HTML as output format using Wand

I'm trying to write simple program which converts some image to html
page, i.e. analogue for `convert img.png img.html', but have a
problem.  Here is a simple code snip without any sanities:

    #include <wand/magick-wand.h>
    
    int
    main()
    {
            MagickWand* w;
            void* blob;
            unsigned int len;
    
            MagickWandGenesis();
            w = NewMagickWand();
    
            MagickReadImage(w, "/path/to/my/image.png");
            MagickSetImageFormat(w, "HTML");
    
            blob = MagickGetImageBlob(w, &len);
            return 0;
    }

This program core dumps, however if i change "HTML" to something more
graphical, like "JPG", "GIF", etc - then everything works as expected
and blob get its data.  What i'm doing wrong with HTML ?

I'm using ImageMagick 6.4.5 built from FreeBSD 6.2 ports

thanks

-- 
lg