Signal Processing

Questions tagged [image-processing]

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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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Why is the albedo obtained greater than $1$?

One of the many applications of image processing is photometric stereo which in turn permits the reconstruction of a 3D surface using a chain of 2D images taken at the same viewpoint but with ...
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Trouble understanding how image digitization works

Quoting Image Processing, Analysis, and Machine Vision, 4th ed. An image to be processed by computer must be represented using an appropriate discrete data structure, for example, a matrix. An image ...
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Is it possible to detect the sparse vector based on a non-invertible matrix

Given a non-invertible matrix $X \in \mathbb{R}$, let's say that matrix is, e.g. : $X = \begin{bmatrix} 0.7500& -0.2500 &-0.2500 & -0.2500 \\ -0.2500& 0.7500& -0.2500 & -0....
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How to rasterise a greyscale image using only black & white pixels?

I want to convert greyscale images to ones that have just black and white pixels. Simply dividing the input pixels into black or white based on being below or above a set grey level, doesn't give nice ...
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137 views

Decomposing Sobel Filter

I am trying to decompose a Sobel filter into two vectors (column and a row) using Matlab. If our Sobel filter is A = [1 0 -1; 2 0 -2; 1 0 -1] we can get the U, S, V ...
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Unexpected result of motion-blurred image deconvolution

In my case I have some images, captured by CMOS-camera (global shutter) during non accelerated motion (with fixed illumination and focus and known velocity and exposure time, so field of view travels ...
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Where to find an implementation of the Structural Symmetry of Strokes (SSP) algorithm for image binarization?

I want to OCR photos of pages of printed text. Nothing too complicated but the images were taken with smartphone cameras, the lighting is suboptimal and sometimes the images were photocopied before. ...
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Could you recommend a tool that can extract (segment) pores on this image of a diatom valve?

There is an image of a diatom valve with pores - short stright black segments. Are three any tools (plugins of ImageJ or something like) that could extract (segment) these areolae?
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Video-Encoding planes

I am currently developing an Android Application for Video-Streaming. Now i came to the point where I wanted to manipulate the stream. From the API I am using I have 6 methods available for each Frame ...
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Image Z Coordinate Clarification

I'm trying to understand 3D image reconstruction, and want to clarify how we can find a z image coordinate. Is the z coordinate for image coordinates (x,y,z) the focal length since that's the distance ...
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Are scipy second-order Gaussian derivatives correct?

For an edge detection algorithm, I need to compute second-order derivatives of an image, and I do this with use of Gaussian derivatives. I assumed that the ...
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66 views

Comparing distribution of vectors with different length?

I have two vectors of different length, each vector contains similarity scores. I need to plot the probabilty density function of the scores in both vectors to compare their distribution using Matlab. ...
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When to Use Composite Filters and When to Use Separable Filters?

I’m a beginner in image processing, and was wondering since seperated (decomposed) filters help give faster and more efficient results, when do we even need to use composite filters? All I heard is ...
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50 views

Help generating non-Gaussian noise

I'm trying to add non-Gaussian noise to an image. The purpose is to synthesize realistic camera noise. I am doing the following: Obtain a noisy image sample by subtracting a low ISO photo from a high ...
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Reprojecting an image to another viewpoint using planar homography

I have an image rendered by a simulated camera in Unity. Using this image and the known (virtual) camera pose it corresponds to, I would like to render a new image from another viewpoint. Having read ...
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What exactly is "connectivity" between pixels in an image?

