Digital watermarking techniques for printed images

Abstract During the last few decades, digital watermarking techniques have gained a lot of interest. Such techniques enable hiding imperceptible information to images; information which can be extracted later from those images. As a result, digital watermarking techniques have many interesting applications for example in Internet distribution. Contents such as images are today manipulated mainly in digital form; thus, traditionally, the focus of watermarking research has been the digital domain. However, a vast amount of images will still appear in some physical format such as in books, posters or labels, and there are a number of possible applications of hidden information also in image printouts. In this case, an additional level of challenge is introduced, as the watermarking technique should be robust to extraction from printed output. In this thesis, methods are developed, where a watermarked image appears in a printout and the invisible information can be later extracted using a scanner or mobile phone camera and watermark extraction software. In these cases, the watermarking method has to be carefully designed because both the printing and capturing process cause distortions that make watermark extraction challenging. The focus of the study is on developing blind, multibit watermarking techniques, where the robustness of the algorithms is tested in an office environment, using standard office equipment. The possible effect of the background of the printed images, as well as compound attacks, are both paid particular attention to, since these are considered important in practical applications. The main objective is thus to provide technical means to achieve high robustness and to develop watermarking methods robust to printing and scanning process. A secondary objective is to develop methods where the extraction is possible with the aid of a mobile phone camera. The main contributions of the thesis are: (1) Methods to increase watermark extraction robustness with perceptual weighting; (2) Methods to robustly synchronize the extraction of a multibit message from a printout; (3) A method to encode a multibit message, utilizing directed periodic patterns and a method to decode the message after attacks; (4) A demonstrator of an interactive poster application and a key based robust and secure identification method from a printout.Tiivistelmä Digitaalinen vesileimaus on parin viime vuosikymmenen aikana runsaasti huomiota saanut tekniikka, jonka avulla kuviin voidaan piilottaa aistein havaitsematonta tietoa. Tämä tieto voidaan myöhemmin poimia esiin, minkä vuoksi sovelluskohteita esimerkiksi Internetin kautta tapahtuvassa jakelussa on useita. Perinteisesti vesileimaustekniikat keskittyvät pelkästään digitaalisessa muodossa pysyvään tietoon. Kuitenkin iso osa kuvainformaatiosta saa yhä vielä myös fyysisen muodon esimerkiksi kirjoissa, julisteissa ja etiketeissä. Myös vesileimauksella on useita sovelluskohteita painettujen kuvienkin osalta. Vesileimausta ajatellen painatus tuo kumminkin omat erityishaasteensa vesileimaustekniikoille. Tässä väitöskirjassa kehitetään menetelmiä, jotka mahdollistavat piilotetun tiedon säilymisen painetussa kuvassa. Piilotettu tieto voidaan lukea käyttämällä skanneria tai matkapuhelimen kameraa tiedon digitalisointiin. Digitalisoinnin jälkeen vesileimausohjelma osaa lukea piilotetun tiedon. Vesileimauksen osalta haasteellisuus tulee vääristymistä, joita sekä kuvien tulostus sekä digitalisointi aiheuttavat. Väitöstyössä keskitytään monibittisiin vesileimaustekniikoihin, joissa alkuperäistä kuvaa ei tarvita vesileimaa poimittaessa. Väitöstyössä kehitetyt menetelmät on testattu toimistoympäristössä standardi toimistolaitteita käyttäen. Käytännön sovelluksia ajatellen, testeissä on kiinnitetty huomiota myös yhdistelmähyökkäysten sekä painetun kuvan taustan vaikutukseen algoritmin robustisuudelle. Ensisijainen tavoite on kehittää menetelmiä, jotka kestävät printtaus ja skannaus operaation. Toinen tavoite on tiedon kestävyys luettaessa tietoa matkapuhelimen kameran avulla. Väitöskirjassa tarkastellaan ja kehitellään ratkaisuja neljälle eri osa-alueelle: (1) Ihmisaisteja mallintavien menetelmien käyttö vesileimauksen kestävyyden lisäämiseksi; (2) Robusti synkronointi luettaessa monibittistä tietoa painotuotteesta; (3) Suunnattuja jaksollisia kuvioita käyttävä menetelmä, joka mahdollistaa monibittisen tiedon koodaamisen ja dekoodaamisen hyökkäysten jälkeen; (4) Sovellustasolla tarkastellaan kahta pääsovellusta: interaktiivinen juliste sekä kestävä ja turvattu avaimen avulla tapahtuva painotuotteen identifiointi

