Caravian develops image models tailored for image compression. Our goal is to enhance the internet experience by cutting the time necessary to deliver graphical material over low speed connections. This page and its links provide detailed background material about some of the work underway at Caravian.
The Piecewise-Constant Image Model is designed for maximum compression of palette images. Palette images are also known as pseudo-color, lookup table, or reduced color images and are usually restricted to 256 or fewer colors. The PWC model is fairly mature with Embedded PWC Viewers available for Win32 versions of Internet Explorer. Technical Papers describing PWC and more detailed Evaluation Packages are available as well.
PWC is designed as a direct replacement for the Graphics Interchange Format (GIF) in internet graphic applications. It is a lossless compression technology that produces compressed files that average about 1/2 the size of equivalent GIF's. PWC compresses vector graphic type images particularly well. Large sparse images can compress to less than 1/10 the size achievable with GIF.
The PWC Embedded Image Viewer is available elsewhere on this site. Once it is installed, click here to view the images described in the 1998 Data Compression Conference paper entitled "Context Models for Palette Images".
The following technical papers have been published in refereed journals and conference proceedings. As such the copyright(s) for these papers are held by various technical organizations. Electronic copies of these papers have been made available online by their author. These copies are not to be redistributed without the express written consent of the copyright holder. Click here for a copy of the IEEE Copyright Notice . Unless otherwise specified, the papers are Microsoft Word 6.0 documents compressed with zip. To download, just right-click on a link and select Save Link/Target As...
"Context Models for Palette Images" , Proceedings Data Compression Conference, Snowbird Utah, Edited by James A. Storer and Martin Cohn, April 1998.
"Image Partition Boundary Coding" , Applications of Digital Image Processing XXI, Andrew G. Tescher Editor, Proceedings of the SPIE Vol, 3460, July 1998.
"A Streaming PWC Model" , Proceedings Data Compression Conference, Snowbird Utah, Edited by James A. Storer and Martin Cohn, April 1999.
"The Skip-Innovation Model for Sparse Images" , Proceedings Data Compression Conference, Snowbird Utah, Edited by James A. Storer and Martin Cohn, March 2000.
"The Piecewise-Constant Image Model" , Proceedings of the IEEE, Vol. 88, No. 11, November 2000, pp. 1779-1789.
These packages are not warranted for any particular purpose and are made available for evaluation purposes only. Unless otherwise specified, the packages are contained in zip archives. To download, just right-click on a link and select Save Link/Target As...
The PWC encoder/decoder evaluation package includes Win32 console codecs, a windowing image viewer and sample images.
The PWC fast streaming library evaluation package includes a Win32 object library and C++ header files.
The expanded image corpus described in the 1999 DCC paper is available here. The CCITT fax documents are in portable bitmap (pbm) format, palette images are in Windows bitmap (bmp) format, and grayscale images are in portable graymap (pgm) format. The images contained in the DCC call for papers, also mentioned in the 1999 DCC paper, are available here.
The vector graphic images referenced in the March 2000 DCC paper are available here.
We are working to apply piecewise methods to lossy image coding. The Piecewise-Smooth Image Model has significant promise for very low bitrate coding. Currently the model is limited to single component (grayscale) images. An evaluation package is available for machines running Microsoft Windows 9x/NT.
The Piecewise-Smooth Image model is described here. The description is outdated in that the boundary code currently used in PWS images is not a chain code but the same code used in PWC.
US5917953 "A Geometry Implicit Sampler for Polynomial Surfaces over Freeform Two-dimensional Domains"
US5956428 "Stroke Code for Image Partitions"
US6128417 "Image Partition Moment Operators".