Improved methods and system for watermarking halftone images

Watermarking is becoming increasingly important for content control and authentication. Watermarking seamlessly embeds data in media that provide additional information about that media. Unfortunately, watermarking schemes that have been developed for continuous tone images cannot be directly applied to halftone images. Many of the existing watermarking methods require characteristics that are implicit in continuous tone images, but are absent from halftone images. With this in mind, it seems reasonable to develop watermarking techniques specific to halftones that are equipped to work in the binary image domain. In this thesis, existing techniques for halftone watermarking are reviewed and improvements are developed to increase performance and overcome their limitations. Post-halftone watermarking methods work on existing halftones. Data Hiding Cell Parity (DHCP) embeds data in the parity domain instead of individual pixels. Data Hiding Mask Toggling (DHMT) works by encoding two bits in the 2x2 neighborhood of a pseudorandom location. Dispersed Pseudorandom Generator (DPRG), on the other hand, is a preprocessing step that takes place before image halftoning. DPRG disperses the watermark embedding locations to achieve better visual results. Using the Modified Peak Signal-to-Noise Ratio (MPSNR) metric, the proposed techniques outperform existing methods by up to 5-20%, depending on the image type and method considered. Field programmable gate arrays (FPGAs) are ideal for solutions that require the flexibility of software, while retaining the performance of hardware. Using VHDL, an FPGA based halftone watermarking engine was designed and implemented for the Xilinx Virtex XCV300. This system was designed for watermarking pre-existing halftones and halftones obtained from grayscale images. This design utilizes 99% of the available FPGA resources and runs at 33 MHz. Such a design could be applied to a scanner or printer at the hardware level without adversely affecting performance

Thorough Investigation, Improvement, and Data Hiding Watermarking in Digital Halftone Images

另外由於數位文件、多媒體處理工具及網際網路間的媒體交流不斷激增，導致數位資料在著作權及傳播上的控管不易，因此目前普遍採用傳統的類比式浮水印觀念提出新一代的數位浮水印技術來解決數位媒體著作權的保護、所有權的追蹤、文件原創性認定及資料的隱藏。這類的技術所需注意的問題包括強健性(資料遭破壞後仍有能力驗證)、隱藏資料容量、資料嵌入後之影像品質、隱藏資料之不可移除性及隱藏資料的解碼辨識率。目前已有許多如何在半色調影像內嵌入數位浮水印的相關技術發表，這類的技術可用於具有安全性質的文件列印處理，例如身份證或鈔票，且避免遭受不合法的複製利用，例如將文件經過掃瞄還原成數位資料形式再予以傳播。 數位浮水印可被設計成脆弱性或強健性。脆弱性浮水印可被一般影像處理輕易破壞，因此較適用於文件是否遭受竄改的偵測與驗證。強健性浮水印用於抵抗惡意或非故意性的攻擊，因此較適用於著作權的保護。一般來說，資料隱藏法(data hiding)屬於脆弱性，數位浮水印技術(digital watermarking)則屬於強健性。在本論文中我們提出一系列數位半色調技術結合資料隱藏法及數位浮水印的混成技術，實驗證明這些方法可在強健性、容量、影像品質、解碼辨識率上得到不錯的結果。Output devices such as halftone printers and palette-based displays are ca-pable of producing only a limited number of colors, whereas the human eye can distinguish around 10 million colors under optimal viewing conditions. Due to the low pass nature of human visual system. The eye perceives only a local spa-tial average of the spots produced by a printing device and is relatively insensi-tive to errors made in high frequencies in an image. Halftoning algorithms therefore aim to preserve these local averages while forcing the errors between the continuous tone image and the halftone image to high frequency regions. Existing halftoning techniques can be broadly classified as ordered dither, error diffusion, and iteration-based halftoning techniques. The evolution of computer and printer technologies, as well as economics, has been driving the current research. Some issues arise and need to be solved. For example, photographic printed quality, dot gain problem, and halftoning speed. In this dissertation, first, we