DCT域基于系數(shù)符號關(guān)系的印刷水印算法

摘 要:針對條碼印刷防偽應(yīng)用，提出一種條碼印刷防偽算法，使水印對一次打印掃描具有魯棒性，對二次打印掃描具有脆弱性，以區(qū)分原始載體作品的真?zhèn)?。根?jù)條碼水印圖像的大小對載體圖像進(jìn)行分塊DCT變換，選取中低頻系數(shù)，同時對這些系數(shù)幅值小的進(jìn)行放大修改，并通過修改系數(shù)符號的正負(fù)性來嵌入二值條碼水印。根據(jù)嵌入水印后圖像的分塊DCT系數(shù)的正負(fù)性來提取水印，水印提取過程實(shí)現(xiàn)了盲提取。通過設(shè)定合適的閾值可以判斷原圖像真?zhèn)?。仿真?shí)驗(yàn)驗(yàn)證了算法具有很好的不可見性，符合印刷品防偽技術(shù)的要求。關(guān)鍵詞:數(shù)字水印; 離散余弦變換; Arnold變換; Radon變換

中圖分類號:TN91891-34文獻(xiàn)標(biāo)識碼:A

文章編號:1004-373X(2010)16-0143-03

DCT Coefficients of Symbols Based on Relationship of the Domain

Watermarking Algorithm in the Printing

SUN Wen-wen， WANG Hui-qin

(Information and Control Engineering College， Xi’an University of Architecture and Technology， Xi’an 710055， China)

Abstract: A watermarking algorithm which is used in anti-counterfeiting is proposed. In order to distinguish the true or the 1 of the watermarked image， watermark is robust to the first PS (print and scan) and fragile to the second PS. The original image is blocked and every block is manipulated by DCT. To embed a binary barcode watermark， the amplitude of the smaller coefficients in low and middle frequency was increased and their signs were modified. The watermark was extracted according to the sign of low and middle frequency coefficients in blocked DCT domain and without the original image. The original image is to be judged as true or 1 with an appropriate threshold. The experiment results show that the algorithm meets the requirements of print anti-counterfeiting and have high practical value.Keywords: digital watermarking; discrete cosine transform; Arnold transform; Radon transform

0 引 言

條碼是由一組規(guī)則排列的條、空以及對應(yīng)的字符組成的標(biāo)記，用以表示一定的字符、數(shù)字及符號組成的信息，在防偽方面應(yīng)用極其廣泛。如商品包裝上和書刊后面的條碼防偽標(biāo)識等，給人們的生活和工作帶了許多便利，但是因?yàn)槠渲饕∷⒃谏唐钒b表面，使得不法分子能夠利用高端掃描儀器仿造條碼標(biāo)識，對假冒商品進(jìn)行包裝，以此謀求暴利。因此，為了既能夠保存條碼標(biāo)識，又能將條碼隱藏起來不被發(fā)現(xiàn)和偽造[1]。

本文通過對打印掃描前后圖像的DCT域失真分析，結(jié)合Arnold變換設(shè)計出一種利用DCT系數(shù)符號關(guān)系的條碼印刷水印算法，并在提取水印后可辨別印刷圖像的真?zhèn)巍?/p>

1 離散余弦變換

DCT是一種可分離的正交變換，并且是對稱的，它具有很好的去相關(guān)能力和能量壓縮能力?！?br>