I'm not sure if it's my Retina MBP, or Mountain Lion, but for some reason when I print screen (Command Shift 3), and then open or paste it into photoshop, the file is HUGE (2880 x 1800 pixels). This is really inconvenient because sometimes I need to printscreen something and have it in it's exact proper size as it is displayed on screen.
It's the Retina display. You could scale the display down before taking a screenshot. Technically, 2880-by-1800 is how it's displayed on your MacBook Pro, since that is the native resolution of the Retina display - however, it's big for anyone else who does not have a Retina display.
__________________ ACMT Mac mini (Mid 2011) 2.7 GHz i7, 8GB RAM, Crucial M4 256GB SSD + 500GB + 1TB FW800 OWC Mercury Elite Pro mini iPhone 4S • iPod nano 8GB • Sound System Audio Engine A2 • Display UltraSharp U2412M 24"
That's because the Retina display runs at 2880x1800.
If you want to make the image the same size as the monitor, then you need to fiddle with the Resolution/DPI in Photoshop. The easiest way to do this is to create a new document, set the Width to 2880 (Pixels), the Height to 1800 (Pixels), and the Resolution to 220 (Pixels/Inch).
Then change the Width and Height units to Inches, and Photoshop will convert the values for you. You should get something like 13.091x8.182". You can create the document and paste in your image. When you print it out, Photoshop should take the new PPI (Pixels Per Inch) into consideration (which is 220), thus changing the physical size of the image to the actual size of the monitor.
This is the only way you're going to be able to do what you want. The "exact proper size" is in fact 2880x1800, because that's the physical resolution of the screen. Your issue is that the standard DPI/PPI settings are usually 72 PPI (for every other monitor on the planet), when in fact your Retina runs at 220 PPI instead.
Thanks for this - off of your suggestion I just changed the resolution in Photoshop on the image from 143.993 to 72 and that completely resizes it to the "exact proper size".
__________________ Apple Certified Macintosh Technician (ACMT) / Support Professional (ACSP) MacBook Air (13-inch, Mid 2012) 8GB RAM, 256GB Flash Storage Mac mini (Late 2012) 16GB RAM, Fusion Drive (128GB SSD/750GB 7200RPM) iPad mini 16GB, iPhone 4S 16GB