As you might expect with my Web site theme of computer tutorials, I have taken tens of thousands of screen captures over the years. Mac, Windows, Linux, Android, you name the OS, I’ve figured out how to get a screenshot from the system. And your SEO pal is correct: smaller files are faster and faster sites gain the boon of higher search ranking. Win win, no question about it.
Fortunately it’s not too difficult to tweak and fine tune what happens when you take a screen capture on your Mac system. You can change where they’re saved, the filename (somewhat) and the output format. There are, of course, lots of third party solutions too, but honestly, the built-in MacOS X solution is pretty darn nice and works for most all my needs, particularly when you learn that Command-Shift-3 is full screen and Command-Shift-4 lets you click and drag to define the box that becomes the screen capture. Handy to know both!
There’s a little bit of nerdy fun involved, however, because there’s no handy window that lets you specify the changes, you’re going to have to type things in directly on the command line, which means you’ll need to use Applications > Utilities > Terminal.app.
To start, launch Terminal then type in:
$ cd ~/Library/Preferences/ $ plutil -p com.apple.screencapture.plist
Note: As a general convention, I show what you’d type in as bold and the result immediately below it (you’ll see what I mean below). Don’t type in the “$” either, that’s just how I represent the command line prompt, though yours will undoubtedly be a bit different.
Take your time and be careful that you get everything correct. If you do, then you’ll see all the settings for your current screencaptures:
$ plutil -p com.apple.screencapture.plist
{
"disable-shadow" => 1
"last-messagetrace-stamp" => 574690824.060235
"last-selection" => {
"Height" => 657
"Width" => 1006
"X" => 480
"Y" => 0
}
"last-selection-display" => 0
"location" => "/Users/taylor/Desktop"
"showsCursor" => 1
"style" => "display"
"type" => "png"
"video" => 0
}
In the above you can see that I have disabled the window shadow effect (disable-shadow), that my screen captures default to being saved in the directory “/Users/taylor/Desktop” (e.g., my Desktop) and that I am using the default style of PNG, the progressive network graphics format.
So let’s change the output format. Your choices are pretty extensive: bmp, pdf, jpg, jp2, tif, pict, tga or png. Of these, 99% of people will want to use PNG or JPG. I prefer JPEG 2000 but not every Web browser supports it, so that’s a non-starter. Definitely switch from PNG to JPEG, though, as it’s a better image format, particularly for images on the Web.
To change the format, carefully type this:
defaults write com.apple.screencapture type jpg
There’s no output, either you get an error or it works. But here’s another wrinkle: The MacOS X window manager won’t check the file to see what’s changed unless you restart the computer. Or… you can force a UI Server restart if you’d prefer by typing in the following:
killall SystemUIServer
Again, no output, but if you watch carefully, a bunch of stuff will vanish from the top menubar (like the clock) and then reappear a second or so later as the window manager restarts. Once it’s restarted, though, you’ll have the changes in place!
In this case I took a full screen capture before I made the change, so I was using PNG format, and after, when it defaulted to JPEG instead. A couple of File > Get Info windows reveals the huge difference in file size:
Look closely: Each is 3840 x 2400, but the middle file is an image that’s 16.1MB in size: It’s the PNG file. On the left is the JPEG copy of the exact same screen capture and it’s 2MB. On the right is JPEG 2000, which is even smaller at 1.9MB. Regardless of JPEG 2000, however, just check that out. A 16MB file reduced down to 2MB by simply changing the image format. SHEESH!
Want to change the default location of your screenshots? That’s another command line invocation:
defaults write com.apple.screencapture location directory
The easiest way to get this right is to open up a Finder window and move it to the location you’d prefer, type in everything but the last word above, then drag and drop the icon off the top bar of the Finder window. It automatically expands to the directory name for that particular folder or directory. A handy trick!
For example, to ensure that I had mine save on the Desktop, I could use:
defaults write com.apple.screencapture location /Users/taylor/Desktop
Make sense? Again, remember the change won’t happen unless you restart or use the killall command shown earlier.
Finally, you can tweak the filename of the saved file too, though it only changes the preface. Look closely again at the above image and notice that the leftmost screen capture – in JPEG format – has a slightly different name. Instead of “Screen Shot [date] at [time]” it has the simplified “screen [date] at [time]”. You can’t get rid of the date or time stamp in the filename, but you can organize things a bit if you’d like something different. That’s done with, you guessed it, another ‘defaults’ command:
defaults write com.apple.screencapture name "screen"
That’s it. One more killall and then you can now use the plutil command to see what’s changed in your preferences:
$ plutil -p com.apple.screencapture.plist
{
"disable-shadow" => 1
"last-messagetrace-stamp" => 574690824.060235
"last-selection" => {
"Height" => 657
"Width" => 1006
"X" => 480
"Y" => 0
}
"last-selection-display" => 0
"location" => "/Users/taylor/Desktop"
"name" => "screen"
"showsCursor" => 1
"style" => "display"
"type" => "jpg"
"video" => 0
}
That’s it. Pretty cool. Oh, and if you decide you want to switch back to the default, very carefully type in a command like the following, which removes the change from the default filename:
defaults delete com.apple.screencapture name
Now go and have fun fine tuning your screen captures and producing faster Web pages!
Pro Tip: I’ve been writing handy Mac tutorials for years and years. My first Apple computer was an Apple II! Please check out my site while you’re here to find lots more that’ll help you out too!
The post Change MacOS Screen Capture Format to JPEG? originally appeared on Ask Dave Taylor.