RGBQUAD

RGBQUAD is a Windows GDI structure used to represent a color in a color table (palette) or in a device-independent bitmap (DIB) palette. It defines a single 32-bit color entry used by paletted bitmaps and by the bmiColors array in a BITMAPINFO structure.

The structure consists of four unsigned byte fields:

- rgbBlue

- rgbGreen

- rgbRed

- rgbReserved

The color components are stored in the order blue, green, red in memory, with the rgbReserved byte typically set to zero. This layout aligns with the little-endian representation used by Windows bitmaps.

Usage and context:

RGBQUAD is primarily used for 8-bit or lower-paletted DIBs, where the image data references color table indices. In such cases, the bitmap’s color table contains an array of RGBQUAD entries (often 256 entries for 8-bit images) that map palette indices to actual colors. In 24-bit or 32-bit bitmaps, color information is stored directly in the pixel data, and a color table of RGBQUAD entries is not used.

Implementation notes:

RGBQUAD is defined in Windows headers (for example, Wingdi.h) as a typedef of a struct with the four BYTE fields. The rgbReserved field is typically unused in standard paletted images, but it can be repurposed in some contexts. For reference, RGBTRIPLE is a related structure that stores only the B, G, and R components without a reserved byte.

See also: BITMAPINFO, BITMAPINFOHEADER, DIB, color table, RGBTRIPLE.