24bit彩色图像转8bit灰度图

char szFileName[MAX_PATH] = "";
OPENFILENAME file={0};
file.lStructSize=sizeof(file);
file.lpstrFile=szFileName;
file.nMaxFile=MAX_PATH;
file.lpstrFilter="BMP Files(*.bmp)\0*.bmp\0JPG Files(*.jpg)\0*.jpg\0All Files\0*.*\0\0";
file.nFilterIndex=1;
if(::GetOpenFileName(&file)){
imgFile = new char[sizeof(szFileName) + 1];
strcpy(imgFile, szFileName);
//::MessageBox(NULL,imgFile,"TEST",MB_OK);
}

char* tmp = new char[255];
sprintf(tmp,"Open File: %s",imgFile);


if(imgFile == NULL || strlen(imgFile)<4){
AfxMessageBox("Image FileName Not Right.");
return;
}

//判断图像格式
USES_CONVERSION;
Bitmap bmp(A2W(imgFile));//加载BMP
int iPF= bmp.GetPixelFormat();

sprintf(tmp,"data.PixelFormat=%d", iPF);
AfxMessageBox(tmp);

if(iPF == PixelFormat8bppIndexed){
objCDib = new CDib();
objCDib->LoadFile(imgFile);

//view->RedrawWindow();
view->Invalidate();
}else if(iPF == PixelFormat24bppRGB){
// Specify a pixel format.
UINT w = bmp.GetWidth();
UINT h = bmp.GetHeight();

// Lock the bitmap's bits.
Rect rect(0, 0, w, h);

BitmapData data;
bmp.LockBits(&rect, ImageLockModeRead, PixelFormat24bppRGB, &data);
unsigned char *pData = static_cast<unsigned char*>(data.Scan0);


int w0 = w;
if(w % 4 !=0){
//w0 += 4-w%4; //这里不需要对齐
}

int bitwidth = w*3;
if(w*3 % 4 !=0){
bitwidth += 4-w*3%4;//原数据已对齐
}

sprintf(tmp,"w=%d,w0=%d,bitwidth=%d",w,w0,bitwidth);
AfxMessageBox(tmp);

BYTE* NewImg = new BYTE[w0*h];
memset(NewImg,0,w0*h);

for(int i=h-1;i>=0;i--) {
//memcpy(NewImg+i*ByteWidth,img+i*width*3,width*3);
for(int j=0;j<w;j++){
UINT R = *(pData+i*bitwidth + j*3);
UINT G = *(pData+i*bitwidth + j*3 +1);
UINT B = *(pData+i*bitwidth + j*3 +2);
UINT Y = 0.299*R+0.587*G+0.114*B;
NewImg[i*w0+j] = R;
}
}

//释放位图资源
bmp.UnlockBits(&data);

注：对24bit位图，一个像素使用3个字节存储。对齐是指行的总字节数对齐，即bitmapWidth*3 % 4必须为0，而不是bitmapWidth%4等于0。

对齐方法：

int bitwidth = w*3;
if(w*3 % 4 !=0){
bitwidth += 4-w*3%4;//原数据已对齐
}