updates

8 files changed, 604 insertions, 10 deletions

diff --git a/src/text_recognizer/datasets/iam_preprocessor.py b/src/text_recognizer/datasets/iam_preprocessor.py
index 5a5136c..a93eb00 100644
--- a/src/text_recognizer/datasets/iam_preprocessor.py
+++ b/src/text_recognizer/datasets/iam_preprocessor.py
@@ -59,7 +59,7 @@ class Preprocessor:
         use_words: bool = False,
         prepend_wordsep: bool = False,
     ) -> None:
-        self.wordsep = "_"
+        self.wordsep = "▁"
         self._use_word = use_words
         self._prepend_wordsep = prepend_wordsep
 
diff --git a/src/text_recognizer/datasets/transforms.py b/src/text_recognizer/datasets/transforms.py
index 60987e0..b6a48f5 100644
--- a/src/text_recognizer/datasets/transforms.py
+++ b/src/text_recognizer/datasets/transforms.py
@@ -1,6 +1,10 @@
 """Transforms for PyTorch datasets."""
+from abc import abstractmethod
+from pathlib import Path
 import random
+from typing import Any, Optional, Union
 
+from loguru import logger
 import numpy as np
 from PIL import Image
 import torch
@@ -18,6 +22,7 @@ from torchvision.transforms import (
     ToTensor,
 )
 
+from text_recognizer.datasets.iam_preprocessor import Preprocessor
 from text_recognizer.datasets.util import EmnistMapper
 
 
@@ -145,3 +150,117 @@ class ToLower:
         """Corrects index value in target tensor."""
         device = target.device
         return torch.stack([x - 26 if x > 35 else x for x in target]).to(device)
+
+
+class ToCharcters:
+    """Converts integers to characters."""
+
+    def __init__(
+        self, pad_token: str, eos_token: str, init_token: str = None, lower: bool = True
+    ) -> None:
+        self.init_token = init_token
+        self.pad_token = pad_token
+        self.eos_token = eos_token
+        if self.init_token is not None:
+            self.emnist_mapper = EmnistMapper(
+                init_token=self.init_token,
+                pad_token=self.pad_token,
+                eos_token=self.eos_token,
+                lower=lower,
+            )
+        else:
+            self.emnist_mapper = EmnistMapper(
+                pad_token=self.pad_token, eos_token=self.eos_token, lower=lower
+            )
+
+    def __call__(self, y: Tensor) -> str:
+        """Converts a Tensor to a str."""
+        return (
+            "".join([self.emnist_mapper(int(i)) for i in y])
+            .strip("_")
+            .replace(" ", "▁")
+        )
+
+
+class WordPieces:
+    """Abstract transform for word pieces."""
+
+    def __init__(
+        self,
+        num_features: int,
+        data_dir: Optional[Union[str, Path]] = None,
+        tokens: Optional[Union[str, Path]] = None,
+        lexicon: Optional[Union[str, Path]] = None,
+        use_words: bool = False,
+        prepend_wordsep: bool = False,
+    ) -> None:
+        if data_dir is None:
+            data_dir = (
+                Path(__file__).resolve().parents[3] / "data" / "raw" / "iam" / "iamdb"
+            )
+            logger.debug(f"Using data dir: {data_dir}")
+            if not data_dir.exists():
+                raise RuntimeError(f"Could not locate iamdb directory at {data_dir}")
+        else:
+            data_dir = Path(data_dir)
+        processed_path = (
+            Path(__file__).resolve().parents[3] / "data" / "processed" / "iam_lines"
+        )
+        tokens_path = processed_path / tokens
+        lexicon_path = processed_path / lexicon
+
+        self.preprocessor = Preprocessor(
+            data_dir,
+            num_features,
+            tokens_path,
+            lexicon_path,
+            use_words,
+            prepend_wordsep,
+        )
+
+    @abstractmethod
+    def __call__(self, *args, **kwargs) -> Any:
+        """Transforms input."""
+        ...
+
+
+class ToWordPieces(WordPieces):
+    """Transforms str to word pieces."""
+
+    def __init__(
+        self,
+        num_features: int,
+        data_dir: Optional[Union[str, Path]] = None,
+        tokens: Optional[Union[str, Path]] = None,
+        lexicon: Optional[Union[str, Path]] = None,
+        use_words: bool = False,
+        prepend_wordsep: bool = False,
+    ) -> None:
+        super().__init__(
+            num_features, data_dir, tokens, lexicon, use_words, prepend_wordsep
+        )
+
+    def __call__(self, line: str) -> Tensor:
+        """Transforms str to word pieces."""
+        return self.preprocessor.to_index(line)
+
+
+class ToText(WordPieces):
+    """Takes word pieces and converts them to text."""
+
+    def __init__(
+        self,
+        num_features: int,
+        data_dir: Optional[Union[str, Path]] = None,
+        tokens: Optional[Union[str, Path]] = None,
+        lexicon: Optional[Union[str, Path]] = None,
+        use_words: bool = False,
+        prepend_wordsep: bool = False,
+    ) -> None:
+        super().__init__(
+            num_features, data_dir, tokens, lexicon, use_words, prepend_wordsep
+        )
+
+    def __call__(self, x: Tensor) -> str:
+        """Converts tensor to text."""
+        return self.preprocessor.to_text(x.tolist())
diff --git a/src/text_recognizer/networks/__init__.py b/src/text_recognizer/networks/__init__.py
index bac5d28..1521355 100644
--- a/src/text_recognizer/networks/__init__.py
+++ b/src/text_recognizer/networks/__init__.py
@@ -8,7 +8,7 @@ from .lenet import LeNet
 from .metrics import accuracy, cer, wer
 from .mlp import MLP
 from .residual_network import ResidualNetwork, ResidualNetworkEncoder
-from .transducer import TDS2d
+from .transducer import load_transducer_loss, TDS2d
 from .transformer import Transformer
 from .unet import UNet
 from .util import sliding_window
@@ -28,6 +28,7 @@ __all__ = [
     "greedy_decoder",
     "MLP",
     "LeNet",
+    "load_transducer_loss",
     "ResidualNetwork",
     "ResidualNetworkEncoder",
     "sliding_window",
diff --git a/src/text_recognizer/networks/cnn_transformer.py b/src/text_recognizer/networks/cnn_transformer.py
index 7133c26..a2d7926 100644
--- a/src/text_recognizer/networks/cnn_transformer.py
+++ b/src/text_recognizer/networks/cnn_transformer.py
@@ -112,11 +112,11 @@ class CNNTransformer(nn.Module):
         if self.max_pool is not None:
             src = self.max_pool(src)
 
