The fan project identified the Australian PAL DVDs as the best base: higher vertical resolution (576i vs. 480i), slightly faster frame rate (25fps vs. 23.976fps), and less compression artifacting.
The journey from standard definition to high definition was complex. Nickelodeon did not simply stretch the original files. They re-transferred the original animation assets to fix deep-seated visual issues. Eliminating Interlacing and Halo Effects
: Jagged edges and blurriness around characters are replaced by sharp, clean linework.
Significantly reduced the "glowy" white borders around black character outlines.
While The Legend of Korra was produced in HD natively (720p/1080p), it does not need the same level of restoration that ATLA does.
This is the delicate part of the conversation. The fan remaster is a derivative work. Since ViacomCBS (now Paramount) owns the copyright, distributing the remastered files is technically copyright infringement.
However, many purists still prefer the fan remaster because it specifically targeted source errors
That changed with the arrival of the "ATLA Remastered in 1080p" project. Whether you are a devoted member of the Fire Nation or a waterbender from the Southern Tribe, here is everything you need to know about the fan effort that made the four nations look sharper than ever.
The Ultimate Viewing Experience: Why Avatar: The Last Airbender Remastered in 1080p Matters