半色調線網浮水印之自我認證與評估研究
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2017
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Abstract
在科技蓬勃發展的現代，市面偽造的有價證券不計其數。由於影像可以方便快速的複製、處理、傳輸與儲存，容易被複製偽造。因此數位圖像的版權保護有許多學者投入研究，但對於印刷輸出的實體浮水印研究是比較少見的。如今已有許多國家的有價證券採用耐用且防偽性高的塑膠透明基材。而此特別材料之相關研究有開拓新的學術研究及產業應用發展空間，因此本研究致力於透明塑膠載體上設計具有防偽功能的浮水印，目的是將浮水印遮罩影像以不同的線網間距透過半色調過網技術，進行邏輯演算得到加密影像，再結合不同寬度光柵遮罩，一同輸出至塑膠透明基材，並以彎曲覆蓋的方式達到自我驗證解碼圖像。
另對於測試與評估光柵遮罩滑動解碼浮水印圖像之效果，先以模擬人眼視覺之模糊化兩階影像後，再以調制轉換函數評估影像自我認證解密的差異程度，而此方法除了能達到辨識真偽之目的，還能加值應用於產品版權的保護。
研究成果證實此自我認證與評估的方式是可行的，不僅可以將自我認證效果量化，亦可依據印刷設備調整加密演算，更能測試出人類視覺對自我驗證浮水印圖像的效果，同時亦可評估出最有效率解出的浮水印的線網參數組合，以利未來應用於許多加值產品及版權保護技術。
Because of the rapid growth in information technology, countless counterfeit products are being forged. Images can be processed, transferred, and saved quickly. However, information nowadays can be easily imitated. Thus, many experts are devoted to copyright protection in digital information, such as sound, images and videos. However, much less work has been devoted to anti-counterfeiting technology for printed images which have been processed digitally before output. Nowadays, many countries have adopted durable and high-security plastic substrates as identification cards or for product protection. Anti-counterfeiting technology can be further developed and applied to this substrate. The purpose of this study is to adopt digital halftoning technique to embed watermarks onto plastic substrates with anti-counterfeiting capability. By using halftoning algorithms with threshold matrices to form binary line-screen microstructures with varied spaces, the watermark mask can be converted into an encrypted image via logical operations. Also, having combined various line-widths allows self-authentication through bending and overlapping an area of grating structure in the same device. The encrypted image can thenbe printed out on a plastic substrate. By using Gaussian blur images to simulate the human visual system (HVS), this study is to test and evaluate the self-authentication by sliding the grating structure onto the encrypted image and checking the effect through decoding. Furthermore, using the modulation transfer function (MTF) to evaluate the effect by different line-widths of grating structures in order to find the optimum self-authenticated parameters. It’s not only used to distinguish counterfeits but also served as protection of value-added products. The study result shows that the self-authentication is reliable. It also can be quantitatively analyzed and the printed image can be obtained with accordance to the encoded algorithms from this research. Thus, it can evaluate how the self-authentication of watermarks works with the HVS. At the same time, it can provide the optimum combination of encoded watermarks and the decoding gratings, and it would be applied to the value-added products.
Because of the rapid growth in information technology, countless counterfeit products are being forged. Images can be processed, transferred, and saved quickly. However, information nowadays can be easily imitated. Thus, many experts are devoted to copyright protection in digital information, such as sound, images and videos. However, much less work has been devoted to anti-counterfeiting technology for printed images which have been processed digitally before output. Nowadays, many countries have adopted durable and high-security plastic substrates as identification cards or for product protection. Anti-counterfeiting technology can be further developed and applied to this substrate. The purpose of this study is to adopt digital halftoning technique to embed watermarks onto plastic substrates with anti-counterfeiting capability. By using halftoning algorithms with threshold matrices to form binary line-screen microstructures with varied spaces, the watermark mask can be converted into an encrypted image via logical operations. Also, having combined various line-widths allows self-authentication through bending and overlapping an area of grating structure in the same device. The encrypted image can thenbe printed out on a plastic substrate. By using Gaussian blur images to simulate the human visual system (HVS), this study is to test and evaluate the self-authentication by sliding the grating structure onto the encrypted image and checking the effect through decoding. Furthermore, using the modulation transfer function (MTF) to evaluate the effect by different line-widths of grating structures in order to find the optimum self-authenticated parameters. It’s not only used to distinguish counterfeits but also served as protection of value-added products. The study result shows that the self-authentication is reliable. It also can be quantitatively analyzed and the printed image can be obtained with accordance to the encoded algorithms from this research. Thus, it can evaluate how the self-authentication of watermarks works with the HVS. At the same time, it can provide the optimum combination of encoded watermarks and the decoding gratings, and it would be applied to the value-added products.
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Keywords
數位半色調技術, 半色調浮水印, 自我認證, Digital halftoning, Halftone watermarking, Self-authentication