RGBA4

RGBA4 is a color encoding format used in computer graphics and digital imaging to represent colors using four components: red, green, blue, and alpha (transparency). It is a variant of the more common RGBA8 format, where each color channel is stored with fewer bits of precision.

In RGBA4, each of the red, green, and blue channels is represented with 4 bits, while the alpha channel also uses 4 bits. This results in a total of 16 bits per pixel (4 bits × 4 channels), allowing for 16 distinct values per channel. The values for each channel range from 0 to 15, which can be interpreted as normalized values between 0.0 and 1.0 by dividing by 15. This format is often used in legacy graphics systems, such as older versions of DirectX and OpenGL, as well as in certain mobile or embedded platforms where memory efficiency is critical.

The reduced bit depth in RGBA4 means that color representation is less precise compared to formats like RGBA8, which uses 8 bits per channel. This can lead to noticeable color banding, particularly in gradients or smooth transitions between colors. Despite this limitation, RGBA4 remains useful in scenarios where memory usage and computational efficiency are prioritized over color fidelity.

RGBA4 is sometimes referred to as "16-bit color" or "high color" in older terminology, though it does not fully match the traditional definition of high color, which typically refers to formats with 16 bits per channel (e.g., RGB565A). The format is rarely used in modern applications due to advancements in hardware and software that favor higher bit depths for better visual quality.