You can try something like this:
library = SiteObjects.MediaLibraries.FirstItem;
if(library != null)
file = library.Files.Where("FileName = 'noimage'").FirstItem;
if(file != null)
imageUrl = GetMediaFileDirectUrl(library.ID, file.FilePath);
This is only a dummy code. You can use better way to find library that you need (f.e. by code name), and also for specific file (f.e. file ID or any other data that you have in you transformation).
You can also move all this in custom macro method and make it easier to call it.