# Questions tagged [image-processing]

For questions related to the collection, processing and interpretation of pixel data from imaging systems.

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### How do you correctly implement Scipy's FFT procedures to produce a low-pass filter - image processing

I'm following this low-pass filter example in the text "Image Operators: Image Processing in Python 1st Edition" by Jason M. Kinser, but can't seem to duplicate their results. The text's ...
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112 views

### Invert a huge sparse operator;

please help me with this question, I want to invert a huge sparse (non-circulant) this below in a $Ax=y$ equation: $$(\lambda I+ \beta D+ \sigma C)x=y$$ where I is an Identity Matrix,D is a Diagonal ...
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### Eigenvalue decomposition for a very huge matrix of medical images (such as the pixel physical coordinates of CT images)

I am trying to do eigenvalue decomposition for a huge matrix larger than 788000×788000 for medical image analysis. The matrix is not sparse and every element in the matrix has a real value. And, for ...
71 views

### Shape recognition of tangientially connected polygons using openCV

Lately, I have encountered the following problem, namely how to recognize the shapes of particular polygons. I have realized that quite straightforward to do so when the polygons are separated by ...
94 views

### How can I compute the gradient of the noiseless image given by the compass operator?

I need to generate an image with 11x11 pixels having in the center of the image a square of 5x5 pixels, with the gray level of the background 0 and the gray level of the square is 50. I need to ...
1 vote
70 views

### How applying the gradient descent method for solving a least square problem can remove the blur from an image?

I got an assignment where it asked to implement (in MATLAB) the gradient descent algorithm in order to resolve an ill posed least square problem: $$\min_u \Vert Gu - f \Vert$$ where $u$ is the ...
• 119
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### Fit spline to point cloud with lowest energy

I am looking for a way to fit a spline of order 2 to a 2d image or point cloud. The input will be an gray scale image. The start and end points are given as 2D coordinates. The goal is to find a ...
1 vote
32 views

### SHREC 2010 Descriptors

I will appreciate if I may find someone how can clarify for me the part regarding the quality of feature descriptor, shown in the figure below: and this screenshot is from the article: SHREC All my ...
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### Evaluate 3D Shape Descriptor

I'm trying to create my own 3d shape descriptor, the idea is that how I may evaluate how much my descriptor is well and good? What I checked is that they evaluate descriptors through shape matching, ...
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1 vote
112 views

### Is it possible to resample grid in such a way so that continuous objects remain continuous?

Suppose I rasterize a rectangle of width 2.5 gridpoints and get the values as shown: =============== | 0 | 1 | 1 | 0.5 | 0 | Now I resample that ...
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### Partial/Extended/Truncated Template Matching

So template matching using correlation is available in a lot of computational packages; OpenCV matchTemplate(), scipy.signal.correlate2d(), IPP CrossCorrNorm, etc. But they all either evaluate ...
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### Palmprint Identification - Why do we align the images before we use the Fourier Transform?

I am currently reading the paper PALMPRINT IDENTIFICATION BY FOURIER TRANSFORM by WENXIN LI, DAVID ZHANG and ZHUOQUN XU about identifying persons based on an image of their palm, one version of the ...
• 121
368 views

### Compute point-spread-function between original and blurred image

Take an image $f$ with some characters on it (below, hjFu3). Let's apply a filter $h$ on it to obtain a second image $g$ where the text is not visible. Is there a way to compute what kind of filter $h$...
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### Methods to implement floor dirt detection algorithm

I'm trying to detect dirty floor areas in a series of images, using MATLAB and its Image Processing Toolbox, like the one that follows: In the image above, there are two distinct areas, the whiter ...
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### Open source implementation of Multiscale Combinatorial Grouping

I would like to use Multiscale Combinatorial Grouping for my PhD research. However, I am restricted to use open-source implementations and this one runs on Matlab. Does anyone know of an equivalent ...
1 vote
872 views

### Iterative camera calibration - No convergence

I am trying to implement the algorithm from the research paper "Accurate Camera Calibration using Iterative Refinement of Control Points" from Datta et al. Running many iterations does not show a ...
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### Which image filter acts like "surface tension"?

I'm looking for an image filter that does the following operation: In my first image, I have two spheres. After applying the filter, I'd like to have them "glued together" which something that kind ...
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1 vote
46 views

### Filter coefficients for convolutional inpainting

I'm working on a project that requires unknown image elements to be filled in, and am using a simple inpainting algorithm, which I would like to understand better. It works by repeatedly convolving a ...
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### Which technique to use for signal/image processing or noise removal?

