Kavita Bala asked, “What is the etymology of ‘tap’ in texture filtering?”
This is a term we use in graphics for taking a sample from a texture map. I didn’t know where it came from, and recall being a bit mystified as to what it even meant when I first encountered it, finally puzzling it out from the context. Searching around now, the earliest reference I could find in 3D graphics literature was in this article, so I asked Dave Luebke, who coauthored that paper.
I think it’s actually very old and references the idea of putting a probe, as in an oscilloscope, to tap a signal (like tapping a pipe, meaning to take water out of it at a particular location, or tapping a maple tree for sap to make syrup from).
Dave asked two other experts.
Lance Williams replied:
It’s traditional filter terminology. For example:
“Filter Coefficients – the set of constants, also called tap weights, used to multiply against delayed signal sample values within a digital filter structure.”
“A direct form discrete-time FIR filter of order N. The top part is an N-stage delay line with N + 1 taps.”
“For FIR filters, there is no denominator in the transfer function and the filter order is merely the number of taps used in the filter structure.”
John Montrym replied:
Follow this trail:
https://en.wikipedia.org/wiki/Finite_impulse_response see phrase “tapped delay line” which takes you to:
“tap” in texture filtering uses the terminology of old-time signal processing. It wouldn’t surprise me if the notion of tapping a delay line takes you back to the 1930’s or 1940’s, though I don’t have a specific reference for you.
Radar was one of the early drivers for the development of signal processing theory & practice.
And your “tapping a water pipe” analogy is a pretty good one.
If you know more, pass it on.