6 files changed, 793 insertions, 0 deletions
diff --git a/text_recognizer/data/utils/build_transitions.py b/text_recognizer/data/utils/build_transitions.py
new file mode 100644
index 0000000..0f987ca
--- /dev/null
+++ b/text_recognizer/data/utils/build_transitions.py
@@ -0,0 +1,261 @@
+"""Builds transition graph.
+
+Most code stolen from here:
+    https://github.com/facebookresearch/gtn_applications/blob/master/scripts/build_transitions.py
+"""
+
+import collections
+import itertools
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+
+import click
+import gtn
+from loguru import logger
+
+
+START_IDX = -1
+END_IDX = -2
+WORDSEP = "▁"
+
+
+def build_graph(ngrams: List, disable_backoff: bool = False) -> gtn.Graph:
+    """Returns a gtn Graph based on the ngrams."""
+    graph = gtn.Graph(False)
+    ngram = len(ngrams)
+    state_to_node = {}
+
+    def get_node(state: Optional[List]) -> Any:
+        node = state_to_node.get(state, None)
+
+        if node is not None:
+            return node
+
+        start = state == tuple([START_IDX]) if ngram > 1 else True
+        end = state == tuple([END_IDX]) if ngram > 1 else True
+        node = graph.add_node(start, end)
+        state_to_node[state] = node
+
+        if not disable_backoff and not end:
+            # Add back off when adding node.
+            for n in range(1, len(state) + 1):
+                backoff_node = state_to_node.get(state[n:], None)
+
+                # Epsilon transition to the back-off state.
+                if backoff_node is not None:
+                    graph.add_arc(node, backoff_node, gtn.epsilon)
+                    break
+        return node
+
+    for grams in ngrams:
+        for gram in grams:
+            istate, ostate = gram[:-1], gram[len(gram) - ngram + 1 :]
+            inode = get_node(istate)
+
+            if END_IDX not in gram[1:] and gram[1:] not in state_to_node:
+                raise ValueError(
+                    "Ill formed counts: if (x, y_1, ..., y_{n-1}) is above"
+                    "the n-gram threshold, then (y_1, ..., y_{n-1}) must be"
+                    "above the (n-1)-gram threshold"
+                )
+
+            if END_IDX in ostate:
+                # Merge all state having </s> into one as final graph generated
+                # will be similar.
+                ostate = tuple([END_IDX])
+
+            onode = get_node(ostate)
+            # p(gram[-1] | gram[:-1])
+            graph.add_arc(
+                inode, onode, gtn.epsilon if gram[-1] == END_IDX else gram[-1]
+            )
+    return graph
+
+
+def count_ngrams(lines: List, ngram: List, tokens_to_index: Dict) -> List:
+    """Counts the number of ngrams."""
+    counts = [collections.Counter() for _ in range(ngram)]
+    for line in lines:
+        # Prepend implicit start token.
+        token_line = [START_IDX]
+        for t in line:
+            token_line.append(tokens_to_index[t])
+        token_line.append(END_IDX)
+        for n, counter in enumerate(counts):
+            start_offset = n == 0
+            end_offset = ngram == 1
+            for e in range(n + start_offset, len(token_line) - end_offset):
+                counter[tuple(token_line[e - n : e + 1])] += 1
+
+    return counts
+
+
+def prune_ngrams(ngrams: List, prune: List) -> List:
+    """Prunes ngrams."""
+    pruned_ngrams = []
+    for n, grams in enumerate(ngrams):
+        grams = grams.most_common()
+        pruned_grams = [gram for gram, c in grams if c > prune[n]]
+        pruned_ngrams.append(pruned_grams)
+    return pruned_ngrams
+
+
+def add_blank_grams(pruned_ngrams: List, num_tokens: int, blank: str) -> List:
+    """Adds blank token to grams."""
+    all_grams = [gram for grams in pruned_ngrams for gram in grams]
+    maxorder = len(pruned_ngrams)
+    blank_grams = {}
+    if blank == "forced":
+        pruned_ngrams = [pruned_ngrams[0] if i == 0 else [] for i in range(maxorder)]
+    pruned_ngrams[0].append(tuple([num_tokens]))
+    blank_grams[tuple([num_tokens])] = True
+
+    for gram in all_grams:
+        # Iterate over all possibilities by using a vector of 0s, 1s to
+        # denote whether a blank is being used at each position.
