Lets discuss the various options in context of their use. So let's say your monitor is 1920x1200, and you have an older game you are playing that only runs at, say, 800x600.
The options you have are:
Scaling Mode Aspect ratio - the image aspect ratio is preserved. Your 800x600 game is 4:3 aspect ratio, but your 1920x1200 monitor is 16:10 ratio. So this option would tell the monitor that your game is actually running at 1600x1200...it 'scales it up' to fit your monitor as best it can maintaining the aspect ratio (in this case, the height is the limiting factor of '1200' - if the game had been scaled to your monitor width of 1920, it would be 1440 pixels high...wouldn't fit). As this doesn't quite fill the whole display, you'll just get black bars on the sides of the 1600x1200 image to fill your 1920x1200 display. Sort of like letterboxing, but sideways.
Full screen - as it sounds, it takes the game and makes it full screen. Your 800x600 game is rendered on the monitor as a 1920x1200 image...which obviously 'stretches' it (makes it wider...circles will appear more like ovals, characters will look 'fatter', etc).
No Scaling - again, as it sounds - there is no scaling done. Your 800x600 image is displayed on your 1920x1200 monitor as...an 800x600 image. Basically, a small window with black all around it filling your display.
Perform scaling on Display - In this option, the video card does whatever is needed based on the above options, and sends that to the monitor as-is. That is, if you chose 'fixed aspect ratio scaling', your 800x600 image is now 1600x1200 to best fit your 1920x1200 monitor, and so the video card is basically sending the 1600x1200 data to the monitor and letting your monitor figure it out. Some monitors know what to do with this, and properly display it 'letterboxed'...some monitors are going to just 'stretch' the 1600x1200 to the 1920x1200, anyway (they don't know what else to do with it), and you get the same effect as if you'd set your scaling options to 'full-screen'. There is really no way to tell what your monitor will do with this - it depends entirely on the monitor. I imagine some monitors actually provide new features when given this option - maybe letting you choose your own letterboxing color, or deciding how to align the image (off to one corner for picture-in-picture goodness, off to one side, etc). But, again, it's totally up to the monitor.
GPU - This is my recommendation for most folks. The GPU figures out what your intent is, knows what your monitor settings are, and just handles it. If you have a 1920x1200 display, what is sent to the monitor with this option is
always 1920x1200 data. Whether you told your 800x600 image to be 'aspect ratio' scaled so that it is 1600x1200, or 'no scaling' so that it's really just 800x600...the GPU handles filling in the black 'letterboxing', so the monitor doesn't have to deal with it. As far as the monitor is concerned, it's just native resolution data, and done.
Override the scaling mode set by programs and games I would leave this unchecked. Basically, some games (notably console emulators) know they are running at lower resolution than your monitor, and have complex algorithms built-in to 'scale up' images with more smooth curves, organic shapes, better color blending, etc. The GPU (or monitor) scaling is simply pure pixel interpolation...same thing you get in Photoshop or MS Paint or whatever. Some programs (again, notably console emulators) do a MUCH more interesting job in making the picture scale up better, and may, as part of that, tell the monitor things about how to scale the image that you probably want to leave as-is. 99% of things won't, so this usually isn't an issue.
(Of course, you may find something you are trying to play actually DOES try to tell the GPU or monitor something about its resolution or refresh scaling
and it's wrong. In that case, you may want to check this 'override' option.)
EDIT: In case it isn't obvious, these settings really only have any relevance when playing older games that do not understand your monitors native resolution...most commonly older games that simply assumed a 4:3 aspect ratio on all displays, while most newer displays are actually 16:10 (2560x1600, 1920x1200, etc) or 16:9 (1920x1080, 1280x720, etc).
post edited by xanderf - 2011/12/26 19:58:44