Pixel Sampling Lab
how sampling rate changes what detail survives
wagon-wheel effect, but for pixels 🖖
When sampling is too slow, high-frequency detail folds into fake lower-frequency motion or texture. The sensor is not seeing less detail linearly; it is seeing the wrong detail.
The two-samples-per-cycle rule 🖖
To capture a wave faithfully, you must sample it more than twice per cycle — that threshold is the Nyquist limit, half the sampling rate Fs. Below it the samples still land somewhere, but they no longer describe the original; the shape you rebuild is an impostor. Push freq above Fs/2 here and watch the yellow reconstruction detach from the green source.
Why CD audio runs at 44,100 Hz 🖖
Human hearing tops out near 20 kHz, so Nyquist demands a sampling rate above 40 kHz — but why the oddly specific 44,100? Early digital audio was stored on video tape: three samples per active line, 245 lines at 60 fields (NTSC) or 294 lines at 50 fields (PAL) both land on exactly 44,100 samples per second. A hearing limit met a videotape format, and the number stuck.
Example problems
- oversampled sine - Safe sampling: Fs well above 2f, waveform shape preserved
- near nyquist - Near Nyquist: detail is captured but reconstruction is fragile
- aliasing case - Undersampled: high frequency appears as a false low-frequency wave
- checker moire - Checker pattern with undersampling creates moire-like artifacts