ARGB1555

ARGB1555 is a 16‑bit color pixel format in which the most significant bit represents the alpha channel, followed by five bits each for red, green, and blue. The format is also called RGB1555 when the alpha component is omitted. Because only five bits per color component are stored, the maximum intensity for each is 31 instead of 255. The alpha value is either 0 (fully transparent) or 1 (fully opaque), so the format is mostly used where simple, binary transparency suffices, such as early handheld gaming consoles and mobile device displays.

The layout of the 16 bits is typically: A RRRRR GGGGG BBBBB. For example, the color white with full opacity is represented as 1 11111 11111 11111 (hex 0xFFFF). Since the alpha is a single bit, the format cannot encode partial transparency; it is therefore unsuitable for modern alpha‑blended compositing but remains attractive for its storage efficiency.

Historical devices that exploited ARGB1555 include the Sharp X68000, the NEC PC‑Engine, and some early Sony PSP homebrew frameworks. Modern graphic libraries still expose the format as a way to pack color data into a 16‑bit buffer for embedded systems or memory‑constrained environments. Conversions between ARGB1555 and 24‑bit or 32‑bit formats are performed by expanding each 5‑bit component to 8 bits, typically by scaling or by bit replication (e.g., multiplying by 255/31).

Compared with packed 16‑bit RGB565, ARGB1555 saves two bits to provide binary transparency, at the cost of one less brightness resolution per channel. It is thus a compromise between memory footprint and color fidelity that found frequent use in early portable consoles and simple GUIs.