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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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What is a basic method to segment “dark blobs”?

I'm new to image processing, but I have good knowledge of general data processing. Could you please suggest an approach which can be used to segment images like this? I suppose it is some kind of ...
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Detection of interesting structure in images?

I'm looking for methods of computing some measure of structure in an image. (I do not have a rigorous definition of "structure" though........) Consider the 15 image blocks below: Suppose for each ...
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What fps can be considered as a hardline for real-time performance? Is there any academic paper that describes this?

I am trying to design a deep learning based inferencing solution for security applications. My deployed program achieves an FPS of 15fps for classification. Can it be considered real-time?
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Sobel and Prewitt operators decomposition

I was reading in the wikipedia page of Sobel operator and Prewitt operator that is possible to decompose these two operators (quote form the Formulation paragraph): "as the products of an ...
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What's logic behind the constuction 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
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Removing noisy lines from image - opencv - python

I want to process different type of image to extract actual text from noisy image .I am using open cv to do this job it is working fine but the problem is I need to set different lower threshold to ...
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283 views

What does opencv `mean` function do when passing a mask of zeros?

INTRO I am looking at this project to implement some changes. The project is written in C++ using openCV library. Its goal is to detect cars in parking area to calculate the number of free spots. It ...
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132 views

In What Way Is the Difference of Gaussian (DoG) More Tunable than the Laplacian of Gaussian (LoG)?

I was reading through this post "What is the difference between Difference of Gaussian, Laplace of Gaussian, and Mexican Hat wavelet?" and noted in Chris Luengo's answer that he mentioned that the ...
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351 views

How Is Laplacian of Gaussian (LoG) Implemented as Four 1D Convolutions?

I am trying to understand the four 1D convolution operations involved in implementation of Laplacian of Gaussian(LoG). I have read this answer and I am also reading ...
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Can an untilted perspective of an object be obtained from a 2D image of a tilted object using angular transformations?

I'm trying to make a height estimation algorithm that works in tandem with a bounding box object detector. The object detector can recognise the objects in images taken at pitch/yaw angular offsets. ...
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68 views

given an image and its fourier transform, find another image fft using fourier properties

I managed to solve few of those questions , but I'm not manage to answer 3 of them correctly, the question is: given an image and its fourier transform, find another image fourier transform ,using ...
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Decoding a video signal, how to get frame output to matrix for calculations?

I'd like to use python to take a video (eventually a stream) and map each frame to an RGB array of pixels. My first thought was to use ffmpeg bindings, and in memory (if possible) convert it to png ...
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Fundamental misunderstanding of windowing

I believe I have a fundamental misunderstanding of windowing. I thought that windowing is applied to a signal with pointwise multiplication, then some sort of filtering is then done to it (say using ...
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177 views

Remove a line in image with FFT

I would like to remove vertical line from an image (an example). I took a 2D FFT and try to apply a mask to suppress the line. Nonethelesse the approch is not very efficient, because i lose an ...
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1answer
29 views

Denoising before or after Geometric Transform?

I am working on a image which needs denoising (bilateral filter) and a geometric transformation. I am not sure in which order these filters should be applied. Personally I think it is better to use ...
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3answers
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How to Classify Image Filter as Low Pass Filter (LPF) or High Pass Filter (HPF)?

I am currently reading on the topics of image filtering and convolution kernels. While the process of convolution is clear to me, I do not understand, how one arrives at the statement, that a certain ...
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SIFT About Difference-of-Gaussian function extrema?

How to get formula (2) by formula(1)?
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136 views

Image zooming with Fourier transform

I want to go from this image into this one: So basically I need to scale the white square. The authors of the paper claim that this can be done in four steps: zero-padding in real space (image is ...
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345 views

What are the advantages and disadvantages separability of Gaussian 2D filter?

I know separability of a Gaussian filter enhances the computational complexity from $\mathcal{O}(L^2*N*M) \to \mathcal{O}((L*N*M)$. How this really reflect on my program? I suppose the number of for ...
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How to Check Separability of 2D Signal / Matrix

suppose x(n1,n2) = {1 ,n1=0,n2=0 ; 2 ,n1=1,n2=0 ; 3 ,n1=0,n2=1 ; 6 ,n1=1,n2=1 } then, how do i prove it is separable.
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Image Interpolation Using the Yule Walker Equations

I have been studying about the Yule-Walker equations for prediction of a time series data from knowledge of past values of the series. Is there any way I can use the same in an image to exploit the ...
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1answer
51 views

Identify the Type of Image Distortion (On Lena Image)

I want to understand the distortions in each of the lena images shown in the image below. I see that the first one is a blur. How can undo the blur. The second one is colored salt and pepper noise. ...
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Is signal processing used in block matching algorithms

I'm working on a custom video codec which uses the standard mean squared error to find blocks. As explained by this youtube video you choose a search area size to find a block in. Each pixel of the ...
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Do chroma signals add any information to luma in YUV?

