Amiga Halfbrite mode

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

This mode uses six bit planes (six bits per pixel).^[3][5][6] 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.^[7] This way 64 simultaneous colors are possible (32 arbitrary colors plus 32 half-bright components) while using only 32 color registers.^[8] The number of color registers is a hardware limitation of pre-AGA chipsets in Amiga computers.

Some contemporary games (Fusion,^[9] Defender of the Crown,^[10] Agony,^[11] Lotus II,^[12] or Unreal^[13]) and animations (HalfBrite Hill^[4]) use EHB mode as a hardware-assisted means to display shadows or silhouettes.^[9][14] EHB is often used as general-purpose 64 color mode with its own 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]