var bgpath="grafika/"
var bgmeny=new Array()
bgmeny[0]=bgpath + "pozadiHttp.jpg"
bgmeny[1]=bgpath + "pozadiMarie.jpg"
bgmeny[2]=bgpath + "pozadiBroz.jpg"
//preload images
var processed=new Array()
for (i=0;i<bgmeny.length;i++){
processed[i]=new Image()
processed[i].src=bgmeny[i]
}

function Zmen(NaCoMenit) {
	switch (NaCoMenit) {
		case "petka" : {
			document.getElementById("navObr").style.background = "black  url(grafika/pozadiHttp.jpg) repeat-x bottom left";
			break;
		};
		case "ctyrka" : {
			document.getElementById("navObr").style.background = "black  url(grafika/pozadiHttp.jpg) repeat-x bottom left";
			break;
		};
		case "trojka" : {
			document.getElementById("navObr").style.background = "black  url(grafika/pozadiMarie.jpg) repeat-x bottom left";
			break;
		};
		case "dvojka" : {
			document.getElementById("navObr").style.background = "black  url(grafika/pozadiBroz.jpg) repeat-x bottom left";
			break;
		};
		case "jednicka" : {
			document.getElementById("navObr").style.background = "black  url(grafika/pozadiHttp.jpg) repeat-x bottom left";
			break;
		};
		<!-- pozadiHttp -->
	};

};

function Vrat() {
	document.getElementById("navObr").style.background = AktivniBarva;
};