The folks behind Code Obsession, creators of Observatory, just put out some new plugins for Acorn to read FITS, XISF and SBIG images:
"Code Obsession’s Acorn Plugins add FITS, XISF and SBIG image support to Acorn. After installing the plugins, you can open any such image as easy as a JPEG or TIFF.
"Calibrate, align and stack your images in Observatory, export as 32 bits FITS, open in Acorn and start post-processing. Add layers, annotations, watermarks. The options are endless."
I wrote the plugin api to do this years ago, but except for a few small examples it was never really used. However, earlier this week Sander Berents from Code Obsession contacted me about it since Acorn's ability to save 64 and 128 bit images with non destructive filters (ie- curves and levels) was perfect for astronomical data. Acorn 5.6.5 was just about to go out and I made a couple of tweaks to the API for him, and that was that.