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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Identify if a Specific Edge Pixel Belongs to Horizontal, Vertical or Diagonal Edge Line

I have a code below that identifies the edge of the text image. Input image is: Output display is: I want to select random points near the edge border of the text. I was thinking to identify if the ...
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1answer
225 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
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What's Logic Behind the Construction of Sobel's Filter in Image Processing?

I am basically very new to this image processing field. I am presently working on edge detection on colour images. While learning the basics of edges and edge detection in images, I encountered image ...
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1answer
183 views

Difference Between Contrast Enhancement and Texture Enhancement in Images

I have a very basic question. I understand that contrast enhancement is exaggerating the difference between the intensity of the adjacent structures and texture in an image is the repeating geometric ...
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13 views

How does PIL.QUAD work internally?

I am working on a computer vision problem involving some basic transformations and could use your help. Input image: Transformed image I understand that we take this quadrilateral and tilt it and ...
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2answers
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How can I remove random dots from an image?

I recently received some scanned pictures which are in a pretty good state, with OK resolution, but they are randomly spattered with a bunch of black dots. These cover everything (clothes, faces, ...
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2answers
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Understanding this Gabor Filter equation

I am working on a project where I need to implement road edge detection. This research paper suits my requirement in the best way, so I am studying it: http://imagine.enpc.fr/publications/papers/...
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3answers
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Understanding Cb and Cr Components of YCbCr Color Space

I am familiar with additive (RGB), substractive (CMYK), and HSV-like colorspaces, but an article I'm currently trying to understand operates on YCbCr color space for image segmentation / object ...
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2answers
99 views

What Is a Weighted Local Histogram?

I'm reading through a couple of academic papers, and this terms often comes up "local weighted histogram". An example of quote is the following: First, cumulative histograms are built for every ...
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Whats the Correct Approach to Estimate the PSF of a Moving Detector

In lab, I did a bunch of scans using a radiation source and a detector. My source emits a gaussian beam (whose dimensions I know), and my detector is a uniform 7mmx7mm square. These are stationary and ...
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32 views

How to Generate Sensing Matrix with Variable Probabilities on Fourier Domain?

Recently, I found a good resource of Compressed Sensing applying on MRI, Michael (Miki) Lustig - Compressed Sensing MRI Resources. The variables "pdf_unif" and "pdf_vardens" store the probabilities of ...
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1answer
37 views

Image processing and compression

I have two questions related to this image; Is it possible to identify any spatial domain features in the frequency domain? My understanding: what I read around they are mostly the same as spatial ...
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What is the best technique for underwater imaging?

I am currently researching what the best method to take underwater images/video is. The papers I have read go into several different methods: Lidar, Synthetic Aperture Sonar (SAS), optical camera plus ...
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2answers
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Confusion regarding lacunarity of koch curves with same fractal dimension but different orders

I'm trying to use the concept of lacunarity to classify images, as per how a few research papers have done it. To verify whether my equations and implementation are correct, I'm trying to verify the ...
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2answers
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Estimating the Variance of Noise Using Median Function Applies on the Gradient of the Image

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 (|\nabla^hx-median(\nabla^hx)|)}...
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1answer
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How to find out if a transform matrix is separable?

In image processing, when we have a series of basis images, how could we know if the transformation is separable or not? For example, I know that following bases are separable and transformation can ...
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1answer
62 views

“plot” command for continous time signal in matlab?uses interpolation?

We know digital computer cannot deal with continuous time signals directly. But then how MATLAB "plot" command works? Does that uses interpolation technique to show an apparently continous time ...
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3answers
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Visual Tracking / Object Tracking: Estimate the Direction the Whale Is Moving

I am trying to find out which way the whale is moving. So I have an image of the whale swimming in the water and I want to find out where is it located and which direction does it swim (with respect ...
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1answer
680 views

The Kernel of the Guided Image Filter

I am trying to understand how to calculate kernel matrix for guided image filter. Following is the formula for kernel calculation. where k is window withing pixels i and j belong i assumed that ...
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1answer
3k views

How Does a Separable Filter Work?

I am new to signal processing, and was reading about filters. I came upon the sobel filter which has the following forms, From what I understand to apply this filter to a 2-d signal, place the ...
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2answers
552 views

Deconvolution of Images - How To?

I'd like to do a deconvolution of image. For example for convolution I'm using a $3\times 3$ mask with all elements $= 1$: $$\begin{bmatrix}1 & 1 & 1 \\ 1 & 1 & 1 \\ 1 & 1 & 1\...
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11answers
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Is deep learning killing image processing/computer vision?

I'm looking forward to enroll in an MSc in Signal and Image processing, or maybe Computer Vision (I have not decided yet), and this question emerged. My concern is, since deep learning doesn't need ...
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21 views

Signal reconstruction using discret wavelet

I am doing a discrete wavelet transform on a Lena.bmp image using the code ...
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0answers
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Image Restoration and Standard Forms of Second Order Cone Programming (SOCP)

I'm studying the application of SOCP methods in Image restoration And I want to understand the difference between the two formulas of SOCP and how they are related. Standard form (1) : min $f^{t}x $ ...
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1answer
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Resize High Resolution Camera Capture to Low Resolution Camera Capture?

Say, you captured a high-res image of a scene and a low-res image of the same scene, using a lower-res camera, ensuring that the lower-res camera is using the same technologies, except for the image ...
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3answers
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Connected Component Labeling - Equivalence Table

I am trying to write a connected component labelling program, I have done the first part to create a label based on the neighbours. For simplicity I am using a 4-connectivity. I am using ...
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1answer
2k views

Cross Correlation Matrix

In my group, we have developed an algorithm which shows abstract information from quantum mechanical systems as images. This way, given a quantum system, we obtain an associated image which has the ...
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1answer
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Image Filtering by Averaging Similar Areas of the Same Image - Patch Based Processing

I heard of filtering algorithms which, to filter an image specific area, find similar areas in the image and average them to reduce the noice of the original area. E.g. an edge of a house can be more ...
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How to extract traffic signs from a photograph?

