关键词: 二维快速傅里叶变换, 喷墨打印文件, 文件检验, 半色调墨点

Abstract:  Objective 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 inkjet-printed 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. Methods 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. Results 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. Conclusion 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.

Key words: two-dimensional fast Fourier transform (2D FFT), inkjet printed document, document examination, halftone ink dot