使用GDI+保存图像为8bpp的灰度图像

//   Greyscale conversion
#define GREY(r, g, b) (BYTE)(((WORD)r * 77 + (WORD)g * 150 + (WORD)b * 29) >> 8)	// .299R + .587G + .114B
//#define GREY(r, g, b) (BYTE)(((WORD)r * 169 + (WORD)g * 256 + (WORD)b * 87) >> 9)	// .33R + 0.5G + .17B

// BOOL GDIPlusImage::SaveToFileWith8pp(TCHAR *pszPath)
// 功能：保存图片为8位的灰度图像
// 参数: pszPath要保存的文件名
BOOL GDIPlusImage::SaveToFileWith8pp(TCHAR *pszPath)
{
Bitmap *ima = this->m_pBitmap;		// GDIPlusImage的Bitmap对象

if (!ima || !pszPath || !*pszPath)
{
return FALSE;
}

int width = m_pBitmap->GetWidth();
int height = m_pBitmap->GetHeight();
int bitcount = 8;			//1, 4, 8, 24, 32

//////////////////////////////////////////////////////////////////////////
//Build bitmap header
BITMAPFILEHEADER bitmapFileHeader;
BITMAPINFOHEADER bitmapInfoHeader;
BYTE			 rgbquad[4];			// RGBQUAD
int				 index = 0;

DWORD stride = ((bitcount*width + 31)/32)*4;		//每行都是4的倍数，或者说是DWORD大小的倍数

switch(bitcount) {
case 1:
index = 2;
bitmapFileHeader.bfOffBits = (DWORD)(sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + 2*4);
break;
case 4:
index = 16;
bitmapFileHeader.bfOffBits = (DWORD)(sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + 16*4);
break;
case 8:
index = 256;
bitmapFileHeader.bfOffBits = (DWORD)(sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + 256*sizeof(RGBQUAD));
break;
case 24:
case 32:
index = 0;
bitmapFileHeader.bfOffBits = (DWORD)(sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER));
break;
default:
break;
}

//构造Bitmap文件头BITMAPFILEHEADER
bitmapFileHeader.bfType = 0x4d42;    // 很重要的标志位  BM 标识
bitmapFileHeader.bfSize = (DWORD)(bitmapFileHeader.bfOffBits + height * stride);		//bmp文件长度
bitmapFileHeader.bfReserved1 = 0;
bitmapFileHeader.bfReserved2 = 0;

//构造Bitmap文件信息头BITMAPINFOHEADER
bitmapInfoHeader.biSize = sizeof(BITMAPINFOHEADER);
bitmapInfoHeader.biWidth = width;
bitmapInfoHeader.biHeight = height;
bitmapInfoHeader.biPlanes = 1;
bitmapInfoHeader.biBitCount = bitcount;
bitmapInfoHeader.biCompression = BI_RGB;				// 未压缩
bitmapInfoHeader.biSizeImage = height * stride;
bitmapInfoHeader.biXPelsPerMeter = 3780;
bitmapInfoHeader.biYPelsPerMeter = 3780;
bitmapInfoHeader.biClrUsed = 0;
bitmapInfoHeader.biClrImportant = 0;

//创建BMP内存映像,写入位图头部
BYTE *pMyBmp = new BYTE[bitmapFileHeader.bfSize];		// 我的位图pMyBmp
BYTE *curr = pMyBmp;									// curr指针指示pMyBmp的位置
memset(curr, 0, bitmapFileHeader.bfSize);

//写入头信息
memcpy(curr, &bitmapFileHeader,sizeof(BITMAPFILEHEADER));
curr = pMyBmp + sizeof(BITMAPFILEHEADER);
memcpy(curr, &bitmapInfoHeader,sizeof(BITMAPINFOHEADER));
curr += sizeof(BITMAPINFOHEADER);

