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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11 views

Is it okay to interpolate between overlapping areas obtained using a sliding window?

I am using a 50x50 pixel sliding window which moves left to right every pixel so that it covers a whole binary image which is about 2000x2000 pixels. In the window, the ratio value of black to white ...
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How does DCT decorrelate images?

I've read in multiple places that DCT decorrelates Toeplitz matrices and images usually have Toeplitz structure. Can you explain with an example how DCT decorrelates a Toeplitz matrix? Example for DFT:...
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1D DCT matlab code

I was writing MATLAB code to compute 1D DCT of sample y. On computing DCT for y=[0,1,2], code generates coefficient ...
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How Does Color Conversion and Downsampling work When JPEG compressing a grayscale image?

For color images I know you have to convert to YCbCr format, and then for downsampling is based on the fact that human beings see differences in Y more than differences in Cb or Cr. How do I do these ...
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Intuition about tag pose estimation accuracy

I have some difficulties to have a correct intuition about expected pose accuracy when dealing with planar pose estimation (e.g. pose estimation from AprilTag detection) and perspective camera model. ...
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1answer
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What Is an Oriented Gaussian Second Derivative Filter

In the paper: Detecting and Localizing Edges Composed of Steps, Peaks and Roofs, the authors refer to an image filter as an oriented second-derivative Gaussian filter. I'm trying to figure out what ...
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How to plot ROC Curve of feature detecttion algorithm? [closed]

I want to compare the performance of feature detection algorithms like Harris, Shi-Tomasi, MSER, ORB, FAST, BRISK and KAZE using ROC Curve. I found that I need TP rate FP rate. How do I derive the TPR ...
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2answers
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MRI K-space to image: why track frequencies in two dimensions?

While trying to better understand how an MRI goes from k-space to an image, I came across this wonderful website that explains how you would represent an image as a collection of rows of pixels where ...
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3answers
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What does this paragraph mean?

I'm reading this paper about about an algorithm to measure image sharpness, and am confused by these sentences in the 6th paragraph: It is well known that the attenuation of high-frequency content ...
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1answer
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What is Bottom-Hat transformation?

I am reading the Digital Image Processing book by Gonzalez and i can't seem to understand Bottom-hat transformation. Can anyone explain it to me in easy terms?
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Selecting a Digital Signal Processor for a Specific Image Sensor

I am working on developing a camera and I am trying to select hardware for the camera. I believe that I may need a digital signal processor to compress image data before it is transmitted to a ...
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Detect lines transitioning to blobs in images

I have the following images (in high resolution, uncompressed). When the process starts, the left image is displayed and it ends something similar to the right image. The first image shows labyrinth-...
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Standard Deviation of Character Gradients in a Document Image

I have the paper titled "CG-DIQA: No-reference Document Image Quality Assessment Based on Character Gradient". It is all about assessing the quality of the document image based on its blurriness. To ...
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Algorithm that Fills the White Holes Within the Character Image

I have this degraded image : Using paintbucket tool in Paint.NET Windows application, I fill the character image black. My ...
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1answer
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Noise problem when transforming and quantizing difference between images

I have a program which does forward and inverse DCT and quantization and dequantization using JPEG matrix. If I apply it to a single image it works fine, but if I try to apply it to a difference ...
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Bilinear Interpolation on A Subsection Of An Image

Is it possible to do bilinear interpolation on each 8 by 8 block of an image one at a time until you cover the entire image rather than doing it on the entire image? What are the consequences of this?
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Compressing sparse vectors based on compressive sensing

I have a sparse vector $x$ of size $N$x$1$ which is sparse with number of non-zeros values are $m$, it means $m$ out of $N$ values are non-zeros, the non-zeros locations are distributed randomly. ...
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security in biometrics

I read the following in one of the research papers: Cancelable biometrics using random projections can be implemented by multiplying a random matrix with a feature vector. The result is a cancelable ...
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What is the gradient of fft?

I have a time-series of length N generated by the following equation: ...
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Computing White Speckle Metric in a Document Image

The paper 'Metric-based No-reference Quality Assessment of Heterogeneous Document Images', discusses about measuring the quality of characters in a document image. I'm having difficulty to understand ...
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1answer
22 views

What happens when you wrap a 3x3 kernel at the corners of an image?

I am puzzled by what actually happens when you process border cases when applying an image filter. For instance if I apply a 3x3 Gaussian kernel to the top left pixel[0][0], the remaining pixels that ...
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Understanding zero-phase filters

I'm reading the book "Digital Image Processing" by Gonzalez and Woods and I'm wondering how their definition of zero-phase-shift filter is equivalent to the one given here. "Digital Image Processing" ...
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Binary image? Only black and white? [closed]

By name, a binary image is one that has two levels. But is it essential that those two colors are black and white? Or any other combination also allowed as shown in attached snap. Snap is output image,...
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1answer
28 views

Advantages and disadvantages of multiplying sparse vector with sparse matrix

Assume I have a sparse vector $x$ whose few values are non-zeros, that vector is multiplied with sparse unitary matrix $Y$ giving $z = Yx$. Are there any advantages of detecting the sparse vector $x$ ...
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1answer
37 views

Zero-phase-shift filters must be symmetric about the origin

In reading Rafael Gonzalez Digital Image Processing, second edition, section 4.10.2, the author writes: Notch filters are the most useful of the selective filters. A notch filter rejects (or passes)...
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What is the DFT of a binomial filter?