What image analysis techniques can I use to extract the traffic signs from an image such as the one below? Edit: After Anisotropic diffusion: The background that i don't want gets cleared a little ...
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2answers
476 views

Convolution of an Image with a Kernel That Is a Product of Two Functions

Suppose that $G(i,j)$ is a Gaussian decay function on the distance between points $i$ and $j$ of an image. In addition, $D(i,j)$ is the difference between the VALUES of the image at those points. Now,...
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1answer
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Ambiguous results of phase correlation in pattern recognition

We are using phase correlation to find pattern on image and what we get is 15% of results is spurious. Ours pattern has 32x32 pixels and image for research has 32x512 pixels. So we put Pattern to ...
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1answer
80 views

Why do we use Difference RGB to grayscale function?

I found this function for RGB to Gray scale converter at this kind: RGB to grayscale This example converts an image with RGB channels into an image with a single grayscale channel. The ...
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53 views

Processing Multiple Images to Detect Moving Object in Low SNR Conditions

I am new to this forum and new to the use of Fast Fourier transforms although I can program in Python 3 a bit. I have an unusual question and am seeking some general advice on (a) whether what I am ...
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1answer
40k views

Difference Between Correlation and Convolution in the Context of Image Processing

Could you please clearly explain what is the difference between correlation and convolution that is done by a filter on an image? I mean in terms of signal processing definition I know that ...
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Performance of MATLAB's `conv2()` vs. `imfilter()`

A lot of people use imfilter to achieve a 2-D convolution between an image and a filter, but the majority of people use conv2 ...
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1answer
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Corner detection using Chris Harris & Mike Stephens [duplicate]

I am not able to understand the formula, What is $W$ (window) and intensity in the formula mean, I found this formula in opencv doc http://docs.opencv.org/trunk/doc/py_tutorials/py_feature2d/...
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74 views

How do i calculate the accuracy of an algoruthm?

I'm doing research on an machine learning image processing algorithm (segmentation algorihtm)i.e. computer vision performs when an image takes as an input and objects in an image are segmented and ...
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3answers
8k views

Why normalize the data set before applying Direct Linear Transform

Direct Linear Transform (DLT for short) is a method of homography estimation, it solves the overdetermined linear system via SVD $$Ah=b$$to find a solution $h$ under constraint $\|h\|=1$. Actually it ...
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2answers
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How do you interpolate between points in an image (2D), e.g. using splines?

I can understand just fine how to use 1-dimensional interpolation on data points where one coordinate is a function of the other: y = f(x). However, when we have an ...
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1answer
243 views

Getting different results when running my program at different times [closed]

I am working on Speckle Noise reduction in Ultrasound Images using MATLAB R2013. I have designed 10 basic filters and trying out hybrid combination using these filters. When I run my program I get ...
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5answers
4k views

How to separate a low amplitude signal of same frequency but different phase

I have a signal consisting of two sine waves of same frequency but have different phase (and also a lot of HF noise). Their amplitudes differ by about $120\textrm{ dB}$. How to I go about separating ...
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1answer
2k views

Generate the Matrix Form of 2D Convolution Kernel

We know that a convolution can be replaced by a multiplication with a Toeplitz / Circulant Matrix. Meaning, assume I have convolution kernel $ h $ and matrix $ I $ (Of size $ m \times m $ for example),...
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2answers
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What Is the Algorithm Behind Photoshop's “Black and White” Adjustment Layer?

Can someone explain the algorithm behind the "Black and White" adjustment layer in photoshop? I have to reproduce it using C++ for an application that emphasizes non-red/magenta(ish) pixels from an ...
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1answer
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How do I evaluate the performance of a segmentation algorithm?

I'm currently on a project of liver tumor segmentation. I segmented the liver using region growing, and I have to assess how accurate the result is. I recently learnt that there are certain metrics ...
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1answer
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removing vertical lines in grayscale images by thickness

Suppose we have a grayscale image that contains vertical lines. Now suppose that not all vertical lines are the same, some of them have different thickness. Question is, is there a way, in MATLAB or ...
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583 views

Spatial wavelength

I was reading a paper on motion magnification, Eulerian Video Magnification for Revealing Subtle Changes in the World by MIT CSAIL researchers, where the equation (14) of the paper uses spatial ...
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2answers
576 views

How Can I Remove Flickering Background in a Video?

I have a black and white video taken with a high speed camera and I notice a background flickering coming from my LED light. The images alternate from dim to bright and it makes the videos quite ...
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Residual error when setting measurement matrix in compresssive sensing

I have an issue when implementing compressive sensing to recover sparse vector. Assume I have sparse vector $x$ of length, for example, $(256,1)$. $x = [x_1,x_2,.....x_{256}]$. This vector is ...
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1answer
60 views

These two images are very similar. Why doesn't SSIM reflect that?

Here are two aligned images (greyscale, but same applies to RGB) that I want to compare using SSIM: Clearly, these are very similar images. It seems that the first image is more blur rr However, the ...
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1answer
495 views

Laplacian of Gaussian Approximation and Gaussian Blur as the Solution of Heat Equation

While I was reading SIFT paper(Lowe, 2004), I came across the method that he apply "heat diffusion equation" to Gaussian function to derive that $$ \frac{∂G}{∂σ} = σ∇^2G $$ I searched Wikipedia and ...

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