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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Spatial wavelength

I was reading a paper on motion magnification, Eulerian Video Magnification for Revealing Subtle Changes in the World by MIT CSAIL researchers, where the equation (14) of the paper uses spatial ...
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These two images are very similar. Why doesn't SSIM reflect that?

Here are two aligned images (greyscale, but same applies to RGB) that I want to compare using SSIM: Clearly, these are very similar images. It seems that the first image is more blur rr However, the ...
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Understanding the Threshold Process in Harris Corner and Edge Detector

I have read the paper Chris Harris , Mike Stephens - A Combined Corner and Edge Detector about the Harris Corner and Edge Detector, but I didn't understand the point that after low and high threshold ...
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How to perform dot annotation for crowd counting in a image file using Matlab?

I have some crowd images having more than 300 people in each image. I want to label each person(i.e. head) with dot annotation such that coordinate of each dot(x,y) is saved in a .mat file. I hope ...
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Image processing for camera health monitoring

I have a set of cameras. I would like to monitor the output of the cameras to make sure they are operating well. So far my ideas: standard deviation and the mean of the picture - to find out if the ...
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Residual error when setting measurement matrix in compresssive sensing

I have an issue when implementing compressive sensing to recover sparse vector. Assume I have sparse vector $x$ of length, for example, $(256,1)$. $x = [x_1,x_2,.....x_{256}]$. This vector is ...
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30 views

Low samples numbers machine vision training for object detection

I'm trying to set-up a machine vision application in which I have to detect the position of a printing nozzle (in the red sqaure in the image) in a field of view in order to prcisely position a ganty ...
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Unexpected Results in Rank Transform Based Disparity Estimation

I am applying a normal rank transform of size 7 x 7 to the right/left shifted images in order to obtain their disparity map using a typical block matching algorithm in MATLAB. My code to obtain to the ...
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Convolution v.s. Cross Correlation in Digital Image Processing

I understand that from mathematical point of view, only difference between Convolution and Cross Correlation is that Convolution is commutative, while Cross Correlation is not. In many articles ...
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Measure how Smooth the Borders are Rendered in an Image

I have two images: I want to measure how smooth the text borders are rendered. First image is rendered perfectly smooth, but the second image is rendered with a lot of curves. How will I measure it ...
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remove outlier spectra

I have a set of spectra (hyperspectral imaging) per class (~10000) and want to remove those spectra which behave different then the mean of the spectra. I want to remove the entire spectra (not ...
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Flat Field Correction - When images are taken at different exposures

The light source I am using is known to have a Gaussian intensity distribution along the height. I took the raw images at "x" seconds of exposure. However, while taking the bright field image, the ...
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Image processing books Gonzalez et al. vs Sonka et al?

I don't know where else to post this question so here it goes. I'm trying to buy a DIP book and the best two right now are: Image Processing, Analysis, and Machine Vision by Roger Boyle, Milan Sonka, ...
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What is the “bilinear interpolation kernel” in personlab paper?

please excuse my ignorance in computer graphics, but what is this bilinear interpolation kernel in the personlab paper page 6 equation (1)? Here it is: $$ h_k(x) = \frac{1}{\pi R^2}\sum_{i=1:N}p_k(...
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What is the difference between an image plane and a virtual image?

I have the following diagram that describes a camera model (I believe it is the pinhole camera model). Wikipedia has an article about the image plane and virtual image, but these articles do not ...
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How to estimate the frequency of a feature in an image?

I have a background in the 1-D signal analysis but I am totally new to image analysis. I would appreciate any help. Given the following original image and the downsampled image, as you could see, ...
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Is it useful to apply edge detection filter as a preprocessing step before applying CNN?

Background: my future boss would like me to apply a number of low level filters to industrial images before applying machine learning methods on them. From my knowledge this doesn't make any sense as ...
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On the Measurement Matrix Used for Compressing Sensing

Assume we have a matrix $x$ of size $(8,8)$ where each column is considered to be sparse with degree of sparsity equals to $4$. it means that every column can have $4$ zeros and $4$ non-zeros values ...
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How to simplify multiple addition and convolution operations into one convolution kernel

I need to perform such a conversion to simplify my image processing problem (sharpening, in green are the knowns, in red the unknowns): \begin{align} y(n,m) &= \color{green}{x(n,m)} * \left[ \...
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27 views

RMS contrast of image interpretation

I have two grayscale images, say A and B, and I want to determine, which one is more contrast. For that I'm calculating an RMS contrast as it is described in Wikipedia. The results are about ...
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Dirty Image Quality Assesment Measure

I was looking for a way to measure how dirty is the document in image processing. Example images below: a. Dirty Backgrounds b. Dirty Backgrounds with Text Can someone give me an initial idea to ...
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How can I cut exactly the first harmonic (H1) from a FFT of an image

I have 4D( 2D + slices along z axis + time frames) gray-scale image for the heart beating on different moments. I do like to take Fourier Transform along time axis(for each slice separately), and ...
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How to solve ADMM for TV Minimization Problem For Different Sizes $A$ and $x$ in $Ax=b$

I have matrix $A$ that is $(M \times M)$ square matrix, $x$ $(M \times N)$ matrix, $b$ is $(M \times N)$ matrix. Knowing $A$ and $b$ I would like to get the $x$ from the equation $Ax=b$. $N=p \times q$...
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Wavelets: Manipulate its phase and reconstruct

Usually when I read about wavelets in image processing, the authors tend to make use of its coefficients and rebuild based on certain criteria, for example de-noising an image where you usually filter ...
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About image compression vs. DCT

I have recently started reading about image processing, my knowledge in image processing is still very limited. What I understood that DCT can help in image compression using Huffman, JPEG or MJPEG ...
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Producing images with subpixel shift in region of interest

Let's say for a zebra image, and at certain pixel location, I would like to makes it "vibrate/warp" to and fro in horizontal direction at a certain frequencies in a sequence of images of time ...
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what is the difference between the convolution and differentiation over image in image processing?