+        if blank == "optional":
+            # Given a gram ab.. if order n, we have n + 1 positions
+            # available whether to use blank or not.
+            onehot_vectors = itertools.product([0, 1], repeat=len(gram) + 1)
+        elif blank == "forced":
+            # Must include a blank token in between.
+            onehot_vectors = [[1] * (len(gram) + 1)]
+        else:
+            raise ValueError(
+                "Invalid value specificed for blank. Must be in |optional|forced|none|"
+            )
+
+    for j in onehot_vectors:
+        new_array = []
+        for idx, oz in enumerate(j[:-1]):
+            if oz == 1 and gram[idx] != START_IDX:
+                new_array.append(num_tokens)
+            new_array.append(gram[idx])
+        if j[-1] == 1 and gram[-1] != END_IDX:
+            new_array.append(num_tokens)
+        for n in range(maxorder):
+            for e in range(n, len(new_array)):
+                cur_gram = tuple(new_array[e - n : e + 1])
+                if num_tokens in cur_gram and cur_gram not in blank_grams:
+                    pruned_ngrams[n].append(cur_gram)
+                    blank_grams[cur_gram] = True
+
+    return pruned_ngrams
+
+
+def add_self_loops(pruned_ngrams: List) -> List:
+    """Adds self loops to the ngrams."""
+    maxorder = len(pruned_ngrams)
+
+    # Use dict for fast search.
+    all_grams = set([gram for grams in pruned_ngrams for gram in grams])
+    for o in range(1, maxorder):
+        for gram in pruned_ngrams[o - 1]:
+            # Repeat one of the tokens.
+            for pos in range(len(gram)):
+                if gram[pos] == START_IDX or gram[pos] == END_IDX:
+                    continue
+                new_gram = gram[:pos] + (gram[pos],) + gram[pos:]
+
+                if new_gram not in all_grams:
+                    pruned_ngrams[o].append(new_gram)
+                    all_grams.add(new_gram)
+    return pruned_ngrams
+
+
+def parse_lines(lines: List, lexicon: Path) -> List:
+    """Parses lines with a lexicon."""
+    with open(lexicon, "r") as f:
+        lex = (line.strip().split() for line in f)
+        lex = {line[0]: line[1:] for line in lex}
+        print(len(lex))
+    return [[t for w in line.split(WORDSEP) for t in lex[w]] for line in lines]
+
+
+@click.command()
+@click.option("--data_dir", type=str, default=None, help="Path to dataset root.")
+@click.option(
+    "--tokens", type=str, help="Path to token list (in order used with training)."
+)
+@click.option("--lexicon", type=str, default=None, help="Path to lexicon")
+@click.option(
+    "--prune",
+    nargs=2,
+    type=int,
+    help="Threshold values for prune unigrams, bigrams, etc.",
+)
+@click.option(
+    "--blank",
+    default=click.Choice(["none", "optional", "forced"]),
+    help="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)",
+)
+@click.option("--self_loops", is_flag=True, help="Add self loops for tokens")
+@click.option("--disable_backoff", is_flag=True, help="Disable backoff transitions")
+@click.option("--save_path", default=None, help="Path to save transition graph.")
+def cli(
+    data_dir: str,
+    tokens: str,
+    lexicon: str,
+    prune: List[int],
+    blank: str,
+    self_loops: bool,
+    disable_backoff: bool,
+    save_path: str,
+) -> None:
+    """CLI for creating the transitions."""
+    logger.info(f"Building {len(prune)}-gram transition models.")
+
+    if data_dir is None:
+        data_dir = (
+            Path(__file__).resolve().parents[2] / "data" / "processed" / "iam_lines"
+        )
+        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)
+
+    # Build table of counts and the back-off if below threshold.
+    with open(data_dir / "train.txt", "r") as f:
+        lines = [line.strip() for line in f]
+
+    with open(data_dir / tokens, "r") as f:
+        tokens = [line.strip() for line in f]
+
+    if lexicon is not None:
+        lexicon = data_dir / lexicon
+        lines = parse_lines(lines, lexicon)
+
+    tokens_to_idx = {t: e for e, t in enumerate(tokens)}
+
+    ngram = len(prune)
+
+    logger.info("Counting data...")
