TIL: Convert a PNG to a JPG with sips

Published on November 5th, 2019

By Armno P.

Today I learn how to use sips to convert a PNG image to a JPG image from the command line from The Robservatory blog.

sips – The Scriptable Image Processing System – is a command line tool that comes pre-installed with macOS (I’m using 10.15 Catalina). It can convert a PNG to a JPG like this:

$ sips --setProperty format jpeg input.png --out output.jpg

With JPG as an output file type, we can add formatOptions property to the command to set JPG quality level of the output file to get smaller file size.

# set quality to 'normal`
$ sips --setProperty format jpeg \
  --setProperty formatOptions normal \
  input.png \
  --out output.jpg

# or set quality to a percentage value
$ sips --setProperty format jpeg \
  --setProperty formatOptions 42.195 \
  input.png \
  --out output.jpg

Convert the last captured screenshot to a JPG

When I captured a screenshot to send via Slack or to attach in a ticket, I often found the captured PNG file is way too big in terms of the file size, especially when the screenshot has photos in it.

Captured screenshot in PNG format — Captured Screenshot in PNG format: 4.5MB

I wanted to quickly convert it to a JPG. I created a bash function in my .functions dotfile to do that.

function peg() {
  filename=$(ls -1t $HOME/Desktop/Screen\ Shot* | head -n 1)
  sips --oneLine --setProperty format jpeg "$filename" --out "$HOME/Desktop/screenshot.jpg"
}

ls -1t $HOME/Desktop/Screen\ Shot*
- List all the files in Desktop folder that starts with Screen Shot
- -1 for 1 row per file
- -t to display the most recently modified first.
| head -n 1 grab only the first one from the list which in this case, is the last created file

So when I captured the screenshot, I go to the terminal and run peg command. I get the JPG version of the file named screenshot.jpg.