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Valentine Tomography
Happy Valentine’s Day! I might not be very romantic, but I had to do something with it. Imaging the heart is an important application of tomography and other techniques in medical imaging. Since hearts...
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The Looming Effect
The animation demonstrates the looming effect that you get when something (a motorbike in this case) approaches you at a constant speed. At first nothing seems to happen, but then the bike suddenly...
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Pi Day 2013
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...
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Astrology For Teh Win!
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...
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Earth-Moon System to Scale
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...
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Earth-Moon System Scale Model
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...
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How to Record a Lion in a Concert Hall
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...
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Exponential Growth
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...
View ArticleGoing Responsive
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...
View ArticleDiscrete-Time Signal Processing
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...
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Impulse Response
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...
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The Perfect Camera
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...
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The PSF of a Pinhole Camera
After introducing the Airy pattern in The Perfect Camera, I will show in this article how the PSF of a pinhole camera looks. A camera with a classical lens focuses the image that would be at infinity...
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Gorsaf Heddlu
A well-labeled police station (gorsaf heddlu in Welsh) in Llangollen, Wales.
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Some Wacky Pinholes and Their PSF
After simulating a round pinhole and showing the resulting point spread function (PSF) both far away (equivalent to the Airy disk) and close by (resulting in a realistic PSF for a DSLR pinhole camera)...
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Color PSFs
After computing The PSF of a Pinhole Camera and showing Some Wacky Pinholes and Their PSF in previous articles, the next step towards ever more realistic PSFs is adding color. A DSLR camera has...
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Finite-Bandwidth Square Wave
How would you produce a square wave on a digital system? At first sight, this seems completely trivial. You might think that you could just alternate a series of +1 values with a series of −1 values...
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Finite-Bandwidth Square Wave in Samples
After introducing the finite-bandwidth square wave in a previous article, I’ll show in this one how such a square wave looks in a digital system, so in sampled form. The figure below shows one period...
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Naive Square Wave
After introducing finite-bandwidth square waves in previous articles, I’ll now describe what happens if you follow the naive approach, and just alternate sequences of 1’s and −1’s. As you might expect...
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What is a Spectrogram?
A spectrogram is a graph that shows the evolution of the spectrum (the frequency contents) of a signal over time. Often, the frequency is on the vertical axis and time is on the horizontal axis. A...
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