Application of Two-dimensional Fast Fourier Transform in the Inspection of Inkjet Printed Documents

Due to the development of inkjet printing technology, in most cases, discernible traces are hardly found on printed documents nowadays. To solve this problem from the perspective of forensic document examination, this study used two-dimensional fast Fourier transform (2D FFT) to convert the ink dot images of inkjetprinted documents into spectral diagrams, and then to analyze the halftone ink dot spectral characteristics of these images as a basis for identifying the types of inkjet printed documents.

Through analysis of the patterns of change in halftone ink dot spectral characteristics of documents printed from the same color inkjet printer under continuous printing and various influencing conditions, this study evaluated the stability of spectral characteristics, identified influencing factors, and demonstrated their forensic value.

The halftone ink dot spectral characteristics from one same color inkjet printer exhibit relative stability across different printing times. Changing the image resolution, ink cartridges, the method of opening word processing software, PDF conversion modes, as well as the brand, material, and weight of printing paper did not significantly affect the halftone ink dot spectral characteristics. However, the halftone ink dot spectral characteristics of different printed contents showed significant differences. Therefore, halftone ink dot spectral characteristics possess high practical value in the examination of inkjet printed documents.

The application of halftone ink dot spectral characteristics in the examination of inkjet printed documents is feasible and provides a new approach to feature-based examination for the authentication of color inkjet printed documents to a certain extent.