It's nearly there. I'm just in the middle of packaging it up and working out how to submit it to extras-devel.

Most of the features are there now. You can change the settings and preview them then save the full-res picture as a jpg. I do need to work on optimising the filter algorithms though - saving a full-res picture takes a few minutes. I'll probably put in an option to save a reduced size image to workaround this.