So, my professor says that two pixels are connected if: they are neighbours; and their intensities satisfy a specified criterion of similarity. And depending on the type of neighbours they are, they ...
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Convert pictures from the same camera with different FOV to pictures with same FOV

I have a camera device that produce two pictures at the time: depth picture with FOV: 87° × 58° RGB picture with FOV: 90 × 65° I expect that they "share" the same objective so their origin ...
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23 views

Finding the system impulse response for 2D system

Im taking a class on medical imaging, but my previous signal processing course did not really cover 2D systems in the greatest of detail. Therefore, I wanted to ask a quick question on determining the ...
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45 views

How to Use Convolution Theorem to Apply a 2D Convolution on an Image

How do I actually apply the convolution theorem? I have my fourier transformed image matrix, and a Fourier transformed kernel, but how do I actually multiply these together to achieve the intended ...
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Discrete Fourier Transform of 2-D Images

I'm a high school student doing an essay on the applications of the Fourier transform on signal processing, but I haven't been able to find much information when applying the discrete fourier ...
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Image conversion - raw ultrasound data to convex image

As a project, I'm trying to decipher raw data coming from a medical ultrasound device. The data contains a 128x1008 matrix. Each one of the 128 columns represents a sensor element. Each row in each ...
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38 views

Sharpen ridges and valleys

I am looking for a way of sharpening ridges and valleys in the following heightmap I think this problem is slightly different than a regular sharpen operation, because sharpening would affect first ...
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Understanding the Bilateral Filter (Image Filtering)

I asked this question already on StackOverflow and was told to ask it here instead, so I will just copy the content of my question. I do understand the general concept of bilateral filtering and I did ...
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Finding the Right Image-Matching Algorithm for Brightfield Microscopy Data

I work predominantly on single-particle-localization algorithms for microscopy data, but we're working to implement a few different methods to extend our tracking methods nicely into the z-axis. One ...
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Order of Operations: Denoise, Resize, Threshold

I am writing a program for converting microscopy images to a FEA model using Python and scikit-image. As part of it, I am writing a function which opens the grayscale image and has to do the following:...
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how to identify the main segmentation step in a paper?

I am trying to summarize the segmentation methods submitted in the Cell Tracking Challenge. Currently, I'm having a problem in identifying the main segmentation step used in each paper. How to ...
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Pixel Shuffle Layer

I was reading multiple sources to get an explanation for the Pixel Shuffle Layer. While I understand how the layer works, I do not get the intuition about why it would be helpful for the case of super-...
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Efficient algorithm to impose boundary conditions while applying a 2d filter

It is possible to filter an image by using a 2d DFT. This will result in periodic boundary conditions. Now, is it possible to use the DFT to filter an image, while maintaining predefined boundary ...
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42 views

Edge Detection Convolution Intuition

I was learning about convolution and how filtering helps us to detect an edge in an image;however I still cannot not understand how the convolution process in the image below does this. I understand ...
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Alternatives to Meyer Windows as Curvelets?

I am looking for alternative to Meyer window functions (Section 4.1) from which one can define a curvelet system. Are there any similar window functions which would be as easy to implement?
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58 views

Converting Hadamard Product into Matrix Multiplication in Image Deconvolution with Total Variation (TV) Using ADMM

I would like to solve the following Image Deconvolution equation by ADMM. $$\mathbf { \min\frac{1}{2}\Vert{Cx-b}\Vert_2^2+\Vert w\circ (D x)\Vert_1 \tag 1}$$ Where, $x$ is a vector of unknown pixel ...
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35 views

Average Power Spectral Density (1D and 2D) of multiple images of different sizes in python

I am trying to calculate avg 1D and 2D PSD of multiple image with different sizes. Any idea how can I do this? Current I'm calculating 1D psd using this function. The problem here is that each image ...
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39 views

How to Remove Temporal and Fixed Pattern Noise and Apply Tone Mapping?

I have a video, whose frames I have extracted and require to work with. 16 bits and grayscale images. My task is to improve the quality of the images, by removing the noise + adding tone mapping and ...
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Podcasts or video channels on applied signal processing

There is already a good list of text media on signal and image processing here. I'm curious if anyone is making audio or video media about new techniques or interesting applications across ...
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21 views

What image augmentations can help a neural network identify the lowest-value pixels within an image?

