The only scanning that was done back in '97 was for inserting cgi into existing shots (for example, the rontos and dewbacks in the background when Ben, Luke and the droids pull up to the Cantina). ILM also recomposited the miniature effects shots digitally. Aside from that, it was a totally photochemical restoration.

In 2003/2004, the negative was scanned, according to that same press conference I downloaded from TFN, "by some post houses here in L.A." (exact quote from the Lowry guys). I'm curious how the '04 changes such as the newer Jabba model were handled. Did they go back to the same film element they used as a starting point for the Jabba scene in '96 and simply rescan it and start all over? Also, I'm not 100% sure but I think the new '97 shots (expanded Mos Eisley, enhanced Death Star attack, recompe, etc) were simply scanned back off of the negative. Unless ILM still had the final renders on some kind of readable storage after almost seven years, I'm pretty sure they were just scanned back off the filmed-out negative (these pieces of the o-neg would still be in pretty good shape since they were only six or seven years old).

Anyway, the scans were color-corrected and (correct me if I'm wrong) the additional changes like the '04 Jabba and Ian's hologram in Empire were added. All of this (the color-correction and additional changes) was done by Lucasfilm before being sent off to Lowry for restoration.