I wanted to convert some .webp images to .png on my Mac. I asked ChatGPT:

On MacOS use CLI to convert webp images to PNG

And it told me about sips:

sips -s format png image.webp --out image.png

Or to run it against all PNGs in a folder:

for file in *.webp; do sips -s format png "$file" --out "${file%.*}.png"; done

I had never heard of sips before – but apparently it’s been a default command on macOS for a very long time.

It stands for “scriptable image processing system”. man sips starts like this:

NAME
     sips – scriptable image processing system.

SYNOPSIS
     sips [image-functions] imagefile ...
     sips [profile-functions] profile ...

DESCRIPTION
     This tool is used to query or modify raster image files and ColorSync ICC
     profiles.  Its functionality can also be used through the "Image Events"
     AppleScript suite.  It also supports executing JavaScript to either
     modify or generate images.

It can run JavaScript!

I asked ChatGPT for an example, but it halucinated something that didn’t actually work.

After some searching I found manicmaniac/sips-js-api which is the only place online I could see that documented how to use the sips --js option. Here’s their example – save this in smile.js:

const canvas = new Canvas(150, 150)
canvas.beginPath()
canvas.arc(75, 75, 50, 0, Math.PI * 2, true)
canvas.moveTo(110, 75)
canvas.arc(75, 75, 35, 0, Math.PI, false)
canvas.moveTo(65, 65)
canvas.arc(60, 65, 5, 0, Math.PI * 2, true)
canvas.moveTo(95, 65)
canva