Amiga Halfbrite mode

Extra Half Brite (also referred to as Extra-Half-Brite or Extra-Halfbrite), usually abbreviated as EHB,[1][2][3][4] is a planar display mode of the Amiga computer.

Normal 32 color mode picture
Fragment of normal 32 color (left) vs. Extra Half Brite 64 color picture (right)
Extra Half Brite 64 color mode picture

This mode uses six bitplanes (six bits/pixel).[3][5][6] The first five bitplanes index 32 colors selected from a 12-bit color space (4096 possible colors). If the bit on the sixth bitplane is set, the display hardware halves the brightness of the corresponding color component.[7] This way 64 simultaneous colors are possible (32 arbitrary colors plus 32 half-bright components) while only using 32 color registers.[8] The number of color registers is a hardware limitation of pre-AGA chipsets used in Amiga computers.

Some contemporary game titles (Fusion,[9] Defender of the Crown[10], Agony,[11] Lotus II[12] or Unreal[13]) and animations (HalfBrite Hill[4]) used EHB mode as a hardware-assisted means to display shadows or silhouettes.[9][14] EHB was also often used as general-purpose 64 color mode with the aforementioned restrictions.[9][15][16][17]

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.[4][2]

See also

References
  1. Mortimore, Eugene P. (1986). Amiga Programmer's Handbook. SYBEX. ISBN 978-0-89588-343-8.
  2. Maher, Jimmy (2018-01-26). The Future Was Here: The Commodore Amiga. MIT Press. ISBN 978-0-262-53569-4.
  3. "Amiga® Hardware Reference Manual: Color Selection in Extra Half Brite (EHB) Mode". Amiga Developer Docs. Retrieved 2022-11-19.
  4. Sullivan, Kevin (1987). "HalfBrite Hill". Amiga Animations. Blair-Sullivan Computer Graphics & Animation. Retrieved 2022-11-19.
  5. "The Atari ST and Amiga computing evolution!". Retroshowcase: oldschool game reference!. Retrieved 2022-11-19.
  6. Peddie, Jon (8 June 2022). "Amiga (1988)". IEEE Computer Society. Retrieved 2022-11-19.
  7. Maher, Jimmy (2018-01-26). The Future Was Here: The Commodore Amiga. MIT Press. ISBN 978-0-262-53569-4.
  8. Amiga ROM Kernel Reference Manual: Libraries. Addison-Wesley. 1992. ISBN 978-0-201-56774-8.
  9. "Extra Half Bright (EHB)". Amiga Graphics Archive. Retrieved 2022-11-19.
  10. "Defender of the Crown - Castle Norman - Amiga Graphics Archive". amiga.lychesis.net. Retrieved 2023-04-12.
  11. "Agony - Loader 1 - Amiga Graphics Archive". amiga.lychesis.net. Retrieved 2023-04-12.
  12. "Lotus 2 - Level 1 - Forest - Amiga Graphics Archive". amiga.lychesis.net. Retrieved 2023-04-12.
  13. "Unreal - Amiga Graphics Archive". amiga.lychesis.net. Retrieved 2023-04-12.
  14. "Enhanced Graphics - Extra Half-Brite (EHB) Mode". Hall Of Light - The database of Amiga games. Retrieved 2023-04-12.
  15. "EHB images". Amiga Graphics Archive. Retrieved 19 September 2011.
  16. Compute. Vol. 11. Small System Services. 1989. pp. 44, 53.
  17. Kroah (2020). "The Bard's Tale serie - Bard's Tale Construction Set". Kroah's Game Reverse Engineering Page. Retrieved 2022-11-19.
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