Ever want to access the details of a JPEG image from Matlab? I wrote the Matlab JPEG Toolbox to do just this. The toolbox contains a number of routines for directly accessing the contents of JPEG files from Matlab, including the Discrete Cosine Transform (DCT) coefficients, quantization tables, Huffman coding tables, color space information, and comment markers and performing DCT block-based processing in Matlab. Two of the routines included in the toolbox, jpeg_read and jpeg_write, are basically Matlab MEX wrappers for the libjpeg library provided by the Independent JPEG Group. Pre-compiled MEX binaries for Windows are included in the toolbox, or you can download libjpeg and compile the mex routines yourself.

Steganography is the art of hiding information. There are many ways to hide information in images and other media, but to avoid detection by statistical means one must take care to avoid changing statistical properties of the cover media. Model-based steganography uses a statistical model of the cover media. An entropy decoder is used to convert uniformly distributed message bits into a set of changes which are distributed according to the model.