-        if self.adaptive_pool is not None:
+        if self.adaptive_pool is not None and len(src.shape) == 4:
             src = rearrange(src, "b c h w -> b w c h")
             src = self.adaptive_pool(src)
             src = src.squeeze(3)
-        else:
+        elif len(src.shape) == 4:
             src = rearrange(src, "b c h w -> b (h w) c")
 
         b, t, _ = src.shape
diff --git a/src/text_recognizer/networks/transducer/__init__.py b/src/text_recognizer/networks/transducer/__init__.py
index fdd6662..8c19a01 100644
--- a/src/text_recognizer/networks/transducer/__init__.py
+++ b/src/text_recognizer/networks/transducer/__init__.py
@@ -1,2 +1,3 @@
 """Transducer modules."""
 from .tds_conv import TDS2d
+from .transducer import load_transducer_loss, Transducer
diff --git a/src/text_recognizer/networks/transducer/tds_conv.py b/src/text_recognizer/networks/transducer/tds_conv.py
index 018caf2..5fb8ba9 100644
--- a/src/text_recognizer/networks/transducer/tds_conv.py
+++ b/src/text_recognizer/networks/transducer/tds_conv.py
@@ -136,8 +136,10 @@ class TDS2d(nn.Module):
         self.tds = None
         self.fc = None
 
-    def _build_network(self) -> None:
+        self._build_network()
 
+    def _build_network(self) -> None:
+        in_channels = self.in_channels
         modules = []
         stride_h = np.prod([grp["stride"][0] for grp in self.tds_groups])
         if self.input_dim % stride_h:
@@ -151,7 +153,7 @@ class TDS2d(nn.Module):
             modules.extend(
                 [
                     nn.Conv2d(
-                        in_channels=self.in_channels,
+                        in_channels=in_channels,
                         out_channels=out_channels,
                         kernel_size=self.kernel_size,
                         padding=(self.kernel_size[0] // 2, self.kernel_size[1] // 2),
@@ -173,12 +175,10 @@ class TDS2d(nn.Module):
                     )
                 )
 
-            self.in_channels = out_channels
+            in_channels = out_channels
 
         self.tds = nn.Sequential(*modules)
-        self.fc = nn.Linear(
-            self.in_channels * self.input_dim // stride_h, self.output_dim
-        )
+        self.fc = nn.Linear(in_channels * self.input_dim // stride_h, self.output_dim)
 
     def forward(self, x: Tensor) -> Tensor:
         """Forward pass.
@@ -193,6 +193,9 @@ class TDS2d(nn.Module):
             Tensor: Output tensor.
 
