2xSAI is a very cool algorythm which doubles the size of the image and interpolates it(calculates mising pixels) through special line and edge detection rutines which make it less blurry compared to simple bilinear filtering. Check out its creators homepage http://elektron.its.tudelft.nl/~dalikifa/. It's great for emulators which emulate low resolution consoles, but is a bit slow and i have no idea why would you want to use it for something else. It has nothing to do with directx, but you could implement it by hand.