Testing paletted JPEG 2000 images

[Jack Ireland]

It appears that including a color palette in a JPEG2000 image can significantly reduce the time taken to turn turn a JPEG2000 image into another image format (or intermediary product) that is used in the creation of screenshots and movies on Helioviewer.org. In addition, it appears that JHV ignores the color palette information in the JPEG2000 file when painting images in the viewing window. Therefore, on first blush, it appears that adding in a color table to all JPEG2000 files would increase the speed of hv.org and have no effect on the performance of JHV.

Clearly, changing all of our source JPEG2000 images to include color palettes must be thoroughly tested to ensure no untoward side-effects on the operation of JHV and HV.org. The first step would be to write out some paletted JPEG2000 images directly. This is possible in IDL. The second step would be to load in some of our existing JPEG2000 files, and write them out again with color palettes included. This is also possible in IDL. It would also be good to explore how to do this using SunPy/OpenJPEG. Thorough testing would be necessary before converting our existing archive of images to include color palettes, and improving JP2Gen to automatically include color palettes.