This was painted for the cover of Myths and Legends of King Arthur and the Knights of the Round Table, a musical evocation of their life and times by Rick Wakeman. 
This image is now available as an open edition print.
These prints produced on museum quality paper with archival  ink.
They are an open edition but with 250 signed by the artist Roger Dean.
The print dimensions are;
Paper size (A2) 593 x 417mm
Image size 554 x 368mm
Paper Somerset Velvet 330gsm