bmp format
来源:互联网 发布:qq三国棋子算法 编辑:程序博客网 时间:2024/05/23 19:53
table of contents
introduction
bitmap file format
general introduction
bmp contents
field details
height field
bits per pixel field
compression field
colors field
important colors field
this document describes the microsoft windows and ibm os/2 picture bitmap files, called bitmaps or bmp files. most of the descriptions of the bmp file concentrate on the microsoft windows bmp structures like the following chapters contain the detailed information on the contents of the bmp file. first more general information will be given regarding the byte order and file alignment. the second chapter will concentrate on the byte-level contents of a bmp file. the third chapter will elaborate on this chapter and explain some of the concepts - like compression - and/or values in detail. the bmp file has been created by microsoft and ibm and is therefor very strictly bound to the architecture of the main hardware platform that both companies support: the ibm compatible pc. this means that all values stored in the bmp file are in the intel format, sometimes also called the little endian format because of the byte order that an intel processor uses internally to store values. the bmp files are the way, windows stores bit mapped images. the bmp image data is bit packed but every line must end on a dword boundary - if that the bmp format has four incarnations, two under windows (new and old) and two under os/2, all are described here. the following table contains a description of the contents of the bmp file. for every field, the file offset, the length and the contents will be given. for a more detailed discussion, see the following chapters. offset field size contents 0000h identifier 2 bytes the characters identifying the bitmap. the following entries are possible: 態 態 慍 慍 慖 慞 0002h file size 1 dword complete file size in bytes. 0006h reserved 1 dword reserved for later use. 000ah bitmap data offset 1 dword offset from beginning of file to the beginning of the bitmap data. 000eh bitmap header size 1 dword length of the bitmap info header used to describe the bitmap colors, compression, 28h - windows 3.1x, 95, nt, 0ch - os/2 1.x f0h - os/2 2.x 0012h width 1 dword horizontal width of bitmap in pixels. 0016h height 1 dword vertical height of bitmap in pixels. 001ah planes 1 word number of planes in this bitmap. 001ch bits per pixel 1 word bits per pixel used to store palette entry information. this also identifies in an indirect way the number of possible colors. possible values are: 1 - monochrome bitmap 4 - 16 color bitmap 8 - 256 color bitmap 16 - 16bit (high color) bitmap 24 - 24bit (true color) bitmap 32 - 32bit (true color) bitmap 001eh compression 1 dword compression specifications. the following values are possible: 0 - none (also identified by bi_rgb) 1 - rle 8-bit / pixel (also identified by bi_rle4) 2 - rle 4-bit / pixel (also identified by bi_rle8) 3 - bitfields (also identified by bi_bitfields) 0022h bitmap data size 1 dword size of the bitmap data in bytes. this number must be rounded to the next 4 byte boundary. 0026h hresolution 1 dword horizontal resolution expressed in pixel per meter. 002ah vresolution 1 dword vertical resolution expressed in pixels per meter. 002eh colors 1 dword number of colors used by this bitmap. for a 8-bit / pixel bitmap this will be 100h or 256. 0032h important colors 1 dword number of important colors. this number will be equal to the number of colors when every color is important. 0036h palette n * 4 byte the palette specification. for every entry in the palette four bytes are used to describe the rgb values of the color in the following way: 1 byte for blue component 1 byte for green component 1 byte for red component 1 byte filler which is set to 0 (zero) 0436h bitmap data x bytes depending on the compression specifications, this field contains all the bitmap data bytes which represent indices in the color palette. note: size # bytes sign char 1 signed word 2 unsigned dword 4 unsigned some of the fields require some more information. the following chapters will try to provide this information: the height field identifies the height of the bitmap in pixels. in other words, it describes the number of scan lines of the bitmap. if this field is negative, indicating a top-down dib, the compression field must be either bi_rgb or bi_bitfields. top-down dibs cannot be compressed. the bits per pixel (bbp) field of the bitmap file determines the number of bits that define each pixel and the maximum number of colors in the bitmap. the bitmap is monochrome, and the palette contains two entries. each bit in the bitmap array represents a pixel. if the bit is clear, the pixel is displayed with the color of the first entry in the palette; if the bit is set, the pixel has the color of the second entry in the table. the bitmap has a maximum of 16 colors, and the palette contains up to 16 entries. each pixel in the bitmap is represented by a 4-bit index into the palette. for example, if the first byte in the bitmap is 1fh, the byte represents two pixels. the first pixel contains the color in the second palette entry, and the second pixel contains the color in the sixteenth palette entry. the bitmap has a maximum of 256 colors, and the palette contains up to 256 entries. in this case, each byte in the array represents a single pixel. the bitmap has a maximum of 2^16 colors. if the compression field of the bitmap file is set to bi_rgb, the palette field does not contain any entries. each word in the bitmap array represents a single pixel. the relative intensities of red, green, and blue are represented with 5 bits for each color component. the value for blue is in the least significant 5 bits, followed by 5 bits each for green and red, respectively. the most significant bit is not used. if the compression field of the bitmap file is set to bi_bitfields, the palette field contains three dword color masks that specify the red, green, and blue components, respectively, of each pixel. each word in the bitmap array represents a single pixel. windows nt specific: windows 95 specific: the bitmap has a maximum of 2^24 