# Tagged Questions

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.

11 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 ...
14 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 ...
31 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 ...
26 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 ...
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 ...
18 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 ...
32 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 ...
37 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 ...
58 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 ...
19 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 ...
50 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 ...
28 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 ...
36 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. ...
18 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 ...
68 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 ...
42 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. ...
43 views

### 8*8 block matrix in JPEG image compression?

In standard JPEG format of a image, Discrete Cosine transform is used. But instead of applying the transform on whole image, we first divide the image in 8x8 block and apply transform on each of them. ...
87 views

### detection algorithm in 2D images

Suppose there is a two-deimensional image which consists of pixels. In every pixel, there are 0 to n apples with different colors， which can be digitalized(e.g.[0,10000]). So we can plot a histogram ...
24 views

### How to go about implementing a program to measure the “intensity”/“saturation” of a color in an image?

I have a task of developing an application to measure the intensity of a color in an image. I am researching about how to go about it. Intensity refers to the purity of a hue. Intensity is also ...
16 views

### what is this mean?“the input image is centered…the mean image…”

in paper-"DenseNet: Implementing Ecient ConvNet Descriptor Pyramids", I can't understand what does this sentence mean- "As a preprocessing step, the input image is centered by subtracting the mean ...
43 views

### How to derive the $\log$ of fraction of two Gaussian distribution

I am designing a function $A(x)$ that map $x\to \{0,1\}$. The function $A$ can be expressed as $$A(x)=\begin{cases} 1 \text{ if p_1(x) \ge p_2(x)}\\ 0 \text{ otherwises} \end{cases}$$ where ...
17 views

### Which image for DoG filter?

I am studying computer vision and have some trouble with difference of Gaussian filter. We apply Gaussian filters with different values of sigma on original image then subtracting from them. However, ...
41 views

### What are the differences between fft and dct? [duplicate]

what are the differences between Fourier transform and cosine transform..... i try to find the typical answer the difference ,from where ,the size of input and output form,in time complexity,the ...
346 views

### How to verify if two images have the same object/content?

I am truly new to computer vision field, but it is fascinating me! I have now a challenge in my hands and I am seeking for mentors/advisers to give me some follow up. My project is: From a picture of ...
59 views

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### Processing line scanner data

I have a line scanner output that is scanning the geometry of a surface. Typically the output looks something like this: Where the x and y axis refers to the coordinate system in mm. (ignore the ...
88 views

### Detecting defects/differences in printed images

I've been experimenting with various methods to detect defects in printed images. Features that are qualified as defects may include scratches, discoloration, etc. I'm not very experienced in image ...
19 views

### Detecting discontinuities in derivatives in images

Considering an grey-scale image as a function z=f(x,y). (Specifically, I'm interested in f=h∗h∗...∗h, where h is the indicator function of a regular hexagon.) I am interested in finding places where f ...
27 views

### To estimate the uncertainty of Slicing holes from an image?

I am thinking to estimate the uncertainty of holes photographed from the bottom and top side. The difference of the same hole photographed from two sides is distributed as Gaussian. The length of ...
43 views

### Estimating the variance of noise using median function (?)

By investigating the implemented code of an accepted paper, I encounter with following relation to estimate the variance of noise in an image:  \sigma = \frac{median ...
66 views

### How do I compute the gradient vector of pixels in an image?

I'm trying to find the curvature of the features in an image and I was advised to calculate the gradient vector of pixels. So if the matrix below are the values from a grayscale image, how would I go ...
60 views

### What's the optimal filter size for a 2D Gabor filter

I started to experiment with Gabor filters to extract various image features from usual camera snapshots (that's the image domain: everyday snapshots with a very diverse range of subjects). ...
40 views

### Which anatomical model to use as “ground truth” for validating an MRI segmentation method?

I am research in brain segmentation task that classify a brain in to 3 classes : White Matter, Gray Matter and CSF. To validate my method, I used Dice Coefficient that compare my result and ground ...
19 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 ...
58 views

### why wavelet is more suitable for image compression compared to DCT?

Everyone knows that JPEG2000 can obtain much better compression result than JPEG. The fundamental transform behind JPEG2000 is wavelet while the basic transform in JPEG is DCT. So my question is why ...