lithography vs offset printing

lithography

noun
  • The process of printing an image by drawing the image with a water-repellent material onto a hard, flat surface (typically metal), then copying the surface by applying water and ink (or the equivalent) to it and pressing another material against it. 

offset printing

noun
  • Printing by the offset process, in which ink is carried from a metal plate to a rubber blanket (“offset cylinder”) and from there to the printing surface. 

How often have the words lithography and offset printing occurred in a corpus of books? (source: Google Ngram Viewer )