Simple nanoc handling of width and height for image items, using the "dimensions" Ruby gem.

image.rb

# Put this in the lib/ directory.

require 'dimensions'

def image_tag(item, attributes={})
  "<img src='#{item.path}' width='#{item[:img_width]}' height='#{item[:img_height]}' alt='#{attributes[:alt]}'" + (attributes[:title] ? " title='#{attributes[:title]}'" : "") + " />"
end

Rules.rb

preprocess do
  @items.each do |item|
    if %w{png gif jpg jpeg}.include? item[:extension]
      dimensions = Dimensions.dimensions(item.raw_filename)
      item[:img_width]  = dimensions[0]
      item[:img_height] = dimensions[1]
    end
  end
end