BITMAPFILEHEADER [3.0] Bitmap File Information The BITMAPFILEHEADER data structure contains information about the type, size, and layout of a device-independent bitmap (DIB) file. typedef struct tagBITMAPFILEHEADER { WORD bfType; DWORD bfSize; WORD bfReserved1; WORD bfReserved2; DWORD bfOffBits; } BITMAPFILEHEADER; The BITMAPFILEHEADER data structure contains the following fields: Field Description bfType Specifies the type of file. It must be BM. bfSize Specifies the size in DWORDs of the file. bfReserved1 Is reserved and must be set to zero. bfReserved2 Is reserved and must be set to zero. bfOffBits Specifies in bytes the offset from the BITMAPFILEHEADER of the actual bitmap in the file. Comments A BITMAPINFO or BITMAPCOREINFO data structure immediately follows the BITMAPFILEHEADER structure in the DIB file. BITMAPINFO [3.0] Device-Indpendent Bitmap Information The BITMAPINFO structure fully defines the dimensions and color information for a Windows 3.0 device-independent bitmap. typedef struct tagBITMAPINFO { BITMAPINFOHEADER bmiHeader; RGBQUAD bmiColors[1]; } BITMAPINFO; The BITMAPINFO structure contains the following fields: Field Description bmiHeader Specifies a BITMAPINFOHEADER data structure that contains information about the dimensions and color format of a device-independent bitmap. bmiColors Specifies an array of RGBQUAD data structures that define the colors in the bitmap. Comments: A Windows 3.0 device-independent bitmap consists of two distinct parts: a BITMAPINFO data structure that describes the dimensions and colors of the bitmap, and an array of bytes that define the pixels of the bitmap. The bits in the array are packed together, but each scan line must be zero-padded to end on a LONG boundary. Segment boundaries can appear anywhere in the bitmap, however. The origin of the bitmap is the lower-left corner. The biBitCount field of the BITMAPINFOHEADER structure determines the number of bits which define each pixel and the maximum number of colors in the bitmap. This field may be set to any of the following values: Value Meaning 1 The bitmap is monochrome, and the bmiColors field must contain 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 bmiColors table; if the bit is set, the pixel has the color of the second entry in the table. 4 The bitmap has a maximum of 16 colors, and the bmiColors field contains up to 16 entries. Each pixel in the bitmap is represented by a four-bit index into the color table. For example, if the first byte in the bitmap is 0x1F, then the byte represents two pixels. The first pixel contains the color in the second table entry, and the second pixel contains the color in the 16th table entry. 8 The bitmap has a maximum of 256 colors, and the bmiColors field contains up to 256 entries. In this case, each byte in the array represents a single pixel. 24 The bitmap has a maximum of 2^24 colors. The bmiColors field is NULL, and each three bytes in the bitmap array represents the relative intensities of red, green, and blue, respectively, of a pixel. The biClrUsed field of the BITMAPINFOHEADER structure specifies the number of color indexes in the color table actually used by the bitmap. If the biClrUsed field is set to 0, the bitmap uses the maximum number of colors corresponding to the value of the biBitCount field. The colors in the bmiColors table should appear in order of importance. Alternatively, for functions that use device-independent bitmaps, the bmiColors field can be an array of 16-bit unsigned integers that specify an index into the currently realized logical palette instead of explicit RGB values. In this case, an application using the bitmap must call device-independent bitmap functions with the wUsage parameter set to DIB_PAL_COLORS. Note: The bmiColors field should not contain palette indices if the bitmap is to be stored in a file or transferred to another application. Unless the application uses the bitmap exclusively and under its complete control, the bitmap color table should contain explicit RGB values. BITMAPINFOHEADER [3.0] Device-Independent Bitmap Format Information The BITMAPINFOHEADER structure contains information about the dimensions and color format of a Windows 3.0 device-independent bitmap. typedef struct tagBITMAPINFOHEADER{ DWORD biSize; DWORD biWidth; DWORD biHeight; WORD biPlanes; WORD biBitCount DWORD biCompression; DWORD biSizeImage; DWORD biXPelsPerMeter; DWORD biYPelsPerMeter; DWORD biClrUsed; DWORD biClrImportant; } BITMAPINFOHEADER; The BITMAPINFOHEADER structure has the following fields: Field Description biSize Specifies the number of bytes required by the BITMAPINFOHEADER structure. biWidth Specifies the width of the bitmap in pixels. biHeight Specifies the height of the bitmap in pixels. biPlanes Specifies the number of planes for the target device and must be set to 1. biBitCount Specifies the number of bits per pixel. This value must be 1, 4, 8, or 24. biCompression Specifies the type of compression for a compressed bitmap. It can be one of the following values:. Value Meaning BI_RGB Specifies that the bitmap is not compressed. BI_RLE8 Specifies a run-length encoded 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. See the following 'Comments' section for more information. BI_RLE4 Specifies a run-length encoded 