The CGI for the Basilisk was rendered natively in 2K, then downscaled. A 1080p Blu-ray transfer reveals the texture of the snake’s scales without exposing the low-res CGI flaws like a 4K remaster might. 1080p is the "forgiving" high-def format for early 2000s VFX.
When searching for high-definition files, you will often encounter the terms "1080p" and sometimes just "1080." While they sound similar, the difference is significant for a film as visually rich as Chamber of Secrets . The CGI for the Basilisk was rendered natively
Harry Potter and the Deathly Hallows: Part 1 (2010) - Alternate versions The CGI for the Basilisk was rendered natively