32位彩色图像转换成256级灰度图的算法

void GrayConversionXu(HDIB& hDib)
{
HDIB hGreyDIB=NULL;
DWORD nWide,nHeight,i,j;
LPBYTE lpBit=(LPBYTE)GlobalLock(hDib);
LPBITMAPINFOHEADER pHeader=(LPBITMAPINFOHEADER)lpBit;
nWide=pHeader->biWidth;
nHeight=pHeader->biHeight;
DWORD dGrayDIBSize;
if(IS_WIN30_DIB(lpBit))
dGrayDIBSize=pHeader->biSize+256*sizeof(RGBQUAD)+(nWide*8+31)/32*4*nHeight;
else
dGrayDIBSize=pHeader->biSize+256*sizeof(RGBTRIPLE)+(nWide*8+31)/32*4*nHeight;
hGreyDIB=(HDIB)GlobalAlloc(GHND,dGrayDIBSize);
LPBITMAPINFO lpGray=(LPBITMAPINFO)GlobalLock(hGreyDIB);
lpGray->bmiHeader=*pHeader;
lpGray->bmiHeader.biBitCount=8;
if(IS_WIN30_DIB(lpBit))
for(i=0;i<256;i++)
{
lpGray->bmiColors[i].rgbBlue=(BYTE)i;
lpGray->bmiColors[i].rgbGreen=(BYTE)i;
lpGray->bmiColors[i].rgbRed=(BYTE)i;
lpGray->bmiColors[i].rgbReserved=(BYTE)0;
}
else
for(i=0;i<256;i++)
{
lpGray->bmiColors[i].rgbBlue=(BYTE)i;
lpGray->bmiColors[i].rgbGreen=(BYTE)i;
lpGray->bmiColors[i].rgbRed=(BYTE)i;
}
LPBYTE lpGrayBit=(LPBYTE)lpGray;

if(IS_WIN30_DIB(lpBit))
lpGrayBit+=pHeader->biSize+256*sizeof(RGBQUAD);
else
lpGrayBit+=pHeader->biSize+256*sizeof(RGBTRIPLE);
int nCountBit=pHeader->biBitCount;

if(nCountBit>8)
{
lpBit+=sizeof(BITMAPINFOHEADER);
int nRGB=(nWide*nCountBit+31)/32*4-nWide*nCountBit/8;
int nGrey=(nWide*8+31)/32*4-nWide;
for(i=0;i<nHeight;i++)
{
for(j=0;j<nWide;j++)
*lpGrayBit++=(*lpBit++)*0.299+(*lpBit++)*0.587+(*lpBit++)*0.114;
lpGrayBit+=nGrey;
lpBit+=nRGB;
}
::GlobalUnlock((HGLOBAL)hDib);
::GlobalFree((HGLOBAL)hDib);
hDib = hGreyDIB;
::GlobalUnlock((HGLOBAL)hGreyDIB);
}

else
{
DWORD nColorCount=1<<nCountBit;
BYTE pGreyTable[256];
RGBQUAD pDIBColors[256];
LPBITMAPINFO lpBitmapinfo=(LPBITMAPINFO)lpBit;
for(i=0;i<nColorCount;i++)
{
if(IS_WIN30_DIB(lpBit))
{
pDIBColors[i].rgbBlue=lpBitmapinfo->bmiColors[i].rgbBlue;
pDIBColors[i].rgbGreen=lpBitmapinfo->bmiColors[i].rgbGreen;
pDIBColors[i].rgbRed=lpBitmapinfo->bmiColors[i].rgbRed;
pDIBColors[i].rgbReserved=lpBitmapinfo->bmiColors[i].rgbReserved;
}
else
{
pDIBColors[i].rgbBlue=lpBitmapinfo->bmiColors[i].rgbBlue;
pDIBColors[i].rgbGreen=lpBitmapinfo->bmiColors[i].rgbGreen;
pDIBColors[i].rgbRed=lpBitmapinfo->bmiColors[i].rgbRed;
}
pGreyTable[i]=pDIBColors[i].rgbBlue*0.114+pDIBColors[i].rgbRed*0.299+pDIBColors[i].rgbGreen*0.587;
}
lpBit=lpBit+sizeof(BITMAPINFOHEADER)+PaletteSize(lpBit);
int nRGB=(nWide*nCountBit+31)/32*4-(nWide*nCountBit)/8;
int nGrey=(nWide*8+31)/32*4-nWide;
switch(nColorCount)
{
case 2:
for(i=0;i<nHeight;i++)
{
for(j=0;j<nWide;j++)
{
BYTE n=1<<(7-j%8);
BYTE Temp=*(BYTE*)lpBit;
Temp&=n;
*lpGrayBit++=pGreyTable[Temp>>(7-j%8)];
if((j+1)%8==0)lpBit++;
}
lpGrayBit+=nGrey;
lpBit+=nRGB;
}

break;
case 16:
for(i=0;i<nHeight;i++)
{
for(j=0;j<nWide;j++)
{

BYTE Temp=*lpBit;
BYTE n=j%2 ?0x0f:0xf0;
Temp&=n;
Temp=Temp>>(j%2 ?0:4);
*lpGrayBit++=pGreyTable[Temp];
if((j+1)%2==0)lpBit++;
}
lpGrayBit+=nGrey;
lpBit+=nRGB;
}
break;
case 256:
for(i=0;i<nHeight;i++)
{
for(j=0;j<nWide;j++)
*lpGrayBit++=pGreyTable[(*lpBit++)];
lpGrayBit+=nGrey;
lpBit+=nRGB;
}

break;
}
::GlobalUnlock((HGLOBAL)hDib);
::GlobalFree((HGLOBAL)hDib);
hDib = hGreyDIB;
::GlobalUnlock((HGLOBAL)hGreyDIB);
}
}