type by feeding the produced data to a 
callback. Can be used when you want to store the image to something 
other than a file, such as an in-memory buffer or a socket.  
If error is set, FALSE will be returned. Possible errors
include those in the GDK_PIXBUF_ERROR domain and whatever the save
function generates.gdkPixbufSaveToCallback(object, save.func, user.data, type, .errwarn = TRUE)save.funcGdkPixbufSaveFunc]  a function that is called to save each block of data that
  the save routine generates.user.datatypeerrorGError]  return location for error, or NULLgdkPixbufSave for more details.  Since 2.4