biWidth

biWidth is a field in Windows bitmap information headers that stores the width of an image in pixels. It is part of structures used to describe bitmap data, such as BITMAPINFOHEADER and related headers, and is defined as a 32-bit signed integer (LONG).

In the Windows BMP and DIB formats, biWidth specifies how many horizontal pixels the image contains. The width is independent of the image’s height, which is described by biHeight. The height field can be positive or negative to indicate the scanline order (bottom-up for positive heights, top-down for negative heights); the sign of biWidth is generally not used to indicate orientation.

biWidth works together with biBitCount and other header fields to determine the memory layout of the pixel data. The width, together with the bits per pixel, determines how many bytes each scanline must contain, including padding. A common rule is that the number of bytes per scanline is ((biWidth * biBitCount + 31) / 32) * 4, ensuring each row starts at a 4-byte boundary. This padding is essential for correctly reading or writing bitmap data across different platforms and libraries.

Practical usage of biWidth includes image creation, loading, and rendering. When manipulating raw bitmap data, developers rely on biWidth to compute pointers to pixel data and to allocate buffers. The field is defined in standard Windows headers and remains a fundamental descriptor across various GDI, GDI+ and Windows Imaging Component workflows.

Notes: while biWidth is the width, other fields such as biClrUsed and biSizeImage influence color data and overall image size. In most contexts, biWidth is treated as a nonnegative value representing pixels.