Thanks for the comments Gents.
Need more time on this.
Allan, anyone else, here are two stacked lrgb fits files, one in lab and one in rgb. They're 99MB each though.
https://www.dropbox.com/sh/eg8w74f20...DxQvKE2ha?dl=0
The lab colour file is still uploading, should be done in 11mins.
Cheers
Alistair