3.1 Introduction
  3.1.1 Why use VIPS?
  3.1.2 I/O styles
 3.2 Programming WIO operations
  3.2.1 Input from an image
  3.2.2 Output to an image
  3.2.3 Polymorphism
 3.3 Programming PIO functions
  3.3.1 Easy PIO with im_wrapone() and im_wrapmany()
  3.3.2 Region descriptors
  3.3.3 Image input with regions
  3.3.4 Splitting into sequences
  3.3.5 Output to regions
  3.3.6 Callbacks
  3.3.7 Memory allocation revisited
 3.4 Programming in-place functions