gistfile1.erb

<div id="main_image" class="<%= content_for :image_width -%>">
  <a href="<%= @product.image_file.downcase %>" rel="popup">
    <%= render :layout => false do %> 
      <% options, itag = medium_image :id => "primary" -%>
      <% content_for :image_width do
        options[:width] > 362 ? "wide_image" : "narrow_image"
      end %>
      <%= itag %>
    <% end -%>
  </a>
</div>