the images: Frame rate Camera height The dataset containes images of person (s) moving ...
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1answer
26 views

Difference between texture and illumination in image

I am new in image processing. What are texture and illumination in image? How can we define these terms?
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1answer
32 views

pixels in the same image are correlated but how can I visualize it?

I am new in image processing.I know that pixels in the same image are correlated with each other but I don't know how can I draw the relationship b/w these pixels in the form of graph?.
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16 views

Edges in Content Based Image Retrieval (Java)

I have developed a programme that currently computes the standard deviation. I am trying to alter this algorithm so that it can extract the edges of an image. I have been told I can do so if I build ...
3
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1answer
60 views

Which is correct representation for function of variable?

I have a function as $$E=\int_\Omega -\log\big( p_i(x)\big) dx$$ where $p_i(x)$ is density distribution which estimated by Parzen window method. $$p_i(x)=\frac{1}{\Omega_i} \int_{\Omega_i}K_\sigma\...
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2answers
76 views

Segmentation of small artifacts - Image Processing

I am working on a task of segmenting small artifacts from a set of images like below: I am looking for a generic approach, but unsure of what to search? I tried looking at density flow analysis, but ...
3
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1answer
46 views

How to calculate a Hann-LP kernel for image processing

I'm currently studying for an exam in image processing and stumbled upon a exercise which i could not answer and my professor will not be available before the exam anymore. The exercise goes as ...
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4answers
65 views

What is the difference between the terms color Intensity and color Saturation?

In Digital Image Processing, what is the difference between the intensity and the saturation of a color? How would you explain the difference to a newbie?
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0answers
113 views

Removing noise from dental radiography

I'm working on a project of applying Active Shape Model to locate tooth in dental radiograph. For those familiar with the technique, I'm currently trying to sample along normal vectors for each ...
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1answer
35 views

Basis functions in DCT

I'm new to Discrete Cosine Transform (DCT) and I have a question relating to basis functions. In DCT, basis functions are defined by: $$\alpha_p\alpha_q\cos\frac{\pi \left(2m+1\right)p}{2M}\cos\frac{\...
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1answer
20 views

The signal in MRI

I am trying to understand the signal formation in MRI and have a confusion. I understand that in the presence of the external magnetic field $B0$, the protons are precessing at the frequency given by ...
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0answers
35 views

Fourier Transform of 2D signals

Hello I've been trying to solve this one for a while and I didn't come up with any solution. Given two 2D signals $g(x,y)$ and $f(x,y)$ as that $g(x,y)=f(ax+by, cx+dy)$ and that the Fourier transform ...
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0answers
37 views

How to classify images based on the amount of colors in the image?

I have a problem where all images have the same object; however, these objects can either have number_of_colors<=3 OR number_of_colors>3 and images are not labeled. My attempt starts by ...
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0answers
37 views

Image Rotation using 3 Shears, Implemented using FFT-based Shifts

So I'm trying to rotate an image using the 3-pass shear. We're implementing the 3 shears in Fourier space, so we're taking the the rowise/colwise FFT, then multiplying it with e^ikx, with necessary k'...
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0answers
20 views

Can Inpainting and Texture Synthesis address same types of image-restoration problems?

Are In-painting and Texture Synthesis used to address different types of problems? For instance, can both methods operate on damaged Old photographs and wooden textures? Are these methods ...
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1answer
37 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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1answer
32 views

Add padding to object in 4-channel image

I have a 4-channel image (.png, .tif) like this one: I am using OpenCV, and I would like to add padding of type BORDER_REFLECT around the flower. ...
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0answers
25 views

How can we add energy to an image using matlab?

In under water images due to attenuation of light in water ,image appears to be blue so in order to compensate that attenuation ,I calculated the energy of light that is attenuated and i am unaware ...
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0answers
6 views

Using multiple input modalities in Computer vision

This might be a rather broad question, but I hope it will result in a couple of insights or even recipes people have used for the following problem: Suppose you have ...
3
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1answer
62 views

What would produce this “hamburger” corruption on images?

I have an image that has gone through an unknown number of jpeg and webp conversions (at least one but more likely 2+). Currently this image is a JPEG and contains corruptions in single color or mild ...
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1answer
39 views

How to achieve image straightening as cam scanner does?