Increasing the capturing angle in print-cam robust watermarking

Abstract It is nowadays more probable that a print media is captured and shared with a mobile phone than with a scanner. The reasons for photographing the print range from intention of copying the image to simply sharing an interesting add with friends. Watermarking offers a solution for carrying side information in the images, and if the watermarking method being used is robust to the print-cam process, the information can be read with a mobile phone camera. In this paper, we present a print-cam robust watermarking method that is also implemented on a mobile phone and evaluated with user tests. Especially, the lens focusing problem when the picture is captured in a wide angle with respect to the printout is addressed. The results show that the method is highly robust to capturing the watermark without errors in angles up to 60° with processing times that are acceptable for real-life applications

Extracting watermarks from printouts captured with wide angles using computational photography

Abstract Thus far the research of print-cam robust watermarking methods has focused on finding new methods for embedding and extracting the watermark. However, the capturing process itself, has been neglected in scientific research. In this paper, we propose a solution for the situation when the watermarked image has been captured in a wide angle and the depth of focus of the camera is not deep enough to capture the whole scene in-focus resulting in unfocused areas. The solution proposed here relies on a subfield of computational photography, namely all-in-focus imaging. All-in-focus images are generated by fusing multiple images from the same scene with different focus distances together, so that the object being photographed is fully in focus. Traditionally, the images to be fused are selected by hand from the focal stack or the whole stack is used for building the all-in-focus image. In mobile phone applications, computational resources are limited and using the full focal stack would result in long processing times and the manual selection of images would not be practical. In addition, we propose a method for optimizing the size of the focal stack and automatically selecting appropriate images for fusion. It is shown here that a watermark can still be recovered from the reconstructed all-in-focus image accurately

Architecture enabling service-oriented digital biobanks

Abstract In Finland, the Biobank Act entered into effect in 2013. The primary motivation for the act is to enable the utilization of collected biological sample material for medical research. However, in order to effectively utilize this data, there exists a need to develop new technological solutions to support the collection and management of potentially large sets of sensitive data through multiple stages of processing. The cumulative data stored within biobanks will enable multi-disciplinary research and new innovations. We propose an architecture that addresses several challenges involved in defining and deploying a biobank infrastructure including consent management, data management and data transfer. Our architecture expedites the development of this important area within the research and industrial communities, and enables the deployment of service-oriented biobanks

Reversible data hiding in FTIR microspectroscopy images with tamper indication and payload error correction

Abstract Fourier transform infrared (FTIR) microspectroscopy images contain information from the whole infrared spectrum used for microspectroscopic analyses. In combination with the FTIR image, visible light images are used to depict the area from which the FTIR spectral image was sampled. These two images are traditionally acquired as separate files. This paper proposes a histogram shifting-based data hiding technique to embed visible light images in FTIR spectral images producing single entities. The primary objective is to improve data management efficiency. Secondary objectives are confidentiality, availability, and reliability. Since the integrity of biomedical data is vital, the proposedmethod applies reversible data hiding. After extraction of the embedded data, the FTIR image is reversed to its original state. Furthermore, the proposed method applies authentication tags generated with keyed Hash-Based Message Authentication Codes (HMAC) to detect tampered or corrupted areas of FTIR images. The experimental results show that the FTIR spectral images carrying the payload maintain good perceptual fidelity and the payload can be reliably recovered even after bit flipping or cropping attacks. It has been also shown that extraction successfully removes all modifications caused by the payload. Finally, authentication tags successfully indicated tampered FTIR image areas

