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{{refimprove|date=April 2024}}
{{Other uses}}
{{Short description|Computing term}}
{{Use American English|date=September 2022}}

In [[computing]], a '''bitmap''' (also called '''raster''') graphic is an image formed from rows of different colored [[pixel]]s.<ref>{{cite web |date=September 22, 2023 |title=ARCHIVED: What are bitmap and vector graphics, and how are they different |url=https://kb.iu.edu/d/afmr |url-status=live |archive-url=https://alightmotionproapks.com |archive-date=April 21, 2024 |access-date=April 21, 2024 |publisher=University Information Technology Servivces |language=en-US}}</ref> A [[GIF]] is an example of a graphics image file that uses a bitmap.<ref>{{cite encyclopedia|url=https://www.britannica.com/technology/bitmap|title=bitmap|encyclopedia=[[Encyclopædia Britannica]]|author=Gregersen, Erik|language=en-GB|url-status=live|date=January 26, 2022|access-date=April 21, 2024|archive-date=April 21, 2024 |archive-url=https://archive.today/20240421072042/https://www.britannica.com/technology/bitmap}}</ref>

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 [[pixel]]s, 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.<ref>{{cite book |author=James D. Foley |url=https://books.google.com/books?id=A4k29b0BdVMC&q=bitmap+pix+map+%22short+for+pixel+map%22&pg=PA13 |title=Computer Graphics: Principles and Practice |publisher=Addison-Wesley Professional |year=1995 |isbn=0-201-84840-6 |pages=13 |quote=The term bitmap, strictly speaking, applies only to 1-bit-per-pixel bilevel systems; for multiple-bit-per-pixel systems, we use the more general term pix-map (short for pixel map).}}</ref><ref>{{cite book |title= Comprehensive Computer Graphics: Including C++ |author= V.K. Pachghare |publisher= Laxmi Publications |pages= 93 |year= 2005 |isbn= 81-7008-185-8 |url= https://books.google.com/books?id=xIKK9RcSTR4C&q=bitmap+pixmap+one-bit+date:2004-2007&pg=PA93}}</ref>

A bitmap is a type of [[computer storage|memory]] organization or [[image file format]] used to store [[digital image]]s. The term ''bitmap'' comes from the [[computer programming]] terminology, meaning just a ''map of bits'', a spatially mapped [[bit array|array of bits]]. Now, along with ''pixmap'', it commonly refers to the similar concept of a spatially mapped array of pixels. [[Raster graphics|Raster]] images in general may be referred to as bitmaps or pixmaps, whether synthetic or photographic, in files or memory.

Many [[graphical user interface]]s use bitmaps in their built-in graphics subsystems.<ref>{{cite book |title= Cross-Platform GUI Programming with Wxwidgets |author1=Julian Smart |author2=Stefan Csomor |author3=Kevin Hock |name-list-style=amp |url= https://books.google.com/books?id=CyMsvtgnq0QC&q=bitmap+pixmap+gui&pg=PA265 |publisher= Prentice Hall |year= 2006 |isbn= 0-13-147381-6}}</ref> For example, the [[Microsoft Windows]] and [[OS/2]] platforms' [[Graphics Device Interface|GDI]] subsystem uses the ''Windows and OS/2 bitmap file format'', usually named with the [[file extension]] <code>.BMP</code> (or <code>.DIB</code> for ''device-independent bitmap''). Besides [[BMP file format|BMP]], other file formats that store literal bitmaps include [[ILBM|InterLeaved Bitmap (ILBM)]], [[Portable pixmap|Portable Bitmap (PBM)]], [[X BitMap|X Bitmap (XBM)]], and [[Wireless Application Protocol Bitmap Format|Wireless Application Protocol Bitmap (WBMP)]]<!-- please keep this list short; detailed list should be below -->. Similarly, most other image file formats, such as [[JPEG]], [[TIFF]], [[Portable Network Graphics|PNG]], and GIF, also store bitmap images (as opposed to [[vector graphics]]), but they are not usually referred to as ''bitmaps'', since they use [[Image compression|compressed]] formats internally.

==Pixel storage==
In typical [[image compression|uncompressed]] bitmaps, image [[pixel]]s are generally stored with a variable number of bits per pixel which identify its color (the [[color depth]]). Pixels of 8 bits and fewer can represent either [[grayscale]] or [[indexed color]]. An [[alpha channel]] (for [[transparency (graphic)|transparency]]) may be stored in a separate bitmap, where it is similar to a grayscale bitmap, or in a fourth channel that, for example, converts 24-bit images to 32 bits per pixel.

The bits representing the bitmap pixels may be [[packed]] or unpacked (spaced out to byte or word boundaries), depending on the format or device requirements. Depending on the color depth, a pixel in the picture will occupy at least ''n''/8 bytes, where {{Var|n}} is the bit depth.

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 (2<sup>n</sup> colors) bitmap, in [[byte]]s, can be calculated as:
:<math>\text{size} = \text{width} \cdot \text{height} \cdot n/8</math>
where width and height are given in pixels.

In the formula above, header size and [[Palette (computing)|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 (computer architecture)|word]], additional bytes may be needed.

==Device-independent bitmaps and BMP file format==
{{Main|BMP file format}}

Microsoft has defined a particular representation of color bitmaps of different [[color depth]]s, as an aid to exchanging bitmaps between devices and applications with a variety of internal representations. They called these device-independent bitmaps "DIBs", and the file format for them is called DIB file format or [[BMP file format]]. According to Microsoft support:<ref name=DIBhelp>{{cite web |url= http://support.microsoft.com/kb/q81498/ |title= DIBs and Their Uses |work= Microsoft Help and Support |date= 2005-02-11}}</ref>

<blockquote>
A device-independent bitmap (DIB) is a format used to define device-independent bitmaps in various [[color resolution]]s. 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).
</blockquote>

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

===Other bitmap file formats===
{{Main|Image file formats}}

The [[X Window System]] uses a similar [[X Bitmap|XBM]] format for [[black-and-white]] images, and [[X PixMap|XPM]] (''pixelmap'') for color images. Numerous other uncompressed bitmap file formats are in use, though most not widely.<ref>{{cite web |url= http://www.file-extensions.org/filetype/extensions/name/Bitmap+image/
 |title= List of bitmap file types |work= File-Extensions.org}}</ref> For most purposes, standardized compressed bitmap files such as [[GIF]], [[Portable Network Graphics|PNG]], [[TIFF]], and [[JPEG]] are used. [[Lossless compression]] in particular provides the same information as a bitmap in a smaller file size.<ref>{{cite book |title= Communicating Science Effectively: a practical handbook for integrating visual elements |author1=J. Thomas |author2=A. Jones |publisher= IWA Publishing |year= 2006 |isbn= 1-84339-125-2 |url= https://books.google.com/books?id=xrgkojGgwDYC&q=gif+png+tiff+jpeg+common&pg=PA26}}</ref> TIFF and JPEG have various options. JPEG is usually [[lossy compression]]. TIFF is usually either uncompressed, or lossless [[Lempel–Ziv–Welch]] compressed like [[GIF]]. PNG uses [[deflate]] lossless compression, another [[Lempel-Ziv]] variant.

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 format]]s, 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==
{{Reflist}}

{{Compression formats}}

{{Authority control}}

[[Category:Bit data structures|Map]]
[[Category:Graphics file formats]]

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[[es:Gráfico rasterizado]]
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