+    ngrams = count_ngrams(lines, ngram, tokens_to_idx)
+
+    pruned_ngrams = prune_ngrams(ngrams, prune)
+
+    for n in range(ngram):
+        logger.info(f"Kept {len(pruned_ngrams[n])} of {len(ngrams[n])} {n + 1}-grams")
+
+    if blank == "none":
+        pruned_ngrams = add_blank_grams(pruned_ngrams, len(tokens_to_idx), blank)
+
+    if self_loops:
+        pruned_ngrams = add_self_loops(pruned_ngrams)
+
+    logger.info("Building graph from pruned ngrams...")
+    graph = build_graph(pruned_ngrams, disable_backoff)
+    logger.info(f"Graph has {graph.num_arcs()} arcs and {graph.num_nodes()} nodes.")
+
+    save_path = str(data_dir / save_path)
+
+    logger.info(f"Saving graph to {save_path}")
+    gtn.save(save_path, graph)
+
+
+if __name__ == "__main__":
+    cli()
diff --git a/text_recognizer/data/utils/download_utils.py b/text_recognizer/data/utils/download_utils.py
new file mode 100644
index 0000000..a5a5360
--- /dev/null
+++ b/text_recognizer/data/utils/download_utils.py
@@ -0,0 +1,73 @@
+"""Util functions for downloading datasets."""
+import hashlib
+from pathlib import Path
+from typing import Dict, Optional
+from urllib.request import urlretrieve
+
+from loguru import logger as log
+from tqdm import tqdm
+
+
+def _compute_sha256(filename: Path) -> str:
+    """Returns the SHA256 checksum of a file."""
+    with filename.open(mode="rb") as f:
+        return hashlib.sha256(f.read()).hexdigest()
+
+
+class TqdmUpTo(tqdm):
+    """TQDM progress bar when downloading files.
+
+    From https://github.com/tqdm/tqdm/blob/master/examples/tqdm_wget.py
+
+    """
+
+    def update_to(
+        self, blocks: int = 1, block_size: int = 1, total_size: Optional[int] = None
+    ) -> None:
+        """Updates the progress bar.
+
+        Args:
+            blocks (int): Number of blocks transferred so far. Defaults to 1.
+            block_size (int): Size of each block, in tqdm units. Defaults to 1.
+            total_size (Optional[int]): Total size in tqdm units. Defaults to None.
+        """
+        if total_size is not None:
+            self.total = total_size
+        self.update(blocks * block_size - self.n)
+
+
+def _download_url(url: str, filename: str) -> None:
+    """Downloads a file from url to filename, with a progress bar."""
+    with TqdmUpTo(unit="B", unit_scale=True, unit_divisor=1024, miniters=1) as t:
+        urlretrieve(url, filename, reporthook=t.update_to, data=None)  # nosec
+
+
+def download_dataset(metadata: Dict, dl_dir: Path) -> Optional[Path]:
+    """Downloads dataset using a metadata file.
+
+    Args:
+        metadata (Dict): A metadata file of the dataset.
+        dl_dir (Path): Download directory for the dataset.
+
+    Returns:
+        Optional[Path]: Returns filename if dataset is downloaded, None if it already
+            exists.
+
+    Raises:
+        ValueError: If the SHA-256 value is not the same between the dataset and
+            the metadata file.
+
+    """
+    dl_dir.mkdir(parents=True, exist_ok=True)
+    filename = dl_dir / metadata["filename"]
+    if filename.exists():
+        return
+    log.info(f"Downloading raw dataset from {metadata['url']} to {filename}...")
+    _download_url(metadata["url"], filename)
+    log.info("Computing the SHA-256...")
+    sha256 = _compute_sha256(filename)
+    if sha256 != metadata["sha256"]:
+        raise ValueError(
+            "Downloaded data file SHA-256 does not match that listed in metadata document."
+        )
+    return filename
diff --git a/text_recognizer/data/utils/iam_preprocessor.py b/text_recognizer/data/utils/iam_preprocessor.py
new file mode 100644
index 0000000..60ecff1
--- /dev/null
+++ b/text_recognizer/data/utils/iam_preprocessor.py
@@ -0,0 +1,209 @@
+"""Preprocessor for extracting word letters from the IAM dataset.
