Question

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?

Answer 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);

where 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