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Encyclopedia > Bitmap
Windows Bitmap
File extension: .bmp or .dib
MIME type: image/x-ms-bmp (unofficial)
Type code: 'BMP '
Uniform Type Identifier: com.microsoft.bmp
Type of format: Raster graphics

In computer graphics, a bitmap or pixmap is a type of memory organization or image file format used to store digital images. The term bitmap comes from the computer programming terminology, meaning just a map of bits, a spatially mapped array of bits. Now, along with pixmap, it commonly refers to the similar concept of a spatially mapped array of pixels. Raster images in general may be referred to as bitmaps or pixmaps, whether synthetic or photographic, in files or in memory. Suppose the smiley face in the top left corner is an RGB bitmap image. ... A bit array (or bitmap, in some cases) is an array data structure which compactly stores individual bits (boolean values). ... A filename extension is a suffix to the name of a computer file applied to show its format. ... Multipurpose Internet Mail Extensions (MIME) is an Internet Standard that extends the format of e-mail to support: text in character sets other than US-ASCII; non-text attachments; multi-part message bodies; and header information in non-ASCII character sets. ... A type code is a mechanism used in pre-Mac OS X versions of the Macintosh operating system to denote a files format, in a manner similar to file extensions in other operating systems. ... A Uniform Type Identifier (UTI) is a string that uniquely identifies the type of a class of items. ... Suppose the smiley face in the top left corner is an RGB bitmap image. ... For the journal by ACM SIGGRAPH, see Computer Graphics (Publication). ... This article does not cite any references or sources. ... See also Category:Graphics file formats Here is a summary of the most common graphics file formats: Some file formats, e. ... A digital image is a representation of a two-dimensional image as a finite set of digital values, called picture elements or pixels. ... “Programming” redirects here. ... A bit array (or bitmap, in some cases) is an array data structure which compactly stores individual bits (boolean values). ... This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ... Suppose the smiley face in the top left corner is an RGB bitmap image. ...


In some contexts, the term bitmap implies one bit per pixel, while pixmap is used for images with multiple bits per pixel.[1][2]


Many graphical user interfaces use bitmaps in their built-in graphics subsystems;[3] 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 .BMP (or .DIB for device-independent bitmap). Besides BMP, other file formats that store literal bitmaps include InterLeaved Bitmap (ILBM), Portable Bitmap (PBM), X Bitmap (XBM), and Wireless Application Protocol Bitmap (WBMP). Most other image file formats, such as JPEG, TIFF, PNG, and GIF, to name just a few, also do ultimately store bitmap images (as opposed to vector images), but they are not as often called bitmaps, since they use compressed formats internally. A graphical user interface (GUI) is a type of user interface which allows people to interact with a computer and computer-controlled devices which employ graphical icons, visual indicators or special graphical elements called widgets, along with text labels or text navigation to represent the information and actions available to... Windows redirects here. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... GDI is short for Graphics Device Interface or Graphical Device Interface, and is one of the three core components or subsystems of Microsoft Windows. ... A filename extension or filename suffix is an extra set of (usually) alphanumeric characters that is appended to the end of a filename to allow computer users (as well as various pieces of software on the computer system) to quickly determine the type of data stored in the file. ... ILBM is a subtype of the Interchange File Format used for storing picture data. ... The portable pixmap file format (PPM), the portable graymap file format (PGM) and the portable bitmap file format (PBM) specify rules for exchanging graphics files. ... In computer graphics, the X Window System uses X BitMap (XBM), an ASCII text monochrome image format, for storing cursor and icon bitmaps used in the X GUI. XBM files differ markedly from most image files in that they take the form of C language source files. ... Wireless Application Protocol Bitmap Format (shortened to Wireless Bitmap and with file extension . ... JPG redirects here. ... This article is about TIFF, the computer image format. ... PNG may stand for: Persona non grata, literally meaning an unwelcome person, is a term used in diplomacy with a specialised and legally defined meaning. ... An example of a GIF image. ... Image compression is the application of Data compression on digital images. ...

Contents

Pixel storage

 uncompressed bitmaps such as are stored in BMP or DIB files, image pixels are generally stored with a color depth of 1, 4, 8, 16, or 24 bits per pixel. Images of 8 bits and fewer can be either greyscale or indexed color. An alpha channel (for transparency) may be stored in a separate file, where it is similar to a greyscale image, or in a fourth channel that converts 24-bit images to 32 bits per pixel. A 32-bit version of BMP with integrated alpha channel has been introduced with Windows XP and is used within its logon and theme system; it has yet to gain wide support in image editing software, but has been supported in Adobe Photoshop since version 7 and Adobe Flash since version MX 2004 (then known as Macromedia Flash). 

