From 8c4a0c2603975cfc63f4e4019386e001387c42c9 Mon Sep 17 00:00:00 2001
From: Gustaf Rydholm <gustaf.rydholm@gmail.com>
Date: Tue, 4 Oct 2022 22:08:38 +0200
Subject: Add greedy decoder

---
 text_recognizer/models/greedy_decoder.py | 51 ++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 text_recognizer/models/greedy_decoder.py

(limited to 'text_recognizer/models/greedy_decoder.py')

diff --git a/text_recognizer/models/greedy_decoder.py b/text_recognizer/models/greedy_decoder.py
new file mode 100644
index 0000000..9d2f192
--- /dev/null
+++ b/text_recognizer/models/greedy_decoder.py
@@ -0,0 +1,51 @@
+"""Greedy decoder."""
+from typing import Type
+from text_recognizer.data.tokenizer import Tokenizer
+import torch
+from torch import nn, Tensor
+
+
+class GreedyDecoder:
+    def __init__(
+        self,
+        network: Type[nn.Module],
+        tokenizer: Tokenizer,
+        max_output_len: int = 682,
+    ) -> None:
+        self.network = network
+        self.start_index = tokenizer.start_index
+        self.end_index = tokenizer.end_index
+        self.pad_index = tokenizer.pad_index
+        self.max_output_len = max_output_len
+
+    def __call__(self, x: Tensor) -> Tensor:
+        bsz = x.shape[0]
+
+        # Encode image(s) to latent vectors.
+        img_features = self.network.encode(x)
+
+        # Create a placeholder matrix for storing outputs from the network
+        indecies = torch.ones((bsz, self.max_output_len), dtype=torch.long).to(x.device)
+        indecies[:, 0] = self.start_index
+
+        for Sy in range(1, self.max_output_len):
+            tokens = indecies[:, :Sy]  # (B, Sy)
+            logits = self.network.decode(tokens, img_features)  # (B, C, Sy)
+            indecies_ = torch.argmax(logits, dim=1)  # (B, Sy)
+            indecies[:, Sy : Sy + 1] = indecies_[:, -1:]
+
+            # Early stopping of prediction loop if token is end or padding token.
+            if (
+                (indecies[:, Sy - 1] == self.end_index)
+                | (indecies[:, Sy - 1] == self.pad_index)
+            ).all():
+                break
+
+        # Set all tokens after end token to pad token.
+        for Sy in range(1, self.max_output_len):
+            idx = (indecies[:, Sy - 1] == self.end_index) | (
+                indecies[:, Sy - 1] == self.pad_index
+            )
+            indecies[idx, Sy] = self.pad_index
+
+        return indecies
-- 
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