Classification of liquid and viscous inks using HSV colour space

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. Ink types liquid ink or viscous ink will be derived from the color properties of ink by extracting its HSV characteristics. This classification helps in distinguishing gel and roller pens versus ball pens, offset and ink jet printers versus laser printers. Different types of inks exhibit different absorption characteristics that causes color and distribution of color pixels to change. So we have done a detailed analysis of all color spaces and in particular HSV color space as it matches human vision. We observed that the saturation histograms of writings or printings reveals difference in absorption characteristics of ink, while hue histograms do not. We found that the saturation histograms can be modeled as Gaussian distribution that resembles process of diffusion of ink into paper. The measures like F ratio, σ ratio, saturation weighted hue variance (ANOVA) are used to classify inks.