propose an iteration-based halftoning, named LMS-halftoning to achieve high quality outputs, which was proved with higher PSNR than error diffusion. Second, a perfect printer model used to overcome the dot gain problem is also proposed here. Finally, a new progress coding scheme applied for order dither images is also included in this work. The proliferation of digital documents, multimedia processing tools, and the worldwide availability of Internet access have created an ideal medium for copyright fraud and uncontrollable distribution of multimedia content. To deal with this problem, conventional analogue watermarking technology has been adapted to digital media as a tool to achieve copyright protection, ownership trace, authentication, or information hiding. The major issues include robustness, capacity, imperceptible, undeletable, undeletable, and unambiguous. Currently, numerous methods using halftones to embed watermarks have been studied. These techniques can be used for printing security documents such as ID card, currency as well as confidential documents, and prevent from illegal duplication and forgery by further scanning these documents to digital forms. Some watermarks are fragile and some are robust. Fragile watermarks are designed to be broken easily by common image processing operations and are good for tampering detection and authentication. Robust watermarks are de-signed to survive hostile and/or unintentional attack and are good for copyright control. Generally speaking, data hiding techniques are fragile, and watemark-ing are robust. In this dissertation, we propose several watermarking and data hiding in halftone images that address all the issues described above.Part 1: Introduction and Halftone Image Quality Evalua-tion…………………………………………………………………….………1 Chapter 1 Introduction……………………………………………………... ..3 Chapter 2 Halftone Image Quality Evaluation………………..….11 2.1 Introduction…………………………………………………………11 2.2 General Criterions…………………………………………………12 2.2.1 Mean Square Error………………………………………..…12 2.2.2 Frequency Weighted Square Error…………………..…13 2.2.3 Five-Class Quality Measures…………….………………14 2.2.4 Optical Equipments……………………………….…………15 2.2.5 Contrast Sensitivity Function (CSF) ………………….16 2.3 Least-Mean-Squares (LMS) adaptive filter…………...19 Part 2: The Thorough Investigation and Improvement of Digital Halftoning……………………………………….…………23 Chapter 3 Traditional and Modern Digital Halftoning…….…25 3.1 Introduction………………………….………………………………25 3.2 Ordered Dithering………………..………………………………27 3.2.1 Traditional Techniques…………..…………………………27 3.2.2 Modern techniques….…………………………………………32 3.3 Error Diffusion……………………………………………………33 3.3.1 Traditional Technique………………………………………33 3.3.2 Modern Techniques……………………………………………36 3.4 Dot Diffusion…………………………….……………………………41 3.4.1 Traditional Technique………………………………………43 3.4.2 Modern Techniques……………………………………………44 3.5 Iteration-based halftoning…….………………………………46 3.6 Others……………………………………………………………………47 3.6.1 Green-Noise Dithering………………..……………………47 3.6.2 Look-Up Table halftoning………………………………48 3.6.3 Inverse Halftoning……………………………………………49 3.7 Summary……………………………………………………………50 Chapter 4 Modified Printer Model………………………………………51 4.1 Introduction…………………………………………………………51 4.2 Modified Printer Model………………………………………53 4.3 Experimental Results……………………………………………60 4.4 Summary……………………………………………………………63 Chapter 5 LMS-Halftoning………………………………………………65 5.1 Introduction……………………………………………….………65 5.2 The LMS-Designed Halftone Technique…………..……66 5.3 Modified Printer Model in LMS-Halftoning…………70 5.4 Experimental Results……………………………………………73 5.5 Summary……………………………………………………………82 Chapter 6 Progressive Coding of Halftone Images………..