Question: Why Do Cartoons Sometimes Look Like Part 2D, Part 3D Animation?
You've likely seen it while watching animated cartoons: in the middle of a fully 2D scene, suddenly the animation (or parts of the scene) will bring in something that looks almost like posterized 3D animation, which almost fits into the 2D scene...but not quite. Why does your 2D animation look like 3D?
Answer: The answer is because it is 3D, rendered to approximate 2D animation. Some shows do this very well; some are mediocre; some are awful. Animators will use 3D animation with the lighting and colors optimized to best fit the 2D scene, rendered to create outlines that match the 2D style. When it's well-done the 3D composited parts are indistinguishable from the rest, or at least either non-intrusive or an enhancement to the 2D animation. When it's poorly done, it looks like posterized 3D blocks zipping around in the middle of otherwise decent animation.
Why is it done? Often to save time and effort animating complex things such as machinery. Most of the time geometric objects survive this treatment fairly well; it's when animated characters or other organics are involved (especially when moving from 2D to 3D animated versions and back again) that the transition is the most jarring.
