reduce cuda memory for basicvsr (#393)

ppgan/models/basicvsr_model.py

@@ -83,10 +83,11 @@ class BasicVSRModel(BaseSRModel):
         self.current_iter += 1
 
     def test_iter(self, metrics=None):
+        self.gt = self.gt.cpu()
         self.nets['generator'].eval()
         with paddle.no_grad():
-            self.output = self.nets['generator'](self.lq)
-            self.visual_items['output'] = self.output[:, 0, :, :, :]
+            output = self.nets['generator'](self.lq)
+            self.visual_items['output'] = output[:, 0, :, :, :].cpu()
         self.nets['generator'].train()
 
         out_img = []
@@ -94,7 +95,7 @@ class BasicVSRModel(BaseSRModel):
 
         _, t, _, _, _ = self.gt.shape
         for i in range(t):
-            out_tensor = self.output[0, i]
+            out_tensor = output[0, i]
             gt_tensor = self.gt[0, i]
             out_img.append(tensor2img(out_tensor, (0., 1.)))
             gt_img.append(tensor2img(gt_tensor, (0., 1.)))