I am training a CNN to identify objects, and I believe the network will learn much faster if it can learn to focus on the pixels with the lowest value. One way to go about this would be to augment the ...
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26 views

Find vertical/horizontal lines

I tried everything including the Hough Transform with different inputs; Laplacian and Sobel and Canny edge detector were run on filtered image but cv2.HoughLinesP and cv2.HoughLines both give me wrong ...
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29 views

What is the condition under which the length of shortest 4-path equal to $D_4$ distance?

The following is a problem of "Digital image processing" book. Consider two points $p$ and $q$. State the condition(s) under which the $D_4$ distance between $p$ and $q$ is equal to the ...
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61 views

ringing artifacts using FFT-based gaussian blurring

I'm trying to do an FFT-based gaussian blur on a grayscale image, and it works, however it seems to introduce ringing artifacts to the result when compared to the expected direct filter. What can I do ...
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224 views

Algorithm for Scale Invariant Template Matching

I am using opencv for finding template images in a video stream. The elements I am trying to find are UI elements of android apps. Classic template matching is working quite well. But only as long as ...
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How can we interpret Spatial Cross Correlation between two images in case of compressed sensing based reconstruction of images?

I am reconstructing images using compressed sensing. The images are used from sipi database. One particular image, named Female Bell Lab, which is giving better result with high PSNR around 42 dB and ...
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1answer
68 views

Appropriate Gaussian filter parameters when resizing image

When scaling an image down it is common to first convolve the image with a Gaussian filter. Given a scale factor $0 < s < 1,$ what is an appropriate $\sigma$ to use? For example, if $s = 0.5$ (...
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What are some good references that define images from a statistical point of view?

I know that images can be studied and understood as 2 dimensional signals. However, I hope you can point me towards references that define and present images rigorously in terms of realisations of a ...
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109 views

OpenCV: Can't find large rectangle contour

I'm trying to re-create the dimensions of an object by setting it up on a grid and taking as close to a top-down photo I can which I will then get the contours of the largest bounding rectangle and ...
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1answer
123 views

How to Solve the Image Dehazing Problem Using ADMM?

I want to solve the image dehazing problem using ADMM. I want to use the proximal algorithm to optimize each element. I refer to this treatise: Efficient image dehazing with boundary constraint and ...
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1answer
58 views

Basic question about RGB planes

If a 3-bit, 2 × 2 RGB image has the following planes: how can we write each plane to a vector of size 3x1?
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1answer
125 views

Is there a way to find the contours of instances in a binary mask image by color?

I need to find the contours for each of the instances of microscopic cells in a binary image mask of dimensions 256 x 256 shown below. My approach involves thresholding the image to get a binary mask ...
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How to find the Wavelet measurement matrix in compressed sensing?

Assume that an image vector x = Ψs. s is a sparse vector in which the image vector x of length N x 1 is sparse in the wavelet Ψ basis. I have issue in finding the measurement matrix A= φ Ψ where φ is ...
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1answer
42 views

The Meaning of $ \mathbb{E} $ Operator in the Pix2Pix Loss Formula of a Neural Network / Convolutional Neural Network

I've been observing the Pix2Pix Paper - Image to Image Translation with Conditional Adversarial Networks and wondered on formulas. For example, the objective of the CGAN is: , where x - observed image,...
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139 views

Generate a Gradient Operator for a Fourier Transform

I came across this equation while trying to process an image $z$, $$ \mathcal{F}\left(\mathbf{D}^T \mathbf{D}\right) \mathcal{F}\left(z\right), $$ where $\mathcal{F}$ is the 2-D Fourier transform, and ...
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74 views

How to Solve Blind Image Deblurring with Total Variation (TV) Prior Using ADMM?

As a continuation of the question How to Solve Non Blind Image Deblurring with Total Variation Prior Using ADMM? I would like to understand how could one solve the Blind Deblurring (Deconvolution) ...

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