Distinguishing liquid and viscous black inks using RGB colour space

Abstract

Analysis of inks on Questioned documents is often required in the field of document examination. This paper provides a novel approach for ink type recognition for black inks. Ink types Liquid ink or Viscous ink will be derived from the colour properties of ink, by extracting its amount of blackness. This classification helps in distinguishing Gel and Roller pens versus Ball pens. Different types of inks exhibit different absorption characteristics that causes colour and distribution of colour pixels to change. We observed that the RGB colour space is useful to reveal the differences in ink types. We used multiple linear regression to model the RGB data points of the writings to a plane. The distance from the origin (pure black) to that plane is calculated to classify inks i.e. liquid inks and viscous inks. The distance measures in RGB and HSV colour spaces are used to identify the particular ink. The accuracy of identification is analysed using Type I and Type II errors.