The BMP file format, sometimes called bitmap or DIB file format (device-independent bitmap), is an image file format used to store bitmap digital images, especially on Microsoft Windows and OS/2 operating systems.
Many older graphical user interfaces used bitmaps in their built-in graphics subsystems; for example, the Microsoft Windows and OS/2 platforms' GDI subsystem, where the specific format used is the Windows and OS/2 bitmap file format, usually named with the file extension of
.dib. In uncompressed BMP files, and many other bitmap file formats, image pixels are stored with a color depth of 1, 4, 8, 16, 24, or 32 bits per pixel (BPP). An alpha channel (for transparency) may be stored in a separate file, where it is similar to a grayscale image, or in a fourth channel that converts 24-bit images to 32 bits per pixel.
Uncompressed bitmap files (such as unindexed BMP) are typically much larger than compressed (with any of various methods) image file formats for the same image. Uncompressed formats are generally unsuitable for transferring images on the Internet or other slow or capacity-limited media.
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