Offset Lithography
The dominant commercial printing process, in which ink is transferred from a plate to a rubber blanket and then to paper.
Measured in
lpi
In depth
Offset achieves very low cost per copy at high volumes because the expense sits in platemaking rather than in each impression, which is why it prints books and magazines and why short runs are uneconomic. Its images are halftone screened in CMYK, sometimes with additional spot inks for colours the four-colour set cannot reach.
Examples in practice
A 5,000-copy photobook is printed offset, with a fifth grey ink added to improve the monochrome plates.