+
+The code is mostly stolen from:
+    https://github.com/facebookresearch/gtn_applications/blob/master/datasets/iamdb.py
+"""
+import collections
+import itertools
+from pathlib import Path
+import re
+from typing import List, Optional, Set, Union
+
+import click
+from loguru import logger as log
+import torch
+
+
+def load_metadata(
+    data_dir: Path, wordsep: str, use_words: bool = False
+) -> collections.defaultdict:
+    """Loads IAM metadata and returns it as a dictionary."""
+    forms = collections.defaultdict(list)
+    filename = "words.txt" if use_words else "lines.txt"
+
+    with open(data_dir / "ascii" / filename, "r") as f:
+        lines = (line.strip().split() for line in f if line[0] != "#")
+        for line in lines:
+            # Skip word segmentation errors.
+            if use_words and line[1] == "err":
+                continue
+            text = " ".join(line[8:])
+
+            # Remove garbage tokens:
+            text = text.replace("#", "")
+
+            # Swap word sep form | to wordsep
+            text = re.sub(r"\|+|\s", wordsep, text).strip(wordsep)
+            form_key = "-".join(line[0].split("-")[:2])
+            line_key = "-".join(line[0].split("-")[:3])
+            box_idx = 4 - use_words
+            box = tuple(int(val) for val in line[box_idx : box_idx + 4])
+            forms[form_key].append({"key": line_key, "box": box, "text": text})
+    return forms
+
+
+class Preprocessor:
+    """A preprocessor for the IAM dataset."""
+
+    def __init__(
+        self,
+        data_dir: Union[str, Path],
+        num_features: int,
+        tokens_path: Optional[Union[str, Path]] = None,
+        lexicon_path: Optional[Union[str, Path]] = None,
+        use_words: bool = False,
+        prepend_wordsep: bool = False,
+        special_tokens: Optional[Set[str]] = None,
+    ) -> None:
+        self.wordsep = "▁"
+        self._use_word = use_words
+        self._prepend_wordsep = prepend_wordsep
+        self.special_tokens = special_tokens if special_tokens is not None else None
+        self.data_dir = Path(data_dir)
+        self.forms = load_metadata(self.data_dir, self.wordsep, use_words=use_words)
+
+        # Load the set of graphemes:
+        graphemes = set()
+        for _, form in self.forms.items():
+            for line in form:
+                graphemes.update(line["text"].lower())
+        self.graphemes = sorted(graphemes)
+
+        # Build the token-to-index and index-to-token maps.
+        if tokens_path is not None:
+            with open(tokens_path, "r") as f:
+                self.tokens = [line.strip() for line in f]
+        else:
+            self.tokens = self.graphemes
+
+        if lexicon_path is not None:
+            with open(lexicon_path, "r") as f:
+                lexicon = (line.strip().split() for line in f)
+                lexicon = {line[0]: line[1:] for line in lexicon}
+                self.lexicon = lexicon
+        else:
+            self.lexicon = None
+
+        if self.special_tokens is not None:
+            special_tokens_ = (*self.special_tokens, "#", "*")
+            self.tokens += special_tokens_
+            self.graphemes += special_tokens_
+
+        self.graphemes_to_index = {t: i for i, t in enumerate(self.graphemes)}
+        self.tokens_to_index = {t: i for i, t in enumerate(self.tokens)}
+        self.num_features = num_features
+        self.text = []
+
+    @property
+    def num_tokens(self) -> int:
+        """Returns the number or tokens."""
+        return len(self.tokens)
+
+    @property
+    def use_words(self) -> bool:
+        """If words are used."""
+        return self._use_word
+
+    def extract_train_text(self) -> None:
+        """Extracts training text."""
+        keys = []
+        with open(self.data_dir / "task" / "trainset.txt") as f:
+            keys.extend((line.strip() for line in f))
+
+        for _, examples in self.forms.items():
+            for example in examples:
+                if example["key"] not in keys:
+                    continue
+                self.text.append(example["text"].lower())
+
+    def _to_index(self, line: str) -> torch.LongTensor:
+        if self.special_tokens is not None and line in self.special_tokens:
+            return torch.LongTensor([self.tokens_to_index[line]])
+        token_to_index = self.graphemes_to_index
+        if self.lexicon is not None:
+            if len(line) > 0:
+                # If the word is not found in the lexicon, fall back to letters.
