[quote="coilbook"Thanks. Do you know any good and easy to learn post prod programs?
Do you think they rendered foreground as alpha and then added background that they tweaked separately?[/quote]
"Good and easy to learn." Well, that's awfully subjective. If this is all new to you, I suggest starting with something free, to learn the basic concepts. Take a look at any of these:
http://topicroomsvfx.com/2018/03/24/top ... softwares/Back with Pixar's ToyStory 1, in the mid 90s, they did basic foreground/background/character element passes, but these days, a normal Hollywood level production involves much more sophisticated rendering and compositing. The Disney's Planes example that you chose is from just a few years ago, and things have gotten a lot more advanced in the 20+ years between the two.
Yes, I'm pretty sure they rendered not just the foreground separately, but probably various elements of the character, the mid-ground trees, the mountains, the mountain trees, the grass, the sky. Not only that, but probably different aspects of each element were rendered separately, such as the reflections, the diffuse color, diffuse lighting, direct lighting, the shadows, a depth map, etc. And that's just the tip of the iceberg.
It's a vast topic. The Otoy forums really aren't the place to get into it, and it's way beyond the scope of this post, but there are a number of online courses for intro compositing and vfx at places like Skillshare, DigitalTutors, and Lynda. There are also more general, free, online communities like CreativeCow and Reddit where you can learn an awful lot from helpful, friendly people.
Good luck!