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BITMAPINFOHEADER

Format information for device-independent bitmaps

The BITMAPINFOHEADER structure stores information about the dimensions and color palette of a device independent bitmap (DIB) used by Windows 3.0 and newer.
   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 members:

Field Type Description
biSize DWORD Specifies the number of bytes required by the BITMAPINFOHEADER structure.
biWidth DWORD Specifies the width of the bitmap in pixels.
biHeight DWORD Specifies the height of the bitmap in pixels. If biHeight is positive, the bitmap is a "bottom-up" DIB and its origin is the lower left corner. If biHeight is negative, the bitmap is a "top-down" DIB and its origin is the upper left corner. Note that many DaVinci functions only support bottom-up bitmaps (biHeight >= 0).
biPlanes WORD Specifies the number of color planes on the target device. In most cases this value must be set to 1.

DaVinci extension: For 48-bit DIBs (bitmaps with 16 bits per color value of resolution), biPlanes should be set to 2.
biBitCount WORD Specifies the number of bits per pixels. This value must be 1, 4, 8 or 24 in the 16 bit version; values of 16 or 32 may also be used in the 32 bit version of DaVinci.
biCompression DWORD Specifies the compression type for a compressed bitmap. The following values are specified as standard for Windows bitmaps:
Value Importance

BI_RGB Standard Windows bitmap; not compressed.

BI_RLE4 RLE (Run Length Encoded) 4bpp (16 color) image. See the following section on bitmap compression formats for more information.

BI_RLE8 RLE (Run Length Encoded) 8bpp (256 color) image. See the following section on bitmap compression formats for more information.
biSizeImage DWORD Specifies the size of the bitmap data section of the image (the actual pixel data, excluding BITMAPINFOHEADER and RGBQUAD structures).
biXPelsPerMeter DWORD Specifies the horizontal resolution of the target device in pixels per metre. Applications often use this value to select the resource bitmap that best matches the characteristics of the current device.
biYPelsPerMeter DWORD Specifies the vertical resolution, in pixels per metre, of the target device for the bitmap.
biClrUsed DWORD Specifies the actual number of color indices in the color table used by the bitmap. If this value is zero, the bitmap uses the maximum number of colors corresponding to the value of the biBitCount member for the compression mode specified by biCompression.

If biClrUsed is nonzero and the biBitCount member is less than 16, the biClrUsed member specifies the actual number of colors the graphics engine or device driver accesses. If biBitCount is 16 or greater, then biClrUsed member specifies the size of the color table. This can be used to optimize performance of Windows color palettes. If biBitCount equals 16 or 32, the optimal color palette starts immediately following the three doubleword masks.

If the bitmap is a packed bitmap (a bitmap in which the bitmap's pixel data array immediately follows the BITMAPINFO header and which is referenced by a single pointer), the biClrUsed member must be either 0 or the actual size of the color table.
biClrImportant DWORD Specifies the number of color indices that are considered important for displaying the bitmap. If this value is zero, all colors are important.

Remarks

The BITMAPINFO structure combines the BITMAPINFOHEADER structure and a color table to provide a complete definition of the dimensions and colors of a DIB. For more information about DIBs, see the description of the BITMAPINFO data structure in the WinAPI helpfiles.

An application should use the information stored in the biSize member to locate the color table in a BITMAPINFO structure, as follows:
pColor = ((LPSTR) pBitmapInfo + (UINT) (pBitmapInfo -> biSize))

A Windows DIB consists of two different parts: the BITMAPINFO data structure containing the bitmap's image dimensions and color table, and a byte field or data array representing the pixels that make up the image itself. The bits in this field are packed, but each screen line (each vertical row of pixels) must be filled with zeros as needed in order to end at a LONG limit. 64 KB segment boundaries for 16 bit applications can appear within one pixel of the graphic.

Note that the origin ("starting point") for DIBs is the lower left corner of the bitmap, while the origin of a DDB is the upper left corner.

biBitCount

The biBitCount member of the BITMAPINFOHEADER structure determines the number of bits in each pixel and also defines the maximum number of colors which may be used in the bitmap. This member may use the following values:

Value Importance

1 The bitmap is monochrome and the bmciColors member of the BITMAPINFO structure must contain two entries. Every bit in the bitmap represents a pixel. If the bit is deleted, the pixel is displayed with the color of first entry in the table bmciColors. If the bit is set, the pixel has the color of second entry in the table. The bits are interpreted in the order 7,6,5,4,3,2,1,0.

4 The bitmap has a maximum of 16 colors and the bmciColors member of the BITMAPINFO structure contains 16 entries. Every pixel in the bitmap is represented by an index four bits long which defines which color in the bitmap's palette will be used by that pixel. If the first byte in the bitmap is 0x1F, for example, then the first pixel will be the color in the second table entry (palette index 1) and the second pixel will be the color in the sixteenth table entry (palette index 15).

8 The bitmap has a maximum of 256 colors and the bmciColors member of the BITMAPINFO structure can contain a maximum of 256 entries. Every byte represents the color in the palette index for an individual pixel.

16 (Only defined for Windows NT 3.5+, Windows 95/98 and Video for Windows.) The bitmap can have a maximum of 32,767 colors. In this case the bmciColors member will be left empty. Every two bytes in the bitmap’s data field represent the relative intensities of red, green and blue (RGB) for a specific pixel.

24 The bitmap can have a maximum of 2^24 (usually referred to, though not entirely accurately, as 16 million) colors. The bmciColors member is left empty. Every three bytes in the bitmap’s data field represent the relative intensities of blue, green and red for (BGR) every pixel. The order of the bytes is blue, green, red.

32 The bitmap can have a maximum of 2^24 colors (see above). The bmciColors field is once again left empty. Every four bytes in the bitmap’s data field represent the relative intensities of blue, green and red (BGR) for a given pixel, and the fourth byte, which is not used, is usually set to 0.

Notes

The biClrUsed member of the structure BITMAPINFOHEADER specifies the actual number of color indices currently in use in that image’s palette.

Colors listed in the bmiColors table should appear in order of their importance.

Bitmap compression formats

Windows provides its own internal bitmap compression formats for 4- and 8-bit-per-pixel images. The RLE (run-length encoding) compression used by Windows will often, but not always, reduce the storage and main memory requirement for bitmaps. DaVinci functions do not support Windows’ RLE image formats directly, however. When images are imported, DaVinci will instead call its own internal decompression routines and return an uncompressed DIB.

See also:

BITMAPINFOHEADER

BITMAPINFO