Consider the YUV 422 picture format that I get from an image sensor. The luma (Y) carries 4 bits of grayscale information. Do the additional 2+2 bits of U+V add any additional info to the overall ...
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124 views

Perspective Transform using depth and scale information

I want to transform perspective on an input image and output image from the new perspective. I have depth map and scale information. The picture roughly demonstrates what I want to do. I have a single ...
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56 views

Facing problem in plotting histogram of DCT coefficient of an image

In digital image forensic, it is assumed that the histogram of DCT coefficients of the un-compressed natural image has the smooth histogram. However, the histogram of DCT coefficients of the ...
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Does Mutual information utilize spatial information to calculate image similarity?

To calculate images similarity based on Mutual Information (MI), histogram and join histogram is required. In the literature, there are 2 contradict opinions about MI operation. 1. MI does not utilize ...
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Selecting gradient orientation for Generalized Hough Transform while scaling and rotation is present

I am using this link to study Generalized Hough Transform. I will explain it briefly. In order to detect a shape, an R-table is created for the shape with $\phi$ indicating gradient orientation for ...
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1answer
28 views

How would I fit a distribution to this image noise?

I have collected some noise data from a dimly lit CMOS image sensor. The distribution of pixel values is tallied below:- I'd like to be able to simulate this sensor noise. How would I fit a ...
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1answer
79 views

Morphology - Why does the concept of opening and closing images exist when we already have erosion and dilation?

If we consider the closing operation of an image, we first dilate the image and then erode it. So, first we expand the foreground (white pixels) and and then we take away some part of the foreground. ...
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1answer
118 views

How to convert DFT to DCT

I've been trying to find a fast 16 point dct2 and dct3 implementation, however I could only find it in literature expressed as mathematical equations, which honestly I couldn't understand. However I ...
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1answer
36 views

JPEG: In image compression why are higher frequency components divided by a larger number during quantization

Once 2D FDCT has been carried out on 8x8 blocks of the image data, the coefficients are quantized. This involves use of a quantization matrix where we simply divide each FDCT coefficient by the ...
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1answer
703 views

blur detection using opencv

I'm writing a script to detect blur images using OpenCV by applying Laplacian filter and calculate the std but there is a problem the std for images that contain motion blur is very close to those ...
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Is the behaviour of the following filter plausible?

I've designed a filter based on this equation $$ E(u) = \frac{1}{2}\int_{\Omega} \left[(u-f)^2 + g(\lVert \nabla u \rVert)\right]dxdy $$ Euler-Lagrange equations in this case are (should be) given ...
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Anisotropic filter implementation wrong?

I've this implementation of the anisotropic filter: ...
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38 views

Are shadows additive

So I was thinking about the problem of shadows in images. From an image processing point of view, would you classify cast shadows in a scene as an additive phenomenon or as a multiplicative phenomenon ...
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Extracting overlapping features in an image when individual features are known

Consider this image: Which is a sum of two different sets of features: The first is a collection of overlapping squares with value of 5 and the second is a collection of overlapping squares with ...
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96 views

Automatically detect an image collage

I'm trying to automatically detect if an image is a collage vs a single photograph. I'm not too concerned with difficult cases of artistic collages. What I'm trying to solve is rectangular collages ...
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Convolution offset and factor in frequency domain

See this link. The following Convolution in Spatial domain code is written in C#. ...
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Chapter 4, section 4.2.1. in Szelisky computer vision, is there a mistake?

I've already asked a similar question in mathematics exchange without getting an answer, I read a bit more and I think the question might be more suitable for the signal processing exchange. ...
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Output of a bank of gabor filters, derive ellipses like regions

I'm trying to implement an algorithm that show how to detect wrinkles in clothes, without going to much into details this is the step that is confusing me. Assuming we have an image $I$ and a set of ...
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44 views

How Does Mean Centering Affect the Result of Using SVD to Compress Images?

I have been learning about using the Singular Value Decomposition to find low rank approximations to matrices. I had an image which I converted to a matrix. I regarded each row of the matrix as a '...
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39 views

2D to 3D back projection for height estimation mathematics error

I'm currently trying to implement the core of the second algorithm implemented in this paper (p5-8, p17-20) in matlab as a prototype for a larger project that requires object height detection. The ...
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Using feature detection as weight function in non linear filtering energy function

In image processing \ computer vision It is known that some filtering operations can be formalized as $$ E(u)=\int_{\Omega} \lVert u - f \rVert^2 + \lambda \lVert \nabla u\rVert^2 d\Omega $$ ...
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1answer
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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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1answer
191 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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54 views

detecting specific words in images?OCR?

i'm not sure if this question belongs here or in stackoverflow but i feel like it belongs here as it is more about the approach than the code itself. i'm trying to write a program that searches in a ...
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1answer
65 views

Transforming Non-Uniformly Sampled Image onto Rectangular Grid

I have an image and associated latitude and longitude matrices. So I know the latitude and longitude of every pixel. However, due to the camera orientation, the image is skewed and thus the latitude ...
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317 views

Fastest Available Algorithm to Blur an Image (Low Pass Filter)

Iam working with a camera that produces ugly artifacts: by using ANY blur filter on the camera's output the visual quality improves drastically: The above image was created using OpenCV's cv::...
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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 ...