HBITMAP to JPEG /PNG without CImage in C++

问题:

I've got a HBITMAP that I want to save into a JPEG/PNG stream or array of bytes. The problem is that I'm using mingw as my compiler so I can't use CImage.. which would have made my life easier.

I can get the pixels from the bitmap without any problems, but I have no idea how to get access to them in JPEG/PNG-format.

Where do I start?

回答1:

If you have access DirectX library you may use IStream to convert your image to JPEG http://msdn.microsoft.com/en-us/library/windows/desktop/aa380034(v=vs.85).aspx

or if you have GDI+ something like this might work

Gdiplus::Bitmap bmp(hbmpImage,(HPALETTE)0);
CLSID pngClsid;
GetEncoderClsid(L"image/png", &pngClsid);
bmp.Save(L"D:\image.png",&pngClsid,NULL);

GetEncoderLCLsid looks like this int GetEncoderClsid(const WCHAR* format, CLSID* pClsid) { UINT num = 0; // number of image encoders UINT size = 0; // size of the image encoder array in bytes

   ImageCodecInfo* pImageCodecInfo = NULL;

   GetImageEncodersSize(&num, &size);
   if(size == 0)
      return -1;  // Failure

   pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
   if(pImageCodecInfo == NULL)
      return -1;  // Failure

   GetImageEncoders(num, size, pImageCodecInfo);

   for(UINT j = 0; j < num; ++j)
   {
      if( wcscmp(pImageCodecInfo[j].MimeType, format) == 0 )
      {
         *pClsid = pImageCodecInfo[j].Clsid;
         free(pImageCodecInfo);
         return j;  // Success
      }    
   }

   free(pImageCodecInfo);
   return -1;  // Failure
}

don't forget to initialize GDI+

 GdiplusStartupInput gdiplusStartupInput;
   ULONG_PTR gdiplusToken;
   GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

if don't have access to either you may use libjpeg but you need to put all the dependencies packages from the GnuWin32 site. Much faster the code in this page should work, just forget about the boost

libjpeg dying without message

回答2:

Another option is to use the WIC API (Windows Imaging Component), which gives direct access to image encoders and decoders. I believe GDI+ may use this under the covers.