              self.samples = None
              self.target = None
              return
          logger.debug("Generating preview")
          if self.preview_feed is None:
              self.set_preview_feed()
          batch = next(self.preview_feed)
          self.samples = batch["samples"]
          self.target = [batch["targets"][self.model.largest_face_index]]
          if self.use_mask:
              self.target += [batch["masks"]]
 
</s> remove         self.target = [batch["targets"][self.model.largest_face_index]]
        if self.use_mask:
            self.target += [batch["masks"]]
 </s> add         self.target = batch["targets"][self.model.largest_face_index]
        self.masks = batch["masks"][0] </s> remove         self.mask = None
 </s> add         self.masks = None </s> remove         retval = [samples[0:num_images]] if samples is not None else [self.samples[0:num_images]]
        if self.use_mask:
            retval.extend(tgt[0:num_images] for tgt in images)
        else:
            retval.extend(images[0:num_images])
 </s> add         masks = masks if masks is not None else self.masks
        samples = samples if samples is not None else self.samples
        retval = [samples[0:num_images], images[0:num_images], masks[0:num_images]] </s> remove         if self.use_mask:
            batch = [[batch["feed"], batch["masks"]], batch["targets"] + [batch["masks"]]]
        else:
            batch = [batch["feed"], batch["targets"]]
        self.generate_preview(do_preview)
        return batch
 </s> add         targets_use_mask = self.model.training_opts["replicate_input_mask"]
        model_inputs = batch["feed"] + batch["masks"] if self.use_mask else batch["feed"]
        model_targets = batch["targets"] + batch["masks"] if targets_use_mask else batch["targets"]
        return model_inputs, model_targets
              self.samples = None
              self.target = None
              return
          logger.debug("Generating preview")


          batch = next(self.preview_feed)
          self.samples = batch["samples"]
          self.target = [batch["targets"][self.model.largest_face_index]]
          if self.use_mask:
              self.target += [batch["masks"]]
keep keep keep keep replace replace keep keep keep keep keep
 Smart Mask Exposure for Extraction & Training (#831)

Smart Masks - Initial Commit 
plugins/train/trainer/_base.py