         """
+        if len(x.shape) == 4:
+            x = x.squeeze(1)  # Squeeze the channel dim away.
+
         B, H, W = x.shape
         x = rearrange(
             x, "b (h1 h2) w -> b h1 h2 w", h1=self.in_channels, h2=H // self.in_channels
diff --git a/src/text_recognizer/networks/transducer/test.py b/src/text_recognizer/networks/transducer/test.py
new file mode 100644
index 0000000..cadcecc
--- /dev/null
+++ b/src/text_recognizer/networks/transducer/test.py
@@ -0,0 +1,60 @@
+import torch
+from torch import nn
+
+from text_recognizer.networks.transducer import load_transducer_loss, Transducer
+import unittest
+
+
+class TestTransducer(unittest.TestCase):
+    def test_viterbi(self):
+        T = 5
+        N = 4
+        B = 2
+
+        # fmt: off
+        emissions1 = torch.tensor((
+            0, 4, 0, 1,
+            0, 2, 1, 1,
+            0, 0, 0, 2,
+            0, 0, 0, 2,
+            8, 0, 0, 2,
+            ),
+            dtype=torch.float,
+        ).view(T, N)
+        emissions2 = torch.tensor((
+            0, 2, 1, 7,
+            0, 2, 9, 1,
+            0, 0, 0, 2,
+            0, 0, 5, 2,
+            1, 0, 0, 2,
+            ),
+            dtype=torch.float,
+        ).view(T, N)
+        # fmt: on
+
+        # Test without blank:
+        labels = [[1, 3, 0], [3, 2, 3, 2, 3]]
+        transducer = Transducer(
+            tokens=["a", "b", "c", "d"],
+            graphemes_to_idx={"a": 0, "b": 1, "c": 2, "d": 3},
+            blank="none",
+        )
+        emissions = torch.stack([emissions1, emissions2], dim=0)
+        predictions = transducer.viterbi(emissions)
+        self.assertEqual([p.tolist() for p in predictions], labels)
+
+        # Test with blank without repeats:
+        labels = [[1, 0], [2, 2]]
+        transducer = Transducer(
+            tokens=["a", "b", "c"],
+            graphemes_to_idx={"a": 0, "b": 1, "c": 2},
+            blank="optional",
+            allow_repeats=False,
+        )
+        emissions = torch.stack([emissions1, emissions2], dim=0)
+        predictions = transducer.viterbi(emissions)
+        self.assertEqual([p.tolist() for p in predictions], labels)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/src/text_recognizer/networks/transducer/transducer.py b/src/text_recognizer/networks/transducer/transducer.py
new file mode 100644
index 0000000..d7e3d08
--- /dev/null
+++ b/src/text_recognizer/networks/transducer/transducer.py
@@ -0,0 +1,410 @@
+"""Transducer and the transducer loss function.py
+
+Stolen from:
+    https://github.com/facebookresearch/gtn_applications/blob/master/transducer.py
+
+"""
+from pathlib import Path
+import itertools
+from typing import Dict, List, Optional, Union, Tuple
+
+from loguru import logger
+import gtn
+import torch
+from torch import nn
+from torch import Tensor
+
+from text_recognizer.datasets.iam_preprocessor import Preprocessor
+
+
+def make_scalar_graph(weight) -> gtn.Graph:
+    scalar = gtn.Graph()
+    scalar.add_node(True)
+    scalar.add_node(False, True)
+    scalar.add_arc(0, 1, 0, 0, weight)
+    return scalar
+
+
+def make_chain_graph(sequence) -> gtn.Graph:
+    graph = gtn.Graph(False)
+    graph.add_node(True)
+    for i, s in enumerate(sequence):
+        graph.add_node(False, i == (len(sequence) - 1))
+        graph.add_arc(i, i + 1, s)
+    return graph
+
+
+def make_transitions_graph(
+    ngram: int, num_tokens: int, calc_grad: bool = False
+) -> gtn.Graph:
+    transitions = gtn.Graph(calc_grad)
+    transitions.add_node(True, ngram == 1)
+
+    state_map = {(): 0}
+
+    # First build transitions which include <s>:
+    for n in range(1, ngram):
+        for state in itertools.product(range(num_tokens), repeat=n):
+            in_idx = state_map[state[:-1]]
+            out_idx = transitions.add_node(False, ngram == 1)
+            state_map[state] = out_idx
+            transitions.add_arc(in_idx, out_idx, state[-1])
+
+    for state in itertools.product(range(num_tokens), repeat=ngram):
+        state_idx = state_map[state[:-1]]
+        new_state_idx = state_map[state[1:]]
+        # p(state[-1] | state[:-1])
+        transitions.add_arc(state_idx, new_state_idx, state[-1])
