Amiga Halfbrite mode explained

Extra Half Brite (also referred to as Extra-Half-Brite, Extra-Halfbrite, or EHB),^{[1] [2]} is a planar display mode of the Amiga computer.

This mode uses six bit planes (six bits per pixel).^{[3] [4] [5]} The first five bit planes index 32 colors selected from a 12-bit color space of 4096 possible colors. If the bit on the sixth bit plane is set, the display hardware halves the brightness of the corresponding color component.^[6] This way 64 simultaneous colors are possible (32 arbitrary colors plus 32 half-bright components) while using only 32 color registers.^[7] The number of color registers is a hardware limitation of pre-AGA chipsets in Amiga computers.

Some contemporary games (Fusion, Defender of the Crown,^[8] Agony,^[9] Lotus II,^[10] or Unreal^[11]) and animations (HalfBrite Hill) use EHB mode as a hardware-assisted means to display shadows or silhouettes.^{[12] [13]} EHB is often used as general-purpose 64 color mode with its own restrictions.^{[14] [15] [16]}

Some early versions of the first Amiga, the Amiga 1000, sold in the United States, lack the EHB video mode, which is present in all later Amiga models.^[17]

See also

• Original Chip Set
• Hold-And-Modify

External links

• Animated demo using Halfbrite mode (requires Java)
• Amiga Graphics Archive - Extra Half-Brite

Notes and References

1. Book: Mortimore, Eugene P. . Amiga Programmer's Handbook . 1986 . SYBEX . 978-0-89588-343-8 . en.
2. Book: Maher, Jimmy . The Future Was Here: The Commodore Amiga . January 26, 2018 . MIT Press . 978-0-262-53569-4 . en.
3. Web site: Amiga Hardware Reference Manual: Color Selection in Extra Half Brite (EHB) Mode . November 19, 2022 . Amiga Developer Docs.
4. Web site: The Atari ST and Amiga computing evolution! . November 19, 2022 . Retroshowcase: oldschool game reference!.
5. Web site: Peddie . Jon . Amiga (1988) . November 19, 2022 . IEEE Computer Society . June 8, 2022 . en-US.
6. Book: Maher, Jimmy . The Future Was Here: The Commodore Amiga . January 26, 2018 . MIT Press . 978-0-262-53569-4 . en.
7. Book: Amiga ROM Kernel Reference Manual: Libraries . 1992 . Addison-Wesley . 978-0-201-56774-8 . en.
8. Web site: Defender of the Crown - Castle Norman - Amiga Graphics Archive . April 12, 2023 . amiga.lychesis.net . en.
9. Web site: Agony - Loader 1 - Amiga Graphics Archive . April 12, 2023 . amiga.lychesis.net . en.
10. Web site: Lotus 2 - Level 1 - Forest - Amiga Graphics Archive . April 12, 2023 . amiga.lychesis.net . en.
11. Web site: Unreal - Amiga Graphics Archive . April 12, 2023 . amiga.lychesis.net . en.
12. Web site: Extra Half Bright (EHB) . November 19, 2022 . Amiga Graphics Archive.
13. Web site: Enhanced Graphics - Extra Half-Brite (EHB) Mode . April 12, 2023 . Hall Of Light - The database of Amiga games.
14. Web site: EHB images . September 19, 2011 . Amiga Graphics Archive.
15. Book: Compute . 1989 . Small System Services . 11 . 44,53 . en.
16. Web site: Kroah . 2020 . The Bard's Tale serie - Bard's Tale Construction Set . November 19, 2022 . Kroah's Game Reverse Engineering Page.
17. Web site: Sullivan . Kevin . 1987 . HalfBrite Hill . November 19, 2022 . Amiga Animations . Blair-Sullivan Computer Graphics & Animation.