How does Nvidia DSR work?

I am new to this whole area. I started looking into it when I found out that games such as Sniper Elite 3 and Metro Last light have Supersampling in their options so I found out that you can do it for other games too using your graphics card control panel but Im confused about the terms, whats the difference between supersampling and downscaling? are they the same thing?

And what does Nvidia DSR do? I have GTX 970 and am trying DSR on Assassin's Creed: Rouge and if I put it on anything else other than my native resolution (1920X1080) and DSR 4x, I get a worse quality... DSR 4X looks alot better ( I have set DSR smoothness to 0 after trying it out on different numbers) than 1920X1080 but then it gives me around 20-30 FPS. But with any other DSR resolution the game looks like its running with resolution lower than 1920X1080! why does this happen? How can I actually use DSR 1.2X or 1.5X without getting worse quality?

http://www.geforce.com/hardware/technology/dsr/technology

@demi0227_basic:

Yeah I have read that already. But why am I getting a worse quality on 2560X1440 than I get on 1920X 1080?

DSR is brilliant but I've found it works much better for older games on the whole. I've had no issues with it on the default smoothness setting of 33% (GTX 970) and your issues could be because you've only tried it on Rouge, which is a new and potentially unoptimised game.

Have you tested it with other titles? It's amazing on games such as GTA IV and the last Tomb Raider.

A single GTX970 cant do that resolution, especially on a brand new game.

i find DSR looks like crap unless i can run it at the full 4k res, the lower dsr options dont seem to work too well for me even with smoothing. But even at that res some games look more blurry then just running at 1080p and using some AA is usually the better option.

A few games i have AA doesn't work and running DSR and using 4k is amazing, so its still nice to have there as backup when AA doesn't do the job.

I have a 970 also and most new games will struggle at 4k so its something i just use on older ones as long as the UI scales properly its alright. I couldn't get it to work in Civ 5 properly, the UI becomes tiny and the game is unplayable at 4k unless you have a magnifying glass.

Doing the monitor tweak for down sampling... Is much better. You don't have messed up UI and the image looks clearer.

If you use dsr turn off anti aliasing. It pretty much does the same thing as aa. I wouldn't go above 1080p on a gtx 970 on assassin's Creed games black flag and newer you will be dropping way below that 60fps. Dsr does look better on older titles. I played dead Island riptide at 4k dsr and it looks amazing. Plus the frame rate for that game can't be set above 60fps so thought why not.