Uncompressed bitmap files (such as BMP) are typically much larger than compressed (with any of various methods) image file formats for the same image. For example, the 1058×1058 Wikipedia logo, which occupies about 287.65 KB in the PNG format, takes about 3281.5 KB as a 24-bit BMP file. Uncompressed formats are generally unsuitable for transferring images on the Internet or other slow or capacity-limited media. This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ... Color depth is a computer graphics term describing the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. ... Indexed color is a type of color space for digital images. ... In computer graphics, alpha compositing is often useful to render image elements in separate passes, and then combine the resulting multiple 2D images into a single, final image in a process called compositing. ... Transparency is possible in a number of graphics file formats. ... In computing, a grayscale or greyscale digital image is an image in which the value of each pixel is a single sample. ... Windows XP is a line of operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. ... Image editing encompasses the processes of altering images, whether they be digital photographs, traditional analog photographs, or illustrations. ... “Photoshop” redirects here. ... It has been suggested that this article be split into articles entitled Adobe Flash Player and Talk:Adobe Flash #Merger proposal, accessible from a disambiguation page. ... Image compression is the application of Data compression on digital images. ... Image File history File links Download high resolution version (1058x1058, 477 KB) aa Wikipedia logo, version 1058px square, no text Wikipedia logo by Nohat (concept by Paullusmagnus); compare Wikipedia File links The following pages link to this file: Arabic language Talk:Anarcho-capitalism Talk:Algorithm Talk:Anno Domini Talk:The... A kilobyte (derived from the SI prefix kilo-, meaning 1000) is a unit of information or computer storage equal to the decimal 1024 bytes (2 to the 10th power, or 1,024 bytes based in the binary system). ... PNG may stand for: Persona non grata, literally meaning an unwelcome person, is a term used in diplomacy with a specialised and legally defined meaning. ... A kilobyte (derived from the SI prefix kilo-, meaning 1000) is a unit of information or computer storage equal to the decimal 1024 bytes (2 to the 10th power, or 1,024 bytes based in the binary system). ...


The bits representing the bitmap pixels may be packed or unpacked (spaced out to byte or word boundaries), depending on the file format. Depending on the color depth, a pixel in the picture will occupy at least n/8 bytes (n is the bit depth, since 1 byte equals 8 bits). Data Structure Alignment is the way data is arranged and accessed in computer memory. ...


For a BMP (uncompressed, packed within rows) file, the approximate size for a n-bit (2n colors) bitmap in bytes can be calculated as: In computer science a byte (pronounced bite) is a unit of measurement of information storage, most often consisting of eight bits. ...


size of BMP file approx 54+4 cdot 2^n+frac{width cdot height cdot n}{8}, where height and width are given in pixels. A pixel (a contraction of picture element) is one of the many tiny dots that make up the representation of a picture in a computers memory. ...


In the formula above, 54 is the size of the header of the bitmap file. And 4 cdot 2^n is the size of the color palette. Notice that this is an approximation, as for an n-bit bitmap image, although there can be maximum 2n colors, a specific image may not use all of these colors. Since the color palette only defines the colors that are used by the image, the actual size of the color palette will be smaller than 4 cdot 2^n. Also, only 8-bit (or less) bitmaps use a palette. For 16-bit (or higher) bitmaps, omit the palette part from the size calculation: In information technology, Header refers to supplemental data placed at the beginning of a block of data being stored or transmitted, which contain information for the handling of the data block. ... A palette, in computer graphics, is a designated subset of the total range of colors supported by a computer graphics system. ...


size of BMP file approx 54+frac{width cdot height cdot n}{8}


Due to effects of dword padding (if the number of bytes matching a horizontal line in the image does not form multiple dwords, i.e. divisible by 4, null bytes are added), the term describing the raw image size is approximated and the calculated size will be slightly different from the actual file size. For detailed information, see the sections on file format below. In computer science, a dword is a unit of data that is twice the size of a word and half the size of a qword. ...


BMP file format

A typical BMP file usually contains the following blocks of data:

BMP Header Stores general information about the BMP file.
Bitmap Information Stores detailed information about the bitmap image.
Color Palette Stores the definition of the colors being used for indexed color bitmaps.
Bitmap Data Stores the actual image, pixel by pixel.

The following sections discuss the data stored in the BMP file in details. This is the standard BMP file format.[citation needed] Some bitmap images may be stored using a slightly different format, depending on the application that creates it. Also, not all fields are used; a value of 0 will be found in these unused fields.


BMP header

This block of bytes is added before the BMP format used internally by GDI and serves for identification. A typical application will read this block first to ensure that the file is actually a BMP file and that it is not damaged.