I have an image that looks like this (it might appear low res in a browser because it is 16 MB). This image was taken with a scanning electron microscope, but because the equipment is outdated there ...
1 vote
83 views

### Can x-ray back-projection be converted to hard-field magnetic induction tomography?

This is a question about hard-field back-projection as used in x-ray tomography, applied magnetic induction tomography. Al-Zeibak and Saunders have shown that x-ray filtered backprojection can be ...
2k views

### Finding intersections of curves in a binary image

I am trying to find the intersection points in images like the one posted below. The intersections I'm trying to find are circled in red in the image below it. My most succesful approach: Thin the ...
1 vote
54 views

### Mathematical physics applications in present-day image processing

During the past few years several important areas of image processing and image classification or generation became dominated by convolutional neural networks. I'm interested if there are any methods ...
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### Is the inverse radon transform considered a linear operation?

I wanted to know if practically the inverse radon transform operation is considered linear and would be a good candidate for the application of compressed sensing. To my understanding it should be ...
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225 views

### Integral image resizing

I'm trying to find an approach for integral image resizing. I found out that I can do it with a bilinear interpolation method, but with this approach I can only resizing by the factor which is a power ...
50 views

### Is there a common way to decribe voxels and greyvalues in formulars

I need to write a report about some image processing topic. I want to describe some kind of density, e.g: $\rho = \frac{\text{voxels with greyvalue 128}}{\text{number of voxels}}$. Is there a common ...
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1 vote
320 views

### How to obtain projections from sinogram in ART reconstruction technique?

I'm kind new in the Computed Tomography field and I'm trying to understand and implement ART technique. Said it, I started to read the book The Mathematics of Medical Imaging - A Beginners Guide by ...
1 vote
119 views

### What is a good algorithm, and framework, to calculate centres of gravity or mass (cog)?

I'd like to take an photograph, subdivide it into a tesselation, either of squares, or (ideally), hexagons, and then find the centre of gravity (or, if you prefer, centre of mass) of each cell of the ...
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1 vote
67 views

### Automatic motion recognition

How difficult is it to program an automatic software using C that is able to read astronomy images of up to 4096x4096 pixels (or other sensor geometries), search ...
• 111
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### Fitting rectangle to segments in image

I have the task to fit a rotated rectangle of known size into an image like This is a synthetic test case, in the real application, everything is rather blurred. The rectangle has to cover as much ...
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1 vote
68 views

### Convolutional Neural Nets for Large Scale Image Classification on Windows?

I need to build some CNN's using very large numbers of photos, to classify which photos contain certain features. I've run into a number of road blocks. As much as I love both Linux and ...
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77 views

### What are the most popular wavelet or tight frame regularizers for image reconstruction problems?

A common approach to image reconstruction is to solve the convex optimization problem $$\text{minimize} \quad \frac12 \| Ax - b \|^2 + \gamma \| Dx \|_1$$ where $b$ is a ...
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### discrete definitions of curl $\nabla \times F$?

I have some data defined in an array (an image) and I need to find the curl of a certain function. Wikipedia has an integral definition of curl that I like, maybe it can be discrete.  \nabla \...
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### Open Source MRI Image Stacks

I'm working on a voxel-based modelling application and one of the features that I've implemented is a method to do a 3D mesh reconstruction from a series of 2D image slices (similar to an MRI). I've ...
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### FFT-based Image Rotation Algorithms More Accurate Than Chirp-Z?

We're currently using a Chirp-Z based implementation: R. W. Cox and R. Tong, "Two- and three-dimensional image rotation using the FFT," IEEE Trans. Image Processing, vol. 8, no. 9, pp. 1297–1299, Sep....
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### How to separate text from the paper on a black and white page?

I tried to discretize an image into black and white and came into some difficult. The difference between the letters and paper is pretty clear to our eyes: However a simple thresholding trick doesn'...
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1 vote
919 views

### Calculate the area and perimeter of a hand-drawn shape

I need to know whether my idea for my final year project could be achieved or not. If its achievable please guide me with the relevant language and other frameworks. The idea I have a piece of paper ...
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578 views

### What are the numerical methods for testing for dissimiliarity between image based probability histograms?

I have several probability distribution histograms of images that I am comparing to test for dissimilarity. Each histogram has 256 bins, the bins are common for all histograms. The images are taken ...
331 views

### Estimating Regions of Flow in Grayscale Video

I am looking to find an algorithm/method by which I can detect regions of flow in a video. The video is that of a grayscale heatmap where the majority of the image is not in motion. The areas that are ...
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1 vote
242 views

### Compare reconstruction of matrices using SVD

I'm interested in how much 'signal' is retained from including k singular values in a Singular Value Decomposition, but I'm having trouble conceptualizing (or ...
• 2,109
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### 1D fit on a surface in matlab

I have a problem fitting a $N\times N$ ($32\times 32$ in this case) matrix in Matlab. Here is the deal I have this image, and I want to create 1 dimensional fit between the points and then be able ...
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1 vote