Retinex model based stain normalization technique for whole slide image analysis

Abstract Medical imaging provides the means for diagnosing many of the medical phenomena currently studied in clinical medicine and pathology. The variations of color and intensity in stained histological slides affect the quantitative analysis of the histopathological images. Moreover, stain normalization utilizing color for the classification of pixels into different stain components is challenging. The staining also suffers from variability, which complicates the automatization of tissue area segmentation with different staining and the analysis of whole slide images. We have developed a Retinex model based stain normalization technique in terms of area segmentation from stained tissue images to quantify the individual stain components of the histochemical stains for the ideal removal of variability. The performance was experimentally compared to reference methods and tested on organotypic carcinoma model based on myoma tissue and our method consistently has the smallest standard deviation, skewness value, and coefficient of variation in normalized median intensity measurements. Our method also achieved better quality performance in terms of Quaternion Structure Similarity Index Metric (QSSIM), Structural Similarity Index Metric (SSIM), and Pearson Correlation Coefficient (PCC) by improving robustness against variability and reproducibility. The proposed method could potentially be used in the development of novel research as well as diagnostic tools with the potential improvement of accuracy and consistency in computer aided diagnosis in biobank applications

Stain normalization methods for histopathology image analysis:a comprehensive review and experimental comparison

Abstract The advent of whole slide imaging has brought advanced computer-aided diagnosis via medical imaging and artificial intelligence technologies in digital pathology. The examination of tissue samples through whole slide imaging is commonly used to diagnose cancerous diseases, but the analysis of histopathology images through a decision support system is not always accurate due to variations in color caused by different scanning equipment, staining methods, and tissue reactivity. These variabilities decrease the accuracy of computer-aided diagnosis and affect the diagnosis of pathologists. In this context, an effective stain normalization method has proved as a powerful tool to standardize different color appearances and minimize color variations in histopathology images. This study reviews different stain normalization methods highlighting the main methodologies, contributions, advantages, and limitations of correlated works. The state-of-the-art methods are grouped into four distinct categories. Next, we select ten representative methods from the groups and conduct an experimental comparison to investigate the strengths and weaknesses of different methods and rank them according to selected performance accuracy measures. The quality performances of selected methods are compared in terms of quaternion structure similarity index metric, structural similarity index metric, and Pearson correlation coefficient conducting experiments on three histopathological image datasets. Our findings conclude that the structure-preserving unified transformation-based methods consistently outperform the state-of-the-art methods by improving robustness against variability and reproducibility. The comparative analysis we conducted in this paper will serve as the basis for future research, which will help to refine existing techniques and develop new approaches to address the complexities of stain normalization in complex histopathology images

Screen-cam robust and blind watermarking for tile satellite images

Abstract To achieve watermark synchronization from an image with perspective distortion is a challenge. This paper proposes a screen-cam robust and blind watermarking scheme for tile satellite images, which means we do not need any user interaction or additional information in watermark detection. To achieve this, at the watermark embedding side, we divide tiles into synchronization tiles and message tiles, and propose a discrete Fourier transform (DFT) based embedding method to cope with the quality degradation caused by screen-cam process. At the extraction side, based on the idea of template matching, we first use a synchronization response index to estimate an appropriate scale level and positions of embedded synchronization watermarks from the noise component, which is estimated by Wiener filter. Then, we propose verification, selection, and precise locations methods to ensure the effectiveness and accuracy of synchronization detection results. After that, we can extract the regions of message tiles. Finally, we extract watermark message based on the local max value from the DFT domain of the noise component. Experimental results demonstrate the validity of the proposed scheme against common attacks and screen-cam attack with a tripod as well as handhold shooting