terminal commands

I've not found a way do set the size in Screenshot's preference file. However, I've created an Automator app that resizes the file when it's dropped on it. I keep it in the Dock:

I've set it to 71% due to the Retina display having more pixels per inch than regular monitors. This gets the image down to what is seen on the screen.

The actual command-line screencapture tool does not provide a switch argument to adjust the quality when choosing jpg images, so there won't be a resource for that in the defaults syntax either.

However, I just took a screen shot of some of the text in your post above, and output to test.jpg on my Desktop. When I ran ImageMagick's identify -verbose ./test.jpg, it showed quality at 93, and rendering intent as perceptual. That is probably good enough by default for a screen capture to JPG.

Here is all the documentation that I could find. I don't see percentage thing, but what the hay:

https://ss64.com/osx/screencapture.html

This page will give more information on how to continue your search.

DYI.

https://apple.stackexchange.com/questions/19899/how-to-list-all-available-plist-keys-on-a-certain-domain-application-by-default

I've run out of time 🤪.

R

Just create an app with the components in my screenshot and set the percentage to whatever works for you. Save as an application, put it in the Applications folder and drag into the Dock.

I did find documentation a bunch of defaults commands. See:

https://www.defaults-write.com/

R