Is it possible to achieve image straightening as cam scanner does I mean selecting a non-rectangular region and converting it to a rectangular region as an image. I can only do re sizing and crop ...
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0answers
41 views

Gibbs energy in MRF

I am stucking in Gibbs energy in MRF. Firstly, let us define some definition Let $S = {(i, j)|1 ≤ i ≤ m, 1 ≤ j ≤ n}$ be the set of sites of a rectangular lattice for a 2D image of $m \times n$ ...
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0answers
16 views

Which kind of noise will show benefit with Guided filter

I am using guided filter function in MATLAB img_filtered = imguidedfilter(img_noise) I knows that guided filter is very good to preserving edge in noise image. ...
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1answer
53 views

Generate a nonuniform illumination (bias field) 2D image

I am creating a nonuniform illumination in MATLAB R2015. The nonuniform illumination (known as bias field) is defined as Nonuniform Illumination (intensity inhomogeneity) which manifests itself as ...
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2answers
330 views

Blending artifacts in OpenCV image stitching

I am using OpenCV to blend a set of pre-warped images. As input I have some 4-channel images (*.png or *.tif) from where I can extract a bgr image and an alpha mask with the region related to the ...
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2answers
60 views

image type after an ifft reconstruction

I reconstruct images from MRI k-space using ifft and root-sum-of-squares method. ...
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2answers
79 views

How does salt and pepper noise occurs in an image

How does salt & pepper noise occur? And, what are some techniques to remove it?
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2answers
38 views

white noise in images

For digital images, noise is assumed to be additive gaussian white noise. I remember noise in images is considered as high frequency. However, from the link https://en.wikipedia.org/wiki/White_noise, ...
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0answers
46 views

Image rotation - bilinear interpolation method

I am trying to rotate an image but I am getting unsuccessful results. I realise I can just use rotate functions in packages but I am trying to do this in a particular way so I can understand what is ...
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0answers
17 views

Applying window function to Gaussian Like distribution

I am trying to calculate the Modulation Transfer Function (MTF) for a CT scan. I get use the differential of multiple line profiles (as recommended by International Electro technical Commission (IEC))....
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1answer
61 views

Algorithm to extract polygones with holes

I have this picture and would like to extract the bones. First I thought of contour-Tracking, but as you can see in some bones there are holes (Like for example at the left finger, in the bone in the ...
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0answers
30 views

how to write the mathematical equation for the concatenation of RGB channels into one image

I have the following RGB channels for a given image (x): R=x(:,:,1); G=x(:,:,2); B=x(:,:,3); I concatenated them using the ...
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1answer
44 views

what is happening when i run this code line? [closed]

I have the following MATLAB code: x=[1 2 3; 4 5 6; 7 8 9;]; u=(0:255)/(255-1).^1.05; x2=u(x+1) when I run this code I get the following as a result in ...
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1answer
40 views

Saliency Map based on itti model

i want to create a Saliency Map based on itti model via OpenCV(Python). what i'm doing is that: 1- first i change image color space from RGB to LAB color space 2- for each color channel, i create a ...
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1answer
49 views

What type of images are required for voxel classification?

In an algorithm, voxel classification approach is used to perform image segmentation. The aim was classifying voxels either as ...
2
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1answer
70 views

Pyramid vs Scale-space in Focus Stacking

I'm working on a focus stacking program, I wrote one a few years ago which used a very simple method, basically taking a DoG approach, but only operating on the single full resolution image. The ...
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1answer
97 views

What is the difference between MSE and PSNR of images?

I have some doubts. What is the difference between quality parameters MSE and PSNR? Which is used when? Is there any advantage of PSNR over MSE or vice versa? Also I have heard people saying that ...
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0answers
23 views

What is the cut off frequency when design pre-filter for downscale image to avoid moire effect?

Let's say I want to downscale an image, to avoid moire pattern, I need to design an low pass filter to blur the image before decimate. The question is: What's the cut off frequency should I set as ...
4
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1answer
126 views

Structure Tensor vs. Hessian Matrix

Hello can someone explain the semantical meaning of the structure tensor and the Hessian matrix. I am aware of how it is calculated, but i find it difficult to comprehend what they describe in the ...
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0answers
29 views

How does correlation work in an image?

The discrete function for correlation over 2 dimensions is $$ C(x,y) = \sum\limits_{p=1}^{x_{res}} \sum\limits_{q=1}^{y_{res}} f(p,q)h(p+x, q+y)$$ where x,y is a coordinate in the image, f is the ...
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1answer
44 views

How to quantify area of interest in an image?

How to find the percentage of a certain colour in a image accurately? For example I am actually trying to find the percentage of barnacles in this image over the red part of the hull. http://thumb1....
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0answers
24 views

Retrieving camera orientation from DLT parameters

I currently have 12 DLT parameters to map 3D points to 2D pixels, the projection/conversion works nicely. Now, I am able to retrieve the camera position from the parameters using equation [25] from ...
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0answers
245 views

How to calculate the scale, rotation angle and translation between 2 images if we know the homography result matrix?result

I got the result of findHomorgraphy in OpenCv. As below: Homography transform matrix: [-1.1534205416542787 0.7834287271121142 527.9064589440736 -0.2415444621693116 0.16412191792642924 ...
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0answers
120 views

How to run PATCHMATCH source code

I would like to inpaint one image with a corrupted part using the patches of another image. in the link below, the authors of PATCHMATCH algorithm has provided the users with the source code. ...