Added function to aggregate attention maps

Closes #35 (closed)

dan/predict/attention.py

@@ -31,6 +31,27 @@ def split_text(text, level, word_separators, line_separators):
     return text_split, offset
 
 
+def compute_coverage(text: str, max_value: float, offset: int, attentions):
+    """
+    Aggregates attention maps for the current text piece (char, word, line)
+    :param text: Text piece selected with offset after splitting DAN prediction
+    :param max_value: Maximum "attention intensity" for parts of a text piece, used for normalization
+    :param offset: Offset value to get the relevant part of text piece
+    :param attentions: Attention weights of size (n_char, feature_height, feature_width)
+    """
+    _, height, width = attentions.shape
+
+    # blank vector to accumulate weights for the current text
+    coverage_vector = np.zeros((height, width))
+    for i in range(len(text)):
+        local_weight = cv2.resize(attentions[i + offset], (width, height))
+        coverage_vector = np.clip(coverage_vector + local_weight, 0, 1)
+
+    # Normalize coverage vector
+    coverage_vector = (coverage_vector / max_value * 255).astype(np.uint8)
+    return coverage_vector
+
+
 def plot_attention(
     image,
     text,
@@ -50,6 +71,7 @@ def plot_attention(
     :param scale: Scaling factor for the output gif image
     :param outname: Name of the gif image
     """
+
     height, width, _ = image.shape
     attention_map = []
 
@@ -64,20 +86,15 @@ def plot_attention(
     tot_len = 0
 
     max_value = weights.sum(0).max()
+
     for text_piece in text_list:
-        # blank vector to accumulate weights for the current word/line
-        coverage_vector = np.zeros((height, width))
-        for i in range(len(text_piece)):
-            local_weight = weights[i + tot_len]
-            local_weight = cv2.resize(local_weight, (width, height))
-            coverage_vector = np.clip(coverage_vector + local_weight, 0, 1)
+        # Accumulate weights for the current word/line and resize to original image size
+        coverage_vector = compute_coverage(text_piece, max_value, tot_len, weights)
+        coverage_vector = cv2.resize(coverage_vector, (width, height))
 
         # Keep track of text length
         tot_len += len(text_piece) + offset
 
-        # Normalize coverage vector
-        coverage_vector = (coverage_vector / max_value * 255).astype(np.uint8)
-
         # Blend coverage vector with original image
         blank_array = np.zeros((height, width)).astype(np.uint8)
         coverage_vector = Image.fromarray(