Offset# Size Purpose
0 2 Store the magic number used to identify the BMP file. Typical values for these 2 bytes are 0x42 0x4D (ASCII code points for B and M).
2 4 Store the size of the BMP file using a dword.
6 2 Reserved. Actual value depends on the application that creates the image.
8 2 Reserved. Actual value depends on the application that creates the image.
10 4 Store the offset, i.e. starting address, of the byte where the bitmap data can be found.

In computer programming, a magic number is a constant used to identify the file or data type employed. ... Image:ASCII fullsvg There are 95 printable ASCII characters, numbered 32 to 126. ... In computer science, a dword is a unit of data that is twice the size of a word and half the size of a qword. ... In computer science, an offset within an array or other data structure object is an integer indicating the distance (displacement) from the beginning of the object up until a given element or point, presumably within the same object. ...

Bitmap information

This block of bytes tells the application detailed information about the image, which will be used to display the image on the screen. It also matches the header used internally by Windows and OS/2 and thus has several different variants. All of them start with a dword field, specifying their size in bytes, so that an application can easily determine the exact format used. The new header variants were introduced with new versions of Windows and OS/2, adding more functionality to the GDI. But since these extended headers are used only with few GDI functions, for compatibility with older programs most applications use the older headers when saving files. With OS/2 being obsolete, for now the only common format is the Windows 3.0 V3 header. See the table below for more information about the variants. In computer science, a dword is a unit of data that is twice the size of a word and half the size of a qword. ...

Size Header Identified by Supported by
40 Windows V3 BITMAPINFOHEADER All Windows OSes since Windows 3.0
12 OS/2 V1 BITMAPCOREHEADER OS/2 and also all Windows OSes since Windows 3.0
64 OS/2 V2
108 Windows V4 BITMAPV4HEADER All Windows OSes since Windows 95/NT4
124 Windows V5 BITMAPV5HEADER Windows 98/2000 and newer

The V3 header: Windows 3. ... Windows 3. ... Windows 95 is a consumer-oriented graphical user interface-based operating system. ... Windows NT 4. ...

Offset # Size Purpose
14 4 Size of this header (40 bytes)
18 4 Store the bitmap width in pixels.
22 4 Store the bitmap height in pixels.
26 2 Store the number of color planes being used. Must be set to 1.
28 2 Store the number of bits per pixel, which is the color depth of the image. Typical values are 1, 4, 8, 16, 24 and 32.
30 4 Define the compression method being used. See the next table for a list of possible values.
34 4 Store the image size. This is the size of the raw bitmap data (see below), and should not be confused with the file size.
38 4 Store the horizontal resolution of the image. (pixel per meter)
42 4 Store the vertical resolution of the image. (pixel per meter)
46 4 Store the number of colors used.
50 4 Store the number of important colors used. This field can be 0 when every color is important.

The compression method field (bytes #30-33) can have the following values:[4] The metre, or meter (symbol: m) is the SI base unit of length. ...

Value Identified by Compression method Comments
0 BI_RGB none Most common
1 BI_RLE8 RLE 8-bit/pixel Can be used only with 8-bit/pixel bitmaps
2 BI_RLE4 RLE 4-bit/pixel Can be used only with 4-bit/pixel bitmaps
3 BI_BITFIELDS Bit field Can be used only with 16 and 32-bit/pixel bitmaps.
4 BI_JPEG JPEG The bitmap contains a JPEG image
5 BI_PNG PNG The bitmap contains a PNG image

The OS/2 V1 header is also popular:[5] Run-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 run. ... A bit field is a common idiom used in computer programming to store a set of Boolean datatype flags compactly, as a series of bits. ... JPG redirects here. ... PNG may stand for: Persona non grata, literally meaning an unwelcome person, is a term used in diplomacy with a specialised and legally defined meaning. ...

Offset Size Purpose
14 4 Size of this header (12 bytes)
18 2 Store the bitmap width in pixels.
20 2 Store the bitmap height in pixels.
22 2 Store the number of color planes being used.
24 2 Store the number of bits per pixel. Typical values are 1, 4, 8 and 24.

Color palette

This block of bytes define the colors being used inside an indexed-color image. As stated above, the bitmap picture will be stored pixel by pixel. Each pixel is described by a value which will be stored using one or more bytes. Therefore, the purpose of the color palette in indexed-color bitmaps is to tell the application the actual color that each of these values corresponds to.


A typical bitmap file uses the RGB color model. In this model, a color is created by mixing different intensities (which can vary from 0 to 255) of red (R), green (G) and blue (B). A color is thus defined using the 3 values for R, G and B. REDIRECT RGB color model ...


In the bitmap file implementation, the color palette contains many entries; the number of entries is the number of colors used in the picture. Each entry contains 4 bytes for a Windows bitmap and 3 bytes for an OS/2 bitmap. The first (and only for OS/2) 3 bytes store the values for blue, green and red respectively while the last one is unused and is filled with 0 by most applications. For each byte, a value of 0 indicates that the corresponding color (either red, green, or blue) is not used to create the current image color. On the other hand, a value of 255 indicates that maximum intensity is used.


