// zmena hlavniho obrazku a jeho popisku kliknutim na nahled

function changeImage(src, width, height, title) {
  var mainImage = document.getElementById('mainimage');
  var mainImageTitle = document.getElementById('mainimage-title');
  
  if (src == "" || width == "" || height == "") return false;
  if (title == "") title = "(bez popisu)";
  
  if (mainImage != null) {
    mainImage.src = src;
    mainImage.width = width;
    mainImage.height = height;
    mainImage.alt = title;
    mainImage.title = title;
  }
  if (mainImageTitle != null) {
    mainImageTitle.innerText = title;
  }
  return false;
}