+
+    if ngram > 1:
+        # Build transitions which include </s>:
+        end_idx = transitions.add_node(False, True)
+        for in_idx in range(end_idx):
+            transitions.add_arc(in_idx, end_idx, gtn.epsilon)
+
+    return transitions
+
+
+def make_lexicon_graph(word_pieces: List, graphemes_to_idx: Dict) -> gtn.Graph:
+    """Constructs a graph which transduces letters to word pieces."""
+    graph = gtn.Graph(False)
+    graph.add_node(True, True)
+    for i, wp in enumerate(word_pieces):
+        prev = 0
+        for l in wp[:-1]:
+            n = graph.add_node()
+            graph.add_arc(prev, n, graphemes_to_idx[l], gtn.epsilon)
+            prev = n
+        graph.add_arc(prev, 0, graphemes_to_idx[wp[-1]], i)
+    graph.arc_sort()
+    return graph
+
+
+def make_token_graph(
+    token_list: List, blank: str = "none", allow_repeats: bool = True
+) -> gtn.Graph:
+    """Constructs a graph with all the individual token transition models."""
+    if not allow_repeats and blank != "optional":
+        raise ValueError("Must use blank='optional' if disallowing repeats.")
+
+    ntoks = len(token_list)
+    graph = gtn.Graph(False)
+
+    # Creating nodes
+    graph.add_node(True, True)
+    for i in range(ntoks):
+        # We can consume one or more consecutive word
+        # pieces for each emission:
+        # E.g. [ab, ab, ab] transduces to [ab]
+        graph.add_node(False, blank != "forced")
+
+    if blank != "none":
+        graph.add_node()
+
+    # Creating arcs
+    if blank != "none":
+        # Blank index is assumed to be last (ntoks)
+        graph.add_arc(0, ntoks + 1, ntoks, gtn.epsilon)
+        graph.add_arc(ntoks + 1, 0, gtn.epsilon)
+
+    for i in range(ntoks):
+        graph.add_arc((ntoks + 1) if blank == "forced" else 0, i + 1, i)
+        graph.add_arc(i + 1, i + 1, i, gtn.epsilon)
+
+        if allow_repeats:
+            if blank == "forced":
+                # Allow transitions from token to blank only
+                graph.add_arc(i + 1, ntoks + 1, ntoks, gtn.epsilon)
+            else:
+                # Allow transition from token to blank and all other tokens
+                graph.add_arc(i + 1, 0, gtn.epsilon)
+
+        else:
+            # allow transitions to blank and all other tokens except the same token
+            graph.add_arc(i + 1, ntoks + 1, ntoks, gtn.epsilon)
+            for j in range(ntoks):
+                if i != j:
+                    graph.add_arc(i + 1, j + 1, j, j)
+
+    return graph
+
+
+class TransducerLossFunction(torch.autograd.Function):
+    @staticmethod
+    def forward(
+        ctx,
+        inputs,
+        targets,
+        tokens,
+        lexicon,
+        transition_params=None,
+        transitions=None,
+        reduction="none",
+    ) -> Tensor:
+        B, T, C = inputs.shape
+
+        losses = [None] * B
+        emissions_graphs = [None] * B
+
+        if transitions is not None:
+            if transition_params is None:
+                raise ValueError("Specified transitions, but not transition params.")
+
+            cpu_data = transition_params.cpu().contiguous()
+            transitions.set_weights(cpu_data.data_ptr())
+            transitions.calc_grad = transition_params.requires_grad
+            transitions.zero_grad()
+
+        def process(b: int) -> None:
+            # Create emission graph:
+            emissions = gtn.linear_graph(T, C, inputs.requires_grad)
+            cpu_data = inputs[b].cpu().contiguous()
+            emissions.set_weights(cpu_data.data_ptr())
+            target = make_chain_graph(targets[b])
+            target.arc_sort(True)
+
+            # Create token tot grapheme decomposition graph
+            tokens_target = gtn.remove(gtn.project_output(gtn.compose(target, lexicon)))
+            tokens_target.arc_sort()
+
+            # Create alignment graph:
+            aligments = gtn.project_input(
+                gtn.remove(gtn.compose(tokens, tokens_target))
+            )
+            aligments.arc_sort()
+
+            # Add transitions scores:
+            if transitions is not None:
