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Images are generally stored with a color depth of 2 (1-bit), 16 (4-bit), 256 (8-bit), 65,536 (16-bit), or 16.7 million (24-bit). An alpha channel (for transparency) may be stored in a separate file, where it is similar to a greyscale image. 8-bit images can also be greyscale instead of color.

BMP files are usually not compressed, so they are typically much larger than compressed image file formats for the same image. The typical true-color bitmap size in byteThis article refers to the unit of binary information. Byte was also the name of a popular computer industry magazine, see Byte magazine. A byte is commonly used as a unit of storage measurement in computers, regardless of the type of data being stored.s can be calculated as: (width in pixelA pixel (a contraction of picture element is one of the many tiny dots that make up the representation of a picture in a computer's memory. Usually the dots are so small and so numerous that, when printed on paper or displayed on a computer monitor, theys)×(height in pixels)×3. So an 800×600 image will occupy almost 1.5 megabyteA megabyte is a unit of measurement for computer storage, memory and information; while its exact definition varies, it is in theory equal to one million bytes. The symbol for megabyte is MB (note B for Byte, lowercase b would mean bit). Three definitionss. As such they are generally unsuitable for transferring images on the InternetThis article is about the Internet the extensive, worldwide computer network available to the public. An internet is a more general term for a set of interconnected computer networks that are connected by internetworking''. WWW information network structu or other slow or capacity-limited media. Compressed imaged employ RLERun-length encoding (RLE is a very simple form of data compression in which runs of data (that is, sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original ru algorithm.

Nevertheless, the simplicity of BMP and its widespread familiarity in MS Windows and elsewhere, as well as the fact that this format is well- documentedIn general terms, documentation is any communicable material (such as text, video, audio, etc. or combinations thereof) used to explain some attributes of an object, system or procedure. It is often used to mean engineering or software documentation, whic and free of patentA patent is a set of exclusive rights granted by a government to an inventor or applicant for a limited amount of time (normally 20 years from the filing date). The term "patent" originates from the term patere which means to lay open (to public inspectios, makes it a very common format that image processing programs from many operating systems can read and write.

The X Window System uses a similar .XBM format for true single- bit black and white images, and .XPM (pixelmap) for color images. There is also a .RAW format, which saves raw data with no other information. The Portable Pixmap file format (.PPM) and Truevision TGA (.TGA) formats also exist, but are rarely used. Yet other formats store as "bitmaps" (as opposed to vector graphics), but use compression or color index es, and thus are not strictly considered true bitmaps.