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 indexes. See the following 'Comments' section for more information. biSizeImage Specifies the size in bytes of the image. biXPelsPerMeter Specifies the horizontal resolution in pixels per meter of the target device for the bitmap. An application can use this value to select a bitmap from a resource group that best matches the characteristics of the current device. biYPelsPerMeter Specifies the vertical resolution in pixels per meter of the target device for the bitmap. biClrUsed Specifies the number of color indexes in the color table actually used by the bitmap. If this value is 0, the bitmap uses the maximum number of colors corresponding to the value of the biBitCount field. See the description of the BITMAPINFO data structure earlier in this chapter for more information on the maximum sizes of the color table. If biClrUsed is nonzero, then the biClrUsed field specifies the actual number of colors which the graphics engine or device driver will access if the biBitCount field is less than 24. If the biBitCount field is set to 24, the biClrUsed field specifies the size of the reference color table used to optimize performance of Windows color palettes. If the bitmap is a 'packed' bitmap (that is, a bitmap in which the bitmap array immediately follows the BITMAPINFO header and which is referenced by a single pointer), the biClrUsed field must be set to 0 or to the actual size of the color table. biClrImportant Specifies the number of color indexes that are considered important for displaying the bitmap. If this value is 0, then all colors are important. Comments: The BITMAPINFO data structure combines the BITMAPINFOHEADER structure and a color table to provide a complete definition of the dimensions and colors of a Windows 3.0 device-independent bitmap. See the description of the BITMAPINFO data structure for more information about specifying a Windows 3.0 device-independent bitmap. An application should use the information stored in the biSize field to locate the color table in a BITMAPINFO data structure with a method such as the following: pColor = ((LPSTR) pBitmapInfo + (WORD) (pBitmapInfo -> biSize)) Bitmap Compression Formats Windows supports formats for compressing bitmaps that define their colors with 8 bits per pixel and with 4 bits per pixel. Compression reduces the disk and memory storage required for the bitmap. The following paragraphs describe these formats. When the biCompression field is set to BI_RLE8, the bitmap is compressed using a run-length encoding format for an 8-bit bitmap. This format may be compressed in either of two modes: 7 Encoded 7 Absolute Both modes can occur anywhere throughout a single bitmap. Encoded mode consists of two bytes: 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 a delta. The interpretation of the escape depends on the value of the second byte of the pair. The following list shows the meaning of the second byte: Second Byte Of Escape Meaning 0 End of line. 1 End of bitmap. 2 Delta. The two bytes following the escape contain unsigned values indicating the horizontal and vertical offset of the next pixel from the current position. Absolute mode is signalled by the first byte set to zero and the second byte set to a value between 03H and FFH. In absolute mode, the second byte represents the number of bytes which follow, each of which contains the color index of a single pixel. When the second byte is set to 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 biCompression field is set to BI_RLE4, the bitmap is compressed using a run-length encoding format for a 4-bit bitmap, which also uses encoded and absolute modes. In encoded mode, the first byte of the pair contains the number of pixels to be drawn using the color indexes in the second byte. The second byte contains two color indexes, one in its high-order nibble (that is, its low-order four bits) and one in its low-order nibble. The first of the pixels is drawn using the color specified by the high-order nibble, the second is drawn using the color in the low-order nibble, the third is drawn with the color in the high-order nibble, and so on, until all the pixels specified by the first byte have been drawn. In absolute mode, the first byte contains zero, the second byte contains the number of color indexes that follow, and subsequent bytes contain color indexes in their high- and low-order nibbles, 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 also apply to BI_RLE4. 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 RGBQUAD [3.0] RGB Color Structure The RGBQUAD data structure describes a color consisting of relative intensities of red, green, and blue. The bmiColors field of the BITMAPINFO data structure consists of an array of RGBQUAD data structures. typedef struct tagRGBQUAD { BYTE rgbBlue; BYTE rgbGreen; BYTE rgbRed; BYTE rgbReserved; } RGBQUAD; The RGBQUAD structure contains the following fields: Field Description rgbBlue Specifies the intensity of blue in the color. rgbGreen Specifies the intensity of green in the color. rgbRed Specifies the intensity of red in the color. rgbReserved Is not used and must be set to zero. #define BI_RGB 0L #define BI_RLE8 1L #define BI_RLE4 2L BITMAPCOREINFO [3.0] Device-Indpendent Bitmap Information The BITMAPCOREINFO