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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shannon interpolation in image processing

I tried to implement Shannon interpolation on a 2D array. First, implemented it on a 1D signal, just for sanity-check: ...
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Grading Images According to the Noise It Contains

I have collected a lot of dirty blank pages and each image is varied in the noise it contains. How will I grade images according to the noise it contains in terms of amount, and other aspects? What ...
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Overlaying A Distorted Text According to its Background

I have several dirty background images, sample image is below: I want to overlay a text on it but I want the text to be as distorted as the background. Example, if the background is a bit wavy, I ...
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What Distance Measure Is Proper for Image Patches?

I have a bunch of image patches extracted from two images. I want to find a proper measure of similarity between each patch from first images to patches from second image. I have made vectors from ...
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How Is the Bandwidth of an Image Reduced by an Octave in Gaussian Pyramid Procedure?

Reference paper 1. For arguments sake, let's say that the maximum and minimum frequency in an image are 256Hz and 1024Hz. When I perform filtering using the gaussian function, the "bandlimit" reduces ...
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Laplacian Filter Implementation in MATLAB

I implemented a Laplacian filter for the Lena image, but I get an unexpected output. For input: I get output: I used the mask ...
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Detecting Intersections

As a part of a math essay, I am writing a program that detects intersections of a line that is drawn with a shape that is inputted. For example, in the shape below, The polygon is the input image of ...
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How Do You Save / Convert an Image to Be in the Frequency Domain?

Quick Note: I don't believe this is a subjective question... however if it is I will gladly modify to be more objective In ImageJ, if I take the FFT of an image, how can I save this new frequency ...
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Detect fixed overlay on set of images

This is quite an "applied" question, but I don't see any more appropriate StackExchange, so here it goes. My situation is the following: I have a sizeable (> 40) set of images (photos) that have been ...
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Image classification in c

i have to do a project for university which is basically to program a tool to classify small greyscale images like those below into person or non-person, in C. The project is scheduled for around ...
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Deconvolution of an Image Acquired by a Square Uniform Detector

So, I acquired some images by scanning a radiation source with a square detector like in the following gif. Where the dashed grid represents reality, the 3x3 square my detector, and the 4x4 my ...
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eigen values and eigen vectors of signal

What does the Eigen values and Eigen vector of a signal or function represent? What is its physical significance? I know about basis vectors of a signal which constitute the orthogonal planes where ...
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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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Licence plate enhancement

Is it possible to enhance the image below and make it more readable? I have tried apply binarization but there is some kind of shadow. So I have tried to convert image to gray scale and then ...
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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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compression algorithm

Steganography can hide one image inside another. If we have a compression algorithm that allows us to fit the bits for two images into the size of one, can we think of a way to modify a run-length ...
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Non Linear Remapping of the Pixel Values

Suppose you take a photo of a beautiful scene of mountains and a lake. The representation devotes half of the scale between black and white to the bright surface of the lake, and the other half to the ...
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What Does It Mean When Cross Correlation Between Two Images Occur at Negative Coordinates

I am using Matlab normxcorr2 to calculate the cross correlation between several images, something like what has been done here: in Matlab documentation. There are some of the examples that I get ...
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Measure that Compares an Actual Old Document from a Synthetic Old Document

I have collected dirty background images, below is the sample: I have also a collection of an actual image of a dirty document with text on it, just like below: My problem with my actual image of a ...
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1answer
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Find common features across images

Consider multiple images that share a common feature. More specifically, they are the sum of multiple features, and I know that one of those is present in all. What is the best method to extract this ...
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What does this notation $g(x) = S\{\delta(t) \}(x)$ mean?

What does this notation mean $g(x) = S\{\delta(t) \}(x)$ mean, where $S$ is a "system", $\delta(t)$ is the impulse function and $g(x)$ the output function of the system? I am really not familiar with ...
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Salt and Pepper impulse Denoising opencv

I am creating a generic method to work on salt and pepper noise and variants. The example images are as shown below : I tried few methods, such as ...
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1answer
418 views

how gabor filter is used on image texture edge detection

as I searched gabor filter is most used tool on texture analysis and edge detection in digital image. its said that it searches a certain frequency as a texure around a pixel or point to find the ...
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how sobel edge detector as a first order derivative is turned to a 2 dim filter?

I want to know theorem behind sobel operator. basically a first order derivative is -1/2 0 1/2 . its a vector. the question is how this vector is turned to a matrix below and what was theory and ...
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Face Recognition: Simplistic Explanation on PCA Eigenface Algorithm

I m working on a project that I have to use eigenface but I have some uncertainty and I dont know how to deal with it. There are some tutorials about it on internet but I can't understand what exactly ...
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How Last Edge Image Can Be Achieved from Law Masks

as we know thechnique of law edge detection has 25 2d masks that is obtained form 5 different 1d filters. we can use each of those masks on image with convolution but how can we obtain final result? ...
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Easy way to get rid of noise in a hand drawing

I would like to take a user's hand drawn input, and filter out "noise", aka small sketches or blobs, where the user might have screwed up and accidentally touched his hand to the drawing device, or ...
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Which Transformation, Or Similarity Metric, Is Rotation, Shift and Scale Invariant?

