Sliced image processing method and three-dimensional printing apparatus

A three-dimensional printing apparatus, comprising:

• a storage device, storing a sliced image and a plurality of modules;
• and
• a processor, coupled to the storage device, and executing the modules to:
• analyze a sliced object in the sliced image to determine whether the sliced object has a nearest first contour line segment and a second contour line segment, wherein the second contour line segment is located within a region encircled by the first contour line segment;
• determine whether vector directions of the first contour line segment and the second contour line segment are opposite when the sliced object has the first contour line segment and the second contour line segment;
• and
• determine whether to correct the vector direction of at least one of the first contour line segment and the second contour line segment when the vector directions of the first contour line segment and the second contour line segment are not opposite.