To expand on the other comment about signal processing filters and lens:

Analogue signals often have noise or other factors you want to get rid of. Maybe there's a low frequency drift you want out, or a high frequency noise you want out. From there, it goes to enhancing and more generally modifying the signal, as in edge detection, but the math is generally the same and so is the name "filtering." Or in position estimation from a signal, like a kalman filter or particle filter.

At that point filters are a hugely broad thing, and if you want to smooth an image, you might filter out the high frequency components (instant automatic airbrush) or maybe you want to remove all the blue (like a lens filter you might physically put in front of your camera) or even enhance all the blue. Then it's a small step to keeping the filtering name (yet again) for all sorts of signal/image/video auto-manipulations.

You start with wanting to get rid of noise or get rid of blue light and end up turning people's videos into cats. That's language for ya.

I don't follow. How are they not filtering?

edit: I see other comments point to instagram. I think that is giving insta way to much credit. This is filtering as in signal processing. It's a common term in audio, image, and video processing.

https://en.wikipedia.org/wiki/Filter_(signal_processing)

Filter means to remove, not to add. Like `filter()` in Python or Swift being given a condition and a list and returning everything that meets the condition.

In image processing "filtering" has for over 30 years meant any algorithmic manipulation of an image as a whole (exhibit A: Photoshop's "Filters" menu). Simplest filters are also filters in the signal processing sense, but the meaning in this context is considerably broader than that.

I reckon filters were initially intended to remove specific frequencies/noise and the term grew from there. Which is how ffmpeg and other software ended up with video filters that don't actually remove anything.

Someone else mentioned lens filters as a possible source for the term but I'm pretty sure the signal processing term is at least partially responsible for the current usage.

So we should be calling these "face mappers" then >:D

I ran into something similar with maven builds today. Filtering resources with maven means replacing text in the resource with text from maven properties.

It is filtering, the input (video) is filtered down to specific features. i.e. in the cat filter it is filtering everything except eye position, mouth and maybe chin position relative to eyes.

"A filter is a computer program or subroutine to process a stream, producing another stream."

https://en.wikipedia.org/wiki/Filter_(software)

Most likely it derives from Instagram filters, which derives from lens filters.

DirectShow (the API for video capture and other things in Windows) has long had the concept of a filter which can be plugged into the video pipeline[0]. I'm not certain if that's the reason that the term is commonly used for effects such as the one discussed here, but this "cat filter" certainly might have been implemented as a DirectShow filter, so it's very plausible the terminology comes from that.

I'm pretty sure apps like this were called filters long before Instagram even existed.

[0] https://docs.microsoft.com/en-us/windows/win32/directshow/di...

I thought it started in Snapchat, where they were just filters at first, but then the AR stuff started getting added and you’d access them the same way you would the plain filters. The name just stuck due to people not caring to call them something else. What else would they be called? Lenses, maybe?

Indeed. Filter suggests removing something. This is clearly adding something.

Instagram started as imitation of photographic filters, then from the same UI they started offering the face modifying “filters” and everyone kept calling it as. Maybe Snapchat was before instagram?

It comes from signal processing terminology.

Only in the sense that physical photographic filters are "signal processing technology".

How so?

Perception?