structure fully defines the dimensions and color information for a device-independent bitmap that is compatible with Microsoft OS/2 Presentation Manager versions 1.1 and 1.2 bitmaps. typedef struct _BITMAPCOREINFO { BITMAPCOREHEADER bmciHeader; RGBTRIPLE bmciColors[]; } BITMAPCOREINFO; The BITMAPCOREINFO structure contains the following fields: Field Description bmciHeader Specifies a BITMAPCOREHEADER data structure that contains information about the dimensions and color format of a device-independent bitmap. bmciColors Specifies an array of RGBTRIPLE data structures that define the colors in the bitmap. Comments An OS/2 Presentation Manager device-independent bitmap consists of two distinct parts: a BITMAPCOREINFO data structure that describes the dimensions and colors of the bitmap, and an array of bytes which define the pixels of the bitmap. The bits in the array are packed together, but each scan line must be zero-padded to end on a LONG boundary. Segment boundaries can appear anywhere in the bitmap, however. The origin of the bitmap is the lower-left corner. The bcBitCount field of the BITMAPCOREHEADER structure determines the number of bits which define each pixel and the maximum number of colors in the bitmap. This field may be set to any of the following values: Value Meaning 1 The bitmap is monochrome, and the bmciColors field must contain 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 bmciColors table; if the bit is set, the pixel has the color of the second entry in the table. 4 The bitmap has a maximum of 16 colors, and the bmciColors field contains 16 entries. Each pixel in the bitmap is represented by a four-bit index into the color table. For example, if the first byte in the bitmap is 0x1F, then the byte represents two pixels. The first pixel contains the color in the second table entry, and the second pixel contains the color in the 16th table entry. 8 The bitmap has a maximum of 256 colors, and the bmciColors field contains 256 entries. In this case, each byte in the array represents a single pixel. 24 The bitmap has a maximum of 2^24 colors. The bmciColors field is NULL, and each three bytes in the bitmap array represents the relative intensities of red, green, and blue, respectively, of a pixel. The colors in the bmciColors table should appear in order of importance. Alternatively, for functions that use device-independent bitmaps, the bmciColors field can be an array of 16-bit unsigned integers that specify an index into the currently realized logical palette instead of explicit RGB values. In this case, an application using the bitmap must call device-independent bitmap functions with the wUsage parameter set to DIB_PAL_COLORS. Note The bmciColors field should not contain palette indexes if the bitmap is to be stored in a file or transferred to another application. Unless the application uses the bitmap exclusively and under its complete control, the bitmap color table should contain explicit RGB values. BITMAPCOREHEADER [3.0] Device-Independent Bitmap Format Information The BITMAPCOREHEADER structure contains information about the dimensions and color format of a device-independent bitmap that is compatible with Microsoft OS/2 Presentation Manager versions 1.1 and 1.2 bitmaps. typedef struct tagBITMAPCOREHEADER { DWORD bcSize; WORD bcWidth; WORD bcHeight; WORD bcPlanes; WORD bcBitCount; } BITMAPCOREHEADER; The BITMAPCOREHEADER structure has the following fields: Field Description bcSize Specifies the number of bytes required by the BITMAPCOREHEADER structure. bcWidth Specifies the width of the bitmap in pixels. bcHeight Specifies the height of the bitmap in pixels. bcPlanes Specifies the number of planes for the target device and must be set to 1. bcBitCount Specifies the number of bits per pixel. This value must be 1, 4, 8, or 24. Comments The BITMAPCOREINFO data structure combines the BITMAPCOREHEADER structure and a color table to provide a complete definition of the dimensions and colors of a device-independent bitmap. See the description of the BITMAPCOREINFO data structure for more information about specifying a device-independent bitmap. An application should use the information stored in the bcSize field to locate the color table in a BITMAPCOREINFO data structure with a method such as the following: pColor = ((LPSTR) pBitmapCoreInfo + (WORD) (pBitmapCoreInfo -> bcSize)) RGBTRIPLE [3.0] RGB Color Structure The RGBTRIPLE data structure describes a color consisting of relative intensities of red, green, and blue. The bmciColors field of the BITMAPCOREINFO data structure consists of an array of RGBTRIPLE data structures. typedef struct tagRGBTRIPLE { BYTE rgbtBlue; BYTE rgbtGreen; BYTE rgbtRed; } RGBTRIPLE; The RGBTRIPLE structure contains the following fields: Field Description rgbtBlue Specifies the intensity of blue in the color. rgbtGreen Specifies the intensity of green in the color. rgbtRed Specifies the intensity of red in the color. ----------------------------------------------------------------------- Non official comments How to distinguish between BITMAPINFO and BITMAPCOREINFO when reading in a BMP file. After reading the BITMAPFILEHEADER read the next DWORD from the file. If it is 12 you are reading a BITMAPCOREHEADER, if it is 40 you are reading a BITMAPINFOHEADER.