Wavelet movies are here!




EIT 195A wavelet movie from May 2002

We are pleased to announce the availability of LASCO C2 and EIT "wavelet" MPEG movies! We have a complete archive of LASCO C2 and EIT 195A, and are now in the final stages of creating our EIT 171A archive. Now you can view the LASCO and EIT images in a way that has never been seen before!

About wavelet movies

Solar physics data in the form of images present complex hierarchical structures. Coronagraph images (e.g. LASCO C2) show pseudo-static and dynamic structures apparently so rich in small scale details that are often misinterpreted or even missed with the use of straight-forward image processing techniques such as background ratio or running differences. Moreover, classical edge-enhancing operators may not be appropriate as they do not work efficiently due to the multiscale nature of coronal features. Something similar occurs with EUV images such as those taken with the EIT instrument. Therefore, multi-resolution approaches, i.e., those techniques where an image can be decomposed into its different components at different scales, are the right first step. The wavelet transform in particular presents considerable advantages compared to traditional methods. Among other things it is able to discriminate structures as a function of scale (size), and thus is able to detect, enhance, and eventually filter small scale structures embedded within larger scale features.

Following the approach presented in Stenborg & Cobelli, 2003 (A&A, Vol. 398, p. 1185-1193) , we treated with an improved algorithm the full field, full res (1024 x 1024) LASCO C2 level-05 images. The resulting product was then binned down to 512 x 512. A similar basic procedure was applied to the corresponding EIT full field, full res EIT 195A images, though the reconstruction scheme was rather different in order to both strengthen the slowly varying components while at the same time extending as far as possible the visibility of the meaningful signal.

As you can see below, the wavelet processing enhances features that are often less clear in our standard movies and image formats.
 
  BEFORE WAVELETS:  
  AFTER WAVELETS:  

The MPEG movies for the above images can be found at the following links:

How to obtain the wavelet movies

We currently offer a complete archive of C2 and EIT 195A, and soon to-be-completed archive of EIT 171A wavelet movies as MPEGs, here. These movies are ideal for browsing the collection, though may not be suitable for making scientific measurements or studies. For those using the "SolarSoft" IDL library, we have the wavelet archive available in the mvi format. People wishing to use the mvi data should contact the LASCO webmaster, making sure to include the words "LASCO wavelet movies" in the subject line

Acknowledgement

Development of the wavelet movie algorithms required a significant amount of effort by Dr. Guillermo Stenborg (SOHO-LASCO Operations Scientist/Catholic University of America). To that end, we ask that any use of the wavelet movies in research papers, publications and/or on websites be accompanied by the following acknowledgement:

"SOHO is a project of international cooperation between ESA and NASA. The LASCO and EIT images have been enhanced using a technique developed by Dr. Guillermo Stenborg."