The perfect camera is diffraction limited. This article is written strictly from an optical point of view, so don’t expect a Nikon / Canon / Leica comparison here… Optically, a camera (or telescope or other optical instrument) can be described by its point spread function (PSF), which…
The impulse response of a system is, perhaps not entirely unexpectedly, the response of a system to an impulse. This article introduces this all important concept, and shows how knowing only the impulse response of an LTI system can be used to…
The title of this article is Discrete-Time Signal Processing, although the term digital signal processing (with the abbreviation DSP) is much more common. Both types of signals are discrete in the time dimension, in the sense that they are sequences of numbers. The difference is that a digital signal is…
Responsive design is a way to make websites work both on desktops, tablets, and smartphones, without having to create a separate site for each of them. Something had to happen with my site to make it more mobile-friendly, and I’ve decided to “go responsive” with this site for several reasons: The percentage of mobile visitors is increasing steadily, so…
In the mind of most people, the term “exponential growth” strongly implies quick growth. However, something that grows exponentially will seem to grow quite slowly at first. In practice, there is a good chance that you won’t notice it at all until it suddenly…
![Promenadikeskus concert hall [image: Helsinki University of Technology]](https://tomroelandts.com/sites/tomroelandts.com/files/styles/thumbnail/public/field/image/promenadikeskus-concert-hall.jpg "Promenadikeskus concert hall [image: Helsinki University of Technology]")
I’d like to kick off a series of articles on signal processing with the answer to a very practical question: How to find out how a lion sounds in a concert hall. I’ll deal with more theoretical subjects in later articles. Smuggling an actual lion unseen into a concert hall seems unlikely to succeed, and might…
It turns out that the balls in two popular sports, basketball and tennis, are almost exactly the right size for an Earth-Moon system scale model. Take a standard NBA basketball, which has a circumference of 29.5 in (74.9 cm). The diameter of the basketball is then 9.39 in (23.85 cm). If we let this ball represent the Earth…
![Sun, Earth, and Moon, all to scale [Sun photo: Thomas Bresson]](https://tomroelandts.com/sites/tomroelandts.com/files/styles/thumbnail/public/field/image/sun-earth-moon.png "Sun, Earth, and Moon, all to scale [Sun photo: Thomas Bresson]")
The illustration shows the Earth-Moon system to scale, with the same scale used for size and distance. The diameter of the Earth is 12742 km, while the diameter of the Moon is 3475 km. So, to draw the Earth-Moon system to scale on a screen, each…
I’ve had it with science and plan to convert this site to be completely about astrology. Astrology (as Wikipedia puts it: “Not to be confused with Astronomy.”) is a shortcut to the truth. After all, if the truth is in the stars (“De Trut Is Uit Daar” as we paraphrase the tagline from The X-Files in Dutch), gathering and analyzing data…
Today is 3/14 in month/day notation, and \(\pi\approx 3.14\). My daughter Noor (8) and I felt like releasing yet another image of \(\pi\) into the world, in addition to all the existing images. We made this using Hama beads. Today is a good occasion…