XISF standard revision re: zstd?


Active member
I noted the mention in the 1.8.9-2 release notes that the zstd compressor has been added to the list of supported XISF compression algos in PixInsight, but it does not appear that the XISF definition document has been revised to reflect this. Will it be revised to add zstd to the list of existing algos? I put the XISF compression support into NINA some years ago and need to know if I should figure a way to add zstd as well now that it's already in a PixInsight release without much notice.
Zstandard compression, with and without byte shuffling, will be added to the XISF specification in a new version that we'll release soon. It's a nonstandard compression codec for now, but for all practical purposes, you can consider it part of the specification.

The compression block parameters are as follows for the Zstandard compression codec, without and with byte shuffling:


Note that these parameters have the same format and meaning as those used for zlib compression.

The compression algorithm that will be part of the XISF specification is the standard described by RFC 8878. Our implementation in PixInsight uses the zstd reference library.