透射光谱成像技术检验黑色签字笔涂抹掩盖字迹研究

摘要

ABSTRACT:Objective To establish a non-destructive, efficient and direct method for visualizing the handwriting covered and smeared by black gel pen inks. Methods 306 smeared and covered handwriting samples prepared with 18 kinds of black gel pen were analyzed by using Nuance420 Spectral Imaging with the technique of transmission spectral imaging, compared with reflective spectral imaging. The results were divided into two types: visual and non-visual. The standard of classification was whether common people who had never seen the original handwritings could correctly recognize the smeared and covered characters. Results Of 306 test samples, 231 samples were visual and 75 ones were non-visual with transmission spectral imaging technique. The visualized rate was 75.49%, by contrast with the visualized rate of 51.96% with reflective spectral imaging. Conclusions Transmission spectral imaging could differentiate the handwriting smeared and covered by black gel pen inks with the exception that the original writings and the smearing and covering layer used same or similar composition inks. Therefore, the technique of transmission spectral imaging is an efficient choice to uncover the smeared and covered handwritings by black gel pen, which can be applied in questioned document examination.%目的：对透射光谱成像技术和反射光谱成像技术检验黑色签字笔间涂抹掩盖字迹进行比较研究，探寻一种无损、高效、直观的黑色签字笔涂抹掩盖字迹的显现方法，提高黑色签字笔间涂抹掩盖字迹显现效率。方法根据不同黑色签字笔油墨物质成分不同，不同物质对光的透射率各异的特征，在相同条件下使用反射光谱成像技术与透射光谱成像技术分别对多个黑色签字笔间涂抹掩盖字迹实验样本进行检验。本文将显现效果分为可显现和不可显现两类。分类标准为从未看过原字迹的非文检人员是否可以辨认出被涂抹掩盖字迹。结果利用透射光谱成像检验系统检验黑色签字笔涂抹掩盖字迹样本，306个样本中，可显现的有231个，不可显现的75个，显效率为75.49%；反射光谱成像技术检验306个样本，其中可显现的有159个，不可显现的有147个，显现效率为51.96%。实验结果表明透射光谱成像检验黑色签字笔涂抹掩盖字迹的显现率高于反射光谱成像检验的检验。结论除了无法显现原字迹与涂抹掩盖笔迹的油墨物质成分、浓度以及组成配比相同或相近的样本之外，透射光谱成像技术能检验常规的光谱成像技术无法显现的黑色签字笔间涂抹掩盖字迹，其显现效果和效率都优于反射光谱成像技术，是一种高效的显现方法,可以应用于刑事物证检验领域。