This is the second of a two-part article on the PDART algorithm. It explains most of the nitty-gritty details. The PDART algorithm needs two extra input parameters to do its magic, a threshold and a gray level. After each SIRT iteration, each pixel of…

This article is a bit of an experiment. In it, I’ll try to explain PDART, an example of current algorithm research in computed tomography (PDART was published in 2011). What the algorithm does is, in a nutshell, a SIRT reconstruction with intermediate…

At first sight, this image has nothing to do with my site. I have not posted it or mentioned it. The picture is real, by the way, it is not “Photoshopped”. It is from TV coverage of the Scottish Open golf tournament in Aberdeen, and the effect is caused by atmospheric refraction. But the details of…

As a practical example of an iterative reconstruction algorithm, as introduced in “Tomography, Part 4: Algebra!”, I present the SIRT (Simultaneous Iterative Reconstruction Technique) algorithm. As in the mentioned article, I start from the system of linear equations…

There’s a truly cool deep space mission that I need to bring to your attention: Rosetta. Visit ESA’s Rosetta page for details. Rosetta is an ESA (European Space Agency) mission. It will be the first spacecraft that…

Compressed sensing (or compressive sensing) is a relatively new technique that is becoming more and more important in image and signal acquisition. The term originates from image compression, where, in the classical workflow, images are first…

How to create a simple band-pass or band-reject filter, given two cutoff frequencies? These filters can be created by combining low-pass and high-pass filters. To do that, you need…

How to create a simple high-pass filter, given a cutoff frequency and a transition bandwidth? A high-pass filter can be created by building a low-pass filter first, and then using spectral inversion to convert it into a high-pass one. Starting from the…

How to create a simple low-pass filter, given a cutoff frequency and a transition bandwidth? A low-pass filter is meant to allow low frequencies to pass, but to stop high frequencies. Theoretically, the ideal (i.e., perfect) low-pass filter is the sinc filter. The sinc function is defined as…

I’ve decided to introduce the world-famous Clippy to improve the interactivity of this site. After all, who am I to doubt the wisdom of Microsoft when they introduced it as the friendly helper that it is, and that already in 1997. You might be skeptical about this, but trust me, it’ll be cool! I haven’t decided yet whether…