This is the personal site of Tom Roelandts. I’m trying to whet your appetite for science with this thing. My education and interests show through, of course, since I focus on stuff that I feel confident writing about. The site used to be solely about the photos, and I still think the thumbnails page is rather cute, but the emphasis has clearly shifted towards the articles lately.

The Wow! Signal, Still a Mystery After 37 Years

The Wow! signal [image: Big Ear Radio Observatory and North American AstroPhysical Observatory]

The famous “Wow!” signal is a radio signal that was received on 15 August 1977 as part of the SETI program. After all these years, it is still the most tantalizing candidate for being a true interstellar signal. Its name comes from the manually written word “Wow!” on… read more

Submitted on 7 September 2014

The PDART Algorithm, Part 2

SIRT (left) and mask (right) at iteration 8

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… read more

Submitted on 24 August 2014

The PDART Algorithm, Part 1

Phantom image (left) and SIRT reconstruction (right)

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… read more

Submitted on 11 August 2014

Why Did this Image Cause a Traffic Spike on TomRoelandts.com?

Floating Ship

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… read more

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Submitted on 31 July 2014

Rosetta

Rosetta and Philae at comet [image: ESA–J. Huart]

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… read more

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Submitted on 5 June 2014

Compressed Sensing

Compressed sensing example with stars. Original image (left), measurements (middle), reconstructed image (right).

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… read more

Submitted on 1 June 2014

How to Create a Simple High-Pass Filter?

Low-pass (left) and high-pass (right) filters

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… read more

Submitted on 27 April 2014

How to Create a Simple Low-Pass Filter?

Normalized windowed-sinc filter

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… read more

Submitted on 15 April 2014

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