  segmentation maps for background. However, ADE20k doesn't include the "background" class in its 150 labels.
  Therefore, reduce_labels is used to reduce all labels by 1, and to make sure no loss is computed for the
  background class (i.e. it replaces 0 in the annotated maps by 255, which is the ignore_index of the loss function
  used by [SegformerForSemanticSegmentation]). However, other datasets use the 0 index as
  background class and include this class as part of all labels. In that case, reduce_labels should be set to
  False, as loss should also be computed for the background class.
As most models, SegFormer comes in different sizes, the details of which can be found in the table below.
| Model variant | Depths    | Hidden sizes    | Decoder hidden size | Params (M) | ImageNet-1k Top 1 |
