support greyscale models

docs/pretrained_models.rst

@@ -113,6 +113,9 @@ Zoobot includes weights for the following pretrained models:
 
     Missing a model you need? Reach out! There's a good chance we can train any model supported by `timm <https://github.com/huggingface/pytorch-image-models>`_.
 
+.. note:: 
+
+    New in Zoobot v2.0.1: greyscale (single channel) versions are available `here <https://huggingface.co/collections/mwalmsley/zoobot-encoders-greyscale-66427c51133285ca01b490c6>`_.
 
 Which model should I use?
 ===========================

zoobot/pytorch/training/finetune.py

@@ -124,7 +124,14 @@ def __init__(
 
         if name is not None:
             assert encoder is None, 'Cannot pass both name and encoder to use'
-            self.encoder = timm.create_model(name, num_classes=0, pretrained=True)
+            if 'greyscale' in name:
+                # I'm not sure why timm is happy to convert color model stem to greyscale 
+                # but doesn't correctly load greyscale model without this hack
+                logging.info('Loading greyscale model (auto-detected from name)')
+                timm_kwargs = {'in_chans': 1}
+            else:
+                timm_kwargs = {}
+            self.encoder = timm.create_model(name, num_classes=0, pretrained=True, **timm_kwargs)
             self.encoder_dim = self.encoder.num_features
 
         elif zoobot_checkpoint_loc is not None: