15bit

15bit generally refers to a color depth used in digital images and video where each color channel is represented by 5 bits, typically yielding 2^15 or 32,768 distinct colors. It is most commonly called RGB555, with red, green, and blue each allocated five bits. In many systems, the 16-bit word used to store pixel data leaves the most significant bit unused or repurposed, for example as an alpha flag in ARGB1555 formats (which use 1 bit of alpha plus 5 bits per color, totaling 16 bits).

Encoding details vary by platform. In the standard RGB555 arrangement, color components range from 0 to 31 and are scaled to the full 8-bit-per-channel range when displayed. The exact bit order (which bits correspond to R, G, and B) can differ between hardware and software, and the unused bit may influence data alignment or alpha handling in some implementations. Some formats also store data as packed RGB in 16-bit words with different endianness.

History and usage. 15-bit color was common in older graphics hardware and displays, including certain VGA modes, early game consoles, and embedded systems where memory and bandwidth were limited. It has largely been superseded by 16-bit color (often RGB565) and, more broadly, by 24- or 32-bit true color in modern displays. Nevertheless, 15-bit color persists in legacy software and in some resource-constrained devices where it remains advantageous to save memory or bandwidth.

Limitations and considerations. The main drawback is reduced color resolution compared with higher bit-depth formats, which can lead to noticeable color banding. Converting to or from 24-bit color requires careful dithering or scaling to minimize artifacts.