function anterior(){
  
  if(lafoto<1){
    var NumImagen = lafoto
  } else {
    var NumImagen = lafoto-=1;
  }
  if(lafoto==0){
	  document.getElementById('prev_ant').style.display='none';	  
	  }
document.imgSrc.src = misImagenes[lafoto];
blendimage('contenedor','imgSrc',misImagenes[lafoto],600,el_pie_imagenes[lafoto]);
document.getElementById('next_sig').style.display='block';
cambiar_tam('imgSrc');
}
function siguiente(){
	
  if(lafoto>(totalfotos-2)){
    var NumImagen = lafoto
  } else {
    var NumImagen = lafoto+=1;
  }
  if(lafoto>0)
  {
	  document.getElementById('prev_ant').style.display='block';
	  }
 document.imgSrc.src = misImagenes[lafoto];
	 if(lafoto==totalfotos-1){ document.getElementById('next_sig').style.display='none';}
 	blendimage('contenedor','imgSrc',misImagenes[lafoto],600,el_pie_imagenes[lafoto]);
	
cambiar_tam('imgSrc');
}

function cambiar_tam(idcalc)
{
  distancia=(parseInt((document.getElementById(idcalc).height)-53)/2);
document.getElementById('colnext').style.marginTop=distancia+'px';
document.getElementById('colprev').style.marginTop=distancia+'px';
	
	}
function opacity(id, opacStart, opacEnd, millisec) {
	//speed for each frame
	var speed = Math.round(millisec / 100);
	var timer = 0;

	//determine the direction for the blending, if start and end are the same nothing happens
	if(opacStart > opacEnd) {
		for(i = opacStart; i >= opacEnd; i--) {
			setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed));
			timer++;
		}
	} else if(opacStart < opacEnd) {
		for(i = opacStart; i <= opacEnd; i++)
			{
			setTimeout("changeOpac(" + i + ",'" + id + "')",(timer * speed));
			timer++;
		}
	}
}

//change the opacity for different browsers
function changeOpac(opacity, id) {
	var object = document.getElementById(id).style; 
	object.opacity = (opacity / 100);
	object.MozOpacity = (opacity / 100);
	object.KhtmlOpacity = (opacity / 100);
	object.filter = "alpha(opacity=" + opacity + ")";
}

function shiftOpacity(id, millisec) {
	//if an element is invisible, make it visible, else make it ivisible
	if(document.getElementById(id).style.opacity == 0) {
		opacity(id, 0, 100, millisec);
	} else {
		opacity(id, 100, 0, millisec);
	}
}

function blendimage(divid, imageid, imagefile, millisec,eltexto_delaimagen) {
	var speed = Math.round(millisec / 100);
	var timer = 0;
	
	//set the current image as background
	//document.getElementById(divid).style.backgroundImage = "url(" + document.getElementById(imageid).src + ")";
	
	//make image transparent
	changeOpac(0, imageid);
	
	//make new image
	
	
	document.getElementById(imageid).src = imagefile;
	
	//cambiando el pie de la foto
	document.getElementById(imageid).title =eltexto_delaimagen;
	document.getElementById(imageid).alt=eltexto_delaimagen;
	
	document.getElementById('pie_delafoto').innerHTML=eltexto_delaimagen;
	
	

	//fade in image
	for(i = 0; i <= 100; i++) {
		setTimeout("changeOpac(" + i + ",'" + imageid + "')",(timer * speed));
		timer++;
	}
}

function currentOpac(id, opacEnd, millisec) {
	//standard opacity is 100
	var currentOpac = 100;
	
	//if the element has an opacity set, get it
	if(document.getElementById(id).style.opacity < 100) {
		currentOpac = document.getElementById(id).style.opacity * 100;
	}

	//call for the function that changes the opacity
	opacity(id, currentOpac, opacEnd, millisec)
}