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Dr Johann A Briffa

Lecturer

Qualifications: B.Eng.(Hons.), M.Phil., PhD

Email:
Phone: Work: 01483 68 9630
Room no: 12 BB 02

Office hours

Semester 2, 2012-2013: Mon 09:00-11:00 during teaching weeks or by appointment

Further information

Research Interests

My general research interests involve Multimedia, Signal Processing, Coding Theory, and Parallel Computing. I am especially interested in applications that cross the boundaries between the different fields, and in practical implementation. Of particular interest are the fields of image forensics, steganography and watermarking, combining signal and image processing with the application of error-control coding and multimedia compression algorithms.

Publications

Highlights

  • Buttigieg V, Briffa JA. (2011) 'Codebook and Marker Sequence Design for Synchronization-Correcting Codes'. St. Petersburg, Russia : IEEE Proc. IEEE Intern. Symp. Inform. Theory, St Petersburg: IEEE International Symposium on Information Theory Proceedings (ISIT), 2011, pp. 1579-1583.
    doi: 10.1109/ISIT.2011.6033810
    Full text is available at: http://epubs.surrey.ac.uk/7652/

    Abstract

    We propose a construction based on synchronization and error-correcting block codes and a matched marker sequence. The block codes can correct insertion, deletion and substitution errors within each codeword. The marker sequence allows the decoder to maintain synchronization at codeword boundaries even at high error rates. An upper bound is given for the performance of these codes over a channel with random substitutions and synchronization errors. It is shown that the performance is largely dependent on the code's minimum Levenshtein distance. The performance of these codes is verified by simulation and compared to published results. In concatenation with a non-binary outer code we obtain a significant improvement in frame error rate at similar overall code rates.

  • Bardyn D, Briffa JA, Dooms A, Schelkens P. (2011) 'Forensic Data Hiding Optimized for JPEG 2000'. IEEE Proc. IEEE Intern. Symp. on Circuits and Systems, Rio de Janeiro, Brazil: IEEE International Symposium on Circuits and Systems (ISCAS), 2011, pp. 2657-2660.
    doi: 10.1109/ISCAS.2011.5938151
    Full text is available at: http://epubs.surrey.ac.uk/7654/

    Abstract

    This paper presents a novel image adaptive data hiding system using properties of the discrete wavelet transform and which is ready to use in combination with JPEG 2000. Image adaptive watermarking schemes determine the embedding samples and strength from the image statistics. We propose to use the energy of wavelet coefficients at high frequencies to measure the amount of distortion that can be tolerated by a lower frequency coefficient. The watermark decoder in image adaptive data hiding needs to estimate the same parameters used for encoding from a modified source and hence is vulnerable to desynchronization. We present a novel way to resolve these synchronization issues by employing specialized insertion, deletion and substitution codes. Given the low complexity and reduced perceptual impact of the embedding technique, it is suitable for inserting camera and/or projector information to facilitate image forensics.

  • Briffa JA, Schaathun HG, Wesemeyer S. (2010) 'An Improved Decoding Algorithm for the Davey-MacKay Construction'. Cape Town, South Africa : IEEE Proc. IEEE Intern. Conf. on Commun., Cape Town: IEEE International Conference on Communications (ICC), 2010, pp. 1-5.
    doi: 10.1109/ICC.2010.5502293
    Full text is available at: http://epubs.surrey.ac.uk/7655/

    Abstract

    The Deletion-Insertion Correcting Code construction proposed by Davey and MacKay consists of an inner code that recovers synchronization and an outer code that provides substitution error protection. The inner code uses low-weight codewords which are added (modulo two) to a pilot sequence. The receiver is able to synchronise on the pilot sequence in spite of the changes introduced by the added codeword. The original bit-level formulation of the inner decoder assumes that all bits in the sparse codebook are identically and independently distributed. Not only is this assumption inaccurate, but it also prevents the use of soft a- priori input to the decoder. We propose an alternative symbol-level inner decoding algorithm that takes the actual codebook into account. Simulation results show that the proposed algorithm has an improved performance with only a small penalty in complexity, and it allows other improvements using inner codes with larger minimum distance.

