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Reconstruction of a Real Dataset, Part 1: Introduction

Figure 1. Raw X-ray image of an apple.

This is part one of a tutorial that describes how to create a reconstruction of a cone-beam computed tomography (CT) dataset. This tutorial includes the preprocessing step that is needed to go from raw X-ray images to projections that…

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  • Image Processing
  • Tomography
Submitted on 7 April 2021

TomRoelandts.com in 2020

2020 was a really quiet year on this blog, with a grand total of four articles posted… I’ve been working full-time (and sometimes a bit more) in my consulting business, and the time to write blog posts often eluded me. Instead of going over the…

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Submitted on 2 January 2021

What is a Voronoi Diagram?

Voronoi diagram

A Voronoi diagram is a partition of the plane into a number of cells, where each cell consists of exactly those points that are closest to the site (or seed point) of that cell. An example with ten seed points is shown in…

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  • Mathematics
Submitted on 9 December 2020

How to Add Noise to Set a Digital Communications Signal to a Given Es/N0

When you are designing a modem, you’ll typically make heavy use of simulations. Much of the design work is concentrated on the algorithmic part of the device, especially in these days of Software-Defined Radio (SDR), where the actual electronics might…

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  • Signal Processing
  • Modems
Submitted on 23 August 2020

Fractional Approximations of Pi

Now that we are just past Pi Approximation Day (22/7 or July 22), I thought about how to find other fractional approximations of pi with small numerators and denominators. I decided that I was going to brute force this thing, just because I can…

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  • Mathematics
  • Software
Submitted on 28 July 2020

Why Are Leap Years Needed?

A year is the time that it takes the Earth to complete one revolution around the Sun. You might think that a day is the time that it takes the Earth to complete one rotation of 360 degrees, but that isn’t true. A full 360 degrees rotation takes only about…

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Submitted on 29 February 2020

TomRoelandts.com in 2019

This article is a wrap-up of what happened on TomRoelandts.com in 2019.

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Submitted on 27 December 2019

There's Only One Parabola

Figure 2. Parabolas.

There is really only one circle. Of course, you have to allow for translation and scaling for this to be true, but I think you’ll agree that a large circle is essentially the same as a small one. The geometrical term for this is similarity. Two objects are similar if…

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  • Mathematics
Submitted on 29 September 2019

What is Steganography?

Figure 1. Photo with hidden image inside.

In the context of images, steganography is the hiding of an image (or other information) within another image. The “carrier image” can then be sent over an untrusted channel (e.g., published on the Internet), and only people that know that the hidden message is there will…

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  • Image Processing
Submitted on 11 August 2019

How to Create a Fractional-Delay Filter

Figure 1. Impulse response (left) and frequency response (right) of a 0.3 samples fractional delay filter with 21 coefficients.

With fractional delay, I mean a delay of a fraction of a sampling period. Introducing a delay of an integer number of samples is easy, since you can do that by simply skipping a number of samples, or buffering them if you don’t want to…

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  • Signal Processing
  • Filter Design
Submitted on 17 June 2019

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