Mac computers have long had the capability to take a snapshot of their screen contents through the system software. This is a convenient tool if your computer freezes up and you need to retain an image of your work before you lose it, or if you want to capture a graphic and don't want to right-click on the image to save it. You can snap a section of the screen by dragging the cursor across a portion it, or let the Mac perform a full window snap. Either way, Mac OS X currently saves the graphic in PNG format; saving it as a JPEG takes a simple step in Preview, which is included on every Mac.
Press and hold the "Command," "Shift" and "3" keys simultaneously to take a shot of the entire screen. Press the "Command," "Shift" and "4" keys to use the crosshairs to drag across a portion of the screen. You hear a camera shutter effect as the Mac snaps the picture.
Locate the captured shot on your desktop, which is designated by "Picture x." Click once on the icon of the screenshot.
Press "Command" and "I" to bring up the screenshot's Info window. Click on the Open With pane in the middle of the window. Select the pull-down menu and choose "Preview."
Double-click on the "Picture x" icon on the screen to open it in Preview. Click "File," "Save As" to open the Save As dialog box. Click on the "Format" pull-down menu and select "JPEG." Assign a filename in the Save As text box and click "Save." Your screenshot is now a JPEG file on your desktop.
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