  • Briffa JA, Culnane C, Treharne H. (2010) 'Imperceptible printer dot watermarking for binary documents'. Proceedings of SPIE - The International Society for Optical Engineering, 7723
    doi: 10.1117/12.854708
    Full text is available at: http://epubs.surrey.ac.uk/7653/

    Abstract

    In this paper we propose a new imperceptible yellow printer dot watermarking scheme for documents printed on a colour printer. The scheme takes advantage of the imperfections of the human visual system to hide thousands of yellow dots over the entire page. It takes inspiration from the methods used by laser printer manufacturers for printer identification. The novelty of our approach is in providing an automatic embedding and detection method that can survive the distortions of printing and scanning. In order to achieve this a new moving window detection method is proposed. An error correction code is employed to handle the errors that could be present following detection. The scheme is evaluated through embedding and detection experiments on different types of documents; including text, architectural drawings and a cartoon. Our scheme offers an embedding capacity of 26,190 bits per page. Experiments were conducted using error correction codes with rates of 1/2 , 1/3 and 1/5 , given payloads of 13,095, 8,730, and 5,238 bits per A4 page respectively. We are able to successfully recover the watermark in all documents at a rate of 1/2 and 1/5 , and in all document except one at 1 3 . Further experiments were conducted with a smaller dot size to evaluate the impact it has on our results. With the smaller dot size we were still able to recover the watermarks from all documents when using an error correction code with rate 1/5 . The capacity offered by this approach far exceeds the capacity offered by existing binary watermarking schemes, which are robust to printing and scanning. The substantially larger capacity opens up a wider range of possible applications as well as the possibility of using more robust cryptographic techniques for authentication. © 2010 SPIE.

Journal articles

Conference papers

  • Alshehri AA, Briffa JA, Schneider SA, Wesemeyer S. (2013) 'Formal Security Analysis of NFC M-coupon Protocols using Casper/FDR'. Zurich: NFC 2013 : 5th International Workshop On Near Field Communication
  • Albukhanajer WA, Jin Y, Briffa JA, Williams G. (2012) 'Evolutionary Multi-Objective Optimization of Trace Transform for Invariant Feature Extraction'. IEEE Proceedings on 2012 IEEE congres on Evolutionary Computation (CEC), Brisbane, Australia: 2012 IEEE congres on Evolutionary Computation (CEC), pp. 1-8.
    doi: 10.1109/CEC.2012.6256160
  • Bateman PJ, Ho ATS, Briffa JA. (2012) 'Image Forensics of High Dynamic Range Imaging'. Atlantic City, New Jersey : Springer 10th International Workshop on Digital-forensics and Watermarking 2011, Atlantic City: 10th International Workshop, IWDW 2011
    doi: 10.1007/978-3-642-32205-1_27
    Full text is available at: http://epubs.surrey.ac.uk/7648/

    Abstract

    This paper introduces a novel area of research to the Image Forensic field; identifying High Dynamic Range (HDR) digital images. We create a test set of images that are a combination of HDR and standard images of similar scenes. We also propose a scheme to isolate fingerprints of the HDR-induced haloing artifact at “strong” edge positions, and present experimental results in extracting suitable features for a successful SVM-driven classification of edges from HDR and standard images. A majority vote of this output is then utilised to complete a highly accurate classification system.

  • Buttigieg V, Briffa JA. (2011) 'Codebook and Marker Sequence Design for Synchronization-Correcting Codes'. St. Petersburg, Russia : IEEE Proc. IEEE Intern. Symp. Inform. Theory, St Petersburg: IEEE International Symposium on Information Theory Proceedings (ISIT), 2011, pp. 1579-1583.
    doi: 10.1109/ISIT.2011.6033810
    Full text is available at: http://epubs.surrey.ac.uk/7652/

    Abstract

    We propose a construction based on synchronization and error-correcting block codes and a matched marker sequence. The block codes can correct insertion, deletion and substitution errors within each codeword. The marker sequence allows the decoder to maintain synchronization at codeword boundaries even at high error rates. An upper bound is given for the performance of these codes over a channel with random substitutions and synchronization errors. It is shown that the performance is largely dependent on the code's minimum Levenshtein distance. The performance of these codes is verified by simulation and compared to published results. In concatenation with a non-binary outer code we obtain a significant improvement in frame error rate at similar overall code rates.

  • Bardyn D, Briffa JA, Dooms A, Schelkens P. (2011) 'Forensic Data Hiding Optimized for JPEG 2000'. IEEE Proc. IEEE Intern. Symp. on Circuits and Systems, Rio de Janeiro, Brazil: IEEE International Symposium on Circuits and Systems (ISCAS), 2011, pp. 2657-2660.
    doi: 10.1109/ISCAS.2011.5938151
    Full text is available at: http://epubs.surrey.ac.uk/7654/

    Abstract

    This paper presents a novel image adaptive data hiding system using properties of the discrete wavelet transform and which is ready to use in combination with JPEG 2000. Image adaptive watermarking schemes determine the embedding samples and strength from the image statistics. We propose to use the energy of wavelet coefficients at high frequencies to measure the amount of distortion that can be tolerated by a lower frequency coefficient. The watermark decoder in image adaptive data hiding needs to estimate the same parameters used for encoding from a modified source and hence is vulnerable to desynchronization. We present a novel way to resolve these synchronization issues by employing specialized insertion, deletion and substitution codes. Given the low complexity and reduced perceptual impact of the embedding technique, it is suitable for inserting camera and/or projector information to facilitate image forensics.