+                aligments = gtn.intersect(transitions, aligments)
+                aligments.arc_sort()
+
+            loss = gtn.forward_score(gtn.intersect(emissions, aligments))
+
+            # Normalize if needed:
+            if transitions is not None:
+                norm = gtn.forward_score(gtn.intersect(emissions, transitions))
+                loss = gtn.subtract(loss, norm)
+
+            losses[b] = gtn.negate(loss)
+
+            # Save for backward:
+            if emissions.calc_grad:
+                emissions_graphs[b] = emissions
+
+        gtn.parallel_for(process, range(B))
+
+        ctx.graphs = (losses, emissions_graphs, transitions)
+        ctx.input_shape = inputs.shape
+
+        # Optionally reduce by target length
+        if reduction == "mean":
+            scales = [(1 / len(t) if len(t) > 0 else 1.0) for t in targets]
+        else:
+            scales = [1.0] * B
+
+        ctx.scales = scales
+
+        loss = torch.tensor([l.item() * s for l, s in zip(losses, scales)])
+        return torch.mean(loss.to(inputs.device))
+
+    @staticmethod
+    def backward(ctx, grad_output) -> Tuple:
+        losses, emissions_graphs, transitions = ctx.graphs
+        scales = ctx.scales
+
+        B, T, C = ctx.input_shape
+        calc_emissions = ctx.needs_input_grad[0]
+        input_grad = torch.empty((B, T, C)) if calc_emissions else None
+
+        def process(b: int) -> None:
+            scale = make_scalar_graph(scales[b])
+            gtn.backward(losses[b], scale)
+            emissions = emissions_graphs[b]
+            if calc_emissions:
+                grad = emissions.grad().weights_to_numpy()
+                input_grad[b] = torch.tensor(grad).view(1, T, C)
+
+        gtn.parallel_for(process, range(B))
+
+        if calc_emissions:
+            input_grad = input_grad.to(grad_output.device)
+            input_grad *= grad_output / B
+
+        if ctx.needs_input_grad[4]:
+            grad = transitions.grad().weights_to_numpy()
+            transition_grad = torch.tensor(grad).to(grad_output.device)
+            transition_grad *= grad_output / B
+        else:
+            transition_grad = None
+
+        return (
+            input_grad,
+            None,  # target
+            None,  # tokens
+            None,  # lexicon
+            transition_grad,  # transition params
+            None,  # transitions graph
+            None,
+        )
+
+
+TransducerLoss = TransducerLossFunction.apply
+
+
+class Transducer(nn.Module):
+    def __init__(
+        self,
+        tokens: List,
+        graphemes_to_idx: Dict,
+        ngram: int = 0,
+        transitions: str = None,
+        blank: str = "none",
+        allow_repeats: bool = True,
+        reduction: str = "none",
+    ) -> None:
+        """A generic transducer loss function.
+
+        Args:
+            tokens (List) : A list of iterable objects (e.g. strings, tuples, etc)
+                representing the output tokens of the model (e.g. letters,
+                word-pieces, words). For example ["a", "b", "ab", "ba", "aba"]
+                could be a list of sub-word tokens.
+            graphemes_to_idx (dict) : A dictionary mapping grapheme units (e.g.
+                "a", "b", ..) to their corresponding integer index.
+            ngram (int) : Order of the token-level transition model. If `ngram=0`
+                then no transition model is used.
+            blank (string) : Specifies the usage of blank token
+                'none' - do not use blank token
+                'optional' - allow an optional blank inbetween tokens
+                'forced' - force a blank inbetween tokens (also referred to as garbage token)
+            allow_repeats (boolean) : If false, then we don't allow paths with
+                consecutive tokens in the alignment graph. This keeps the graph
+                unambiguous in the sense that the same input cannot transduce to
+                different outputs.
+        """
+        super().__init__()
+        if blank not in ["optional", "forced", "none"]:
+            raise ValueError(
+                "Invalid value specified for blank. Must be in ['optional', 'forced', 'none']"
