Amiga Halfbrite mode

Extra Half-Brite,[1][2] usually abbreviated as EHB, is a planar display mode of the Amiga computer.

Normal 32 color mode picture
Extra Half-Brite 64 color mode picture

This mode uses six bitplanes (six bits/pixel).[3][4][5] 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.[6] This way 64 simultaneous colors are possible (32 arbitrary colors plus 32 half-bright components) while only using 32 color registers.[7] The number of color registers is a hardware limitation of pre-AGA chipsets used in Amiga computers.

Some contemporary game titles and animations used EHB mode as a hardware-assisted means to display shadows or silhouettes.[8] EHB was also often used as general-purpose 64 color mode with the aforementioned restrictions.[8][9][10][11]

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.[12][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. "The Atari ST and Amiga computing evolution!". Retroshowcase: oldschool game reference!. Retrieved 2022-11-19.
  5. Peddie, Jon. "Amiga (1988)". IEEE Computer Society. Retrieved 2022-11-19.
  6. Maher, Jimmy (2018-01-26). The Future Was Here: The Commodore Amiga. MIT Press. ISBN 978-0-262-53569-4.
  7. Amiga ROM Kernel Reference Manual: Libraries. Addison-Wesley. 1992. ISBN 978-0-201-56774-8.
  8. "Extra Half Bright (EHB)". Amiga Graphics Archive. Retrieved 2022-11-19.
  9. "EHB images". Amiga Graphics Archive. Retrieved 19 September 2011.
  10. Compute. Vol. 11. Small System Services. 1989. pp. 44, 53.
  11. Kroah (2020). "The Bard's Tale serie - Bard's Tale Construction Set". Kroah's Game Reverse Engineering Page. Retrieved 2022-11-19.
  12. Sullivan, Kevin (1987). "HalfBrite Hill". Amiga Animations. Blair-Sullivan Computer Graphics & Animation. Retrieved 2022-11-19.
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