Rails - Nov 2005 - image conversion w/ file column

hey

I''m trying to find a way to convert images that were uploaded using
file_column *before* file_column generates a thumb and copies them to
the final dir - this because 50x50 is pretty small and png would be a
much better format (in smaller dimensions) than jpg or gif.

This is what i have in my model (using rmagick for the conversion):

file_column :image, :magick => {:versions => { "thumb" =>
"50x50" }}
  before_validation :convert_to_png

  def convert_to_png
    if self.image_just_uploaded?
      imgpath = self.image()
      img = ImageList.new(imgpath)
      imgpath = imgpath.sub(/(jpg)$/, ''png'')
      img.write(imgpath)
    end
  end

Which manages to save a png version of the original image in the final
dir but the thumb is still being derived from the jpg.

Any clues?

spe.