5 Image compression

Astronomical image compression in the context of ALADIN has been discussed in detail by Louys et al. ([1999]).

For the ALADIN Java interface and for the ALADIN previewer, the current choice has been to deliver to the user an image in JPEG 8-bit format, constructed from the original FITS images. JPEG is a general purpose standard which is supported by all current Internet browsers. The size of such an image does not exceed 30 kBytes, and thus the corresponding network load is very small.

In the near future, the Pyramidal Median Transform (PMT) algorithm, implemented in the MR-1 package (Starck et al. [1996]), will be used within ALADIN for storing or transferring new image datasets, such as additional high resolution images (see again Louys et al. [1999] for details). The corresponding decompression package is being written in Java code, and could be downloaded on request for use within the Java interface.