+                tokens = [
+                    t
+                    for w in line.split(self.wordsep)
+                    for t in self.lexicon.get(w, self.wordsep + w)
+                ]
+            token_to_index = self.tokens_to_index
+        if self._prepend_wordsep:
+            tokens = itertools.chain([self.wordsep], tokens)
+        return torch.LongTensor([token_to_index[t] for t in tokens])
+
+    def to_index(self, line: str) -> torch.LongTensor:
+        """Converts text to a tensor of indices."""
+        if self.special_tokens is not None:
+            pattern = f"({'|'.join(self.special_tokens)})"
+            lines = list(filter(None, re.split(pattern, line)))
+            return torch.cat([self._to_index(line) for line in lines])
+        return self._to_index(line)
+
+    def to_text(self, indices: List[int]) -> str:
+        """Converts indices to text."""
+        # Roughly the inverse of `to_index`
+        encoding = self.graphemes
+        if self.lexicon is not None:
+            encoding = self.tokens
+        return self._post_process(encoding[i] for i in indices)
+
+    def tokens_to_text(self, indices: List[int]) -> str:
+        """Converts tokens to text."""
+        return self._post_process(self.tokens[i] for i in indices)
+
+    def _post_process(self, indices: List[int]) -> str:
+        """A list join."""
+        return "".join(indices).strip(self.wordsep)
+
+
+@click.command()
+@click.option("--data_dir", type=str, default=None, help="Path to iam dataset")
+@click.option(
+    "--use_words", is_flag=True, help="Load word segmented dataset instead of lines"
+)
+@click.option(
+    "--save_text", type=str, default=None, help="Path to save parsed train text"
+)
+@click.option("--save_tokens", type=str, default=None, help="Path to save tokens")
+def cli(
+    data_dir: Optional[str],
+    use_words: bool,
+    save_text: Optional[str],
+    save_tokens: Optional[str],
+) -> None:
+    """CLI for extracting text data from the iam dataset."""
+    if data_dir is None:
+        data_dir = (
+            Path(__file__).resolve().parents[2]
+            / "data"
+            / "downloaded"
+            / "iam"
+            / "iamdb"
+        )
+        log.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)
+
+    preprocessor = Preprocessor(data_dir, 64, use_words=use_words)
+    preprocessor.extract_train_text()
+
+    processed_dir = data_dir.parents[2] / "processed" / "iam_lines"
+    log.debug(f"Saving processed files at: {processed_dir}")
+
+    if save_text is not None:
+        log.info("Saving training text")
+        with open(processed_dir / save_text, "w") as f:
+            f.write("\n".join(t for t in preprocessor.text))
+
+    if save_tokens is not None:
+        log.info("Saving tokens")
+        with open(processed_dir / save_tokens, "w") as f:
+            f.write("\n".join(preprocessor.tokens))
+
+
+if __name__ == "__main__":
+    cli()
diff --git a/text_recognizer/data/utils/image_utils.py b/text_recognizer/data/utils/image_utils.py
new file mode 100644
index 0000000..c2b8915
--- /dev/null
+++ b/text_recognizer/data/utils/image_utils.py
@@ -0,0 +1,49 @@
+"""Image util functions for loading and saving images."""
+from pathlib import Path
+from typing import Union
+from urllib.request import urlopen
+
+import cv2
+import numpy as np
+from PIL import Image
+
+
+def read_image_pil(image_uri: Union[Path, str], grayscale: bool = False) -> Image:
+    """Return PIL image."""
+    image = Image.open(image_uri)
+    if grayscale:
+        image = image.convert("L")
+    return image
+
+
+def read_image(image_uri: Union[Path, str], grayscale: bool = False) -> np.array:
+    """Read image_uri."""
