Bitmap

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In computing, a bitmap (also called raster) graphic is an image formed from rows of different colored pixels.^[1] A GIF is an example of a graphics image file that uses a bitmap.^[2]

As a noun, the term "bitmap" is very often used to refer to a particular bitmapping application: the pix-map, which refers to a map of pixels, where each pixel may store more than two colors, thus using more than one bit per pixel. In such a case, the domain in question is the array of pixels which constitute a digital graphic output device (a screen or monitor). In some contexts, the term bitmap implies one bit per pixel, whereas pixmap is used for images with multiple bits per pixel.^[3][4]

A bitmap is a type of

For an uncompressed, packed within rows, bitmap, such as is stored in Microsoft DIB or BMP file format, or in uncompressed TIFF format, a lower bound on storage size for a n-bit-per-pixel (2ⁿ colors) bitmap, in bytes, can be calculated as:

${\displaystyle {\text{size}}={\text{width}}\cdot {\text{height}}\cdot n/8}$

where width and height are given in pixels.

In the formula above, header size and color palette size, if any, are not included. Due to effects of row padding to align each row start to a storage unit boundary such as a word, additional bytes may be needed.

Device-independent bitmaps and BMP file format

Microsoft has defined a particular representation of color bitmaps of different color depths, as an aid to exchanging bitmaps between devices and applications with a variety of internal representations. They called these device-independent bitmaps as DIBs, and the file format for them is called DIB file format or BMP file format. According to Microsoft support:^[6]

A device-independent bitmap (DIB) is a format used to define device-independent bitmaps in various

color resolutions

. The main purpose of DIBs is to allow bitmaps to be moved from one device to another (hence, the device-independent part of the name). A DIB is an external format, in contrast to a device-dependent bitmap, which appears in the system as a bitmap object (created by an application...). A DIB is normally transported in metafiles (usually using the StretchDIBits() function), BMP files, and the Clipboard (CF_DIB data format).

Here, "device independent" refers to the format, or storage arrangement, and should not be confused with device-independent color.

Other bitmap file formats

The

There are also a variety of "raw" image files, which store raw bitmaps with no other information; such raw files are just bitmaps in files, often with no header or size information (they are distinct from photographic raw image formats, which store raw unprocessed sensor data in a structured container such as TIFF format along with extensive image metadata).

See also

• Free space bitmap
  , an array of bits that tracks which disk storage blocks are in-use
• Raster graphics
• Raster scan
• Rasterization
• Sprite (computer graphics)
• Voxels
• Vector graphics
• Image tracing

References