DUO

"DUO" is a set of similar graphics formats for the Atari computers with unknown origin. The original name, if anything, is unknown.

Identification
Files are exactly 113600 bytes long.

From the AtariForumWiki page: DUO   *.DU1 *.DUO (low resolution) *.DU2      (medium resolution)

Created by Anders Eriksson: http://ae.dhs.nu/ These are essentially 2 screens with over-scan interlaced together.

Low resolution files are 416x273 pixels:

16 words      palette 56784 bytes   screen 1 56784 bytes   screen 2 --- 113600 bytes  total

Medium resolution files are 832x273 pixels:

4 words       palette 56784 bytes   screen 1 56784 bytes   screen 2 24 bytes      padding if present, otherwise total size is 113576 bytes --- 113600 bytes  total

Both screens use the same palette, but when viewed the human eye merges the two alternating images into one.

Software

 * RECOIL
 * abydos

Sample files

 * https://telparia.com/fileFormatSamples/image/duStar/

Links

 * https://web.archive.org/web/20191221202304/http://www.atari-wiki.com/index.php/DUO_file_format