I have an algorithm to to detect copy-move forgeries in images. I used block matching to detect regions of an image that were forged with copy-move forgery and highlighted the alleged areas. For block ...
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How to Match 2 Signals which Are a Shifted and Scaled Version of Each Other

I have 2 signals S1 and S2 that contain the same information, but S2 is shifted and scaled compared to S1 by an unknown amount (but small; eg shift would be of the order of 1-10 samples). What is the ...
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Finding defects in wall paint (finding difference in textures)

I have been experimenting with computer vision techniques to find defects in paintings, more specifically defective brush strokes. I have tried a handful of techniques such as different filters, One ...
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2answers
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Indices in 2D Convolution Operations - Handle Out of Bounds Indices

Referring to the answer here: https://www.quora.com/Why-are-convolutional-nets-called-so-when-they-are-actually-doing-correlations, the equation for a discrete 2D convolution is specified as: $$C(x,y)...
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OpenCV/C++ connect nearby contours based on distance between them

I have to connect nearby contours in an image based on the distance between them which specifies if the contours are to be connected. Now there's a question already on the same problem here https://...
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1answer
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Different representations of frequency space of 2D image FFT

I'm learning images processing using FFT. In my test example provided below the input pixel values are clamped 0-1 (0-255), but I do eventually want to process floating point heightfield pixel values....
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Reconstract the image from the modulus of its Fourier transform

In Reference, it is shown than one can recover the image by using only the modulus of its Fourier transform. It provides two iterative algorithm which is really similar to Gerchberg–Saxton method. ...
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confusion sampling vs quantization?

while converting analog signal to digital equivalent,we have a process that is called analog to digital conversion and it has two main steps/stages sampling and quantization? I am confused whether y ...
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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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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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video resources for learning image processing?(for EE background)

Please kindly recommend some youtube links for learning image processing. I have EE background and i want to study/learn image processing in this way Also i have confusion that Computer science ...
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Anisotropic Diffusion Filter - Intuition Behind Parameters

I need to know what is iteration and divergence in anisotropic diffusion filter technique. Isotropic diffusion $$\frac{\partial I(x, y, z)}{\partial t}={\rm div}\left[c\cdot \nabla I\left(x, y, ...
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Correlation Performed by Convolution

Background: The question here is related to images in particular and not signal/waveforms. I have been reading a lot of answers about the difference between convolution and correlation but I am stuck ...
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1answer
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How Can an Object Move by Less Than a Pixel Between Two Consecutive Frames?

I think video is a series of picture frames. Consider a black & white scenario (no RGB). A picture frame is a 2D array of pixel. Each pixel has a single color. A pixel can't be half black or half ...
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How to create different Time frequency images from a data

I'm new to Python. I have a time series in a CSV file that has about 5000 rows and 3 columns. I have split the data into training and testing in ratio 70:30 respectively. However, I have a problem ...
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How to find position, scale and rotation of a known shape/contour in an image?

I have an image of an object. The image shows a high contrast outline of the object. It is guaranteed that the image shows exactly one object. The shape/contour of that outline is known. It is not ...
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Image extraction post processing to increase similarity

I’m trying to train an OCR model, but I need to get my extracted images to look more like the training images. However I’m not sure of how to go about it and what techniques I can use. For instance ...
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1answer
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The Kernel in 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
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How is WSNR (weighted signal to noise ratio) defined?

I'm studying about comparison between images to determine quality. I've learned about MSE, SNR and PSNR, and now I'm trying to understand WSNR, which I assume is similar to SNR but with weights. I ...
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How can I get better results from Phase Correlation

I am using Phase Correlation to register 3D data. There's a clear distinction in the y direction so the resulting shifts seem to be correct. But since there is a lot of similarity in the x direction ...
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Shifting in DFT (FFT)

Input image Listing-1 i = imread('Untitled.png'); i = rgb2gray(i); F = fft2(i); %%%F = fftshift(F); F = abs(F); F = log(F+1); F = mat2gray(F); imshow(F); ...
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How to use the Walsh-Hadamard transform to filter 24 bit RGB color values in a localized spatial region?

After reading this Signal processing Stack Exchange article tonight, What is the Walsh-Hadamard Transform and what is it good for?, I became interested in applying the Walsh-Hadamard transform to ...
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Looking for Open Source Image Processing Library that is equivalent to HIPS

Note -- would appreciate any comments on ho to improve the question -- I did the best I could but it I feel it may still be sup-par. HIPS was/is an excellent image processing software. It was ...

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