A Parametric Model for Multispectral Scanners

Efficient acquisition and utilization of remotely sensed data requires an extensive a priori evaluation of the performance of the basic data collection unit, the multispectral scanner. The objective is the development of a fully parametric technique to theoretically evaluate the systems response in any desired operational environment and provide the necessary information in selecting a set of optimum parameters. In this paper the multispectral scanner spatial characteristics are represented by a linear shift-invariant multiple-port system where the N spectral bands comprise the input processes. The scanner characteristic function, the relationship governing the transformation of the input spatial and hence spectral correlation matrices through the systems, is developed. Specific cases for Gaussian point spread functions are examined. The integration of the scanner spatial model and a parameter classification error estimator provides the necessary technique to evaluate the performance of a multispectral scanner. A set of test statistics are specified and the corresponding output quantities computed by the characteristic function. Two sets of classification accuracies, one at the input and one at the output are estimated. The scanner\u27s instantaneous field of view is changed and the variation of the output classification performance monitored

Watermarking of compressed multimedia using error-resilient VLCs

Abstract-Error-resilient variable length codes (VLCs) have been proposed to counter bit errors over error-prone channels. In this work we establish a linkage between channel coding and watermarking by observing that watermark bits are, in effect, intentional bit errors. Using a recently introduced resynchronizing VLC, we have developed a compressed-domain watermarking algorithm where the inherent errorresilient property of the code is exploited to implement lossless, oblivious watermarking. The algorithm is implemented on MPEG-2 video Keywords—watermarking, MPEG-2, error-resilient coding I

Compression and Rotation Resistant Watermark Using a Circular Chirp Structure

Digital watermarks for images can be made relatively robust to luminance and chrominance changes. More challenging problems are geometric or combined intensity/geometric attacks. In this work we use an additive watermarking model, commonly used in spread spectrum, using a new spreading function. The spreading function is a 2D circular chirp that can simultaneously resist JPG compression and image rotation. Circular chirp is derived from a block chirp by polar mapping. The resistance to compression is achieved by the available tuning parameters of a block chirp. Tuning parameters are chirp’s initial frequency and chirp rate. These two parameters can be used to perform spectral shaping to avoid JPEG compression effects. Rotational invariance is achieved by mapping the block chirp to a ring whose inner and outer diameters are selectable. Watermark is added in spatial domain but detection is performed in polar domain where rotation translates to translation