Compression and Progressive Transmission of Astronomical Images
**Previous
abstract** **Next
abstract**

**Session 115 -- WGAS**
*Oral presentation, Thursday, 12, 1995, 10:00am - 11:30am*

## [115.04] Compression and Progressive Transmission of Astronomical Images

*R. L. White (STScI), J. W. Percival (U.Wisconsin)*

An image compression algorithm has been developed that is well-suited
to astronomical images. The method has 3 steps: an intensity mapping
to generate an image that has roughly constant noise in each pixel, an
orthonormal wavelet transform, and quadtree coding of the bit-planes of
the wavelet coefficients. The quadtree values may be further
compressed by any standard compression technique, such as Huffman or
arithmetic coding. If the 2-dimensional Haar transform is used, the
calculations can be carried out using integer arithmetic, and the
method can be used for both lossy and lossless compression. The Haar
transform basis functions are well-suited to most astronomical images
because they are highly localized. The performance of the algorithm
using smoother, longer range wavelets has also been explored; they can give
slightly better lossy compression at the cost of an increase in
artifacts around point sources, but they are not effective for lossless
compression using this scheme. The algorithm using Haar transforms
is being used for compression of the STScI Digitized Sky Survey now
being distributed on CD-ROMs.

This technique has been used as the basis of a progressive image
transmission system that can be used for either remote observing or
access to remote image archives. After less than 1\% of the data have
been received, the image is visually similar to the original, so it is
possible to assess the quality of images very quickly. If necessary,
the entire compressed data set can be sent so that the original image
is recovered exactly. J.~Percival describes the remote observing
system in an accompanying paper.

**Thursday
program listing**