網點加密圖像光學擷取比對辨識研究

Abstract

印刷圖像防偽技術除了在印刷材料與製程技術提昇改進外；亦可考慮印刷品進行數位資料加密（Data Hiding）以提高其安全性。本研究針對紙張上印刷過網圖像進行加密與比對辨識實驗，將資料加密技術結合數位過網演算法製作網點加密圖像，並對圖像進行光學擷取後再進行資料辨識。旨在探討網點加密圖像在不同過網解析度（150/300LPI）下以不同光學資料擷取解析度（600/1200/2400DPI）對加密資料的比對識正確率高低，瞭解網點加密圖像比對辨識條件。 研究結果顯示，六組實驗組合除300LPI－600DPI實驗組合之辨識正確率<=0.95之外，其餘實驗組合150LPI－600DPI、150LPI－1200DPI、150LPI－2400DPI、300LPI－1200DPI及300LPI－2400DPI其辨識正確率均顯著＞0.95。而300LPI－600DPI實驗組合其辨識正確率較低之原因，因其影像擷取解析度600DPI取樣不足使影像模糊辨識不易導致。 由150LPI與300LPI兩圖像辨識結果得知，150LPI圖像其辨識正確率在光學解析度600DPI時達到0.99730；在光學解析度達1200DPI時達到0.99985，在光學解析度達2400DPI以上達到0.99990。而300LPI圖像其辨識正確率在光學解析度600DPI時達到0.86426；在光學解析度達1200DPI時有0.99819，而在光學解析度達2400DPI以上達到0.99893。 本研究印刷圖像辨識錯誤現象，在圖像過網解析度150LPI時，以光學解析度1200或 2400DPI擷取圖像其辨識錯誤次數最少可獲得最穩定辨識結果。在150LPI－600DPI與300LPI－1200DPI實驗組合，發生”白點辨識為黑點”的現象高於”黑點辨識為白點”。將網點圖像予以加密複製於平面媒體上，有利於印刷品防止變造與安全保護。In addition to improve the materials and the process for printing images, counterfeiting technology can be used for digital data hiding on prints to enhance their security. The objective of this research is focusing on the printing halftone image on papers to make an experiment on data hiding and recognition to combine the data hiding technology with digital halftoning algorithms to produce data hiding in halftone image and to process the data recognition after optical retrieving of images. In order to understand the most optimized condition for the recognition of data hiding in halftone image, we could discuss the influence of different optical data acquirement resolution (600/1200/2400DPI) under different halftoning resolution (150/300LPI) on the correct rate of the recognition of encrypted image data. According to the results of the research, among the six experimental groupings, except for the group 300 LPI－600DPI's correct rate in under or equal to 0.95, the correct rate of other groupings such as 150LPI－600DPI, 150LPI－1200DPI, 150LPI－2400DPI, 300LPI－1200DPI, 300LPI－2400DPI are significance above 0.95. The insufficient sampling of the acquiring image resolution 600DPI contribute to the unrecognizable images, which caused the low correct rate of the recognition of the experimental grouping 300 LPI－600DPI. As the results of the recognition rate of the two images 150LPI and 300LPI, we found the following information. The pixels correct rate of recognition of image 150LPI reached to 0.99730 with optical resolution 600DPI, reached to 0.99985 with optical resolution 1200DPI, and reached to 0.99990 with optical resolution 2400DPI. The pixels correct rate of recognition of image 300LPI reached to 0.86426 with optical resolution 600DPI, reached to 0.99819 with optical resolution 1200DPI, and reached to 0.99990 with optical resolution 2400DPI. Using optical resolution 1200 or 2400 DPI to acquire the images with image halftoning resolution 150LPI, the error recognition phenomenon of this printing image research can obtain the steadiest recognized results with low-error-frequency. For the experimental combination of 150LPI－600DPI with 300LPI－1200DP, the phenomenon of "false positive" happens more frequently than the phenomenon of "false negative". It is beneficial to encrypt halftone images on the plane media for the authentication and security protection of print matters.