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总结一下个人所知道的使用GDI+缩放图片的方法.
方法一:最简单的,使用GetThumbnailImage,这个方法的局限性对支持内嵌缩略图的图片文件无效. 因为MSDN中提到:如果图片文件有内嵌的缩略图,那么就提取这个缩略图返回,否则就缩放原图片,不过我想对位图还是安全的:
Bitmap * image = new Bitmap(L"MagicLinux.bmp");
Image* pScaledImage = NULL;
UINT nWidth = image->GetWidth()/2;
UINT nHeight= image->GetHeight()/2;
pScaledImage = image->GetThumbnailImage(nWidth, nHeight, NULL, NULL);
delete pScaledImage;
delete image;
方法二,使用Graphics::DrawImage,这样还可以控制InterpolationMode(插值模式,在缩放和旋转时候使用),即可以控制缩放质量高低.也可以通过Graphics对象做其他的控制.
方法也比较简单,但是却费了我好久时间才研究出来,没办法,不熟悉GDI+,在MSDN中翻来翻去,:)
但是有个问题是,传入的Bitmap必须是24位以上的才行,也就是传入前必须要先做好转换,因为Graphics::FromImage不能接收16位及一下的格式,
Bitmap * ScaleBitmap(Bitmap * pBitmap,UINT nWidth,UINT nHeight)
{
Bitmap * pTemp = new Bitmap(nWidth,nHeight,pBitmap->GetPixelFormat());
if( pTemp )
{
Graphics * g = Graphics::FromImage(pTemp);
if( g )
{
// use the best interpolation mode
g->SetInterpolationMode(InterpolationModeHighQualityBicubic);
g->DrawImage(pBitmap,0,0,nWidth,nHeight);
delete g;
}
}
return pTemp;
}
pScaledImage = ScaleBitmap(image,nWidth,nHeight);
方法三,是从Codeguru上一个帖子上看到,和方法二类似,但是用了GDI的东东,我试了试,没成功,得到的是一幅黑图片,可能的原因是Bitmap::FromHBITMAP的第二个参数设置不对
原文代码如下:
Bitmap * bitmap = new Bitmap(TempBuf); // Create the bitmap
HDC Screen = GetDC(WindowVars.Handle);
piTemp->hdc = CreateCompatibleDC(Screen); // Create a memory DC
HBITMAP hbitmap;
if (bStretchPictures)
hbitmap = CreateCompatibleBitmap(Screen, Size.X, Size.Y);
else
hbitmap = CreateCompatibleBitmap(Screen, bitmap->GetWidth(), bitmap->GetHeight());
SelectObject(piTemp->hdc, hbitmap); // Initialize the DC
Graphics * graphics = new Graphics(piTemp->hdc); // Create the Graphics class
if (bStretchPictures)
graphics->DrawImage(bitmap, 0, 0, Size.X, Size.Y); // Draw the scaled image
else
graphics->DrawImage(bitmap, 0, 0, bitmap->GetWidth(), bitmap->GetHeight());
ReleaseDC(WindowVars.Handle, Screen);
delete graphics;
delete bitmap;
另外再补上保存图片的代码:
bool SaveAsImageFile(Image * pImage,LPCWSTR lpszFileName,LPCWSTR lpszImageType)
{
UINT num = 0;
// number of image encoders
UINT size = 0;
// size of the image encoder array in bytes
ImageCodecInfo* pImageCodecInfo = NULL;
if(GetImageEncodersSize(&num, &size)!= Ok || size == 0 )
return false; // Failure
pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
if(pImageCodecInfo == NULL)
return false; // Failure
if(GetImageEncoders(num, size, pImageCodecInfo)!= Ok )
return false;
bool bOk = false;
for(UINT j = 0; j < num; ++j)
{
if( wcscmp(pImageCodecInfo[j].MimeType, lpszImageType) == 0 )
{
pImage->Save(lpszFileName,&(pImageCodecInfo[j].Clsid));
bOk = true;
break;
}
}
free(pImageCodecInfo);
return bOk;
}
调用象这样就可以保存成各种图片(当然要求有对应的encoder才行):
SaveAsImageFile(pScaledImage,L"1.bmp",L"image/bmp");
SaveAsImageFile(pScaledImage,L"1.jpg",L"image/jpeg");
SaveAsImageFile(pScaledImage,L"1.png",L"image/png");
方法四: ?
最后
一个不错的GDI+ FAQ site: http://www.bobpowell.net/faqmain.htm
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