add validation step

model.py

@@ -64,6 +64,18 @@ class ColorTransformerModel(L.LightningModule):
         self.log("s_loss", s_loss)
         return loss
 
+    def validation_step(self):
+        inputs, labels = batch  # these are true HSV labels - no learning allowed.
+        outputs = self.forward(inputs)
+        distance = torch.minimum(
+            torch.abs(outputs - labels), torch.abs(1 + outputs - labels)
+        )
+        mean_loss = torch.mean(distance)
+        max_loss = torch.max(distance)
+        self.log("val_mean_loss", mean_loss)
+        self.log("val_max_loss", max_loss)
+        return mean_loss
+
     def configure_optimizers(self):
         optimizer = torch.optim.SGD(
             self.parameters(),