Interactive Graphics Streams (IG or IGS) is the main graphics format for interactive menus in HDMV mode.

Interactive Graphics

Type of format	Graphics Format
First released	2006
Developer	Blu-ray Disc Association
Filename extension	None*
Limits	32 Streams
Open Format?	Yes
Free Format?	?
Magic Number	?

Interactive Graphics are displayed on its own independent layer on top of the Presentation Graphics; it is similar to Presentation Graphics (PG) used for subtitles (both layers are on top of the Primary Video). The graphics (along with its code, X-Y coordinates, and other data) are stored inside M2TS files, separated by ones used for video, audio, and subtitles. The graphics are decoded from the Blu-ray player's special graphics decoder. The max file size is 6 MB (48mbps) per M2TS file and can only use 32 streams. The max graphics memory buffer size is 16 MB in HDMV mode. Interactive Graphics are not available on BD-J mode as they are replaced with Java Graphics.

Interactive Graphics on top of the Primary Video

Features:  

•  It uses simple 8-bit colors and transparency (256 color palette), this is useful for simple graphics but complex ones like photos will cause dithering a la GIF.  

• Example of Dithering

   Unlike Java Graphics (PNG, JPEG), Interactive Graphics use simple animations: Fade In/Out, Color changing, Wipe In/Out, and Scrolling. Despite being simple, they take a lot of space in the graphics memory buffer.

•  It's resolution plane size supports 1920x1080/1280x720/720x480/720x576. 

•  Uses Run-length encoding, a simple compression method.

Interactive Graphics do not support true overlapping, but can be categorized into "Button Overlap Groups" (BOGs). Example: 0005.m2ts contains the graphics and code for the menu. A single BOG would contain 3 objects for a single button, Normal (not selected), Hover (selected), and Pressed.

BOG Example w/ 3 objects

0005 (IG stream) > 0000 (BOG) > 0000 (Object) 

0005_0000_0000 - Normal
0005_0000_0001 - Hover
0005_0000_0002 - Pressed

Interactive Graphics cannot be "opened" on a normal image program on a computer (it can't be demuxed with normal demuxing software), it must be opened by specialized Blu-ray editing software such as BDedit, BDReauthor, IGEditor, etc. Some of these programs can let you create the graphics using PNG or PSD files and then convert those files to IGS format and vice versa.

BDedit can edit IG and corresponding code

Footnotes

• *It doesn't use a file extension in a traditional sense. BD editing programs use other image formats and converts them to IG. Scenarist uses the .ies file format for import, export, and editing (doesn't contain any magic numbers).

Sources

• Scenarist BD Development manual, BD-ROM Whitepaper (2010), and original research.
• Blu-ray Disc Demystified
• BDedit 

Author(s) : Æ Firestone