#pragma  pack(1)
struct BMFH	// Bitmap File Header
{
	char         bmtype_[2];
	unsigned int fileSize_;
	short int    reserved1_;
	short int    reserved2_;
	unsigned int offsetBits_;
}; // 18 Bytes
#pragma pack()

#pragma pack(1)
struct BMIF	// Bitmap Info Header
{
	unsigned int sizeHeader_;
	unsigned int width_;
	unsigned int height_;
	short int    planes_;
	short int    bpp_;
	unsigned int compression_;
	unsigned int sizeImage_;
	unsigned int xPelsPerMeter_;
	unsigned int yPelsPerMeter_;
	unsigned int clrUsed_;
	unsigned int clrImportant_;
}; // 40 Bytes
#pragma pack()

enum BitCompression
{
	RGB  = 0,
	RLE8,
	RLE4,
	BITFIELDS
};

BMFH bmfh;
	BMIF bmif;

	bmfh.bmtype_[0]		= 'B';
	bmfh.bmtype_[1]		= 'M';
	bmfh.fileSize_		= sizeof(BMFH) + sizeof(BMIF) + sizeof(image_->rgb_); // rgb ist das array mit den daten
	bmfh.reserved1_		= 0; // darf das 0 sein?
	bmfh.reserved2_		= 0; // darf das 0 sein?
	bmfh.offsetBits_	= 54;

	bmif.sizeHeader_	= sizeof(BMFH);
	bmif.width_			= image_->width_;
	bmif.height_		= image_->height_;
	bmif.planes_		= 1;
	bmif.bpp_			= image_->bpp_;
	bmif.compression_	= RGB; --
	bmif.sizeImage_		= sizeof(image_->rgb_);
	bmif.xPelsPerMeter_	= 0;// darf das 0 sein?
	bmif.yPelsPerMeter_	= 0;// darf das 0 sein?
	bmif.clrUsed_		= 0;// darf das 0 sein?
	bmif.clrImportant_	= 0;// darf das 0 sein?

lw

msdn schrieb:

bfReserved1
Reserved; must be zero.
bfReserved2
Reserved; must be zero.

zu bih: dürfte vermutlich für dich uninteressant für dich sein.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/bitmaps_62uq.asp

evtl hilft dir die ein beispiel aus meiner bitmap klasse

static void Write(
				std::ostream &s,
				size_t nWidth,
				size_t nHeight,
				size_t nBpp,
				unsigned char *pData)
			{
				// bitmapfileheader
				struct
				{
					unsigned char	B, M;
					unsigned long	nSize;
					unsigned short  nReserved1;
					unsigned short  nReserved2;
					unsigned long   nOffsetBits;
				} Bfh;
				// bitmapimageheader
				struct
				{
					unsigned long 	nSize;
					long  			nWidth;
					long  			nHeight;
					unsigned short 	nPlanes;
					unsigned short 	nBPP;
					unsigned long 	nCompression;
					unsigned long 	nImageSize;
					long  			nWidthPPM;
					long  			nHeightPPM;
					unsigned long 	nColorUsed;
					unsigned long 	nColorImportant;
				} Bih;

				Bfh.nSize			= sizeof(Bfh); // grösse überprüfen
				Bfh.B				= 'B';
				Bfh.M				= 'M';
				Bfh.nReserved1		= 0;
				Bfh.nReserved2		= 0;
				Bfh.nOffsetBits		= sizeof(Bfh) + sizeof(Bih); // grösse überprüfen

				Bih.nSize			= sizeof(Bih); // grösse überprüfen
				Bih.nPlanes			= 1;
				Bih.nBPP			= static_cast<unsigned short>(nBpp);
				Bih.nCompression	= 0;
				Bih.nImageSize		= nWidth * nHeight * (nBpp >> 3);
				Bih.nWidthPPM		= 0;
				Bih.nHeightPPM		= 0;
				Bih.nColorUsed		= 0;
				Bih.nColorImportant	= 0;
				Bih.nWidth			= nWidth;
				Bih.nHeight			= nHeight;

				// um 'padding-bytes' zu vermeiden wird alles einzeln gespeichert
				s.write((char*)&Bfh.B, sizeof(unsigned char));
				s.write((char*)&Bfh.M, sizeof(unsigned char));
				s.write((char*)&Bfh.nSize, sizeof(unsigned long));
				s.write((char*)&Bfh.nReserved1, sizeof(unsigned short));
				s.write((char*)&Bfh.nReserved2, sizeof(unsigned short));
				s.write((char*)&Bfh.nOffsetBits, sizeof(unsigned long));

				s.write((char*)&Bih, sizeof(Bih));
				s.write((char*)pData, Bih.nImageSize);
			}