Rails - Jan 2006 - File_column : how can I resize/convert/whatever an image according to form-submitted values?

Hi guys,

I want to have a file upload form which would allow the user to ask for 
certain transformations of the image before saving it - most importantly, to 
resize it.

Now, how can I make an instance of FileColumn enabled model process these 
imagemagick instructions? 

My model looks looks somewhat like :

class Image < ActiveRecord::Base

attr_accessor :resize_dimension, :resize_to

before_save   :resize_image

file_column :path,
	    :versions => { "thumbnail" => "100x100>" }

private
def resize_image
  # stuff that processes the image with the form-provided values 
[:resize_dimension] (can be "w" (width) or "h" (height) )
and [:resize_to],
so as to obtain the equivalent of "convert -resize ''250x''
stuff.jpg" or
"convert -resize ''x100'' stuff.jpg"
end

end

What should I put in that resize_image callback function? Would a callback be 
the DRY way, to begin with?

Any tips, ideas, previous experiences, anyone?



TIA,

Dominique Rose-Rosette