+
+    if isinstance(image_uri, str):
+        image_uri = Path(image_uri)
+
+    def read_image_from_filename(image_filename: Path, imread_flag: int) -> np.array:
+        return cv2.imread(str(image_filename), imread_flag)
+
+    def read_image_from_url(image_url: Path, imread_flag: int) -> np.array:
+        url_response = urlopen(str(image_url))  # nosec
+        image_array = np.array(bytearray(url_response.read()), dtype=np.uint8)
+        return cv2.imdecode(image_array, imread_flag)
+
+    imread_flag = cv2.IMREAD_GRAYSCALE if grayscale else cv2.IMREAD_COLOR
+    image = None
+
+    if image_uri.exists():
+        image = read_image_from_filename(image_uri, imread_flag)
+    else:
+        image = read_image_from_url(image_uri, imread_flag)
+
+    if image is None:
+        raise ValueError(f"Could not load image at {image_uri}")
+
+    return image
+
+
+def write_image(image: np.ndarray, filename: Union[Path, str]) -> None:
+    """Write image to file."""
+    cv2.imwrite(str(filename), image)
diff --git a/text_recognizer/data/utils/make_wordpieces.py b/text_recognizer/data/utils/make_wordpieces.py
new file mode 100644
index 0000000..8e53815
--- /dev/null
+++ b/text_recognizer/data/utils/make_wordpieces.py
@@ -0,0 +1,112 @@
+"""Creates word pieces from a text file.
+
+Most code stolen from:
+
+    https://github.com/facebookresearch/gtn_applications/blob/master/scripts/make_wordpieces.py
+
+"""
+import io
+from pathlib import Path
+from typing import List, Optional, Union
+
+import click
+from loguru import logger as log
+import sentencepiece as spm
+
+
+def iamdb_pieces(
+    data_dir: Path, text_file: str, num_pieces: int, output_prefix: str
+) -> None:
+    """Creates word pieces from the iamdb train text."""
+    # Load training text.
+    with open(data_dir / text_file, "r") as f:
+        text = [line.strip() for line in f]
+
+    sp = train_spm_model(
+        iter(text),
+        num_pieces + 1,  # To account for <unk>
+        user_symbols=["/"],  # added so token is in the output set
+    )
+
+    vocab = sorted(set(w for t in text for w in t.split("▁") if w))
+    if "move" not in vocab:
+        raise RuntimeError("`MOVE` not in vocab")
+
+    save_pieces(sp, num_pieces, data_dir, output_prefix, vocab)
+
+
+def train_spm_model(
+    sentences: iter, vocab_size: int, user_symbols: Union[str, List[str]] = ""
+) -> spm.SentencePieceProcessor:
+    """Trains the sentence piece model."""
+    model = io.BytesIO()
+    spm.SentencePieceTrainer.train(
+        sentence_iterator=sentences,
+        model_writer=model,
+        vocab_size=vocab_size,
+        bos_id=-1,
+        eos_id=-1,
+        character_coverage=1.0,
+        user_defined_symbols=user_symbols,
+    )
+    sp = spm.SentencePieceProcessor(model_proto=model.getvalue())
+    return sp
+
+
+def save_pieces(
+    sp: spm.SentencePieceProcessor,
+    num_pieces: int,
+    data_dir: Path,
+    output_prefix: str,
+    vocab: set,
+) -> None:
+    """Saves word pieces to disk."""
+    log.info(f"Generating word piece list of size {num_pieces}.")
+    pieces = [sp.id_to_piece(i) for i in range(1, num_pieces + 1)]
+    log.info(f"Encoding vocabulary of size {len(vocab)}.")
+    encoded_vocab = [sp.encode_as_pieces(v) for v in vocab]
+
+    # Save pieces to file.
+    with open(data_dir / f"{output_prefix}_tokens_{num_pieces}.txt", "w") as f:
+        f.write("\n".join(pieces))
+
+    # Save lexicon to a file.
+    with open(data_dir / f"{output_prefix}_lex_{num_pieces}.txt", "w") as f:
+        for v, p in zip(vocab, encoded_vocab):
+            f.write(f"{v} {' '.join(p)}\n")
+
+
+@click.command()
+@click.option("--data_dir", type=str, default=None, help="Path to processed iam dir.")
+@click.option(
+    "--text_file", type=str, default=None, help="Name of sentence piece training text."