I hope this question is not too simple, I just started learning digital image processing. The 1D binomial filter of size 2 is defined by $B_2 = \frac{1}{4}\begin{bmatrix}1 & 2 & 1\end{bmatrix}$...
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What is Maximally Stable Extremal Regions (MSER)?

In the paper , MSER is being defined. Please help me understand what is MSER and how to implement it. The paper says, The regions are defined solely by an extremal property of the intensity ...
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1answer
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Comparision between SSIM and MAD Image Quality Assessment Algorithms

I have been working with Most Apparent Distortion(MAD) tool to evaluate the quality of images. I have read a paper that compares SSIM, PSNR, FSIM, etc. with MAD. I am uncertain about some calculations ...
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Reconstruct signal from imprecise sampling?

I'm trying to digitize a VGA signal with a low-power consumer computer running a consumer OS and am having issues with the stability of the sampling rate. What I did so far: grabbing the green ...
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What does it mean to rotate an image by 0.1 degrees?

In the old Tangent Prop paper (you don't need to know this paper), the tangent vector of the rotation transformation (think of this as a vector-valued function) at some input image is approximated by (...
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Smoothing jagged lines in an image?

I have an image like this - I would like to smoothen the lines in this (as you can see they lines are a little jaggy.) How can I do this? I obtained the lines by isolating them from another image ...
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1answer
28 views

Image Processing [closed]

I have an image and I am trying to find its rows and columns. A = imread('lena.jpg'); nrows = size(A,1) ncols = size(A,2) This is 3 dimensional matrix. Output ...
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1answer
33 views

Justification for Squared $ {L}_{2} $ Data and Smoothness Term as an Error Bound

Often in variational methods (and not only) we have an energy that is of the form: $$E(u) = \frac{1}{2}\|f-u\|^2_2 + \frac{\alpha}{2}\|\psi(u)\|^2_2,$$ where the first term is referred to as the data ...
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Questions in a Character Degradation Model Paper

I have questions in the ‘Noise region definition’ and ‘Noise generation process’ of the paper “A character degradation model for grayscale ancient document images”. In Noise region definition, ...
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How can I stitch bottom of some image to topside of another image by erasing as much overlapped image as possible?

I have 2 images of size 1920*1080 and I want to try image-stitching on them. These are images (images are from wind turbine blade.) This is the first image And the second image. I already have ...
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What is the difference between template matching and object detection?

What is the difference between template matching and object detection? Is the only difference that the template is typically rectangular while the objects can be of any form (including rectangular)? ...
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How to know what kind of noise?

Im working with friends on a computer vision project for university. For the preprocessing part we are going to use a Gaussian filter. One of my project partner said I have to justify the use of a ...
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59 views

Is rotation of a Fourier transform the same thing as Fourier transform of a rotation?

I'm working on an image processing problem and wondering if DFT(rotation(image)) == rotation(DFT(image)) (1). My final goal is to apply rotations in the Fourier domain then do an inverse Fourier ...
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2answers
32 views

Average image over $N$ frames with one frame buffer

Can you give some filter that is averaging an image over $N$ samples in a recursive way that only needs one frame buffer? $\frac{1}{N} \sum_{k=1}^{N} y_{k}(m,n)$ I can only imagine filters that need ...
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54 views

Mapping ring asteroids in Elite Dangerous by image processing

In the game Elite Dangerous, which is an online spaceflight-based sandbox game set in a procedurally-generated galaxy, one of the most profitable in-game occupations is mining commodities from ...
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2answers
29 views

Downsampling Image

Can you suggest me a good downsampling algorithm for an image. I explored area averaging method, but I am looking for better. I am using good in the sense that it should be less computational ...
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Gaussian filter vs median filter vs wiener filter??Noise tackling performance with image corrupted with salt and pepper noise

I am trying to remove noise in an image usig three different filters,but i am bit confused in output performance of each filter. I think gaussian filter has best performance in this case(please guide ...
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How to implement a single shot object detector with only “one” anchor box per feature-map cell

I am newbie to SSD model, I have some images of products on a shelf , I trying to detecting that products using SSD with one anchor box per feature map, please help me out, how to prepare the data and ...
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1answer
35 views

Confusions regarding meaning of “kernel” in signal processing and image processing? [duplicate]

While studying filters in DSP and DIP, the term "kernel" is often encountered What is the meaning of "kernel" in context of filters??Please kindly explain in simple words with an example I have also ...
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Learn the relationship between the pixels in a chunk of an image and then search for more chunks like this one

I've just started to learn computer vision and I have a doubt about if I can do the following and how can I do it. If a 4x4 square of the image is like this one: Here I want to detect another chunk ...
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Building a spatio-temporal filter

I want to implement a spatio-temporal filter for my images which are a set of silhouettes of a cycle of walking. So I gather all the images in an array and convolve the 3D array with my spatio-...
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Confusions regarding frame rate?

We know that when many image are shown in succession they create illusion of video But what is the minimum rate of frame/images so that still images appear as video? In this case, images/frames are ...
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1answer
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change in size of an individual pixel? [duplicate]

If we want to change resolution of an image,we can achieve that by increasing or decreasing the number of pixels Is there any other way ? Can we change dimensions of an indvidual pixel,rather then ...
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how formula for saturation component is working in RGB-HSI conversion?

As shown in attached snapshot,chap6 of gonzalez 3rd edition How the highlighted expression for S in eq 6.2-3 is working? and what will be range of values of S? By range,i mean,maximum and minimum ...
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How do you apply DCT steganography on an RGB image?

I am working on a DCT-based steganography program in Python and I found a working model in Github. The program, however, can only encode on one of the RGB channels. Resulting in a discolored image. ...

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