How much has changed since the start of One Piece? I recently started watching One Piece, and noticed as I reached episode 590 that the animation quality seems to have changed quite a bit since episode 1. 

Now I was wondering, are there any other big changes they made since episode one besides quality changes? And how did they do those quality changes? I did not notice any changes until quite a bit in. Is there some particular technique they used? 

So, summed up, this is my question. 


What are the big changes in quality/animation they have made since the start?
Are there any other big changes they made besides quality?
How did they do the quality changes?
The anime moved to Bandai Entertainment since Episode 205, and then it started to run in widescreen and not 4:3.
Quality changes are just because this anime exists for about 15 years, so it's only natural for the video quality itself to improve over time.
Edit: In the anime, the change between old One Piece and new One Piece is alot more clear than in the manga. The quality of the animation started being alot better after One Piece moved to Bandai Entertainment.

Yes there are big changes.
Episodes 517+ happen in a time called "post-timeskip" and in "the new world".
Episodes 1-516 are referred as "pre-timeskip", because after episode 400 alot of big things happen, and they change the whole world of One Piece, but I'm not going to spoil your experience, I can just tell you this: enjoy the East Blue saga, expect big things and surprises, and have fun.