add image buffers for gan

engine/util/container.py

@@ -1,3 +1,6 @@
+import torch
+
+
 class LossContainer:
     def __init__(self, weight, loss):
         self.weight = weight
@@ -7,3 +10,57 @@ class LossContainer:
         if self.weight > 0:
             return self.weight * self.loss(*args, **kwargs)
         return 0.0
+
+
+class GANImageBuffer:
+    """This class implements an image buffer that stores previously
+    generated images.
+    This buffer allows us to update the discriminator using a history of
+    generated images rather than the ones produced by the latest generator
+    to reduce model oscillation.
+    Args:
+        buffer_size (int): The size of image buffer. If buffer_size = 0,
+            no buffer will be created.
+        buffer_ratio (float): The chance / possibility  to use the images
+            previously stored in the buffer.
+    """
+
+    def __init__(self, buffer_size, buffer_ratio=0.5):
+        self.buffer_size = buffer_size
+        # create an empty buffer
+        if self.buffer_size > 0:
+            self.img_num = 0
+            self.image_buffer = []
+        self.buffer_ratio = buffer_ratio
+
+    def query(self, images):
+        """Query current image batch using a history of generated images.
+        Args:
+            images (Tensor): Current image batch without history information.
+        """
+        if self.buffer_size == 0:  # if the buffer size is 0, do nothing
+            return images
+        return_images = []
+        for image in images:
+            image = torch.unsqueeze(image.data, 0)
+            # if the buffer is not full, keep inserting current images
+            if self.img_num < self.buffer_size:
+                self.img_num = self.img_num + 1
+                self.image_buffer.append(image)
+                return_images.append(image)
+            else:
+                use_buffer = torch.rand(1) < self.buffer_ratio
+                # by self.buffer_ratio, the buffer will return a previously
+                # stored image, and insert the current image into the buffer
+                if use_buffer:
+                    random_id = torch.randint(0, self.buffer_size, (1,)).item()
+                    image_tmp = self.image_buffer[random_id].clone()
+                    self.image_buffer[random_id] = image
+                    return_images.append(image_tmp)
+                # by (1 - self.buffer_ratio), the buffer will return the
+                # current image
+                else:
+                    return_images.append(image)
+        # collect all the images and return
+        return_images = torch.cat(return_images, 0)
+        return return_images