halftone vs photoengrave

halftone

verb
  • To reproduce a photograph or other continuous tone image by the use of dots of various sizes. 

noun
  • A picture made by using the process of half-toning. 

  • An intermediate or middle tone in a painting, engraving, photograph, etc.; a middle tint, neither very dark nor very light. 

  • Synonym of semitone, half the interval between two notes on a scale. 

photoengrave

verb
  • To make a photoengraving of an image 

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