From Film: Blogging the Reel World (slashfilm.com):
Previous director Glen Keane (now Executive Producer) developed a new look for this computer animated film, which is said to look and feel more like a traditional hand-drawn Disney Classic, but in 3D. Apparently the film uses a non-photorealistic rendering technique which will make the surface look like it is painted but still containing depth and dimensions. The movie's visual style is (still) being based on French Rococo artist Jean-Honore Fragonard’s painting “The Swing” (this is most apparent in the fifth and last image below).Rather than try to rephrase this sentiment, I'll just quote Peter Sciretta (from Film: Blogging the Reel World):
NOTE: words in parentheses and italics are my additions
"Hopefully the new non-photorealistic rendering technique employed on this production will help capture some of the painting-like beauty of these pieces."I couldn't have said it better myself.