colors, and the palette field does not contain any entries. each 3-byte triplet in the bitmap array represents the relative intensities of blue, green, and red, respectively, for a pixel. the bitmap has a maximum of 2^32 colors. if the compression field of the bitmap is set to bi_rgb, the palette field does not contain any entries. each dword in the bitmap array represents the relative intensities of blue, green, and red, respectively, for a pixel. the high byte in each dword is not used. if the compression field of the bitmap is set to bi_bitfields, the palette field contains three dword color masks that specify the red, green, and blue components, respectively, of each pixel. each dword in the bitmap array represents a single pixel. windows nt specific: windows 95 specific: the compression field specifies the way the bitmap data is stored in the file. this information together with the bits per pixel (bpp) field identifies the compression algorithm to follow. the following values are possible in this field: value meaning bi_rgb an uncompressed format. bi_rle4 an rle format for bitmaps with 4 bits per pixel. the compression format is a two-byte format consisting of a count byte followed by two word-length color indices. for more information, see the following remarks section. bi_rle8 a run-length encoded (rle) format for bitmaps with 8 bits per pixel. the compression format is a two-byte format consisting of a count byte followed by a byte containing a color index. for more information, see the following remarks section. bi_bitfields specifies that the bitmap is not compressed and that the color table consists of three double word color masks that specify the red, green, and blue components, respectively, of each pixel. this is valid when used with 16- and 32- bits-per-pixel bitmaps. when the compression field is bi_rle8, the bitmap is compressed by using a run-length encoding (rle) format for an 8-bit bitmap. this format can be compressed in encoded or absolute modes. both modes can occur anywhere in the same bitmap. the first byte specifies the number of consecutive pixels to be drawn using the color index contained in the second byte. in addition, the first byte of the pair can be set to zero to indicate an escape that denotes an end of line, end of bitmap, or delta. the interpretation of the escape depends on the value of the second byte of the pair, which can be one of the following: 0 end of line. 1 end of bitmap. 2 delta. the two bytes following the escape contain unsigned values indicating the horizontal and vertical offsets of the next pixel from the current position. the first byte is zero and the second byte is a value in the range 03h through ffh. the second byte represents the number of bytes that follow, each of which contains the color index of a single pixel. when the second byte is 2 or less, the escape has the same meaning as in encoded mode. in absolute mode, each run must be aligned on a word boundary. the following example shows the hexadecimal values of an 8-bit compressed bitmap. 03 04 05 06 00 03 45 56 67 00 02 78 00 02 05 01 02 78 00 00 09 1e 00 01 this bitmap would expand as follows (two-digit values represent a color index for a single pixel): 04 04 04 06 06 06 06 06 45 56 67 78 78 move current position 5 right and 1 down 78 78 end of line 1e 1e 1e 1e 1e 1e 1e 1e 1e end of rle bitmap when the compression field is bi_rle4, the bitmap is compressed by using a run-length encoding format for a 4-bit bitmap, which also uses encoded and absolute modes: the first byte of the pair contains the number of pixels to be drawn using the color indices in the second byte. the second byte contains two color indices, one in its high-order four bits and one in its low-order four bits. the first of the pixels is drawn using the color specified by the high-order four bits, the second is drawn using the color in the low-order four bits, the third is drawn using the color in the high-order four bits, and so on, until all the pixels specified by the first byte have been drawn. the first byte is zero, the second byte contains the number of color indices that follow, and subsequent bytes contain color indices in their high- and low-order four bits, one color index for each pixel. in absolute mode, each run must be aligned on a word boundary. the end-of-line, end-of-bitmap, and delta escapes described for bi_rle8 also apply to bi_rle4 compression. the following example shows the hexadecimal values of a 4-bit compressed bitmap. 03 04 05 06 00 06 45 56 67 00 04 78 00 02 05 01 04 78 00 00 09 1e 00 01 this bitmap would expand as follows (single-digit values represent a color index for a single pixel): 0 4 0 0 6 0 6 0 4 5 5 6 6 7 7 8 7 8 move current position 5 right and 1 down 7 8 7 8 end of line 1 e 1 e 1 e 1 e 1 end of rle bitmap the colors field specifies the number of color indices in the color table that are actually used by the bitmap. if this value is zero, the bitmap uses the maximum number of colors corresponding to the value of the bbp field for the compression mode specified by the compression field. if the colors field is nonzero and the bbp field less than 16, the colors field specifies the actual number of colors the graphics engine or device driver accesses. if the bbp field is 16 or greater, then colors field specifies the size of the color table used to optimize performance of windows color palettes. if bbp equals 16 or 32, the optimal color palette starts immediately following the three double word masks. if the bitmap is a packed bitmap (a bitmap in which the bitmap array immediately follows the bitmap header and which is referenced by a single pointer), the colors field must be either 0 or the actual size of the color table. the important colors field s
- BMP format
- BMP Format
- bmp format
- bmp format
- BMP file format
- BMP file format
- BMP file format
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- BMP文件格式详解(BMP file format)
- Windows内存机制(转)
- WINCE中的gwes.dll功能?
- MeeGo体系结构
- 在一个没有熟人的地方扔下几个字
- BPM与ERP、OA等的关系
- bmp format
- 又回来了
- Struts2.2.1必需的jar包
- FAT32文件系统
- 好无聊
- 关于常州SEO的思考
- 认识IDE硬盘(上)(转)
- 鼠标中键拖动滚动条
- U-boot移植日志(7)--使u-boot的help命令支持通配符(*)