I have a bunch of archival QT files that are 720x486 Quicktimes. What will give me the best image quality: 1)importing into Avid as 2:1 SD then bringing into an HD timeline, 2)AMA linking and then transcoding to 1920x1080 (this messes the aspect ratio up) 3)using external software to uprezz into 1920x1080 4)ingesting into Avid as 2:1 SD, laying clips out to Beta tape and then recapturing using our Kona card to uprezz on ingest
If you have Boris Continuum Complete, then you can use the UpRez filter in there. Much nicer for blowups than traditional Avid scaling.
To use it, import the SD into an HD project with the setting to not resize smaller images. This will give you a small, slightly squeezed SD frame inside a black canvas. Add Boris UpReze, set the source to NTSC SD, the destination to 1920x1080 HD, and choose a scaler type (Magic Smooth or Magic Sharp often do the trick for me).