  • Briffa JA, Schaathun HG, Wesemeyer S. (2010) 'An Improved Decoding Algorithm for the Davey-MacKay Construction'. Cape Town, South Africa : IEEE Proc. IEEE Intern. Conf. on Commun., Cape Town: IEEE International Conference on Communications (ICC), 2010, pp. 1-5.
    doi: 10.1109/ICC.2010.5502293
    Full text is available at: http://epubs.surrey.ac.uk/7655/

    Abstract

    The Deletion-Insertion Correcting Code construction proposed by Davey and MacKay consists of an inner code that recovers synchronization and an outer code that provides substitution error protection. The inner code uses low-weight codewords which are added (modulo two) to a pilot sequence. The receiver is able to synchronise on the pilot sequence in spite of the changes introduced by the added codeword. The original bit-level formulation of the inner decoder assumes that all bits in the sparse codebook are identically and independently distributed. Not only is this assumption inaccurate, but it also prevents the use of soft a- priori input to the decoder. We propose an alternative symbol-level inner decoding algorithm that takes the actual codebook into account. Simulation results show that the proposed algorithm has an improved performance with only a small penalty in complexity, and it allows other improvements using inner codes with larger minimum distance.

  • Briffa JA, Culnane C, Treharne H. (2010) 'Imperceptible printer dot watermarking for binary documents'. Proceedings of SPIE - The International Society for Optical Engineering, 7723
    doi: 10.1117/12.854708
    Full text is available at: http://epubs.surrey.ac.uk/7653/

    Abstract

    In this paper we propose a new imperceptible yellow printer dot watermarking scheme for documents printed on a colour printer. The scheme takes advantage of the imperfections of the human visual system to hide thousands of yellow dots over the entire page. It takes inspiration from the methods used by laser printer manufacturers for printer identification. The novelty of our approach is in providing an automatic embedding and detection method that can survive the distortions of printing and scanning. In order to achieve this a new moving window detection method is proposed. An error correction code is employed to handle the errors that could be present following detection. The scheme is evaluated through embedding and detection experiments on different types of documents; including text, architectural drawings and a cartoon. Our scheme offers an embedding capacity of 26,190 bits per page. Experiments were conducted using error correction codes with rates of 1/2 , 1/3 and 1/5 , given payloads of 13,095, 8,730, and 5,238 bits per A4 page respectively. We are able to successfully recover the watermark in all documents at a rate of 1/2 and 1/5 , and in all document except one at 1 3 . Further experiments were conducted with a smaller dot size to evaluate the impact it has on our results. With the smaller dot size we were still able to recover the watermarks from all documents when using an error correction code with rate 1/5 . The capacity offered by this approach far exceeds the capacity offered by existing binary watermarking schemes, which are robust to printing and scanning. The substantially larger capacity opens up a wider range of possible applications as well as the possibility of using more robust cryptographic techniques for authentication. © 2010 SPIE.

  • Briffa JA, Schaathun HG, Wahab AWA. (2009) 'Has F5 Really Been Broken?'. London : IET Intern. Conf. on Imaging for Crime Detection and Prevention (ICDP), London: 3rd International Conference on Crime Detection and Prevention (ICDP 2009), pp. 1-5.
    doi: 10.1049/ic.2009.0245
    Full text is available at: http://epubs.surrey.ac.uk/7657/

    Abstract

    The publicly-available F5 software (F5Software) implementation takes a possibly compressed cover image, decompresses it if necessary, and embeds the hidden message during a second compression process. This procedure introduces a risk that the stego image goes through ‘double compression’. While this is not a problem from the embedding and extraction point of view, any steganalysis process trained on such a scheme will potentially detect artifacts caused either by the embedding process or the second compression process. In this paper we review published steganalysis techniques on F5. By re-implementing an isolated F5 embedding algorithm excluding the decompression and recompression process (F5Py), we show that published steganalysis techniques are unable to defeat F5 when its ideal operational condition is not violated. In other words, published techniques most likely detected the compression artifacts rather than the embedding process when the message size is not exceeding the optimum F5 capacity. This is an important fact that has been ignored before. Furthermore, we look for the optimum embedding rate for F5 in order for it to take advantage of matrix encoding for better embedding efficiency. From here we found that the low embedding rate considered for F5 in the previous works are actually relatively high for it. This is also important since bigger message size might degrade F5 to F4. In addition, we also verify that, as expected, steganalysis performance depends on the message size.

