My MAC screensaver uses photos that are on my machine. They really look great. What kind of image tweaks are applied?
YOU COULD ALWAYS LOAD IT WITH PIXELS USING PREVIEW AS YOU CAN GO AS NEAR TO 300 PIXELS/SQU INCH;I FIND VASTLY IMPROVES DEFINITION
Nothing. The images weren't edited in any way. Perhaps a white border was added. The panning and Ken Burns effects probably made it look very nice as well. But no, if it were to edit your images before showing up as a screensaver, your Mac would be unresponsive.
The images are greatly reduced in size to display so many on the screen and high resolution images look better the smaller they get! I just tried it with my own images and there is no other modifications.