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…
The Geiger counter (or Geiger-Müller counter) from The Clustering Illusion is actually quite interesting in itself. For starters, the script does not need an external audio file. Because the audio fragment is very short, I’ve just put it in a…
The clustering illusion is the human tendency to expect random events to appear more regular or uniform than they are in reality, resulting in the assumption that clusters in the data cannot be caused by chance alone. An important example of this is that the stars in the night sky seem clumped together in some regions, while…
Here’s a challenge for you: Reconstruct the given sinogram using the the ASTRA Tomography Toolbox that I introduced in the previous article. You’ll have to figure out the exact meaning of a sinogram like this to be able to do that. For more information…
If you are into computed tomography (CT) from the perspective of algorithm development, or if you want to do the reconstruction yourself instead of using a standard software package (e.g., the one that was included with your scanner), you cannot ignore the ASTRA Tomography Toolbox. This toolbox was developed by…
Happy Valentine’s Day! This is a bit of a trick post; after luring you in with the cute heart, I’ll explain in this article how image filtering can be implemented in frequency space…
After deciding on the name, “Impulse Response”, for my consultancy company, the next step was to create a suitable logo for it. As I’ve explained before, impulse response is a basic concept from signal and image processing. For the logo, I wanted…
There is a fundamental difference between adding Gaussian noise and applying Poisson noise. In practice, people often talk about adding Poisson noise anyway, but this is not accurate. I will be looking at this from the image processing perspective in this article, and I’ll show purely visual examples. An application of this could be…