As mentioned above, the color palette is not used when the bitmap is 16-bit or higher.


Bitmap data

This block of bytes describes the image, pixel by pixel. Pixels are stored starting in the bottom left corner going from left to right and then row by row from the bottom to the top. Each pixel is described using one or more bytes. If the number of bytes matching a horizontal line in the image is not divisible by 4, the line is padded with null-bytes. The null character (also null terminator) is a character with the value zero, present in the ASCII and Unicode character sets, and available in nearly all mainstream programming languages. ...


Miscellaneous

The simplicity of BMP and its widespread familiarity in Windows and elsewhere, as well as the fact that this format is well-documented and free of patents, makes it a very common format that image processing programs from many operating systems can read and write. In general terms, documentation is any communicable material (such as text, video, audio, etc. ... For other uses, see Patent (disambiguation). ...


While BMP files have a relatively large file size, many BMP files can be considerably compressed with lossless data compression algorithms such as ZIP because they contain redundant data. Lossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. ... The ZIP file format is a popular data compression and archival format. ...


Related formats

The X Window System uses a similar XBM format for black-and-white images, and XPM (pixelmap) for color images. There are also a variety of RAW formats, which saves raw data with no other information. The Portable Pixmap (PPM) and Truevision TGA formats also exist, but are less often used - or only for special purposes. For example, TGA can contain transparency information. “X11” redirects here. ... In computer graphics, the X Window System uses X BitMap (XBM), an ASCII text monochrome image format, for storing cursor and icon bitmaps used in the X GUI. XBM files differ markedly from most image files in that they take the form of C language source files. ... Black-and-white or black and white) can refer to a general term used in photography, film, and other media (see black-and-white). ... X Pixmap (XPM) is an ASCII-text-based image format used by the X Window System. ... Color is an important part of the visual arts. ... A raw image file contains minimally processed data from the image sensor of a digital camera or image scanner. ... For other uses, see Data (disambiguation). ... The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ... The portable pixmap file format (PPM), the portable graymap file format (PGM) and the portable bitmap file format (PBM) specify rules for exchanging graphics files. ... Truevisions (now Pinnacle Systems) TGA File Format, often referred to as TARGA File Format, is a raster graphics file format. ...


See also

This is a comparison of graphics file formats. ... Windows Picture and Fax Viewer is an image viewer. ... Microsoft Paint (officially titled Paint; sometimes called MS Paint; formerly Paintbrush for Windows) is a simple graphics painting program that has been included with all versions of Microsoft Windows since its first release. ...

References

  1. ^ James D. Foley (1995). Computer Graphics: Principles and Practice. Addison-Wesley Professional, p.13. ISBN 0201848406. “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 pixmap (short for pixel map).” 
  2. ^ V.K. Pachghare (2005). Comprehensive Computer Graphics: Including C++. Laxmi Publications, p.93. ISBN 8170081858. 
  3. ^ Julian Smart, Stefan Csomor, and Kevin Hock (2006). Cross-Platform GUI Programming with Wxwidgets. Prentice Hall. ISBN 0131473816. 
  4. ^ The image size field can be 0 for BI_RGB bitmaps.
  5. ^ The OS/2 V1 bitmaps cannot be compressed and cannot be 16 or 32 bits/pixel.

External links


  Results from FactBites:
 
bitmaps (5018 words)
Then for each square, we initialize the rank_attacks[square][rank_contents] to the bitmap that matches the squares that a rook/queen on "square" could move to, assuming the rank is occupied as per the eight bit value "rank_contents".
For example, take the occupied_squares bitmap used earlier, but add a rook on square F5 instead of a bishop as in the previous example (figure 8), and assume we are trying to initialize rank_attacks[37][100] (37 is the square F5, and 100 represents the occupied squares on that rank, 01100100).
Perhaps the primary performance improvement to using bitmaps came from the Crafty project however, when the concept of "rotated bitmaps" was developed as an alternative to the classic incremental update approach used in chess 4.0, because this produced a substantial performance increase with no loss at all in capability.
A Beginners Guide to Bitmaps (2500 words)
Bitmaps are defined as a regular rectangular mesh of cells called pixels, each pixel containing a colour value.
As with 8 bit grey bitmaps each pixel has one byte associated with it only now the value in that byte is no longer a colour value but an index into a table of colours, called a palette or colour table.
A common operation that reduces the size of large 24 bit bitmaps is to convert them to indexed colour with an optimised palette, that is, a palette which best represents the colours available in the bitmap.
  More results at FactBites »

 
 

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