Charles G. Boncelet

A multiresolution watermark for digital images

We introduce a new multiresolution watermarking method for digital images. The method is based on the discrete wavelet transform (DWT). Pseudo-random codes are added to the large coefficients at the high and middle frequency bands of the DWT of an image. It is shown that this method is more robust to often proposed methods to some common image distortions, such as the wavelet transform based image compression, and image halftoning. Moreover, the method is hierarchical. The computation load needed to detect the watermark depends on the noise level in an image.

LUM filters: a class of rank-order-based filters for smoothing and sharpening

A new class of rank-order-based filters, called lower-upper-middle (LUM) filters, is introduced. The output of these filters is determined by comparing a lower- and an upper-order statistic to the middle sample in the filter window. These filters can be designed for smoothing and sharpening, or outlier rejection. The level of smoothing done by the filter can range from no smoothing to that of the median filter. This flexibility allows the LUM filter to be designed to best balance the tradeoffs between noise smoothing and signal detail preservation. LUM filters for enhancing edge gradients can be designed to be insensitive to low levels of additive noise and to remove impulsive noise. Furthermore, LUM filters do not cause overshoot or undershoot. Some statistical and deterministic properties of the LUM filters are developed, and a number of experimental results are presented to illustrate the performance. These experiments include applications to 1D signals and to images. >

Ll-filters-a new class of order statistic filters

The Ll-filters are introduced to generate the order statistic filters (L-filters) and the nonrecursive linear, or finite-duration impulse-response (FIR), filters. Such estimators are particularly effective filtering signals that do not necessarily follow Gaussian distributions. They can be designed to restore one-dimensional or multidimensional signals corrupted by noise of impulsive type. Such filters are appealing since they are suitable for being made robust against the presence of spurious outliers in the data. >

The NTMAC for authentication of noisy messages

This paper introduces a new construct, called the Noise Tolerant Message Authentication Code (NTMAC), for noisy message authentication. The NTMAC can tolerate a small number of errors, such as might be caused by a noisy communications channel. The NTMAC uses a conventional Message Authentication Code (MAC) in its constructions and it inherits the conventional MACs resistance to forgeries. Furthermore, the NTMAC gives an indication of the number and locations of the errors.

The CRC–NTMAC for Noisy Message Authentication

The paper introduces a novel message authentication code based on the recently proposed NTMAC structure, called CRC-NTMAC, for noisy message authentication. As with the NTMAC, the CRC-NTMAC can tolerate a small number of errors, which might be caused by a noisy communication channel. The CRC-NTMAC replaces the truncated conventional MACs by cyclic redundancy check (CRC) codes in its constructions as the sub-MACs. This modification helps the CRC-NTMAC obtain much lower false acceptance rates than the NTMAC. Security analysis under a chosen message attack is also developed to verify the security of the proposed CRC-NTMAC.

Frequency analysis and synthesis of a class of nonlinear filters

Nonlinear filters are analyzed from a spectral point of view. The equivalent frequency behavior of a filter is described by its linear part, which represents the linear nonrecursive filter, that best matches, in the mean-square sense, the behavior of the filter. The class considered includes all the order statistic filters (L-filters) such as median, midrange, alpha-trim, and some new order statistic filters (Ll-filters) defined by the authors to generalize L-filters and FIR filters. The formulation leads to a technique for imposing on the nonlinear filters a given spectral behavior. A simulation of the design for a low-pass Ll-filter is given. >

BACIC: a new method for lossless bi-level and grayscale image compression

BACIC is a new method of lossless bi-level image compression introduced to replace JBIG and G3, the current standards for bi-level and facsimile image compression. This paper applies the BACIC (block arithmetic coding for image compression) algorithm to reduced grayscale and full grayscale image compression. BACICs compressed files are slightly smaller than JBIGs, twice as small as G3s, and at least thirty percent smaller than lossless-JPEGs (when lossless JPEG uses Huffman coding) for reduced grayscale images with fewer than 7 bits/pixel.

Lossless Compression-Based Steganalysis of LSB Embedded Images

A new method of steganalysis for images with embedded messages is presented. We consider two embedding methods: least significant bit (LSB) replacement and plusmn1 LSB embedding. Our method uses lossless image compression to generate statistics that are fed into a support vector machine classifier. We compare results against the pairs method, one of the best existing LSB steganalysis methods. Both our method and pairs performs well for LSB replacement. However, while pairs cannot detect plusmn1 LSB embedding at all, our method can.

Lossless Image Compression with BCTW

We present a new lossless image compression algorithm called BCTW, for bitplane context tree weighting, and a corresponding study into lossless image compression using several number representations and various algorithms. BCTW processes the image bitplane by bitplane and uses context tree weighting (CTW) to estimate the probability of each pixel bit being a 1 or 0. The bit is then compressed with an entropy coder, most likely an arithmetic coder. BCTW is a very good lossless image compressor. In the study, we also look at several number representations (twos-complement, Gray coding, and sign-magnitude) and compare BCTW to MedBzip2 and JPEG-LS. On the Waterloo Bragzone GreySet2 dataset, BCTW outperforms JPEG-LS by 13% and MedBzip2 by 5%. We find that representing the pixels in a Gray code does not help. Sign-magnitude helps sometimes, but not in BCTW. The MED transform helps bzip2, but not BCTW.

Image authentication and tamperproofing for noisy channels

We present a new method for authenticating and tamperproofing images. It is based on the recently developed NT-MAC (noise tolerant message authentication code). The NTMAC is designed for multimedia transmitted over noisy channels. Unlike ordinary cryptographic codes, the NT-MAC fails gradually in the presence of noise or bit errors. In this work, we show how a combination of structural and random partitions allows the NTMAC to identify regions which might represent forgeries while distinguishing between forgeries and minor errors caused by communications noise. The paper concludes with a simple example of a forged image and the NTMACs estimate of the changes.