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Sips: Scriptable Image Processing System

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:

     sips – scriptable image processing system.

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

     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.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)
canvas.arc(90, 65, 5, 0, Math.PI * 2, true)
const output = new Output(canvas, sips.outputPath)

Then run:

sips -j smile.js -o smile.png

This produces an alpha-transparent PNG of a smiling face.

A smiling face

The only other relevant documentation I could find was this section of the man sips page:

     HTML Canvas objects can be created and used to create a 2D drawing context.  The commands for drawing into the context are well documented elsewhere.  This
     section will describe the sips global object and other interesting classes.

     Global variable (sips) properties
           Valid images passed as arguments converted into an array of Image objects
           Arguments passed into the program as an array of strings
     size  Recommended size for output. Setting the crop or resample flags will set this value.
           If specified, the value of the -Z/--resampleHeightWidthMax option. [default: 0]
           Output directory [default: current directory]

     Image Object
     name  Name of image
     size  Size of image (pixels)
           Image properties
           Return the image property for name, if any.
           Return the size that will contain the image with the longest edge set to length. Maintains aspect ratio.

     Output Object
     new Output(context, name[, type])
           Output the context to disk with name and optional type (extension or UTI).
           Adds the output to the queue to be written to disk.

           Output to standard output. Equivalent to console.log(str).


Created 2023-02-18T10:28:00-08:00 · Edit

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