In image processing the differentiation and convolution are the terms that are used interchangeably . what is the difference between applying convolution and differentiation over the image ?? How we ...
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Why we have to multiply the images with $(-1)^{x+y}$ to center the transform in frequency domain filtering?

To perform the filtering infrequency domain we perform multiplication of $(-1)^{x+y}$ why??
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How the Grayscale images are converted back to RGB?

In case of RGB to grayscale conversion we take the average of R,G,B channels and convert them to Grayscale which has songle channel. How to convert back the Grayscale to RGB ??
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Create 2-d Dirichlet kernel for use in image processing

I am working on frequency domain CNNs for image classification task, in which I initialize complex kernels of size (k*k). For performing point-wise multiplication between the kernel and the Fourier ...
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Adaptive threshold value transformation based on brightness

This is the homework of my son: My wife gets such images taken with a mobile phone form other mothers, whenever my son misses a lesson. She can not print those images, because they are almost black, ...
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What is Magnitude and Phase actually represents in Fast Fourier Transform?

When we reconstruct the image from its magnitude only using Inverse Fast Fourier Transform, then why the resulting image looks nothing like but the original image? Can someone please explain me in ...
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Converting IQ to RF data [duplicate]

I appreciate any help: I wanna convert IQ data to its RF data, representing an image. The center frequency and sampling rate are available. What I do is: First I do up-sampling in MATLAB by applying ...
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Identifying the boundary points of a shape based on the centroid

I have a set of binary 2D images with objects in white and their boundaries in black (attached example). I also have a list of centroids (x,y coordinate pairs) identifying all objects. For each ...
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Frequency contour detection in spectrogram

I have an image of a spectrogram and I wish to detect the tracks/contours of prominent frequencies present in the spectrogram. In the end, I want to be able to get various prominent curves from the ...
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Estimating the Signal by Deconvolution with a Prior on the Filter Coefficients and the Signal Samples

Assume I have signal $y[n]$ which is a result of convolution between channel $h[n]$ and signal $x[n]$. which means: $$y[n] = h[n] \ast x[n]$$ where $\ast$ is the convolution operation The signal $...
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How to prepare different input size in CNN

I'm doing a research about personality identification based on their signature using CNN method, however the learning feature for the personality traits have a different input size. I understand that ...
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49 views

Is HSV Color Space Sufficient for Rudimentary Color ID and Edge Detection

I want to, as part of a C++ school project (no OpenCV), work with an RGB image taken from a camera filming smarties (round colored pellets) from above and extract the number of candies in each color. ...
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Why are 8 points needed to compute a fundamental matrix?

Homograpies have 8 degrees of freedom. Fundamental matrices have 7. Essential matrices have 5. To the best I could find, all those matrices are obtained by using the 8 point algorithm. I don't see ...
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Array bounds check o(1) (Integral image?)

Not sure if this is the correct place to ask but I have a question about techniques for processing an array of pixels with o(1) complexity. That is to get the sum of a subset of an array but if this ...
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Fast Document Enhancement

I followed Dropbox's blog - Fast Document Rectification and Enhancement To enhancement image, I need solve this formula J(x,y) = gain(x,y) * I(x,y) + offset(x,y) Where J is image after ...
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Making images taken under daylight conditions appear as if they were taken at night using image processing elementary techniques

I know that these days' style-transfer GANs should be able to style-transfer day images into night images. I however prefer to do it using a set of elementary image processing manipulations, so I can ...
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Detecting and Recognizing a pattern in the 2D-FFT

More theory before I ask a practical question based on the task I have. I've discovered that performing a 2D-FFT (python or matlab implementations) on some test imagery I have results in a unique ...
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34 views

Why we need Laplacian for edge detection?

I am studying some trivial computer vision processing techniques and I came across edge detection algorithms. IMO sharp changes in the gradient are enough indications to detect the edges in an image ...
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34 views

Harris Corners Detector squared derivatives

I have trouble understanding something (small) regarding the math behind Harris Corners Detector. (for example I looked at this explanation - https://aishack.in/tutorials/harris-corner-detector/) In ...
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174 views

Discrete Cosine Transform (DCT) Coefficient Distribution

I have two images : Original Image Binarize Image I have applied Discrete Cosine Transform to the two images by dividing the 256x256 image into 8x8 blocks. After, I want to compare their DCT ...
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Image Transformation Functions to Identify if the Text in the Document Originally There or Just Synthetically Overlaid

I have a copy of scanned ancient dirty document and synthetically generated ancient dirty documents. I want to use Discrete Cosine Transform to characterize noise types existing in the document and ...
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Parameters for inverse image distortion

I'm trying to simulate camera (barrel/radial) distortion, and to reverse it. I.e. a process that would do: Image --> Distorted Image --> ~ Image In ...
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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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