Apparently they went back and fetched the old raw materials of the movies, which Lucas had saved in the hopes of making SE's.
They then washed and reprocessed them (as seen in every sci-fi documentary show known to man) and readded many visual effects, plus added some CGI of their own.

Now, the original sabre-photography shows the fighters wielding plastic sticks that are later painted frame by frame into glowing sabres. Here they could've simply added new colours and higher resolution fields.
SO WHY DIDN'T THEY FIX THE OBI-WAN/VADER FIGHT???
Obi-Wan's sabre dissappears for a while in 3/4 of the fight, and Vaders sabre turns bright blue when he turns around and watches the Millenium Falcon.

I'll bet you have some real killer-answers for me, so I'll just put out my chin to make it easier. *points on chin*
"Here! You want a piece of me? Come get some! That's right!"

Or so that they would have something left to fiddle with when the Special Special Edition comes out in a few years?

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Not even a god can deny that I have squared the circle of a static Earth and cubed the Earth sphere by rotating it once to a dynamic Time or Life Cube.
--
Gene Ray
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Read three (three!) chapters of "Dirk Tungsten in...The Disappearing Planet" Or don't. You know, whatever.

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"If you can't beat your computer at chess, try kickboxing."

--Jonah

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"It's obvious I'm dealing with a moron..."