How do you crop an image with carrierwave 'after the fact' in rails?

What I’d like to do is upload an image, then take the user to a new
page where I will use Jcrop to let the user select the part of the
image they want to crop, and then store that image. Essentially, I
want to make it a 2-stage process.

I know how to do the javascript part, and I understand the basic flow
of how to create this functionality. However, I am not aware of the
carrierwave specifics on how to accomplish this.

The closest thing I can find is:


But I still can’t pass in the height/width and starting x,y to crop

For example, how can I tell carrierwave to do the cropping ‘after the
fact’ - i.e. not when the image is uploaded for the first time? I see
methods to “process” the image, but they happen automatically with
fixed Height and Width. How can I delay this?


This is the best I can do. There’s probably an easier way to do it,
but this is my hack:

Here is my ‘POST’ controller action when the cropping info is passed:

  def update_crop
    @user = User.find(
    @user.crop(params[:x].to_i, params[:y].to_i, params[:h].to_i,


    redirect_to(profile_path, :notice => 'Your profile and avatar

was successfully updated.’)

Here is the method to add to the User model that contains an “avatar”
image uploader:

  def crop(x, y, h, w)
    image =
    cropped_image = image.crop(x, y, h, w)


Basically this just hi-jacks the current one, overwrites it, and then
tells Carrierwave to create the thumbnail again with the new cropped
version. Seems to work.

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