//构造调色板
if(8 == bitcount)
{
rgbquad[3] = 0;										//rgbReserved
for(int i = 0; i < 256; i++)
{
rgbquad[0] = rgbquad[1] = rgbquad[2] = i;
memcpy(curr, rgbquad, sizeof(RGBQUAD));
curr += sizeof(RGBQUAD);
}
}else if (4 == bitcount)
{
rgbquad[3] = 0;
for (int i = 0; i < 16; i++)
{
rgbquad[0] = rgbquad[1] = rgbquad[2] = i;
memcpy(curr, rgbquad, sizeof(RGBQUAD));
curr += sizeof(RGBQUAD);
}
}
else if(1 == bitcount)
{
rgbquad[3] = 0;										//rgbReserved
for(int i = 0; i < 2; i++)
{
rgbquad[0] = rgbquad[1] = rgbquad[2] = (256 - i)%256;
memcpy(curr, rgbquad, sizeof(RGBQUAD));
curr += sizeof(RGBQUAD);
}
}

//用GDI+加载数据源，也可以是其他的，写入文件数据
Rect rect(0,0,width,height);		// Gdiplus+
BitmapData bmData;
Status iSucess = ima->LockBits(
&rect,
ImageLockModeRead,
ima->GetPixelFormat() ,
&bmData);

BYTE *_pixels = (BYTE*)bmData.Scan0;	//原图rect区域内存位置的起始指针，以BYTE作为单元类型
BYTE *_pRow;
int _strideoff8 = stride - width;			//前面计算的索引图像的stride
BYTE _grey;

// build pixles, GDI+ （windows）的图像数据的原点在左下角，参考一下OpenCV的IplImage结构体
switch(ima->GetPixelFormat())
{
case PixelFormat24bppRGB:
{
int _strideoff24 = stride - 3*width;			//前面计算的索引图像的stride

//  灰度化
for (int i=height-1; i >= 0; i--)
{
_pRow = _pixels + i*bmData.Stride;		// 当前的行

for (int j=width-1; j >= 0; j--)
{
BYTE* _pixels_b;		//b
BYTE* _pixels_g;		//g
BYTE* _pixels_r;		//r

_pixels_b = _pRow++;  //blue
_pixels_g = _pRow++;  //green
_pixels_r = _pRow++;  //red

_grey = GREY(*_pixels_r, *_pixels_g, *_pixels_b);

*curr = _grey;    //根据红绿蓝求出此像素的灰度值
curr++;
}
curr += _strideoff8;
}
}
break;

case PixelFormat32bppARGB:
{
//  灰度化
for (int i=height-1;i>=0;i--)
{
_pRow = _pixels + i*bmData.Stride;

for (int j=width-1;j>=0;j--)
{
BYTE* _pixels_b;
BYTE* _pixels_g;
BYTE* _pixels_r;

_pixels_b = _pRow++;  //blue
_pixels_g = _pRow++;  //green
_pixels_r = _pRow++;  //red
_pRow++;

_grey = GREY(*_pixels_r, *_pixels_g, *_pixels_b);

*curr = _grey;
curr++;
}
curr += _strideoff8;
}
}
break;
case PixelFormat8bppIndexed:  // Gdi+只能保存成24位真彩色的图像
{
// 不能直接用memcpy复制，需要水平镜像，memcpy(curr, _pixels, height * stride);
for (int i=height-1; i >= 0; i--)
{
_pRow = _pixels + i*bmData.Stride;
// 				for (int j=width-1;j >= 0;j--)
// 				{
// 					_grey = *_pRow++;
// 					*curr = _grey;
// 					curr++;
// 				}
memcpy(curr, _pRow, width);
curr += stride;
}
}
break;
default:
break;
}

// 保存图像 pMyBmp 到文件
try
{
CFile f(pszPath, CFile::modeCreate | CFile::modeWrite );
f.Write(pMyBmp, bitmapFileHeader.bfSize);
f.Close();
}
catch( CFileException* e )
{
TCHAR szCause[255];
e->GetErrorMessage(szCause, 255);

CString msg;
msg.Format(_T("file error: %s, m_cause：%d\n"),szCause, e->m_cause);

TRACE1("%s",msg);
AfxMessageBox(msg);
e->Delete();
}

//clean:
ima->UnlockBits(&bmData);
delete[] pMyBmp;

return TRUE;
}