Problem using rmagick in model class

I’m refactoring some code in order to conform to “the right way” of
doing
things. That is, I’m moving my image-saving code from my controller to
my
model. What worked fine in the controller class is not working in the
model
class.

Currently, my code looks somewhat like this:
##############
class RegistrantsController < ApplicationController
def upload_image
@registrant = Registrant.find(session[:registrant_id])
if request.post?
if(params[:crop_params])
@registrant.save_image(params[:image_to_crop],
params[:crop_params])
redirect_to :action => :index
else
@registrant.image = params[:registrant][:image]
File.chmod(0644, @registrant.image)
end
end
end
end

class Registrant < ActiveRecord::Base
require_gem ‘rmagick’

def save_image(image_to_crop, crop_params)

img_base = RAILS_ROOT + "/public/images/registrants/"
img_file =  self.id.to_s + ".jpg"
y, x, w, h = crop_params.split(',')

img = Magick::ImageList.new(image_to_crop) # this is throwing

“uninitialized constant ImageList”

img.crop!(x.to_i, y.to_i, w.to_i, h.to_i)
img.resize!(120, 120)
color_thumb = img.resize(32, 32)
grey_img = img.quantize(256, Magick::GRAYColorspace)
img.write(img_path + img_filename)
grey_img.write(img_base + 'greyscale/' + img_filename)
color_thumb.write(img_base + 'thumbnail/' + img_filename)

end
end
##############

Note the comment in there (# this is throwing “uninitialized constant
ImageList”)

Can anyone see what I’ve done wrong, or otherwise help out?

Thanks,
David R.