bitmapInfo

BITMAPINFO is a Windows GDI data structure used to describe the dimensions, color format, and color table of a device-independent bitmap (DIB) or a Windows BMP image. It pairs a header with an optional color table and is passed to various GDI routines to specify how pixel data should be interpreted.

The structure consists of two parts: bmiHeader, a BITMAPINFOHEADER that defines fields such as biSize, biWidth, biHeight, biPlanes, biBitCount, biCompression, biSizeImage, biXPelsPerMeter, biYPelsPerMeter, biClrUsed, and biClrImportant; and bmiColors, an array of RGBQUAD structures that form the color palette. The color table is required for paletted image formats (1, 4, or 8 bits per pixel) and contains 2^biBitCount entries (each RGBQUAD). For true color formats (24-bit and 32-bit with BI_RGB, BI_BITFIELDS, etc.), the color table is not used. In C, BITMAPINFO is declared with bmiColors[1] as a flexible tail, and actual memory allocation includes space for the needed number of palette entries.

BITMAPINFO is used with functions such as GetDIBits, SetDIBits, and CreateDIBSection to retrieve, create, or manipulate pixel data. The biHeight field also indicates orientation: a positive value denotes a bottom-up DIB, while a negative value indicates a top-down DIB. The structure is frequently paired with a BITMAPINFOHEADER in BMP file parsing and in memory representations of DIBs within Windows applications.