fix: handle 4D

nithumb.py

@@ -34,7 +34,8 @@ def main():
     image = ((image - image.min()) *
              (255 / (image.max() - image.min()))).astype('uint8')
 
-    # Select the centre slice if 3D.
+    # Select the centre slice if 3D. Centre frame if 4D
+    image = image[:, :, :, image.shape[3]//2] if image.ndim == 4 else image
     image = image[:, :, image.shape[2]//2] if image.ndim == 3 else image
 
     # Generate and save the snapshot and its thumbnail.