message: minor update to the image filename format
diff: @@ -134,8 +134,7 @@ def get_image_sample_groups(dir, features):
  if (suffix.isdecimal() or
  (suffix.endswith('spp') and suffix[:-3].isdecimal()) or
  suffix == 'ref' or suffix == 'reference' or
  - suffix == 'gt' or suffix == 'groundtruth' or
  - suffix == 'target'):
  + suffix == 'gt' or suffix == 'target'):
  group = prefix
  image_groups[group].add(image_name)
  