  • Wahab AW, Briffa JA, Schaathun HG, Ho ATS. (2009) 'Conditional Probability Based Steganalysis for JPEG Steganography'. IEEE COMPUTER SOC PROCEEDINGS OF THE 2009 INTERNATIONAL CONFERENCE ON SIGNAL PROCESSING SYSTEMS, Singapore, SINGAPORE: International Conference on Signal Processing Systems (ICSPS 2009), pp. 205-209.
    doi: 10.1109/ICSPS.2009.71
  • Wahab AWA, Briffa JA, Schaathun HG. (2008) 'On the Performance of Wavelet Decomposition Steganalysis with JSteg Steganography'. SPRINGER-VERLAG BERLIN DIGITAL WATERMARKING, Korea Inst Informat Secuity & Cryptol, Busan, SOUTH KOREA: 7th International Workshop on Digital Watermarking 5450, pp. 342-349.
    Full text is available at: http://epubs.surrey.ac.uk/7660/
  • Briffa JA, Schaathun HG. (2008) 'Non-Binary Turbo Codes and Applications'. IEEE 2008 5TH INTERNATIONAL SYMPOSIUM ON TURBO CODES AND RELATED TOPICS, Lausanne, SWITZERLAND: 5th International Symposium on Turbo Codes and Related Topics, pp. 294-298.
    doi: 10.1109/TURBOCODING.2008.4658714
  • Briffa JA, Schaathun HG. (2008) 'Improvement of the Davey-MacKay Construction'. IEEE 2008 INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY AND ITS APPLICATIONS, VOLS 1-3, Auckland, NEW ZEALAND: International Symposium on Information Theory and Its Applications, pp. 234-237.
  • Briffa JA, Das M. (2003) 'Channel models for high-capacity information hiding in images'. SPIE-INT SOC OPTICAL ENGINEERING MATHEMATICS OF DATA/IMAGE CODING, COMPRESSION, AND ENCRYPTION V, WITH APPLICATIONS, SEATTLE, WA: Conference on Mathematics of Data/Image Coding, Compression and Encryption V, with Applications 4793, pp. 135-144.
    Full text is available at: http://epubs.surrey.ac.uk/7656/
  • Briffa JA, Buttigieg V. (2000) 'Interleavers for unpunctured symmetric Turbo codes'. IEEE International Symposium on Information Theory - Proceedings, , pp. 450-450.
    Full text is available at: http://epubs.surrey.ac.uk/7658/

    Abstract

    The Turbo code interleaver design problem is considered for relatively large block sizes, where the effect of trellis termination is less marked. An optimised interleaver design technique based on simulated annealing is proposed - performance is significantly better than the Berrou-Glavieux interleaver without an increase in delay.

  • Briffa JA, Buttigieg V. (1998) 'Investigation of the error performance of Tunstall coding'. IEEE 1998 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY - PROCEEDINGS, MIT, CAMBRIDGE, MA: IEEE International Symposium on Information Theory, pp. 202-202.
    Full text is available at: http://epubs.surrey.ac.uk/7659/

Teaching

COM2027 - Software Engineering Project

Team development of a game for mobile phones using Android SDK. Supported online through SurreyLearn and SVN.

COM3012 - Parallel Architectures

Implementation of parallel algorithms on emerging architectures, currently focusing on nVidia GPUs (using CUDA). Previously also included the Cell BE (as in the Sony Playstation 3). Supported online through SurreyLearn and SVN.

COMM038 - Advanced Multimedia Security

Focus on current topics in Multimedia Security, including Steganography & Steganalysis, and Image Forensics. Includes a substantial practical component, using Python. Supported online through SurreyLearn and SVN.

Departmental Duties

BSc Projects Coordinator

Module convenor for COM3001 - Professional Project; organizing:

  • Project selection process, including allocation of supervisor and examiner
  • Assessment, including formulation of marking criteria, moderation and monitoring

MSc Projects Coordinator

Module convenor for COMM002 - MSc Dissertation; organizing:

  • Project selection process, including allocation of supervisor and examiner
  • Assessment, including formulation of marking criteria, moderation and monitoring

PTY Visiting Tutor

Visiting tutor to a number of students on an industrial placement year.