Need som help writing raw data to a jpg

Hi!

I'm just starting using libgd and I wold need some help. I'm trying to make a 
program that should be able to write some raw data I've got on a float 
pointer to a jpg file. I couldn't find the correct way to do it looking at 
the examples on the gd page. 

so long I got

	im = gdImageCreate(outsamples, outlines);
	black = gdImageColorAllocate(im, 0, 0, 0);
	white = gdImageColorAllocate(im, 255, 255, 255);

	if((quick=fopen(argv[2], "wb"))==NULL)
	{
		printf("No se pudo abrir el jpg archivo de salida %s\n", argv[2]);
		return 2;
	}
	gdImageJpeg(im, quick, 70);

but I cant put my data into the im pointer. I I'm not sure which function 
should I use to do it. I tried: gdImageCreateFromJpegPtr(int size, void 
*data) withpout any help.

I'm now starting to doubt if gd can do such thing.

 Any sugestion?

   Tomas