Birgit M. Planitz

The correspondence framework for 3D surface matching algorithms

Beyond the inherent technical challenges, current research into the three dimensional surface correspondence problem is hampered by a lack of uniform terminology, an abundance of application specific algorithms, and the absence of a consistent model for comparing existing approaches and developing new ones. This paper addresses these challenges by presenting a framework for analysing, comparing, developing, and implementing surface correspondence algorithms. The framework uses five distinct stages to establish correspondence between surfaces. It is general, encompassing a wide variety of existing techniques, and flexible, facilitating the synthesis of new correspondence algorithms. This paper presents a review of existing surface correspondence algorithms, and shows how they fit into the correspondence framework. It also shows how the framework can be used to analyse and compare existing algorithms and develop new algorithms using the frameworks modular structure. Six algorithms, four existing and two new, are implemented using the framework. Each implemented algorithm is used to match a number of surface pairs. Results demonstrate that the correspondence framework implementations are faithful implementations of existing algorithms, and that powerful new surface correspondence algorithms can be created.

Scaling Acoustic Data Analysis through Collaboration and Automation

Monitoring and assessing environmental health is becoming increasingly important as human activity and climate change place greater pressure on global biodiversity. Acoustic sensors provide the ability to collect data passively, objectively and continuously across large areas for extended periods of time. While these factors make acoustic sensors attractive as autonomous data collectors, there are significant issues associated with large-scale data manipulation and analysis. We present our current research into techniques for analysing large volumes of acoustic data effectively and efficiently. We provide an overview of a novel online acoustic environmental workbench and discuss a number of approaches to scaling analysis of acoustic data, collaboration, manual, automatic and human-in-the loop analysis.

A Study of Block-Based Medical Image Watermarking Using a Perceptual Similarity Metric

Medical image watermarking has been proposed as an appropriate method for enhancing data security, content verification and numerical image fidelity. Due to the sensitive nature of the data, medical image watermarking requires that any additional information that is stored within an image must not affect the perceptual integrity of the image. In typical approaches, additional information is generally hidden in the entire image, or in the background regions of an image (so as not to affect the medical data). This paper presents a novel model whereby medical image regions are watermarked differently so that perceptual degradation due to watermarking is limited. The model partitions images into regions and characterises each region according to some feature(s). Each region is then watermarked with a particular watermark method and payload capacity such that perceptual degradation is limited. This paper presents the model in conceptual form and then uses one instance of it to demonstrate how it would be used in practise. Results on MR and CT images demonstrate that less visually sensitive areas on images can be watermarked using more robust techniques and more sensitive areas can be watermarked using lighter or no embedding.

Medical image watermarking for multiple modalities

Transfer of digital medical images between multiple parties requires the assurance of image identity and integrity, which can be achieved through image watermarking. This raises concerns for loss in viewer performance due to degradation of image quality. Here we describe an approach to ensure that impact on the image quality is well below the threshold of visual perceptibility. The principles on which this approach rests are the choice of a suitably light payload, and the use of different watermarking methods and parameters for different medical image types. We provide examples of this approach applied to MR, CT and CR images

A Comparison of DCT and DWT Block Based Watermarking on Medical Image Quality

Hiding watermark information in medical image data files is one method of enhancing security and protecting patient privacy. However the research area of medical image watermarking has not been particularly active, partly due to concerns that any distortion could affect the diagnostic value of the medical image. These concerns can be addressed by ensuring that any image changes are kept below visual perception thresholds. In this paper the effects of image watermarking and common image manipulations are measured using the Peak Signal-to-Noise Ratio (PSNR), Structural Similarity Measure (SSIM) and Steerable Visual Difference Predictor (SVDP) numerical metrics. Two methods of block based watermarking are compared: the Discrete Cosine Transform (DCT) and Discrete Wavelet Transform (DWT). To ensure a fair comparison a 128-pixel block size is used which allows an identical amount of information to be embedded for each method (3072 bits multiplied by embedding strength). The results suggest that although the two methods are similar, the DCT method is preferable if localization of changes is required. If localization is not required the DWT method is supported.

Synthesising surface matching algorithms using the correspondence framework

Computer vision tasks such as registration, modeling and object recognition, are becoming increasingly useful in industry. Each of these applications employs correspondence algorithms to compute accurate mappings between partially overlapping surfaces. In industry, it is essential to select an appropriate correspondence algorithm for a given surface matching task. A correspondence framework has recently been proposed to assist in the selection and creation of correspondence algorithms for these tasks. This paper demonstrates how to use the correspondence framework to create a new surface matching algorithm, which uses stages of an existing model matching algorithm. The efficiency with which the new algorithm is created using the correspondence frame work is emphasized. In addition, results show that the new algorithm is both robust and efficient.