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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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 ...
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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 ...
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1answer
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 ...
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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 ...
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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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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 ...
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1answer
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 ...
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1answer
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 ...
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1answer
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 ...
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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 ...
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1answer
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 ...
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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 ...
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1answer
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. ...
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0answers
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 ...
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0answers
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 ...
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0answers
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. ...
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1answer
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. ...
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1answer
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 ...
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1answer
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 ...
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0answers
16 views

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

in paper-"DenseNet: Implementing Ecient 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 ...
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1answer
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 ...
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1answer
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, ...
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1answer
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 ...
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1answer
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 ...
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2answers
59 views

Magnitude of Sobel filter result, vector or scalar?

I have a question about image gradient magnitude, given an image $I$. The horizontal and vertical derivatives resulting from Sobel filters are defined as: $$K_x= \begin{bmatrix} -1 ...
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2answers
54 views

How to represent a given equation more clear, profressional and short form?

I have a image $U_{m \times n}:\Omega \to \mathbb R^2$, the output $P$ can be define as $$P=\mu J_{m \times n} - U$$ where $\mu = \max \{ u_{ij} : 1 \leq i \leq m, 1 \leq j \leq n\}$, $J_{m \times ...
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2answers
45 views

Segment highly packed nuclei with dotted high intensity signal inside each object

I collected high magnification images on cell nuclei and I need to segment them (red circle in the image). The edges of the nuclei are visible but inside each nuclear object there are bright spots of ...
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0answers
14 views

Doubt about the LFW‏ database

I post below a part of the mail I wrote to the creators of the database LFW: i am currently working on a face recognizer which has given me very good results in small tests performed, now i would ...
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1answer
33 views

How to solve a two variable equation of images?

I have two equations of images $$g_1=f_1+h_2*f_2$$ and $$g_2=f_2+h_1*f_1$$ where $*$ is convolution and $g_1,g_2,h_1,h_2$ are known. How do I find $f_1$ and $f_2$?
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1answer
33 views

Converting blobs to circles

I have this binary image with some blobs of random sizes. I would like to convert the blobs into circles of uniform diameter. it doesn't really matter what diameter but they need to be circles and ...
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3answers
119 views

HDR Imaging - Exposure Compensation

Tried HDR Algorithms of OpenCV. Since the algorithm takes pretty much time. I tried few alternative steps as follows. Took sample images from: HDR Images 1. Divided the image into four equal regions ...
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45 views

Classify areas of an image based on color

I have some tree canopy images that I would like to process, but not sure how to get started as image processing is a little outside my area of expertise. Any help would be appreciated. I have tree ...
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1answer
17 views

Convergence criteria for Active contour model

Currently, active contour convergence is checked visually. So how can we set a convergence criteria? I looked into some unsupervised segmentation method for image segmentation but couldn't got a ...
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2answers
55 views

Is there a difference between Image Alignment and Stereo Rectification for stereo correspondence or matching?

As far as I know, Image alignment just finds the best fit given two images of the same scene. Whereas Image rectification, with regards to stereo vision, warps the images so that the epipolar lines ...
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0answers
34 views

Find horizontal and vertical derivatives of image

I need to find the horizontal and vertical derivatives of an image using the kernels [ 1 0 -1] and its transpose respectively, using Python. I am a newbie in Python, and don't seem to find any inbuilt ...
2
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1answer
35 views

Invariance of curvature in Curvature Scale Space

PDF is here I have read this PDF. But i don't know what the Invariance means in page 3 and 5. Calculation/estimation of κ is NOT invariant and Invariant to viewpoint. What's the meaning of these ...
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2answers
91 views

texture matching between patches of an image

I have an image A which I have divided into 4 x 4 subband images. For a given patch P1 in ...
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1answer
50 views

Understand about maximum a posteriori probability (MAP) in classfication 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... N:\Omega_i ...
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1answer
31 views

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 ...
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1answer
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 ...
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0answers
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 ...
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0answers
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 ...
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1answer
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 ...
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1answer
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 ...
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0answers
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). ...
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1answer
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 ...
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1answer
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 ...
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1answer
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 ...
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2answers
40 views

Selective image compression?

Forgive me if this is the wrong site for this question. Here's my problem: I am creating a game where players have to search for a hidden detail within the overall image. I downloaded an 11MB ...
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0answers
46 views

Image Subtraction using Pre-bayer data (.pgm)

Not sure if this is the best stack exchange but I'll give it a shot. I am performing background subtraction to collect Electroluminescent emission (i.e image w/ emission - image w/o emission = ...