+)
+@click.option(
+    "--output_prefix",
+    type=str,
+    default="word_pieces",
+    help="Prefix name to store tokens and lexicon.",
+)
+@click.option("--num_pieces", type=int, default=1000, help="Number of word pieces.")
+def cli(
+    data_dir: Optional[str],
+    text_file: Optional[str],
+    output_prefix: Optional[str],
+    num_pieces: Optional[int],
+) -> None:
+    """CLI for training the sentence piece model."""
+    if data_dir is None:
+        data_dir = (
+            Path(__file__).resolve().parents[2] / "data" / "processed" / "iam_lines"
+        )
+        log.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)
+
+    iamdb_pieces(data_dir, text_file, num_pieces, output_prefix)
+
+
+if __name__ == "__main__":
+    cli()
diff --git a/text_recognizer/data/utils/sentence_generator.py b/text_recognizer/data/utils/sentence_generator.py
new file mode 100644
index 0000000..8567e6d
--- /dev/null
+++ b/text_recognizer/data/utils/sentence_generator.py
@@ -0,0 +1,89 @@
+"""Downloading the Brown corpus with NLTK for sentence generating."""
+import itertools
+import re
+import string
+from typing import Optional
+
+import nltk
+from nltk.corpus.reader.util import ConcatenatedCorpusView
+import numpy as np
+
+from text_recognizer.data.base_data_module import BaseDataModule
+
+NLTK_DATA_DIRNAME = BaseDataModule.data_dirname() / "downloaded" / "nltk"
+
+
+class SentenceGenerator:
+    """Generates text sentences using the Brown corpus."""
+
+    def __init__(self, max_length: Optional[int] = None) -> None:
+        """Loads the corpus and sets word start indices."""
+        self.corpus = brown_corpus()
+        self.word_start_indices = [0] + [
+            _.start(0) + 1 for _ in re.finditer(" ", self.corpus)
+        ]
+        self.max_length = max_length
+
+    def generate(self, max_length: Optional[int] = None) -> str:
+        r"""Generates a word or sentences from the Brown corpus.
+
+        Sample a string from the Brown corpus of length at least one word and at most
+        max_length, padding to max_length with the '_' characters if sentence is
+        shorter.
+
+        Args:
+            max_length (Optional[int]): The maximum number of characters in the sentence.
+                Defaults to None.
+
+        Returns:
+            str: A sentence from the Brown corpus.
+
+        Raises:
+            ValueError: If max_length was not specified at initialization and not
+                given as an argument.
+
+            RuntimeError: If a valid string was not generated.
+
+        """
+        if max_length is None:
+            max_length = self.max_length
+        if max_length is None:
+            raise ValueError(
+                "Must provide max_length to this method or when making this object."
+            )
+
+        for _ in range(10):
+            try:
+                index = np.random.randint(0, len(self.word_start_indices) - 1)
+                start_index = self.word_start_indices[index]
+                end_index_candidates = []
+                for index in range(index + 1, len(self.word_start_indices)):
+                    if self.word_start_indices[index] - start_index > max_length:
+                        break
+                    end_index_candidates.append(self.word_start_indices[index])
+                end_index = np.random.choice(end_index_candidates)
+                sampled_text = self.corpus[start_index:end_index].strip()
+                return sampled_text
+            except Exception:
+                pass
+        raise RuntimeError("Was not able to generate a valid string")
+
+
+def brown_corpus() -> str:
+    """Returns a single string with the Brown corpus with all punctuations stripped."""
+    sentences = load_nltk_brown_corpus()
+    corpus = " ".join(itertools.chain.from_iterable(sentences))
+    corpus = corpus.translate({ord(c): None for c in string.punctuation})
+    corpus = re.sub(" +", " ", corpus)
+    return corpus
+
+
+def load_nltk_brown_corpus() -> ConcatenatedCorpusView:
+    """Load the Brown corpus using the NLTK library."""
+    nltk.data.path.append(NLTK_DATA_DIRNAME)
+    try:
+        nltk.corpus.brown.sents()
+    except LookupError:
+        NLTK_DATA_DIRNAME.mkdir(parents=True, exist_ok=True)
+        nltk.download("brown", download_dir=NLTK_DATA_DIRNAME)
+    return nltk.corpus.brown.sents()