Use ImageMagick to create optimised and progressive JPGs

Use the following command to optimise a JPG and make it progressive:

convert -strip -interlace Plane -quality 80 input-file.jpg output-file.jpg 

Batch all the images in a folder like this:

for i in source/images/backgrounds/*.jpg; do convert -strip -interlace Plane -quality 80 $i $i; done  

With Carrierwave and MiniMagick you can create an optimise function like this:

def optimize
  manipulate! do |img|
      return img unless img.mime_type.match /image\/jpeg/
      img.strip
      img.combine_options do |c|
          c.quality "80"
          c.depth "8"
          c.interlace "plane"
      end
      img
  end
end

And use it in your uploader like this:

version :large do
  process :optimize
end