Amiga Halfbrite mode

Extra Half Brite (also referred to as Extra-Half-Brite, Extra-Halfbrite, or EHB), is a planar display mode of the Amiga computer.

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