+            )
+        self.tokens = make_token_graph(tokens, blank=blank, allow_repeats=allow_repeats)
+        self.lexicon = make_lexicon_graph(tokens, graphemes_to_idx)
+        self.ngram = ngram
+        if ngram > 0 and transitions is not None:
+            raise ValueError("Only one of ngram and transitions may be specified")
+
+        if ngram > 0:
+            transitions = make_transitions_graph(
+                ngram, len(tokens) + int(blank != "none"), True
+            )
+
+        if transitions is not None:
+            self.transitions = transitions
+            self.transitions.arc_sort()
+            self.transitions_params = nn.Parameter(
+                torch.zeros(self.transitions.num_arcs())
+            )
+        else:
+            self.transitions = None
+            self.transitions_params = None
+        self.reduction = reduction
+
+    def forward(self, inputs: Tensor, targets: Tensor) -> TransducerLoss:
+        TransducerLoss(
+            inputs,
+            targets,
+            self.tokens,
+            self.lexicon,
+            self.transitions_params,
+            self.transitions,
+            self.reduction,
+        )
+
+    def viterbi(self, outputs: Tensor) -> List[Tensor]:
+        B, T, C = outputs.shape
+
+        if self.transitions is not None:
+            cpu_data = self.transition_params.cpu().contiguous()
+            self.transitions.set_weights(cpu_data.data_ptr())
+            self.transitions.calc_grad = False
+
+        self.tokens.arc_sort()
+
+        paths = [None] * B
+
+        def process(b: int) -> None:
+            emissions = gtn.linear_graph(T, C, False)
+            cpu_data = outputs[b].cpu().contiguous()
+            emissions.set_weights(cpu_data.data_ptr())
+
+            if self.transitions is not None:
+                full_graph = gtn.intersect(emissions, self.transitions)
+            else:
+                full_graph = emissions
+
+            # Find the best path and remove back-off arcs:
+            path = gtn.remove(gtn.viterbi_path(full_graph))
+
+            # Left compose the viterbi path with the "aligment to token"
+            # transducer to get the outputs:
+            path = gtn.compose(path, self.tokens)
+
+            # When there are ambiguous paths (allow_repeats is true), we take
+            # the shortest:
+            path = gtn.viterbi_path(path)
+            path = gtn.remove(gtn.project_output(path))
+            paths[b] = path.labels_to_list()
+
+        gtn.parallel_for(process, range(B))
+        predictions = [torch.IntTensor(path) for path in paths]
+        return predictions
+
+
+def load_transducer_loss(
+    num_features: int,
+    ngram: int,
+    tokens: str,
+    lexicon: str,
+    transitions: str,
+    blank: str,
+    allow_repeats: bool,
+    prepend_wordsep: bool = False,
+    use_words: bool = False,
+    data_dir: Optional[Union[str, Path]] = None,
+    reduction: str = "mean",
+) -> Tuple[Transducer, int]:
+    if data_dir is None:
+        data_dir = (
+            Path(__file__).resolve().parents[4] / "data" / "raw" / "iam" / "iamdb"
+        )
+        logger.debug(f"Using data dir: {data_dir}")
+        if not data_dir.exists():
+            raise RuntimeError(f"Could not locate iamdb directory at {data_dir}")
+    else:
+        data_dir = Path(data_dir)
+    processed_path = (
+        Path(__file__).resolve().parents[4] / "data" / "processed" / "iam_lines"
+    )
+    tokens_path = processed_path / tokens
+    lexicon_path = processed_path / lexicon
+
+    if transitions is not None:
+        transitions = gtn.load(str(processed_path / transitions))
+
+    preprocessor = Preprocessor(
+        data_dir, num_features, tokens_path, lexicon_path, use_words, prepend_wordsep,
+    )
+
+    num_tokens = preprocessor.num_tokens
+
+    criterion = Transducer(
+        preprocessor.tokens,
+        preprocessor.graphemes_to_index,
+        ngram=ngram,
+        transitions=transitions,
+        blank=blank,
+        allow_repeats=allow_repeats,
+        reduction=reduction,
+    )
+
+    return criterion, num_tokens + int(blank != "none")