Does GDI+ have standard image encoder CLSIDs?

The GDI+ Image::Save method requires a CLSID parameter to specify the encoder to use. The documentation points to some sample code for getting the encoder associated with a particular MIME type, such as image/jpeg or image/png. However I'm balking at the thought of copying a half-page function just to support a 1-line debugging aid where I save an intermediate result out to disk.

Shouldn't there be a list of standard CLSIDs for the standard encoders? Where would I find such a list? I haven't been able to find one by searching Microsoft's include files.

There isn't one. I think they intended the codec list to be extensible and support plugins, but never got around to it. Given that they haven't made any changes to GDI+ in quite some time, they likely won't anytime soon. You could probably get away with generating your own hard coded list based on an enumeration of Gdiplus::GetImageEncoders.

That is:

image/bmp  : {557cf400-1a04-11d3-9a73-0000f81ef32e}
image/jpeg : {557cf401-1a04-11d3-9a73-0000f81ef32e} 
image/gif  : {557cf402-1a04-11d3-9a73-0000f81ef32e} 
image/tiff : {557cf405-1a04-11d3-9a73-0000f81ef32e}
image/png  : {557cf406-1a04-11d3-9a73-0000f81ef32e}

Here's the function I routinely cut&paste between projects for getting at the CLSID of the encoder. You could modify it to be a table lookup.

HRESULT GetGdiplusEncoderClsid(__in LPCWSTR pwszFormat, __out GUID *pGUID)
{
    HRESULT hr = E_FAIL;
    UINT  nEncoders = 0;          // number of image encoders
    UINT  nSize = 0;              // size of the image encoder array in bytes
    CAutoVectorPtr<BYTE> spData;
    Gdiplus::ImageCodecInfo* pImageCodecInfo = NULL;
    Gdiplus::Status status;
    bool fFound = false;

    // param check

    if ((pwszFormat == NULL) || (pwszFormat[0] == 0) || (pGUID == NULL))
    {
        return E_POINTER;
    }

    *pGUID = GUID_NULL;

    status = Gdiplus::GetImageEncodersSize(&nEncoders, &nSize);

    if ((status != Gdiplus::Ok) || (nSize == 0))
    {
        return E_FAIL;
    }


    spData.Allocate(nSize);

    if (spData == NULL)
    {
        return E_FAIL;
    }

    pImageCodecInfo = (Gdiplus::ImageCodecInfo*)(BYTE*)spData;

    status = Gdiplus::GetImageEncoders(nEncoders, nSize, pImageCodecInfo);

    if (status != Gdiplus::Ok)
    {
       return E_FAIL;
    }

    for(UINT j = 0; j < nEncoders; ++j)
    {
        if( wcscmp(pImageCodecInfo[j].MimeType, pwszFormat) == 0 )
        {
            *pGUID = pImageCodecInfo[j].Clsid;
            fFound = true;
            break;
        }    
    }

    hr = fFound ? S_OK : E_FAIL;

    return hr;
}

You will probably want to use ImageCodecInfo with GetImageEncodersSize() and GetImageEncoders() I'm not aware of any easier way.

EDIT: If you know specifically what you want and damn all the rest you can get away with doing something like this ...

CLSID pngClsid;
GetEncoderClsid("image/png", &pngClsid);
image.Save("imagename.png", &pngClsid, NULL);

James Newton

If you just want to write a PNG, this appears to work:

// image/png  : {557cf406-1a04-11d3-9a73-0000f81ef32e}
const CLSID pngEncoderClsId = { 0x557cf406, 0x1a04, 0x11d3,{ 0x9a,0x73,0x00,0x00,0xf8,0x1e,0xf3,0x2e } }; 
stat = image->Save(L"test.png", &pngEncoderClsId, NULL);

Note the reformatting of the hex values.

From: How to initialize a constant CLSID

来源：https://stackoverflow.com/questions/5345803/does-gdi-have-standard-image-encoder-clsids

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