For those of you who were wondering why Apple chose PNG’s as the screen capture format, you’re not alone. I’ve thought about it quite a bit, and I think the reasoning is a quality/size issue. I suspect that Apple decided on PNG format for their screen captures because:
A) The format employs a lossless compression algorithm meaning your images will not have compression artifacts
B) Due to the compression algorithm employed, the filesize is quite small for images and graphics
C) The DEFLATE image compression scheme employed is non-patented, thus creating a good, cheap solution that is better than the patented LZW data compression scheme, and
D) PNG supports alpha transparency, and is thus used for many of the OS’s key transparency features for AQUA, Apple’s GUI
“Ok, but how do I change the default PNG format to JPEG in Screen Capture” you ask? Well, look no further. Here is how you do it, step by step. (It’s really simple).
First of all, fire up Terminal, Apple’s Built-in Command Line interface application. You can find this in: /Applications/Utilities/Terminal. Once it is started up, copy and paste ONE OF THE LINES BELOW.
defaults write com.apple.screencapture type pdf
defaults write com.apple.screencapture type png
defaults write com.apple.screencapture type jpg
defaults write com.apple.screencapture type tif
As you can see, you can choose between multiple formats, including PDF, PNG, JPG, and TIF. If you prefer, you can use JPEG instead of JPG, and likewise TIFF instead of TIF. Feel free to tinker with it. I have Leopard installed, and this worked perfectly the minute I pasted this into Terminal. I have read that you may need to restart for the changes to take effect, specifically in Apple’s Tiger OS. However, this was not necessary in my case.
***ANOTHER QUICK NOTE: If you are having issues getting this to stick, AND you are getting a prompt in Terminal saying “PERMISSION DENIED”, then you may need to use SU (SuperUser), or SUDO if you have not created a Root Password and enabled Root Access. Here is the code you will need to use if you encounter a problem related to permissions:
sudo defaults write com.apple.screencapture type pdf
sudo defaults write com.apple.screencapture type png
sudo defaults write com.apple.screencapture type jpg
sudo defaults write com.apple.screencapture type tif