Roland Norcen

Confidential storage and transmission of medical image data

We discuss computationally efficient techniques for confidential storage and transmission of medical image data. Two types of partial encryption techniques based on AES are proposed. The first encrypts a subset of bitplanes of plain image data whereas the second encrypts parts of the JPEG2000 bitstream. We find that encrypting between 20% and 50% of the visual data is sufficient to provide high confidentiality.

Selective encryption of the JPEG2000 bitstream

In this paper, we propose partial encryption of JPEG2000 coded image data using an AES symmetric block cipher. We find that encrypting 20% of the visual data is sufficient to provide a high level of confidentiality. This percentage of encryption also provides security against replacement attacks, which is discussed at length.

Cache issues with JPEG2000 wavelet lifting

In this paper, we have a close look at the runtime performance of the intra-component transform employed in the reference implementations of the JPEG2000 image coding standard. Typically, wavelet lifting is used to obtain a wavelet decomposition of the source image in a computationally efficient way. However, so far no attention has been paid to the impact of the CPUs memory cache on the overall performance. We propose two simple techniques that dramatically reduce the number of cache misses and cut column filtering runtime by a factor of 10. Theoretical estimates as well as experimental results on a number of hardware platforms show the effectivity of our approach.

Parallel JPEG2000 image coding on multiprocessors

In this paper, we discuss how the two reference implementations of the upcoming JPEG2000 image coding standard can be parallelized for the execution on shared memory multiprocessors. By runtime analysis, we identify two major stages in the coding process of JPEG2000 where parallelism can be exploited. We present techniques to exploit the parallelism within these two stages, and speedup results obtained on several hardware platforms. We focus on OpenMP as well as JAVA threads for programming within shared-memory environments.

Encryption of wavelet-coded imagery using random permutations

In this paper we investigate the impact of using random coefficient permutation to provide confidentiality in wavelet-based still image compression pipelines. We compare the changes in compression performance of JPEG 2000 and SPIHT-based schemes and discuss key management scenarios. The results also have interesting implications with respect to the significance of the zerotree hypothesis.

High performance JPEG 2000 and MPEG-4 VTC on SMPs using OpenMP

JPEG 2000 and MPEG-4 Visual Texture Coding (VTC) are both wavelet-based and state of the art in still image coding. In this paper we show sequential as well as parallel strategies for speeding up two selected implementations of MPEG-4 VTC and JPEG 2000 using the popular shared memory programming paradigm OpenMP. Furthermore, we discuss the sequential and parallel performance of the improved versions and compare the efficiency of both algorithms.

Performance analysis of block-based permutations in securing JPEG2000 and SPIHT compression

We investigate and compare combined compression-encryption schemes. We assess the respective security, and we show how encryption affects the image coding efficiency. The techniques employ the wavelet-based compression algorithms JPEG2000 and SPIHT, and we randomly permute and rotate blocks of wavelet coefficients in different wavelet-subbands to encrypt image data within the compression pipeline. We identify weak points of the propsed encryption techniques, and possible attacks are highlighted. The investigated methods allow to trade off security for compression performance. The results also have interesting implications with respect to the significance of the zerotree-hypothesis as stated in the context of compression schemes.

Robust Visual Hashing Using JPEG 2000

Robust visual hash functions have been designed to ensure the data integrity of digital visual data. Such algorithms rely on an efficient scheme for robust visual feature extraction. We propose to use the wavelet-based JPEG2000 image compression algorithm for feature extraction. We discuss the sensitivity of our proposed method against different malicious data modifications including local image alterations and Stirmark attacks.

Experiments in JPEG2000-based INTRA coding for H.26L

In this paper we compare the coding performance of the JPEG2000 still image coding standard with the INTRA coding method used in the H.26L project. We discuss the basic techniques of both coding schemes and show the effect of improved I-frame coding to the overall performance of a H.26L-based system. The coding efficiency as well as the runtime behaviour is considered in our comparison.

Approaching real-time processing for matching pursuit image coding

One approach to transformation based compression is the Matching Pursuit Projection (MPP). MPP or variants of it have been suggested for designing image compression and video compression algorithms and have been among the top performing submissions within the MPEG-4 standardization process. In the case of still image coding, the MPP approach has to be paid with an enormous computational complexity. In this work we discuss sequential, as well as parallel speedup techniques of a MPP image coder which is competitive in terms of rate-distortion performance.