…83 6.1 Introduction…………………………………………………………83 6.2 Bit-Interleaving……………………………………………………..85 6.3 Progressive Coding with Lossy and Entropy Cod-ing…………………………………………………………………………..85 6.4 Experimental Results…………………………………….……..90 6.5 Summary…………………………………………………….………….95 Chapter 7 Other Issues of Digital Halftoning………………………97 7.1 Introduction…………………………………………………..………97 7.2 Architecture…………………………………………………………98 7.3 Sobel Gradient Evalution and Active Region Detec-tion…………………………………………………………………..98 7.4 Segregation of Global and Local Smooth Regions in An Image………………………………………………………………...99 7.5 Binarization of Global and Local Smooth Re-gions…………………………………………………………………….100 7.6 Experimental Results…………………………………………101 7.7 Summary…………………………………………….…………104 Part 3: Data Hiding and Digital Watermarking in Digital Halftoning……………………………………………………………105 Chapter 8 Data Hiding in Halftone images……………………………107 8.1 Introduction…………………………………………………………………107 8.2 Secret Data Embedded into Dithering Images……108 8.2.1 Encoding Scheme…………………………………………108 8.2.2 Decoding Scheme…………………………………………110 8.2.3 Experimental Results……………………………………111 8.3 Summary………………………………………………….……115 Chapter 9 Watermarking in Halftone images……..…………117 9.1 Introduction………………………………………………………117 9.2 Robust Watermarking in Dithered Halftone Im-age……………………………………………………………………118 9.2.1 Paired Sub-image Matching Ordered Dithering (PSMOD) ……………………………………………………118 9.2.2 Blind Paired Sub-image Matching Ordered Dither-ing (BPSMOD) …………………………………...…122 9.2.3 Watermark Extraction after Printed-and-Scanned Process………………………………………………….……122 9.2.4 Experimental Results……………………………….........…124 9.3 Summary………………………………………………………133 Chapter 10 Hybrid Data Hiding Watermarking in Halftone images……………………………………………………………135 10.1 Introduction………………………………………………………135 10.2 Hybrid Pixel-Based Data Hiding and Block-Based Watermarking for Error-Diffused Halftone Im-ages……………………………………………………………………137 10.2.1 Introduction………………………………………………137 10.2.2 Pixel-Based Data Hiding with Noise-Balanced Error Diffusion………………………………………………138 10.2.3 Block-Based Digital Watermarking with Ker-nels-Alternated Error Diffusion………….…………144 10.2.4 Hybrid Pixel-Based Data Hiding and Block-Based Watermarking for Error-Diffused Halftone Im-ages…………………………………………………………150 10.2.5 Experimental Results…………………………………153 10.2.6 Summary………………………………………………180 10.3 High-Capacity Data Hiding Watermarking in Half-tone Images using Minimal Error Bit Search-ing……………………………………………………………………..182 10.3.1 Introduction………………………………………………182 10.3.2 Data Hiding with Minimal Error Bit Searching (MEBS) ………………………………………………………183 10.3.3 Self-Decoding Mode and Watermarking Exten-sions………………………………………………………188 10.3.4 Least-Mean-Square-Designed Halftone Tech-nique……………………………………………………192 10.3.5 Experimental Results…………………………………197 10.3.6 Summary………………………………………………219 10.4 Watermarking in Halftone Images with Hybrid Error Diffusion and Ordered Dithering………………220 10.4.1 Introduction………………………………………………220 10.4.2 Average Ordered Dithering…………………………221 10.4.3 Watermarking with Cooperating Ordered Dithering and Error Diffusion………………………………………222 10.4.4 Decoding……………………………………………………224 10.4.5 Secret Sharing and Color Image Extension…226 10.4.6 Experimental Results…………………………………228 10.4.7 Summary……………………………………………241 10.5 Watermarking in Halftone Images with Par-ity-Matched Error Diffusion…………….……………243 10.5.1 Introduction……………………………….……………243 10.5.2 Watermarking with Parity-Matched Noise Bal-anced Error Diffusion………………………..…………243 10.5.3 Experimental Results…………………….…………247 10.5.4 Summary………………………………….…………256 Part 4: Conclusions and Future Works…………….……257 Chapter 11 Conclusions and Future Works……………….……259 References……………………………………………………………………………26