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bitmap format (file format) (BMP)

Bitmap(BMP) is a pixel-oriented file format for raster graphics that corresponds to the physical appearance of information. Bitmap files can be uncompressed or compressed with lossless run-length encoding( RLE).

The file format offers B/W representations, grayscale or color representations according to the RGB color model. The three color channels have a color depth of 16 bits each, but there is no alpha channel for transparent representations. The maximum file size is 32,000 x 32,000 pixels.

Characteristics of bitmap files

Characteristics of bitmap files

Bitmap files are images consisting of individual pixels arranged in a row. Each individual pixel, of the image resolved into columns and rows, has its own RGB values.

Structure of the bitmap file format

Structure of the bitmap file format

The file format of the bitmap files consists of the header with the file header, the bitmap header, the color palette and the bitmap data. The file header is a 14-bytedata field containing the file identification and the file size. The file header is followed by the bitmap header with a length of 108 bytes. It contains the data for the graphic size in pixels for the width and height, the number of color palettes and the color depth. It also includes information about compression, the size of the stored bitmap in bytes and the colors used. The following optional data field is the color palette, which is only present for color depths of 1, 4 and 8 bits. This data field is followed by the bitmap data field with the color values for each pixel. The color values are listed from bottom left to top right.

Pixel representation of a 4x4 pixel graphic in original size and enlarged

Pixel representation of a 4x4 pixel graphic in original size and enlarged

Bitmap was originally developed for Windows. This original version is called Device Dependent Bitmap( DDB) and, as the name implies, is device dependent. The later version was device independent and is therefore called Device Independent Bitmap( DIB). There is also Wireless Bitmap(WBMP) for mobile devices. This graphics format is for WML pages created with Wireless Markup Language (WML) and displayed on mobile devices.

The file extensions for bitmap files are *.bmp and *.dib.

Informations:
Englisch: bitmap format (file format) - BMP
Updated at: 22.01.2019
#Words: 341
Links: basic multilingual plane (BMP), file format, raster graphics, information, encoding
Translations: DE
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