the callback function is called. If not specified, the callback is called at
every step.   Returns 
ImagePipelineOutput or tuple
  
If return_dict is True, ImagePipelineOutput is returned, otherwise a tuple is
returned where the first element is a list with the generated images.
  The call function to the pipeline for generation.  Examples:   Copied >>> from diffusers import VersatileDiffusionPipeline
>>> import torch
>>> import requests
>>> fr