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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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HVS models and rods and cones

It is common to say that the YUV color model is inspired from the human visual system (HVS), knowing that we have many more rods than cones, and consequently, we are more sensitive to light than color....
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How to get the orientation value of a rotated square?

Suppose we have a square shape rotated by $d$ degrees counterclockwise (or $-d$ degrees clockwise) in a binary image as the following: I'm trying to rotate it by 'Orientation' value of regionprops ...
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How to resize a Summed Area Table/Integral Image?

There is very clear explanation on how a Summed Area Table/Integral Image works here: https://uk.mathworks.com/help/vision/ref/integralimage.html How to you scale this SAT/Integral Image? For ...
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Discretized Beltrami energy

In the paper "An Approach Based on Hybrid Genetic Algorithm Applied to Image Denoising Problem", I encounter this fitness function that by minimizing it, a denoised image of a noisy image is obtained. ...
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Camera Calibration - why do you have to move the calibration board?

I understand the mathematical derivation of Zhang's Method for camera calibration but what I don't understand is why we need to move and rotate the calibration board for several frames in order to get ...
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Multiple-image dense point cloud reconstruction with camera extrinsics/intrinsics

I have the following data available: Images from different angles X, Y, Z, pitch, yaw, and roll for each camera/image, together with the timestamp Lens distortion parameters and intrinsic camera ...
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Scale Image by using FFT

Can we change the scale of image by using FFT? I mean, how should i do process on frequency domain of image to upscale or downscale the orginal image? The other question of mine is that how can ...
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Image Processing/ Computer Vision: How is separability of filters implemented?

I am trying to convince myself that a separable 2D filter can be implemented via two 1D filters. So, I took the example of following Sobel filter: $1/8\begin{bmatrix}-1&0&1\\-2&0&2\\-...
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CIE-Lab changes on Light intensity changes

I am planning to use CIE-Lab color model for an image segmentaion method. If the light intensity of sun, some led source changes on the objectm then does it affects the a and b value of the data ...
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coherence calculation in sparse sensing

i have an image I of size 32*32. I perform the DCT of this image using the matlab function DCT2(I). I get a sparse representation of my image which is again a 32*32 image. I construct a circulant ...
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How to count the number of threads in a bolt or nut using image processing?

How can I count the number of threads in a Nut with image processing? I know that I need to find the place of threads and count them. Ok, But how can I find the place of threads? This is a sample ...
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When does a color channel such as RGB carry more info than a grayscale channel or image?

Typically a gray-scale image gives us more information about an image in terms of a signal processing problem. But when does a color channel carry more info than a gray-scale channel? I understand ...
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Is it possible to reconstruct the original image from Laplacian pyramid?

In our computer vision course, my professor said we can reconstruct the original image from the Laplacian pyramid. It just feels to me that information is lost after doing subsampling and upsampling. ...
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Why so many color spaces for digital image representation?

In RGB representation, we use 24 bits, so we can get 2^24 or about 16 million colours. And our eye can not distinguish so many colors. So perhaps we can find the distinct colors (which would be a ...
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1answer
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Brightness equalization between different images

I am dealing with a proprietary whole slide image format from 3DHistech, namely MRXS. This image is produced by scanning a glass slide biopsy. The scanner takes pictures at certain positions which ...
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What's the point of using Morphological processing concerning images?

I dig deeper in internet to figure out what's the point of morphological processing on images, but i'd rather to hear the answer from people with experience, can you give me a hand with this? Thank ...
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What should I know about Morphological processing [duplicate]

i'm studying my first year as technical student , and we are studying image processing, so last week we got delivered a topic to work on : Morphological processing /opening , i'm trying to dig deeper ...
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What are the advantages of wavelet transform for image multiresolution analysis? [closed]

Compared to gaussian pyramid and laplacian pyramid, what are the advantages and disadvantages of wavelet decomposition for multiresolution image analysis? Thank you.
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How can I detect pipeline cracks using OpenCV and Python?

I have developed a robot that captures images of the pipeline interior as it moves. The requirement was to be able to detect cracks inside. So far i tried several OpenCV codes that find the crack ...
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Fitting a grid to points in a 2d space

I have this problem where I have multiple points in a 2D space. A subset of these points makes up a rectangular grid. Some points of the grid might be missing. The shape and number of points the grid ...
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2answers
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How do you apply a filter after DFT on an image?

Let's say size of the image is 100 x 100 and the kernel matrix is 5x5. I took the DFT of both the image and the kernel. But how do I multiple these two matrices? And which parts involve in these ...
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1answer
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Bilinear interpolation implemented by convolution

I read the paper Deep Feature Flow for Video Recognition https://arxiv.org/abs/1611.07715. In Sec.3, the author implements bilinear interpolation like this: $$f_i^c(p)=\sum\limits_{q}G(q,p+\delta p)...
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How to add additive noise to an image?

I have the following image I and I want to add additive noise using the array N below. Can you please give me a calculation example of how to achieve this? Do I have to move from image space to ...
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How to get general projection of rect function?

To be more clear I want to get a general expression for PƟ(t)= ∫∫rect(x)rect(y)δ(xcosƟ+ysinƟ-t)dxdy I also want to find particular projection for Ɵ=0 and Ɵ=45 and also Fourier Transform of the ...
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Check whether a given equation is linear

$ a = (x, y) \in \mathbb{Z}^2 $ is given as a pixel. My equation in which $g$ is image(matrix) is defined as, $f(x, y) = 56g(x,y)+93g(x−1,y)+92g(x+1, y)−57g(x, y−1)+555g(x, y+1) $ How can we know ...
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How can I trace a path around an image consisting of only black and white lines?

I'm looking for a way to trace a closed curve (i.e. a long list of pixel values all connected by lines in between) that approximates a bitmap image of black and white lines. The image starts out as ...
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1answer
81 views

How to represent impulse function in 2D?

To be more specific I want to show that impulse function in 2D can be represented as $β(r)=δ(r)/πr$. Also I want to show that each projection of a two dimensional impulse function at the origin is a ...
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1answer
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Why delete high frequence in fft return the area of the most changes?

I'm new to ||image-processing|| and || fft filters || I have a relative smooth $\mathtt{2D}$ (circle) gaussian surface (height $10$) with several "holes" in it, and the surrounding area [has] some ...
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1answer
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What do the Contour Levels Produced by Matlab Function Contourc Represent

I have been trying to understand what the contour levels are. As far as I understand a contour of the function $Z(x,y)$ is a set of points in the $(x,y)$ plane, such that $Z(x,y)$ is fixed at some ...
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29 views

“Image Processing” [closed]

I'm an Italian student. I'm studying Gnu Radio and I would like to upload a photo, can I upload it with "file image source" or other blocks? I need to make FFT of an a image. -> image 2D Thank you ...
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991 views

Why should an image be blurred using a Gaussian Kernel before downsampling?

I recently read that before downsampling an image, it should be blurred using a Gaussian Kernel. This way, the downsampled image is better than just picking a single pixel out of a NxN block or ...
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Efficient determination of pixel cluster boundaries

Im looking to replace the values of pixels / pixel clusters in a greyscale image with the average of the values of their boundaries. Suppose the greyscale image is given by $I$ and the pixels to ...
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Basic confusion about the DFT and convolution

I am learning DSP (with Digital Images) and I have some elementary confusion about the convolution between two discrete periodic signals. Specifically, I have learnt that when filtering an image, we ...
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1answer
58 views

Edge detection in a crack pattern image

Here's an image of a cracked pattern. I wish to convert it to binary image where the continuous crack lines form the only discernible pixels. The main problems I am having in the lack of uniform ...
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Excluding points too close to a set of coordinates

I was wondering if anyone can help me. My ultimate aim is to take an image like the one shown and draw line between the white and black blobs that show a direction and output the coordinates in the ...
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What is the meaning of the sum of kernel components in digital image filtering?

When analyzing an image signal as a series of Dirac impulses in the continuous spatial domain, I applied continuous low pass filters (to reconstruct or smooth it) with area equal to 1 to preserve the ...
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Image processing - Why is sum of values of a blurring filter = 1?

Usually, blurring filters have the sum of all the values in the filter matrix equal to $1$. Why is it so?
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1answer
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How to draw a vector between light and dark spots on an image

I'm very new to Python and I need to draw vectors between dark and light spots on an image. Ive managed to convert it to greyscale but I'm struggling with identifying the dark and light spots. If I ...
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1answer
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Fast morphological erosion/dilation with variable window sizes

I want to perform the following operation on an image: consider a square window around every pixel, find the maximum value in this window, and replace the central pixel value with this maximum value. ...
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2answers
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Why are edges in spatial images represented as edges in their Fourier transform image?

Here is a well-known image and its Fourier Transform (magnitude). If I understand correctly the theory behind the FFT, each pixel in the FFT image represents a certain 2D sine wave with frequency ...
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Is this statement contradicting with the band-limiting theorem?

The following sentences are from the footnote of page 240 in R.C. Gonzalez's Digital Image Processing (3rd): An important special case is when a function that extends from -Inf to +Inf is band-...
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Relation between variance of gaussian noise and intensity variance in Bilateral filter

So I implemented the code for bilateral filter from here and ran it for various values of spatial sigma and intensity sigma. I noticed that when I add gaussian noise to an image with variance say 0.02,...
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1answer
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Producing masks from mostly-static-background subtraction when given the background

My data set contains a number of high resolution greyscale images containing a person's face. A single image containing the background without the face is provided. The background is mostly static in ...
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converting digital length to physical length using reference object

I am trying to find actual length of an object, say X, from an image. For that I'm using a reference object , say Y, ( object of known dimensions ). From image while converting pixel length of X to ...
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1answer
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Correlation between slightly misaligned images

I am matching camera images of projection screens with rendered pages of PDF documents using Pearson's and Spearman's correlation coefficient. When the images (3, 4, 5) are aligned, this works fine in ...
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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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1answer
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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 ...