Bitmap format
This page illustrates the bitmap file format used in the SampleGrabber sample.
Bitmap file format overview
The Bitmap format used in SampleGrabber sample is very simple. The Bitmap file consists of BITMAPFILEHEADER, BITMAPINFOHEADER, and RGB data.
| BITMAPFILEHEADER |
| BITMAPINFOHEADER |
| RGB data |
BITMAPFILEHEADER
The BITMAPFILEHEADER structure is defined as the following.
typedef struct tagBITMAPFILEHEADER {
WORD bfType;
DWORD bfSize;
WORD bfReserved1;
WORD bfReserved2;
DWORD bfOffBits;
} BITMAPFILEHEADER;
- bfType
- Identifier information comes first in the Bitmap file. The first two bytes of a bitmap file will be 'B' + 'M'.
- bfSize
- File size. The file size of the output bitmap file of the SampleGrabber sample is, sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + (width x height x 3).
- bfReserved1, bfReserved2
- unused.
- bfOffBits
- The offset from the head of the file to the first RGB data. The value will show the number of bytes to the first RGB data. In the SampleGrabber sample, this value will be, sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER).
BITMAPINFOHEADER
The BITMAPINFOHEADER structure is defined as the following.
typedef struct tagBITMAPINFOHEADER{
DWORD biSize;
LONG biWidth;
LONG biHeight;
WORD biPlanes;
WORD biBitCount;
DWORD biCompression;
DWORD biSizeImage;
LONG biXPelsPerMeter;
LONG biYPelsPerMeter;
DWORD biClrUsed;
DWORD biClrImportant;
} BITMAPINFOHEADER;
- biSize
- size of the structure.
- biWidth
- width of image (in pixels)
- biHeight
- height of image (in pixels)
- biPlanes
- number of planes. must be 1.
- biBitCount
- bits-per-pixel
- biCompression
- the used compression technology. BI_RGB(no compression), BI_RLE8, BI_RLE4(run length encoded, 8bpp, 4bpp), BI_JPEG, BI_PNG.
- biSizeImage
- image size. can be 0 when BI_RGB.
- biXPelsPerMeter
- width by pixel-per-meter.
- biYPelsPerMeter
- height by pixel-per-meter.
- biClrUsed
- number of color index used.
- biClrImportant
- number of color to show the color index.
RGB data
The RGB data structure is defined as the following. The directshow sample shown in this site uses MEDIASUBTYPE_RGB24 (24 bit RGB). However, please note there are other formats that can be used too.
BYTE red;
BYTE green;
BYTE blue;
The RGB data will contine for the number of pixels. For example, if the image size is 720x480, the RGB data will contine 720x480 times. The whole RGB data will be 720x480x3 = 1036800 bytes.
