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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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Determining parameters of S-function

I know that S-function (membership function from fuzzy set theory) is a commonly used function for image enhancement. I am reading a paper titled 'A Novel Fuzzy Image Enhancement using S-Shaped ...
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Performing inverse DFT after taking conjugate of the result of DFT

The following is a question I got in my school assignment. Pick an image and follow the operations Multiply image by (−1)x+y. Compute the DFT. Take the complex conjugate of the ...
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Performing DFT twice on an image. Why am I getting an inverted image? [duplicate]

I was asked to perform DFT on an image twice as a part of my school assignment. Why am I getting a blurry inverted image when I perform DFT on an image twice? Sorry, I'm new to image processing and ...
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How to set sigmas and kernels for 3D-Laplacian of Gaussian filters to blob detection in Matlab?

I have written code according to a paper for Lung CT images, but its output wasn't correct. I think it is because of the setting of its parameters. The paper is about a multi-scale method using a ...
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Searching for particular area in the picture

I have some experience in programming but I’m very new in ML, neural networks and image processing. I have problem to which I think I can apply these things. I want to read meter status from picture ...
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232 views

What is different between Euclidean distance and the Geodesic distance?

We have two kinds of distance in image: Euclidean distance and the Geodesic distance. What is different between them? Could you show mathematic formula or visualization to make it clear? The reference ...
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Which algorithms can efficiently identify rectangular regions in noisy greyscale image?

I have a large number (~50000) of square greyscale images, about 180x180 pixels. I need to efficiently scan them for containing significant block like regions. See the following pictures where I have ...
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Multifractal analysis of an image using wavelets

I want to measure the fractal character of images using a wavelet approach (if possible) in python. (E.g., maybe things like roughness, anisotropy, or just the fractal dimension - perhaps just ...
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How can I prove that image gradient magnitude is rotation invariant? [closed]

I have an image with the gradients represented by Gx and Gy for the X and Y directions respectively. There's no other data. How can I prove that the magnitude of the gradients at a point is ...
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python: how to compute the color distribution of image in the paper with python and openCV

I am computing the color distribution of image as mentioned in the paper: https://arxiv.org/pdf/1202.2158.pdf. ...
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Detecting moved and dirty areas between two snapshots/images

I'm new to image processing and trying to figure out best way to identify 'moved' and 'dirty' areas between two desktop screenshots.Basically, lets say there is a round circle moving in a browser ...
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Can Normalized Cut be used to find connected components in binary images?

I'm unsure whether Normalized Cut can or can't be used to find connected components in binary images. I would argue that it could, but could not validate this argument.
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Can We Measure Diameter and Length from Camera using MatLAB? [closed]

Can we measure a circle diameter or line length from camera using matlab? If we can, how can it works?
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Converting RGB to ARGB image [closed]

I am doing a project in MATLAB where I compare the encryption performances of RGB and ARGB images.Is there anyway to convert a particular RGB image to ARGB image?How can I do it?
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1answer
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python: how to compute the sharpness features of image

I am extracting the sharpness features of image as shown in the following image mentioned in a paper. I have done with the following code. Firstly, use the open cv convert the RGB to HSL (luminance ...
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MatLab-Finding error in hough line transform

Can I calculate the number of error in Hough Line Transform using MatLab? I did Hough Line Transform process from Canny Edge Detection, but it is unable to detect all the lines. Thanks.
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Chroma key algorithm with unknown background color

Suppose that I have an image with a foreground subject and a monochrome background. The image is a real world picture so the pixels belonging to the background do not share the same exact value. I ...
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1answer
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python: how to compute the gray level histogram features as mentioned in the paper, and

Hi I am extracting the grey level features of image mentioned in this paper (part 4.5 low level features). "We describe two low level features that are particu- larly important for photo quality ...
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How to add Gaussian noise to a multiband image in Matlab?

I am confused that when adding Gaussian noise to multiband, is it to add noise to each band or add noise to each pixel where each pixel is a vector? And how to calculate the interchannel covariance ...
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Numerator of Transformation from RGB to HSI color Space [closed]

So below is the formula for Conversion From RGB to HSI Color Space that I got from Digital Image Processing using MATLAB by Gonzalez We can see in the numerator of theta that (R-G)+(R-B), So,my ...
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How do piecewise affine transformation work?

How can piecewise affine transform be used to warp an arbitrary collection of input landmark coordinates to a corresponding set of base coordinates? Can anyone give any physical examples, the book I ...
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28 views

On Human (Face) Detection

There are many face detection and recognition algorithms and APIs out there; however, most of them can produce same results for paintings and avatars as for human face. So, is there any specific ...
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Amplifying the difference of luminance between pixels of color images?

I'm doing some research on digital watermarking and came across an article that embeds QR codes on mostly grayscale images and the extraction part for color images is quite confusing the article ...
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1answer
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Zoom an image with respect to a given image

I posted this question in stack overflow, but I think it is more appropriate here: I have a reference image - 'image_01.png' of size 200x200 and resolution 72 px/in. I have another image 'image_02....
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Correspondence between spatial frequency and pixel position

I have a very basic image processing question for which I have not been able to find an answer so far: On several occasions I have encountered descriptions of image filters given in the frequency ...
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1answer
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Skeletonization of a Circle - Image Processing

What will be the output of skeletonization of a circle? In my class my instructor said that it will be a single dot in the center but what I found on the Internet was a cross. I discussed with a ...
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Burst Deblurring algorithm - Understanding the results

I've attempt to implement the algorithm from the paper "Burst Deblurring: Removing Camera Shake Through Fourier Burst Accumulation". The main idea is to take several frames of the same scene, each ...
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2answers
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How to approximate gaussian kernel for image blur

From wiki, a $3 \times3$ gaussian kernel is approximated as: $$\frac{1}{16}\begin{bmatrix}1&2&1\\2&4&2\\1&2&1 \end{bmatrix}.$$ Applying this kernel in an image equals to ...
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Extracting straight line and curves from an edge image using fourier coefficients

I came across Fourier coefficients and my understanding is that it is very efficient in analysing image properties such as shape etc.. I know we can use Fourier descriptors to describe shape... But in ...
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Suzuki and Abe Boundary-Tracing Algorithm: Wrong Topology Results

Note that I use the terms Boundary and Contour interchangeably, but mean the same thing by both. I've implemented the "Topological Structural Analysis of Digitized Binary Images by Border Following” ...
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1answer
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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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Contrast Limited Adaptive Histogram Equalization (CLAHE) redistribution of excess pixels

I'm having troubles understanding how the pixels are redistributed when using the CLAHE on images. I have read through the following links: wikipedia(clahe) Opencv(clahe) MathWorks(clahe) And as ...
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1answer
55 views

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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1answer
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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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1answer
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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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1answer
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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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1answer
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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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1answer
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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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How to find corresponding points between two photos when there's a repeated pattern?

Suppose that I have two photos, I1 and I2 and I want to find a set of corresponding points between the two photos to define a homography between them. There are many algorithms for this purpose, ...
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1D and 2D Image Filters: how to calculate composite filter and its Fourier transform

Suppose the below 1D image filter as: $\begin{matrix}h[-1] = 1,&h[0] = 2,& h[1] = 1\end{matrix}$ Apply this filter to an image first vertically then horizantally, so i get this: $h_1 = \...
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1answer
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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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1answer
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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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1answer
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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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2answers
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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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2answers
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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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Probabilistic color recognition of an object

I am trying to detect an object using a probabilistic approach. One the main attributes is its overall yellow color, apart from some portions than will reflect white-yellow, depending on ambient ...
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1answer
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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 ...