autoshape() update for PIL greyscale inputs (#1279)

models/common.py

 # This file contains modules common to various models
 
 import math
+
 import numpy as np
 import torch
 import torch.nn as nn
@@ -144,7 +145,8 @@ class autoShape(nn.Module):
         shape0, shape1 = [], []  # image and inference shapes
         batch = range(len(x))  # batch size
         for i in batch:
-            x[i] = np.array(x[i])[:, :, :3]  # up to 3 channels if png
+            x[i] = np.array(x[i])  # to numpy
+            x[i] = x[i][:, :, :3] if x[i].ndim == 3 else np.tile(x[i][:, :, None], 3)  # enforce 3ch input
             s = x[i].shape[:2]  # HWC
             shape0.append(s)  # image shape
             g = (size / max(s))  # gain